Numerical simulation studies of the dispersion of dimethyl sulfide (DMS) in the air have increased over the last two decades in parallel with the interest in understanding its role as a precursor of non-sea salt aerosols in the lower to middle levels of the troposphere. Here, we review recent numerical modeling studies that have included DMS emissions, their atmospheric oxidation mechanism, and their subsequent impacts on air quality at regional and global scales. In addition, we discuss the available methods for estimating sea–air DMS fluxes, including parameterizations and climatological datasets, as well as their integration into air quality models. At the regional level, modeling studies focus on the Northern Hemisphere, presenting a large gap in Antarctica, Africa, and the Atlantic coast of South America, whereas at the global scale, modeling studies tend to focus more on polar regions, especially the Arctic. Future studies must consider updated climatologies and parameterizations for more realistic results and the reduction in biases in numerical simulations analysis.

The global energy transition is pivotal in mitigating climate change. In Chile, the energy system that includes hydropower faces challenges from prolonged megadroughts, necessitating diversification toward renewable energy sources like solar and wind energy. However, research gaps persist in understanding how these sources can optimally address climate-induced vulnerabilities. This study conducts a bibliometric analysis to identify global research trends on renewable energy strategies under extreme drought conditions, distinguishing it from systematic or narrative reviews. A bibliometric analysis was conducted using Scopus, incorporating 82 selected documents analyzed via Bibliometrix and VOSviewer to map co-authorship networks, keywords, and publications. Results revealed a significant increase in research on solar energy (26.83%) and renewable energy (25.61%) within the study period (2005–2024), with the most notable growth occurring in the last six years. Key findings include the predominance of studies on energy optimization, with solar and wind technologies emerging as pivotal for enhancing resilience in water-scarce regions. These insights underscore the strategic role of renewable energies in addressing climate vulnerabilities while supporting sustainable energy transitions. The implications of this work lie in guiding future research and policy frameworks to enhance energy security and environmental sustainability.

Chile’s mining industry, a global leader in copper production, faces challenges due to increasing volumes of mining waste, particularly Waste Rock Dumps (WRD) and Leaching Waste Dumps (LWD). The  National Service of Geology and Mining (SERNAGEOMIN) requires assessment of the physical stability (PS) of these facilities, but current methods are hindered by data scarcity and resource constraints. This study proposes a simplified evaluation methodology using first-order parameters from open-access data. By integrating Geographic Information Systems (GIS) and Artificial Intelligence (AI)—utilizing models like YOLOv11 and convolutional neural networks—we automate the detection and characterization of WRD and LWD from satellite imagery, extracting critical parameters for PS assessment. This  approach reduces analysis time and minimizes human error. Validated in the Antofagasta Region, Chile’s primary mining area, we identified and evaluated 70 WRD and 54 LWD. The results demonstrate the effectiveness of prioritizing deposits based on potential risk, enhancing SERNAGEOMIN’s capacity for supervision. The successful application suggests scalability to other mining regions and adaptability to different facility types, including tailings storage facilities. This work offers a practical tool to improve safety and risk management
 in the mining industry, addressing critical challenges in PS evaluation under current regulatory constraints.

In this comprehensive analysis of Chile's air quality dynamics spanning 2016 to 2021, the utilization of data from the National Air Quality Information System (SINCA) and its network of monitoring stations was undertaken. Quintero, Puchuncaví, and Coyhaique were the focal points of this study, with the primary objective being the construction of predictive models for sulfur dioxide (SO2), fine particulate matter (PM2.5), and coarse particulate matter (PM10). A hybrid forecasting strategy was employed, integrating Autoregressive Integrated Moving Average (ARIMA) models with Artificial Neural Networks (ANN), incorporating external covariates such as wind speed and direction to enhance prediction accuracy. Vital monitoring stations, including Quintero, Ventanas, Coyhaique I, and Coyhaique II, played a pivotal role in data collection and model development. Emphasis on industrial and residential zones highlighted the significance of discerning pollutant origins and the influence of wind direction on concentration measurements. Geographical and climatic factors, notably in Coyhaique, revealed a seasonal stagnation effect due to topography and low winter temperatures, contributing to heightened pollution levels. Model performance underwent meticulous evaluation, utilizing metrics such as the Akaike Information Criterion (AIC), Ljung-Box statistical tests, and diverse statistical indicators. The hybrid ARIMA-ANN models demonstrated strong predictive capabilities, boasting an R2 exceeding 0.90. The outcomes underscored the imperative for tailored strategies in air quality management, recognizing the intricate interplay of environmental factors. Additionally, the adaptability and precision of neural network models were highlighted, showcasing the potential of advanced technologies in refining air quality forecasts. The findings reveal that geographical and climatic factors, especially in Coyhaique, contribute to elevated pollution levels due to seasonal stagnation and low winter temperatures. These results underscore the need for tailored air quality management strategies and highlight the potential of advanced modeling techniques to improve future air quality forecasts and deepen the understanding of environmental challenges in Chile.

This article presents a high-frequency characterization from 1 up to 10 GHz of electroplated conductive filaments in 3D printed microwave topologies. This study implements different microstrip lines and antennas to compare their performance as-is and with the electroplating process. The results for the microstrip lines show a significant decrease in losses for the electroplated devices, even reaching loss levels of pure copper devices. In addition, considerations about the required thickness for the conductor are analyzed by considering the skin depth requirement for nonideal conductors. The results for a patch antenna measurement confirm that the antenna height can be reduced to extremely low levels.

The volumetric mass transfer coefficients (kLa) of oxygen during sorption and desorption were analyzed using nanobubbles (NBs) of air and pure oxygen under various experimental conditions. The results showed that oxygen NBs achieved an increase in dissolved oxygen (DO) levels during absorption, reaching peaks of 30–34 mg∙L−1 and stabilizing at 31.3 ± 0.2 mg∙L−1, with a volumetric mass transfer coefficient of 0.105 ± 0.002 min−1. In comparison, air NBs showed a lower efficiency, with peak DOs of 8∙10 mg∙L−1 and kLa of 0.048 ± 0.001 min−1. In desorption studies, oxygen NBs had higher DO retention, reducing from 30.0 mg∙L−1 to 15.0 mg∙L−1 in 300 min, with a kLa of 0.042 ± 0.003 min−1, while air NBs decreased more rapidly, with a kLa of 0.028 ± 0.002 min−1. When oxygen was used, kLa outperformed air in both absorption and desorption, with a higher kLa during absorption, a lower kLa during desorption, and higher stability. In addition, the results show that the residence time has an important impact on the performance of NBs, showing that the direct influence of the flow dynamics and surface/to/volume ratio influences the value of kLa. The results highlight the superior performance of oxygen NBs versus air NBs in terms of mass transfer efficiency and stability and highlight the effect of residence time and NB composition in applications requiring efficient oxygen transfer, given the promising prospects for the development of advanced aeration technologies in industrial and environmental contexts.

Graphene oxide membranes have emerged as cutting-edge materials in desalination and wastewater treatment technologies due to valuable attributes such as ready accessibility, mechanical strength, chemical affinity, high water permeability, and pollutant selectivity. However, a significant challenge arises from the distortion of the nanochannels responsible for water transport due to the hydration of oxidized groups over the graphene oxide nanoplates. This compromises selectivity and alters water transport dynamics. To surmount this drawback, innovative strategies involve the incorporation of additives, or crosslinkers, into the graphene oxide matrix to stabilize these critical nanochannels. This comprehensive review investigates the performance of graphene oxide membranes for desalination and wastewater treatment, where graphene oxide was functionalized through crosslinker integration. A novel classification based on the connector element is considered for relating the crosslinker nature and performance in water treatment, accompanied by a statistical analysis highlighting key factors influencing the performance. It was found that additives based on metallic connectors offer a high likelihood of obtaining high performance while incorporating oxygen-based additives shows the highest performance. Furthermore, the hydrophobic character of the selective graphene oxide layer arises as the key factor in determining the final performance in water depuration.

This study presents the development and application of a mathematical optimization model to improve decision-making in the supply chain for high-energy-density pellet (HEDP) production and commercialization. Focused on the Metropolitan Region of Chile, the research involved a detailed analysis of key supply chain components, including identifying landfills and controlled dumps, waste volume assessments, plant location analysis, technology evaluation, and market potential exploration. The model revealed that the available raw material in the region was sufficient to meet 100% of HEDP demand, with a surplus of 2,161,952 tons remaining after satisfying maximum demand. An optimization analysis of potential plant locations identified Santa Marta as the optimal choice, resulting in annual cost savings of USD 100,000 compared to other sites. This work underscores the role of mathematical optimization in enhancing supply chain efficiency for biomass-based energy products, offering valuable insights for strategic decision-making in similar contexts.

This study analyzes the behavior of sodium polyacrylate (NaPA) as a rheological modifier for clay-based tailings. Special emphasis is placed on the impact of calcium and magnesium ions in industrial water, which are analyzed through rheograms, zeta potential measurements, and molecular dynamics simulations. The results are interpreted as electrostatic interactions, steric phenomena, and cation solvation. This interpretation integrates experimental studies with microscopic analyses, employing molecular dynamics simulations to elucidate the underlying mechanisms. In allcases, a decrease in the yield stress of synthetic slurries is observed as the dosing of NaPA increases due to greater repulsion between tailings particles through an increase in electrostatic repulsion and larger steric forces that hinder agglomeration. However, efficiency is reduced in the presence of divalent cations as zeta potential measurements suggest a reduction in the electrical charges of the particles and the polymer, making its application more challenging. The differences obtained in the presence of calcium compared to magnesium are explained in terms of the solvation of these ions and their impact on the polymer conformation in solution and adsorption on the mineral surfaces. This explanation is reinforced by molecular dynamics studies, which indicate that polymer adsorption on minerals depends on the type of mineral and type of ion. Particularly for quartz, the highest adsorption of NaPA occurs in the presence of calcium, whereas for a kaolinite surface, the highest polymer adsorption is obtained in the presence of magnesium. The competitive effect of these phenomena leads to the rheological behavior of the tailings being dominated by the effects originating in the clay. 

The health risks associated with the presence of heavy metals in drinking water can be
 severe. To address this issue, membrane separation technology is one of the consolidated alternatives. Inorganic, porous membranes were found in applications where low energy consumption is highly desirable. The selectivity of these membranes is attained by functionalisation. Graphene oxide functionalised membrane technology is promising for removing heavy metal ions. This work summarises, discusses and presents the relationship between adsorption and overall membrane separation process performance for heavy metal ions removal from wastewater when a graphene oxide-functionalised membrane is used. The separation performance depends on the hydrophobic interactions of the membrane and the solute. The electrostatic interaction between the negatively charged membrane surface and positively charged metal ions facilitates the adsorption, leading to the rejection of these metal ions. The influences of the chemical nature of the modifiers of graphene oxide layers are highlighted.

Ferromanganese crusts are mineral resources distributed in the planet’s oceans. These deep-sea minerals stand out for their abundance and diversity of metals, with Mn and Co being the most abundant elements. These minerals are a good alternative to diversify the extraction of elements, which today are found at low grades on the Earth’s surface. For the co-processing of ferromanganese crusts to recover Co and Mn, there are few studies. These generally worked with the use of a reducing agent, and in many cases previous roasting processes. In the present investigation, two ferromanganese crusts that were collected from two seamounts in the central eastern Atlantic Ocean were characterized. Subsequently, these crusts were leached in an acid-reducing medium, adding steel waste (slag) with 99.73% Fe3O4 and 0.27% metallic iron from the steel industry as a reducing agent. Acid-reducing processes have previously been shown to yield high and rapid recoveries of Co and Mn from seabed minerals. However, there is no previous study using smelting slag as a reducing agent for the treatment of ferromanganese crusts. The best results of this research were obtained when working at 60 C, achieving joint extractions of Co and Mn of ~80% and ~40%, respectively, in 10 min. In addition, the process residues were analyzed, and the formation of contaminating elements or the precipitation of Co and Mn species was not observed.

T Silica-based membranes exhibit significant promise for the separation of hydrogen from other larger gas mole cules based on size sieving mechanism, particularly when employed in membrane reactors. Nevertheless, the migration of silanol bonds (Si–OH) formed under hydrothermal conditions leads to alterations in pore size, ultimately compromising the performance of the membrane. Therefore, this study focuses on determining the pore size of cobalt-doped silica membranes before and after hydrothermal treatment by the apparent activation energy of gas permeation. The Oscillator model and the effective medium theory are employed to estimate the potential pore size distribution, as well as to calculate the apparent activation energy and permeability. The calculated apparent activation energy is compared with experimental data to identify the most probable pore size distribution, which showed the minimum activation energy error to the experimental value. The calculated permeability based on the identified pore size distribution is in line with experimental permeability, which validated the identified pore size distribution. Since silica-based membrane is generally applied in hydrothermal conditions, our model successfully identifies the changes in pore size of silica-based membranes after hydrothermal treatment. The results demonstrated that hydrothermal treatment significantly impacts the pore size of silica-based membranes. Specifically, 5-membered rings are prevalent in the intact membrane, but after hydrothermal treatment, there is a gradual shift of the pore size distribution towards larger pores, potentially leading to a decrease in sieving performance. This methodology presents a promising approach for determining intriguing pore size information of porous materials.

he city of Valdivia, located in southern Chile, has high levels of particulate matter, mainly due to the heating system based on wood used during winter. As a corrective measure, environmental authorities established the Air Pollution Management Plan for Valdivia in 2017, seeking to decrease the effects on the population’s health and provide a better quality of life for inhabitants. An alternative to reduce indoor air quality problems in homes is to implement a district heating plant. This study evaluated the air quality if a district heating plant is implemented in the zone. The WRF-SMOKE-CMAQ model was applied in August 2018 to simulate the effect of this new system on air quality. An adequate fit was achieved for the actual case between the 24-h average concentrations of PM and PM 10 2.5 from the simulated and observed values, obtaining correlation factor (r) values of 0.76 and 0.78, respectively. By simulating the scenario with a district heating plant (thus eliminating emissions from residences), it was found that if this plant is located in the southern area of the city, the daily concentrations would be reduced by an average of 53.52% and 51.40% for PM2.5 and PM10, respectively. The results of this study showed that the implementation of a district heating plant results in a reduction in air pollution problems compared to the current scenario, achieving the values established in the primary air quality standards.

Nanobubble technology has emerged as a transformative approach in bioprocessing, significantly enhancing mass-transfer efficiency for effective microbial activity. Characterized by their nanometric size and high internal pressure, nanobubbles possess distinct properties such as pro longed stability and minimal rise velocities, allowing them to remain suspended in liquid media for extended periods. These features are particularly beneficial in bioprocesses involving aerobic strains, where they help overcome common obstacles, such as increased culture viscosity and diffu sion limitations, that traditionally impede efficient mass transfer. For instance, in an experimental setup, nanobubble aeration achieved 10% higher soluble chemical oxygen demand (sCOD) removal compared to traditional aeration methods. Additionally, nanobubble-aerated systems demonstrated a 55.03% increase in caproic acid concentration when supplemented with air nanobubble water, reaching up to 15.10 g/L. These results underscore the potential of nanobubble technology for opti mizing bioprocess efficiency and sustainability. This review delineates the important role of the mass-transfer coefficient (kL) in evaluating these interactions and underscores the significance of nanobubbles in improving bioprocess efficiency. The integration of nanobubble technology in bio processing not only improves gas exchange and substrate utilization but also bolsters microbial growth and metabolic performance. The potential of nanobubble technology to improve the mass transfer efficiency in biotechnological applications is supported by emerging research. However, to fully leverage these benefits, it is essential to conduct further empirical studies to specifically assess their impacts on bioprocess efficacy and scalability. Such research will provide the necessary data to validate the practical applications of nanobubbles and identify any limitations that need to be addressed in industrial settings.

High-molecular-weight anionic polyacrylamide was used to analyze the effect of kaolin on the structure of particle aggregates formed in freshwater and seawater. Batch flocculation experiments were performed to determine the size of the flocculated aggregates over time by using focused beam reflectance measurements. Sedimentation tests were performed to analyze the settling rate of the solid–liquid interface and the turbidity of the supernatant. Subsequently, a model that relates the hindered settling rate to the aggregate size was used to determine the mass fractal dimension (𝐷𝑓). Flocculation kinetics revealed that greater amounts of kaolin generated larger aggregates because of its lamellar morphology. The maximum size was between 10 and 20 s of flocculation under all conditions. However, the presence of kaolin reduced the settling rate. The fractal dimension decreased with the increase in the kaolin content, resulting in the formation of irregular and porous aggregates. By contrast, factors such as the flocculation time, water quality, and quartz size had limited influences on the fractal dimension. Seawater produced a clearer supernatant because of its higher ionic strength and precoagulation of particles. Notably, the harmful effect of clays in seawater was reduced.

This study explores the Hydrothermal Carbonization (HTC) treatment of lignocellulosic biomass blends, delving into the influence of several key parameters: temperature, additive nature and dosage, residence time, and biomass composition. Rapeseeds, Pinus radiata sawdust, oat husks, and pressed olive served as the studied biomasses. One hundred twenty-eight experiments were conducted to assess the effects on mass yield (MY), energy yield (EY), higher heating value (HHV), and final ash content (ASH) by a Factorial Experimental Design. The derived model equations demonstrated a robust fit to the experimental data, averaging an R 2 exceeding 0.94, affirming their predictive accuracy. The observed energy yield ranged between 65% and 80%, notably with sawdust and olive blends securing EY levels surpassing 70%, while rapeseed blends exhibited the highest HHV at 25 MJ/kg. Temperature emerged as the most influential factor, resulting in an 11% decrease in MY and a substantial 2.20 MJ/kg increase in HHV. Contrastingly, blend composition and additive presence significantly impacted ASH and EY, with all blends exhibiting increased ASH in the presence of additives. Higher initial hemicellulose and aqueous extractive content in raw biomass correlated proportionally with heightened HHV.

The meat industry uses phosphates to improve the water-holding capacity (WHC) of meat products, although excess phosphates can be harmful to human health. In this sense, protein hydrolysates offer an alternative with scientific evidence of improved WHCs. Salmon frames, a by-product rich in protein, must be processed for recovery. Enzymatic technology allows these proteins to be extracted from muscle, and the sequential batch strategy significantly increases protein nitrogen extraction. This study focused on evaluating the WHC of protein hydrolysates from salmon frames obtained through double- and triple-sequential batches compared to conventional hydrolysis. Hydrolysis was carried out for 3 h at 55 °C with 13 mAU of subtilisin per gram of salmon frames. The WHC of each hydrolysate was measured as the cooking loss using concentrations that varied from 0 to 5% (w/w) in the meat matrix. Compared with those obtained through conventional hydrolysis, the hydrolysates obtained through the strategy of double- and triple-sequence batches demonstrated a 55% and 51% reduction in cooking loss, respectively, when they were applied from 1% by weight in the meat matrix. It is essential to highlight that all hydrolysates had a significantly lower cooking loss (p ≤ 0.05) than that of the positive control (sodium tripolyphosphate [STPP]) at its maximum allowable limit when applied at a concentration of 5% in the meat matrix. These results suggest that the sequential batch strategy represents a promising alternative for further improving the WHC of hydrolysates compared to conventional hydrolysis. It may serve as a viable substitute for polyphosphates.

This paper presents a numerical model for thermal energy storage systems’ design, development, and feasibility. The energy storage was composed of a tank that stores phase change material (AlSi12) and internal pipes with heat transfer fluid (Cerrolow 117), coupled to a power block to dispatch electrical energy on a small scale for off-grid industrial applications. Subsequently, the evolution of the temperature in charge/discharge cycles, temperature degradation, and storage efficiency was determined with the appropriate magnitudes and behavior through the resolution of a numerical model. In addition, for the proposed electric power generation plant for an off-grid pumping system in the mining industry of Chile, a numerical model was developed using the finite volumes method to simulate the thermocline performance. As a result, the temperature history reflects stable thermal behavior, low degradation, and high efficiency of approximately 92%, with a storage time increasing up to 13 [h] and 384.8 [kWh] capacity. Also, implementation was feasible on a small scale due to its compact, modular, and economically competitive characteristics in a concentrated solar power plant. Finally, the proposed design was proven to be an accurate and reliable alternative for small-scale off-grid mining applications.

As part of a route for the valorisation of liquid effluents from copper metallurgical plants, the recovery and generation of sulphuric acid using electrodialysis from synthetic sulphate-rich solutions, similar to those of copper electrometallurgy, was investigated. Sulphate-bearing solution, having sulphuric acid ranging from 45 to 180 g/L and copper from 0 to 40 g/L, and having impurities of Co (0.2 g/L) and Fe (3.0 g/L), were electrodialysed at various current densities at several temperatures. A recovery of sulphuric acid of 0.5 kg/h/m2 was obtained at 300 A/m2 and 55°C, with a final concentration of 216 g/L of high purity H2SO4 with a SEC of 1.95 kWh/kg. Electrodialysis at 700 A/m2 resulted in an acid rate recovery of 1.5 kg/h/m2 , with a final concentration of 328 g/L, and a SEC of 2.46 kWh/kg. The mass transport of metal ions and the effect of solution’s viscosity on acid recovery are discussed.

This work analyzed the effect of sodium acid pyrophosphate as a rheological modifier of concentrated clay-based tailings in saline waters. The yield stress was obtained by the stress sweep method in logarithmic form using the vane-in-cup geometry. Oscillatory rheology complemented the information through amplitude and frequency sweep that correlated with the particle dispersion, evaluated by the Focused Beam Reflectance Measurement technique. Rheological properties increased with solids concentration, kaolin content, and salinity. The addition of sodium acid pyrophosphate generated decrease in all rheological parameters, following exponential decay for the yield stress case. As the proportion of clays increases, the tailings require higher reagent dosage, which was observed through changes in the characteristic dosage. The chord length distribution verified the particles' dispersion after adding sodium acid pyrophosphate, showing fine particles release and fewer number of coarse aggregates. The tetravalent anionic phosphate molecules adsorbed on the particle's surfaces, increasing the magnitude of the zeta potential; however, it did not occur in the same order as the rheological changes. It suggests that the dispersion mechanism is caused by both electrostatic and steric repulsion.

In Chile, the budget for managing environmental liabilities such as abandoned tailings impoundments is limited. Using native and endemic plant species to remove heavy metals from tailings represents a low-cost alternative. Ex situ phytoremediation experiments were conducted over a period of seven months. The endemic species Lycium chilense and native species Haplopappus foliosus were used to remove copper and lead from mine tailings. The results indicate that both species can concentrate levels of Cu and Pb higher than the toxicity threshold in the roots and aerial parts, and present high removal efficiency for Cu higher than 50%. In both species, the concentrations of the target elements are higher in the roots than in the aerial parts. Haplopappus foliosus presents the best performance, accumulating higher concentrations of Cu and Pb than Lycium chilense, and presenting a bioconcentration of over one for Cu. 

Spodumene flotation stands as the most commonly used method to concentrate lithium
minerals. However, it faces significant challenges related to low collector recoveries and similarity in the surface characteristics of the minerals, which make the effective separation of this valuable mineral difficult. For this reason, numerous researchers have conducted studies to address and confront this problem. In this work, an exhaustive bibliographic search was carried out using keywords and search queries, and the results were structured in three sections according to temporal, methodological, and thematic criteria. The first section covers the period from 1950 to 2004, focusing on experimental tests. The second section covers from 2004 to the present and focuses on flotation tests and measurement analysis. Simultaneously, the third section spans from 2011 to the present and is based on molecular dynamics simulations. Topics covered include spodumene surface properties, the influence of metal ions, pre-treatment techniques, and the use of collectors. Ultimately, molecular dynamics simulations are positioned as a tool that accurately represents experimental phenomena. In this context, specialized software such as Materials Studio or Gromacs prove to be reliable instruments that allow a detailed study of mineral surfaces and other elements to be carried out, which justifies their consideration for future research in this scientific field. 

Ethanol is an ideal hydrogen carrier, which can be converted to hydrogen-rich syn-gas via the steam reforming reaction. Sorption-enhanced steam reforming is a promising approach to produce high-purity hydrogen by mixing the sorbent and catalyst particles. The idea of bi-functional materials, loading both sorption and catalytic site in a single particle, could transform the inter-particle heat-mass transfer to intra-particle heat-mass transfer. This work studied the sorption-enhanced steam reforming of ethanol (SESRE) over Ni-CaO-CaZrO3 bi-functional catalysts containing sorption and catalytic sites. Bi-functional Ni-CaO-CaZrO3 catalysts were synthesized using a simple sol-gel technique. The influence of operating conditions including temperature, steam-to-carbon ratio (S/C) and weight hourly space velocity (WHSV) on Ni10-Ca90Zr10 bi-functional materials were discussed. The operating condition with a temperature of 600 ◦C, weight hourly space velocity of 0.34 h− 1 and steam-to-carbon ratio of 3 was the most suitable reaction condition for hydrogen production in this study. Over the optimized operation conditions, the influence of Ni loadings on hydrogen production performance was further studied. The result indicated that 10 wt% is the best Ni loading in this study for Ni-CaO-CaZrO3, which enables >95% hydrogen purity in the gaseous product in the pre-breakthrough stage, with the longest breakthrough time (90 min). Furthermore, under the best operation conditions, the Ni10-Ca90Zr10 displayed excellent stability over 10 cyclic tests. In the 10th cycle, about 90% hydrogen purity was constantly obtained for at least 60 min during the pre-breakthrough stages. This study demonstrated that the Ni10-Ca90Zr10 bi-functional material is effective and stable for producing hydrogen from ethanol and has the potential to establish a method of generating clean energy with minimal carbon emission.  

Rockburst phenomena pose significant challenges in the mining industry, particularly with increased underground activities at greater depths. These sudden failures not only jeopardize personnel safety but also impact mining investments. Consequently, it becomes crucial to assess the reliability and effectiveness of empirical methods employed for predicting rock burst occurrences and their severity, an ongoing subject of debate within the scientific community. This research presents a comprehensive review of empirical approaches for rock burst prediction. Subsequently, these approaches are applied to predict rock burst occurrences and its intensity within sections of a tunnel at the new level of El Teniente mine in Chile. Most of these methods rely on single-factor criteria to predict the likelihood and severity of rock bursts. However, inconsistencies are observed in the results obtained from these approaches in numerous cases. This discrepancy highlights the influence of various input parameters on rock burst estimations and emphasizes that single-index criteria may not encompass all the pertinent factors that contribute to this phenomenon. Consequently, such criteria may inadequately estimate or reflect the probability of rock burst occurrences. Given the multifaceted nature of rock burst phenomena, which depend on multiple factors, it becomes imperative to explore new approaches that consider a broader range of influencing factors, thereby yielding more realistic results. Hence, continued research is essential to develop new methods that address this issue comprehensively and ensure the safety of the mining industry.

Hydrogen (H2) permeance across silica-based membranes increases with temperature, but carbon dioxide (CO2) permeance decreases. Because of the opposite signs of activation energies for H2 and CO2 permeation, silica- based membranes are widely used in separating H2 and CO2 at high temperatures due to the elevated difference between H2 and CO2 permeabilities. However, there has not been an explanation of the diverging permeance between H2 and CO2 with temperature. This study developed a gas permeation model encompassing gas penetration through silica matrix, Knudsen diffusion, and viscous flow. An Oscillator model with an effective medium approach was used to screen all possible pore size distributions and calculate the gas penetration through the silica matrix. However, no pore size distribution could allow positive activation energy for hydrogen and negative activation energy for carbon dioxide at the same time. After including Knudsen diffusion and viscous flow, the diverging permeance between H2 and CO2 with temperature was successfully interpreted. The pore size distribution and the fractional contribution from Knudsen diffusion and viscous flow, which could best fit experimental activation energies for H2 and CO2 permeation, were identified. In the silica matrix that formed the membranes, 5-membered rings were the dominant structures in pores, which was responsible for the positive apparent activation energy for H2. The negative CO2 apparent activation energy indicated that it was inevitable to have some Knudsen diffusion and viscous flow through some imperfections of the membrane. Our model demonstrated the importance of high-temperature gas separation, as high temperature could minimize the undesirable gas flow through imperfections. This study also implied that further improvement of H2/CO2 separation by silica-based membranes could be achieved by reducing imperfections.   

The management of the increasing volume of municipal solid waste is an essential activity for the health of the environment and of the population. The organic matter of waste deposited in landfills is subject to aerobic decomposition processes, bacterial aerobic decomposition, and chemical reactions that release large amounts of heat, biogas, and leachates at high temperatures. The control of these by-products enables their recovery, utilization, and treatment for energy use, avoiding emissions to the environment. UAVs with low-cost thermal sensors are a tool that enables the representation of temperature distributions for the thermal control of landfills. This study focuses on the development of a methodology for the generation of 3D thermal models through the projection of TIR image information onto a 3D model generated from RGB images and the identification of thermal anomalies by means of photointerpretation and GIS analysis. The novel methodological approach was implemented at the Meruelo landfill for validation. At the facility, a 4D model (X,Y,Z temperature) and a 13.8 cm/px GSD thermal orthoimage were generated with a thermal accuracy of 1.63 °C, which enabled the identification of at least five areas of high temperatures associated with possible biogas emissions, decomposing organic matter, or underground fires, which were verified by on-site measurements and photointerpretation of the RGB model, in order to take and assess specific corrective measures.

Mine tailings deposits are often overlooked by the industry, posing significant environ-
mental challenges due to chemical hazards and inadequate maintenance. Nevertheless, such mineral deposits hold considerable economic potential for processing, and the adoption of innovative technologies may also address critical chemical and physical stability issues. Existing research has 
demonstrated the feasibility of recovering target metals—i.e., copper, iron, manganese, cobalt, zinc, and others—through the application of acid leaching techniques with consistently high yields and metal recovery rates. Therefore, a compilation was carried out from 2008 onwards, on working conditions such as leaching agent, acid concentration, oxidizing-reducing reagent, particle size, O2 pressure, stirring speed, solid–liquid ratio, temperature, and leaching time. At present, there are no reviews on the recovery of metals via acid leaching in tailings, so this study can serve as support for future researchers who want to project themselves in this area, ordering the procedures and the results obtained by the research carried out. Regarding the evaluation, it can be commented that research has shown that acid leaching of tailings has achieved recoveries of over 90% in different metals, such as Zn, Cu, and Fe, which indicates that the treatment is efficient and recommended for different types of tailings.

Global population growth and rising consumption levels have significantly increased resource use and energy demand, leading to higher greenhouse gas concentrations and increased waste output. As a result, alternative waste treatment methods for sustainable municipal solid waste (MSW) management are crucial. This research evaluates the efficiency of integrating hydrothermal carbonization (HTC) and gasification for an optimized MSW biomass blend. HTC was conducted for one hour at 220˚C in a 5 L reactor, followed by gasification in a hybrid porous medium gasifier. The study investigated the effects of different filtration speeds on combustion temperature and hydrogen concentrations. The results showed that a filtration speed of 35 cm/s resulted in a maximum combustion temperature of 1035.7˚C. The temperature remained consistent across filter speeds, while higher velocities yielded higher hydrogen concentrations. Additionally, increasing the filtration velocity raised temperatures in the hybrid bed while increasing the volumetric fraction of biomass decreased maximum temperatures. This research contributes to the understanding of merging HTC and gasification for MSW biomass blend treatment, aiming to reduce environmental impacts and costs while promoting renewable resources for long-term energy production.

Janus nanoparticles (JNPs) represent a singular group of functional materials that exhibit an asymmetrical structure, namely two hemispheres of different chemical compositions. Currently, several raw materials are employed to develop Janus nanoparticles. Among them, silica nanoparticles exhibit significant advantages over other starting materials due to their relatively simple synthesis and modification, high porosity, excellent adsorption capacity, extraordinary colloidal stability, and biocompatibility. Therefore, this review aims to offer a systematic assessment of silica-based Janus nanoparticles, providing a clear description and illustration of the available synthesis methods, which for clarity have been classified into three main categories: masking, self-assembly, and phase separation. The review also discusses the most convenient paths for determining the amphiphilic character of these particles due to the relevance of this property, as well as their potential application in three main areas, including medicine, environment, and energy. Additionally, the reader can find an account of the SiO₂-based JNPs shapes reported in the literature, which are summed up in tables to facilitate the identification of their properties and proved applications. The last section is dedicated to discussing the prospects for the synthesis methods of JNPs, the behavioral prediction, and approaches for their characterization and further application.

It is well-known that the mining industry in Chile and the world is searching for ecofriendly, highly efficient mineral treatments. This is because the content of toxic elements such as arsenic, antimony, and bismuth have increased in the copper concentrates in the last years. This trend has affected the market of this metal, as well as increased the potential of producing solid wastes that represent a threat to the environment. In this paper, a review on the fundamentals of the current treatments aimed at removing arsenic, antimony, and bismuth from copper concentrates under roasting conditions is presented. The literature survey included the research conducted from 2000 until now and is focused on the different types of roasting of copper concentrates reported in the literature. A summary of the experimental conditions and major findings of each work is discussed. Depending on the type of roasting, the behavior of arsenic, antimony, and bismuth species during the experiments is analyzed.

The enzymatic hydrolysis of proteins is hindered by product inhibition during batch reactor operation. Thus, withdrawing reaction products has been proposed to increase the reaction efficiency. The sequential batch strategy was evaluated for the hydrolysis of salmon frame proteins by subtilisin to improve the efficiency of the process. After one hydrolysis batch the soluble phase was withdrawn, and the remaining solids were further hydrolyzed in the absence of the inhibition products. The operation of two sequential batches were compared to a one-stage batch operated for 2 h with 13 AU subtilisin per kg of salmon frame at 55 °C. The one-stage batch yielded 27% nitrogen recovery after 2 h of reaction. The sequential batch operation yielded 22% and 24% nitrogen recovery in the first and second batch, respectively, resulting in a total of 46%. The second batch yielded 21% when operated without protease addition, resulting in a total yield of 42%. Different distributions of the operating time and protease dose between the first and second batch were tested. The sequential batch strategy resulted in a higher productivity and lower operating costs for the enzymatic hydrolysis of salmon frame proteins, representing significant progress in byproducts valorization and circular economy.  

In this study, we present a pre-feasibility analysis that examines the viability of implement ing autonomous green hydrogen production plants in two strategic regions of Chile. With abundant renewable energy resources and growing interest in decarbonization in Chile, this study aims to provide a comprehensive financial analysis from the perspective of project initiators. The assessment includes determining the optimal sizing of an alkaline electrolyzer stack, seawater desalination system, and solar and wind renewable energy farms and the focus is on conducting a comprehensive financial analysis from the perspective of project initiators to assess project profitability using key economic indicators such as net present value (NPV). The analyses involve determining appropriate sizing of an alkaline electrolyzer stack, a seawater desalination system, and solar and wind renewable energy farms. Assuming a base case production of 1 kiloton per year of hydrogen, the capital expenditures (CAPEX) and operating expenses (OPEX) are determined. Then, the manufacturing and production costs per kilogram of green hydrogen are calculated, resulting in values of USD 3.53 kg−1 (utilizing wind energy) and USD 5.29 kg−1 (utilizing photovoltaic solar energy). Cash flows are established by adjusting the sale price of hydrogen to achieve a minimum expected return on investment of 4% per year, yielding minimum prices of USD 7.84 kg−1 (with wind energy) and USD 11.10 kg−1 (with photovoltaic solar energy). Additionally, a sensitivity analysis is conducted to assess the impact of variations in investment and operational costs. This research provides valuable insights into the financial feasibility of green hydrogen production in Chile, contributing to understanding renewable energy-based hydrogen projects and their potential economic benefits. These results can provide a reference for future investment decisions and the global development of green hydrogen production plants.

Polymetallic nodules, also called manganese nodules (due to their high content of this element), contain various valuable metals such as Cu, Ni and Co. These seabed minerals are a good alternative source of Co and Mn due to the decrease in the grade of mineral deposits on the earth’s surface. For the treatment of manganese nodules, acid-reducing leaching is apparently the most attractive, due to its low cost compared to other processes, short operational times, and it is more friendly to the environment. In this investigation, the extraction of Mn and Co from manganese nodules from two different locations was studied in acid media and by reusing a steel slag obtained from a steel smelting process. An ANOVA analysis was performed to determine the most appropriate Manganese Nodule/Fe(res) ratio and time to dissolve Co and Mn from the nodules. Effect of temperature on the process was evaluated, and then a residue analysis was carried out. Finally, it was discovered that the best results were obtained when working at 60 ◦C in a time of 15 min, obtaining extractions of approximately 98% Mn and 55% Co. Additionally, the formation of polluting elements was not observed, nor the precipitation of Mn and Co species in the studied residues.

The leaching of minerals is one of the main unit operations in the metal dissolution process, and in turn it is a process that generates fewer environmental liabilities compared to pyrometallurgical processes. As an alternative to conventional leaching methods, the use of microorganisms in mineral treatment processes has become widespread in recent decades, due to advantages such as the non production of emissions or pollution, energy savings, low process costs, products compatible with the environment, and increases in the benefit of low-grade mining deposits. The purpose of this work is to introduce the theoretical foundations associated with modeling the process of bioleaching, mainly the modeling of mineral recovery rates. The different models are collected from models based on conventional leaching dynamics modeling, based on the shrinking core model, where the oxidation process is controlled by diffusion, chemically, or by film diffusion until bioleaching models based on statistical analysis are presented, such as the surface response methodology or the application of machine learning algorithms. Although bioleaching modeling (independent of modeling techniques) of industrial (or large-scale mined) minerals is a fairly developed area, bioleaching modeling applied to rare earth elements is a field with great growth potential in the coming years, as in general bioleaching has the potential to be a more sustainable and environmentally friendly mining method than traditional mining methods.

The presence of ultrafine clay particles that are difficult to remove by conventional filtration creates many operational problems in mining processing systems. In this work, the removal of clay suspensions has been investigated using an electroflotation (EF) process with titanium electrodes. The results show that EF is a viable and novel alternative for removing ultrafine particles of kaolinite type clay present in sedimentation tank overflows with low salt concentrations (<0.1 mol/L) in copper mining facilities based on the saline water splitting concept. Maximum suspended solid removal values of 91.4 and 83.2% in NaCl and KCl solutions, respectively, were obtained under the experimental conditions of the constant applied potential of 20 V/SHE, salinity concentration of 0.1 mol/L, and electroflotation time of 10 and 20 min in NaCl and KCl solutions, respectively. Furthermore, the visual evidence of particle aggregation by flocculation during the experiments indicates a synergy between EF and electrocoagulation (EC) that enhances the removal of ultrafine particles of kaolinite.

Iron ore is a fundamental pillar in construction globally, however, its process is highly polluting and deposits are becoming less concentrated, making reusing or reprocessing its sources a sustainable solution to the current industry. A rheological analysis was performed to understand the effect of sodium metasilicate on the flow curves of concentrated pulps. The study was carried out in an Anton Paar MCR 102 rheometer, showing that, in a wide range of dosages, the reagent can reduce the yield stress of the slurries, which would result in lower energy costs for transporting the pulps by pumping. To understand the behavior observed experimentally, computational simulation has been used by means of quantum calculations to represent the metasilicate molecule and the molecular dynamics to study the adsorption of metasilicate on the hematite surface. It has been possible to obtain that the adsorption is stable on the surface of hematite, where increasing the concentration of metasilicate increases its adsorption on the surface. The adsorption could be modeled by the Slips model where there is a delay in adsorption at low concentrations and then a saturated value is reached. It was found that metasilicate requires the presence of sodium ions to be adsorbed on the surface by means of a cation bridge-type interaction. It is also possible to identify that it is absorbed by means of hydrogen bridges, but to a lesser extent than the cation bridge. Finally, it is observed that the presence of metasilicate adsorbed on the surface modifies the net surface charge, increasing it and, thus, generating the effect of dispersion of hematite particles which experimentally is observed as a decrease in rheology.

The effect of nitrogen and phosphorus availability on the growth of Sulfolobus metallicus was analyzed. This archaeon was subjected to a series of nitrogen and phosphorus limitation conditions to determine their effects on growth. The results indicate that Sulfolobus metallicus showed a relationship between one of the intermediate oxidation products (tetrathionate) and cell concentration during the exponential growth phase in the absence of nitrogen. Furthermore, significant differences were found in the specific growth rates under different scenarios with ammonia and phosphorus limitation, with values of 0.048 h−1 in the ammonia limitation case. The biomass substrate yield obtained was 0.107 gcel·g S−1 . Meanwhile, in the absence of phosphorus, the specific growth rate was 0.017 h−1 , and the substrate to biomass yield was 0.072 gcel·g S−1 . The results indicate that the ability of Sulfolobus metallicus to bio-oxidize H2S depends on the availability of such nutrients (nitrogen and phosphorus), which affect cellular growth and the types of products generated. This, in turn, influences the oxidation process of various sulfur compounds, resulting in changes in the predominant products formed and the final oxidation of sulfate ions.

Oceans are the largest source of biogenic emissions to the atmosphere, including aerosol precursors like marine halocarbons and dimethyl sulfde (DMS). During the last decade, the CAMS-GLOB-OCE dataset has developed an analysis of daily emissions of tribromomethane (CHBr3), dibromomethane (CH2Br2), iodomethane (CH3I), and DMS, due to its increasingly recognized role on tropospheric chemistry and climate dynamics. The potential impacts of these compounds on air quality modeling remain, however, largely unexplored. The lack of a reliable and easy methodology to incorporate these marine emissions into air quality models is probably one of the reasons behind this knowledge gap. Therefore, this study describes a methodology to adapt the CAMS-GLOB-OCE dataset to be used as an input of the preprocessor software Sparse Matrix Operator Kernel Emissions (SMOKE). The method involves nine steps to update fle attribute properties and to bilinearly interpolate compound emission felds. The procedure was tested using halocarbon and DMS emissions felds available within the CAMS-GLOB-OCE database for the Southern Ocean around Antarctica. We expect that this methodology will allow more studies to include the marine emissions of halocarbons and DMS in air quality studies.

Background: Phosphates are used in the food industry to improve water retention and product quality. However, when consumed in excess, they can be harmful to health. Instead, bovine skin gelatin hydrolysates present health benefits such as being a rejuvenating agent, stimulating collagen production, and improving food quality, in addition to being a source of protein. The effect of the addition of bovine skin gelatin hydrolysates on the texture and color of thermally processed chicken meat (boiled type) and antioxidant activity was evaluated. (2) Methods: Hydrolysates were prepared with subtilisin with the degree of hydrolysis being 6.57 and 13.14%, which were obtained from our previous study. (3) Results: The hydrolysates improved the firmness of the meat matrix compared to the control. Additionally, the hydrolysate with a 13.14% degree of hydrolysis reached the same firmness (p > 0.05) as the commercial ingredient sodium tripolyphosphate at its maximum limit allowed in the food industry when it was applied at 5% (w/w meat) in the meat matrix, improving firmness over the control by 63%. Furthermore, both hydrolysates reached a similar color difference to sodium tripolyphosphate at its maximum allowed limit when applied at a concentration of 2% (w/w meat). Additionally, it was found that these hydrolysates obtained the same antioxidant activity as sodium tripolyphosphate, capturing free radicals at 10%. (4) Conclusion: The findings of this study suggest that bovine skin gelatin hydrolysates can be applied as an ingredient with functional properties, being an alternative to phosphates to improve the quality of meat products  

Analytical models are of vital importance to study the dynamics of complex systems, including the heap leaching process. In this work, a methodology to study the dynamics of copper recovery in the heap leaching by means of fit of analytical models that capture the leaching dynamics product of variations of leaching agents as a function of the feeding is proposed, establishing a first mode of operation keeping the leaching agent fixed (H2SO4) and a second operation mode, where Cl− is added to accelerate the reaction kinetics of sulfide minerals (secondary sulfides). Mineral recovery was modeled for the different modes of operation, dependent on the independent variables/control parameters time, heap height, leach flow rate, and feed granulometry. The results indicate that the recovery of ore from sulfide minerals is proportional to the addition of Cl−, reaching recovery levels of approximately 60%, very close to 65% recovery in conventional oxide leaching, using only H2SO4 as leaching agent. Additionally, high copper recoveries from sulfide ores are achieved at medium Cl− concentrations, but the increase in recovery at high Cl− concentrations is marginal.

In copper smelting processes, acidic effluents are generated that contain inorganic contaminants such as arsenic and copper. Nowadays, the treatment of wastewater is done by physicochemical methods without copper recovery. Electrodialysis is an alternative process that can recover copper. Moreover, when electrocoagulation is applied to remove arsenic from wastewater, a more stable final sludge of less volume is obtained. The present research studies the application of a combined electrodialysis and electrocoagulation process to (1) recover Cu and (2) precipitate and remove arsenic simultaneously in the same batch reactor, using synthetic wastewater that simulates wastewater from a copper smelter. Copper and arsenic could be removed and separated by the electrodialysis part, and the electrocoagulation of arsenic was verified. With electrodialysis, the arsenic and copper removals were 67% and 100%, respectively, while 82% of the arsenic arriving at the electrocoagulation part of the cell could be precipitated and removed by this process. Initial concentrations were around 815 mg L−1 Cu and 7700 mg L−1 As. The optimal current was found to be 1.36 A due to the shorter treatment times necessary to get removal percentages, recovery percentages and energy/removed copper mass ratios in the same ranges as the values achieved with a current of 1.02 A. In summary, the combined process is a promising tool for simultaneous copper recovery and arsenic removal.

Mining activities have been a part of the history of Chile since time immemorial, generating pollution and environmental liabilities. Due to the lack of regulation, many tailings are deposited close to rivers or/and on unstable ground, near which towns have been built, generally in locations with no budget for their treatment. This study tested three plant species from Northern and Central Chile to remove total chromium, nickel, and zinc from tailings: Solidago chilensis, Haplopappus foliosus, and Lycium chilense, which complements the few existing studies on heavy metals removal with native or endemic Chilean shrubs. The experiments were conducted ex situ, and the initial and final concentrations of metals were determined in tailings and plants to obtain the removal efficiency, translocation and bioconcentration factors. Among these species, the best performance was obtained using Solidago chilensis, achieving removal efficiencies of 24% for Cr, 19% for Ni, and 17% for Zn, showing the ability to phytostabilize chromium and the higher resistance concerning the toxicity threshold. Haplopappus foliosus and Lycium chilense presented a slight tendency to stabilize chromium. Only Solidago chilensis showed little ability to extract Zn.

The mining industry has resorted to using seawater while trying to find a solution to the water shortage, which is severe in some regions. Today, the industry looks to tailings dams to re cover more water and, thus, increase recirculation. The migration of interstitial water due to the consolidation of particle networks can give rise to large water mirrors in different dam areas. These pools can contain enough water to be recovered and recirculated if the external stress caused by the weight of the pulp exceeds the compressive yield stress. The density and rheological properties of the discarded pulps determine the feasibility of water expulsion during tailings consolidation. As these conditions are largely established in the thickening stage, it is necessary to revisit operations, looking at the dam as a water source. Thus, a thorough understanding of the compressive properties that determine the level of consolidation of typical pulps and their relationships to aggregate properties, such as size and fractal dimension, is crucial. Here, the effect of two types of water, industrial water and synthetic seawater, on kaolin flocculation, sedimentation rate, yield stress, and compressive yield stress were studied. In addition, the relationship of these properties with the flocculant dose and the resulting aggregate size and fractal dimension was examined. One promising finding to practitioners was that salt and small doses of high molecular weight flocculant improved the consolidation of kaolin slurries under compression. These conditions generated low compressive yield stress compared to fresh water and water with low salt content, favoring the consolidation of the pulps and the release of water.

Methane steam reforming is a representative reaction to convert carbon-rich fuel to carbon-free fuel. However, the thermodynamic equilibrium limits the conversion from methane to hydrogen. Separating hydrogen in-situ from hydrocarbon reforming reactions by inorganic membranes is an effective way to overcome the thermo dynamic equilibrium, which improves the conversion of the reforming reactions and the efficiency of hydrogen production. Silica-based membrane, due to its size sieving effect, could separate hydrogen molecules from other larger gases at high temperatures, but the poor hydrothermal stability of silica in steam conditions remains a challenge for the application in hydrogen production. In this study, to improve the hydrothermal stability cobalt was doped in silica membrane precursors with varying ratios. After a series of characterizations by dynamic light scattering, Fourier Transform Infrared spectroscopy, X-ray diffraction, nitrogen adsorption and Scanning Elec tron Microscope, a cobalt-silica membrane with a cobalt/silicon ratio of 1/4 was fabricated by dip-coating technique. At 500 ◦C the membrane delivered helium permeance of 9.37 × 10− 8 mol m− 2 s − 1 Pa− 1 , helium/ nitrogen perm-selectivity of 258.48, and helium/carbon dioxide perm-selectivity of 242.19. The membrane was then employed in methane steam reforming for in-situ hydrogen separation to enhance methane conversion and hydrogen production. Raising the reaction temperature favors the performance of the membrane reactor, but temperature over 550 ◦C was still challenging due to hydrothermal stability issue. Increasing reaction pressure from 0 to 0.3 MPa favored methane conversion, but pressure over 0.4 MPa led to concentration polarization. Steam to carbon (S/C) ratio of 3 was suitable to avoid nickel/alumina catalyst coking and methane dilution. Reducing the gas hourly space velocity (GHSV) ensured sufficient residence time for methane and favored methane conversion. At T = 500 ◦C, Δp = 0.3 MPa, S/C = 3 and GHSV = 30 ml g− 1 h− 1 , the membrane elevated the methane conversion from 45.36% (without membrane) to 83.71%. With a cobalt-silica membrane 4.32 ml min− 1 of hydrogen was continuously produced with a purity of 82.12 vol% compared to 2.34 ml min− 1 of hydrogen with a purity of 65.0 vol% in the case without a membrane. As expected, the micro-morphology of the cobalt-doped membrane after the 20-day steam reforming test showed little visible change in scanning electron microscope. The reduction of pore volume was only 15% as compared to 25% for pure silica material. This membrane demonstrated promising potential in the efficient production of hydrogen.   

In the present study, the assessment of heavy metal contaminant migration from fresh mine tailings was conducted using the electrokinetic remediation technique (EKR). In this sense, a pilot EKR cell was designed to evaluate the recovery potential of copper, nickel, and cobalt species. In particular, the focus was on the impacts of electric field intensity and pH in initial mixture and testing their interaction in copper, nickel, and cobalt migration. Experiments were made using a 22 factorial experimental design with a central point, using DC electric fields from 1.0 to 2.0 V cm−1 and H2SO4 pretreatment solutions from 1.0 to 2.0 mol L−1, along with an ANOVA test with error reduction. The metal removal rates were approximately 7% for cobalt, neglectable for copper, and 6% for nickel. In the best cases, the highest concentrations by migration at the cathodic zone were 11%, 31%, and 30%, respectively. According to ANOVA tests, factor interaction was proven for each metal in the half cell near the cathode and the closest zone from the cathode specifically. Both factors affected metal concentrations, which indicates that when the goal aims for species accumulation in a narrower section, each factor has a significant effect, and their interaction makes a proven enhancement. Thus, using 2.0 V cm−1 and 2.0 mol L−1 showed a high improvement in metal concentration in the cathodic zone.

The reaction mechanisms during thermal decomposition in As-S systems are complex to describe due to the physicochemical characteristics of arsenic and its sulfides. Non-isothermal tests were carried out in a NETZSCH DTA/TG thermal analysis equipment, and interrupted tests were carried out in a vertical oven adapted for this purpose; both tests were carried out in an inert nitrogen atmosphere. The information obtained experimentally was analyzed and correlated to determine the phases and reaction mechanisms during the thermal decomposition of an arsenic sulfide (V) sample. As a result of this study, the mechanism of thermal decomposition of an arsenic sulfide sample was obtained and the apparent activation energy was determined by the Kissinger and Ozawa methods.

Sand tailings dams have historically been the most commonly used technology for tailings storage in Chile. Although engineering advances have resulted in the construction of approximately 250-m-high facilities, some operational challenges still remain, including compaction control. Control is currently performed at a few control points in a dam embankment, without considering a series of factors that affect its mechanical behavior (e.g.,layer thickness and material variability). Within this context, geostatistics can be applied in combination with low-cost geotechnical tools as an alternative to improve compaction control in tailings storage facilities. In this study, an extensive field investigation was carried out. A total of 91 PANDA penetrometer tests were conducted to monitor the degree of compaction in an experimental classified sand tailings dam. The results were analyzed using stochastic interpolation for ordinary kriging and considering the spatial distribution of the cone resistance and the degree of compaction determined for the dam. The results showed that spatial variability was associated with the material variability of sand tailings and the compaction method used, and deviations from design requirements. The article shows the value of the use of geostatistics in decision-making in the case of classified sand tailings dams. This is mainly due to the fact that it allows optimization of the compaction process used in these tailings dams. Additionally, a useful database is generated to continue deepening studies of physical stability during the useful life of the tailings storage facilities.

Keywords: sand tailings dams; compaction control; variability; Lightweight Penetrometer PANDA

The rock masses are mineral based geomaterials which have been formed by different mineralogical compounds in terms of dimensions and mechanical properties. Geomaterials are often classified as inhomogeneous anisotropic materials due to the orientation of minerals, frequently asymmetric distribution of mechanical properties, porosity, layering, and discontinuities. Differences in deformation properties of mineral crystals under applied stresses is a potential source for crack initiation/propagation in geomaterials. Meanwhile, weathering, alteration, and thermo-chemical agents can change the distribution of mechanical properties by causing unequal effects on different minerals. Redistribution of properties changes the intensity of heterogeneity and anisotropy and ultimately changes the rock fracture mechanism. Therefore, in this study, with the use of transgranular and intergranular enrichment functions and an interaction integral for inhomogeneous materials the failure mechanism of graded and degraded rocks affected by altering factors is simulated. The concept of energy release rate was used to predict the crack initiation angle and the crack trajectory within or between mineral grains. To verify and validate this approach, the results are compared with experimental test results and those reported in the literature. The results show that the crack trajectory significantly depends on the properties of minerals and their boundaries. The smaller the ratio of intergranular to transgranular critical fracture energy is, the more likely the crack to propagate between the grains. Simulation of crack propagation in altered specimens also showed that the crack tends to preferably propagate in weaker minerals. It is also found that using homogenization techniques instead of explicit modeling of minerals may produce inaccurate results. That is because it predicts pure fracture modes at angles in which the mixed tensile-shear modes should be detected.

The discontinuities are main factor on discontinuous, anisotropic, and non-elastic behavior of rock mass. The objective of this paper is to present a new discontinuity rating system called “Universal Discontinuity index” (UDi), based on the combination of quantitative and measurable parameters of the discontinuity network, damage mechanics, vectorial based criteria of Warburton for kinematic rock block failure analysis, and Mohr-Columb criteria for shear failure analysis. Applying the UDi permits to capture the heterogeneous and anisotropic nature of the rock mass strength or equivalently the degree of damage. A new, simple, and fast procedure for logging geomechanical drill cores is proposed, which allows UDi to be applicable at every stage of rock engineering projects. We used the UDi for the prediction of the spatial geometry of over-excavation along a tunnel. There is a good agreement between the variational trend computed using UDi and over-excavation along a tunnel observed at El Teniente mine, Chile. Moreover, the good correlation between rock mass quality rating from UDi and Rock Mass index (RMi) demonstrate the reliability of the UDi rating system.

In this paper, a statistical analysis is performed on the data obtained from magnetic surveys. The purpose of this analysis is to introduce the U-spatial statistics as a method for obtaining geomagnetic anomaly areas and improving the results in the potential limit of iron. For this purpose, the 6000 magnetic data of the Baba-Ali iron limit on the west of the Sanandaj-Sirjan zone of Iran have been used. The U-spatial statistics method is a moving averaging method that considers the spatial position of data or geophysical properties in statistical analysis. To apply this method, the optimum values of U were first estimated on the raw magnetic data. Then the U-values map of the Earth’s magnetic field intensity for the upper and lower MI sensors were obtained by a kriging interpolation technique, and anomalous zones were determined by criteria U¯¯¯¯U¯ + SD. By subtracting these maps in the GIS environment, the gradient of the U-values of the Earth’s magnetic field on this anomaly was illustrated. The geomagnetic anomaly zones obtained from the U-spatial statistics method are in good agreement with the results of the previous surveys. Also, the study of two-dimensional sections to validate the results showed that this method could increase the resolution of anomalous areas with more confidence and help improve the results by reducing the intensity of background data and increase the intensity of anomalous data. In addition to proposing a drilling point, this method can propose an optimal area of the region to continue exploration operations by providing a potential area (U^* ≥ 0.33).

This work investigates the use of positron annihilation lifetime spectroscopy (PALS) for the in-situ structural characterisation of silica derived thin film membranes. By using a quantified maximum entropy method, PALS allowed for the measurement of a pore size distribution depth profile. PALS measurements were carried out on a series of silica derived membranes where alumina supports were coated with four layers of cationic HTBA surfactant cobalt silica sols wherein the surfactant/cobalt molar ratio loading varied from 0 to 3. PALS results showed that the coated layers adjacent to the porous alumina substrate were characterised by micropores and broad mesopores, a clear indication that the porosity of the substrate affected the pore size at the substrate and thin film interface. The last coated layer resulted in a high concentration of ultra-micropores (d_p < 6 Å). This was attributed to the surface smoothness conferred by three previous coated layers. Higher surfactant loadings resulted in an increase in gas permeation and reduction of He/CO₂ permselectivity from 91.5 to 3.8. A strong correlation with R² up to 0.999 was found between the ultra-micropores in the top layer and gas permselectivity, a clear indication that gas separation is controlled by small pore sizes. In this work, PALS showed to be a powerful tool for the characterisation of the structural features of thin films.

We are now witnessing a dramatic growth of heterogeneous data, consisting of a complex set of cross-media content, such as texts, images, videos, audio, graphics, spatio-temporal data, and multivariate time series. The inception of modern techniques from computer science have offered very robust and hi-tech solutions for data and information analysis, collection, storage, and organization, as well as product and service delivery to customers. Recently, technological advancements, particularly in the form of big data, have resulted in the storage of enormous amounts of potentially valuable data in a wide variety of formats. This situation is creating new challenges for the development of effective algorithms and frameworks to meet the strong requirements of big data representation and analysis, knowledge understanding, and discovery.

Response surface methodology (RSM) is one of the most effective tools for optimizing processes, and it has been used in conjunction with the Analysis of Variance (ANOVA) test to establish the effect of input factors on output factors. However, when this methodology is used in mineral flotation, its polynomial model usually performs poorly. An alternative is to use artificial neural networks (ANNs) in such situations. Within this context, the ANOVA test is not the best option for these model types; moreover, it requires statistical assumptions that are difficult to satisfy in flotation. This work proposes replacing the polynomial model of the RSM with ANNs and the Sobol methods to determine the influential input factors instead of the ANOVA test. This proposal is applied to two porphyry copper ores with a high content of pyrite, clay, and dilution media. In addition, this study shows how other computational intelligence techniques, such as swarm intelligence, can be incorporated into this type of problem to improve the learning process of ANNs. The results gave an adjustment of over 0.98 for R² using ANNs, in comparison to values of around 0.5 when the polynomial model of RSM was utilized. On the other hand, the application of Global Sensitivity Analysis (GSA) identified the aeration rate and P₈₀ size as the most influential variables in copper recovery under the conditions studied. Additionally, we identified significant interactions that affect the recovery of copper, with the interactions between the aeration rate, frother concentration, and P₈₀ size being the most important.

Global sensitivity analysis (GSA) is a fundamental tool for identifying input variables that determine the behavior of the mathematical models under uncertainty. Among the methods proposed to perform GSA, those based on the Sobol method are highlighted because of their versatility and robustness; however, applications using complex models are impractical owing to their significant processing time. This research proposes a methodology to accelerate GSA via surrogate models based on the modern design of experiments and supervised machine learning (SML) tools. Three case studies based on an SAG mill and cell bank are presented to illustrate the applicability of the proposed procedure. The first two consider batch training for SML tools included in the Python and R programming languages, and the third considers online sequential (OS) training for an extreme learning machine (ELM). The results reveal significant computational gains from the methodology proposed. In addition, GSA enables the quantification of the impact of critical input variables on metallurgical process performance, such as ore hardness, ore size, and superficial air velocity, which has only been reported in the literature from an experimental standpoint. Finally, GSA-OS-ELM opens the door to estimating online sensitivity indices for the equipment used in mineral processing.

Process design procedures under uncertainty result in stochastic optimization problems whose resolution is complex due to the large uncertainty space, which hinders the application of optimization approaches, as well as the establishment of relationships between input and output variables. On the other hand, supervised machine learning (SML) offers tools with which to develop surrogate models, which are computationally inexpensive and efficient. This paper proposes a procedure based on modern design of experiments, deterministic optimization, SML tools, and global sensitivity analysis (GSA) to reduce the size of the uncertainty space for stochastic optimization problems. The proposal is illustrated with a case study based on the stochastic design of flotation plants. The results reveal that surrogate models of stochastic formulation enable the prediction of the structure, profitability parameters, and metallurgical parameters of designed flotation plants, as well as reducing the size of the uncertainty space via GSA and, consequently, establishing relationships between the input and output variables of the stochastic formulation.

Uncertainty in industrial processes is very common, but it is particularly high in the grinding process (GP), due to the set of interacting operating/design parameters. This uncertainty can be evaluated in different ways, but, without a doubt, one of the most important parameters that characterise all GPs is the particle size distribution (PSD). However, is the PSD a good way to quantify the uncertainty in the milling process? This is the question we attempt to answer in this paper. To do so, we use 10 experimental grinding repetitions, 3 grinding times, and 14 Tyler meshes (more than 400 experimental results). The most relevant results were compared for the weight percentage for each size (WPES), cumulative weight undersize (CWU), or the use of particle size distribution models (PSDM), in terms of continuous changes in statistical parameters in WPES for different grinding times. The probability distribution was found to be changeable when reporting the results of WPES/CWU/PSDM, we detected the over-/under-estimation of uncertainty when using WPES/CWU, and variations in the relationships between sizes were observed when using WPES/CWU. Finally, our conclusion was that the way in which the data are analysed is not trivial, due to the possible deviations that may occur in the uncertainty process

In the present work an intense bibliographic search is developed, with updated information on the microscopic fundamentals that govern the behavior of flotation operations of chalcopyrite, the main copper mineral in nature. In particular, the effect caused by the presence of pyrite, a non-valuable mineral, but challenging for the operation due to its ability to capture a portion of collector and float, decreasing the quality of the concentrate, is addressed. This manuscript discusses the main chemical and physical mechanisms involved in the phenomena of reagent adsorption on the mineral surface, the impact of pH and type of alkalizing agent, and the effect of pyrite depressants, some already used in the industry and others under investigation. Modern collector reagents are also described, for which, although not yet implemented on an industrial scale, promising results have been obtained in the laboratory, including better copper recovery and selectivity, and even some green reagents present biodegradable properties that generate a better environmental perspective for mineral processing.

The search for polymers that meet the demands of the water recovery process in mining is a contingent challenge. Both the presence of clays and saline waters can impair water recovery from tailings when conventional flocculants are used. In this work, the adsorption of polyacrylamide (PAM), hydrolyzed polyacrylamide (HPAM), poly(2-acrylamido-2-methyl-1-propane sulfonic acid) (PAMPS), polyacrylic acid (PAA), polyethylene oxide (PEO), and guar gum (GUAR) on a kaolinite surface (010) was investigated using classical molecular dynamics. The results show that the presence of sodium chloride modifies the affinities of the polymers with kaolinite (010). At low salt concentrations, the PAM and GUAR polymers generally show higher adsorption due to the formation of hydrogen bridges. However, the highest adsorptions occur in salt solutions in the presence of HPAM by cationic bridging with sodium ions as a mediator. This high affinity of HPAM is not efficient for flocculation because it re-disperses the particles, but it is promising for the design of new additives produced by grafting HPAM groups onto advanced polymers.

In this study, we report a straightforward and reproducible hydrothermal synthesis of copper oxide nanowires, their morphological and chemical characterization, and their application in gas sensing. Results show that the hydrothermal process is mainly influenced by the reaction time and the concentration of the reducing agent, demonstrating the synthesis of fine and long nanowires (diameter of 50–200 nm and length of 25 µm) after 10 h of reaction with 0.1 M of pyrrole. Two different annealing temperatures were tested (205 and 450 °C) and their effect on the morphology, chemical composition, and crystal size of the nanowires was analyzed by SEM, XPS, and XRD techniques, respectively. The analysis shows that the Cu²⁺ oxidation state is mainly obtained at the higher annealing temperature, and the nanowires’ shape suffers a transformation due to the formation of agglomerated crystallites. The gas sensing tests for acetone, ethanol, toluene, and carbon monoxide show preferential response and sensitivity to acetone and ethanol over the other analytes. The annealing temperature proves to have a higher influence on the stability of the nanowires than on their gas sensitivity and selectivity, showing better medium-term stability for the nanowires annealed at 450 °C.

Mercury is a toxic pollutant that can negatively impact the population’s health and the environment. The research on atmospheric mercury is of critical concern because of the diverse process that this pollutant suffers in the atmosphere as well as its deposition capacity, which can provoke diverse health issues. The Minamata Convention encourages the protection of the adverse effects of mercury, where research is a part of the strategies and atmospheric modelling plays a critical role in achieving the proposed aim. This paper reviews the study of modelling atmospheric mercury based on the southern hemisphere (SH). The article discusses diverse aspects focused on the SH such as the spatial distribution of mercury, its emissions projections, interhemispheric transport, and deposition. There has been a discrepancy between the observed and the simulated values, especially concerning the seasonality of gaseous elemental mercury and total gaseous mercury. Further, there is a lack of research about the emissions projections in the SH and mercury deposition, which generates uncertainty regarding future global scenarios. More studies on atmospheric mercury behaviour are imperative to better understand the SH’s mercury cycle.

This work aims to understand how relevant properties of polymers lead to different adsorption modes on a quartz surface (1 0 1). For this purpose, six polymers were considered: polyacrylamide (PAM), hydrolyzed polyacrylamide (HPAM), poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS), polyacrylic acid (PAA), polyethylene oxide (PEO) and guar gum (GUAR). The reagents have diverse physicochemical properties, with differences in charge density, structure, and functional groups. Classical molecular dynamics (CMD) simulations were performed with the generalized Amber force field (GAFF). The results clearly distinguish the different behaviors of charged polymers with respect to neutral polymers and their relevance to the adsorption modes and the conformation of the polymer on the surface. The highest affinity was achieved in neutral polymers, this considering that quartz is weakly charged at pH 7. Charged polymers adsorb but in stretched conformations leaving the tails of the polymers away from the surface, which is beneficial to producing polymer bridges. Salinity can impair or benefit the adsorption of reagents, depending mainly on their electrical charge. This study helps to understand the critical factors of a flocculant in the search for new additives for mineral aggregation and dispersion applications, a topic of special relevance in solid-liquid separation operations in the mining industry.

The effect of the partition coefficient on the simulation of the operation of a biotrickling filter treating a mixture of sulfur compounds was analyzed to evaluate the pertinence of using Henry’s law in determining its removal capacity. The analysis consisted of the simulation of a biotrickling filter that bio-oxides hydrogen sulfide (H₂S), dimethyl sulfide (DMS), methyl mercaptan (MM) and dimethyl disulfide (DMDS) using different types of models for determining the partition coefficient: Henry’s law for pure water, Henry’s law adjusted from experimental data, a mixed model (Extended UNIQUAC) and a semi-empirical model of two-parameters. The simulations were compared with experimental data. It was observed that Henry’s law for pure water could produce significant deviations from empirical data due to the liquid phase not being pure water. The two-parameter model better fits with similar results compared to the extended UNIQUAC model, with a lower calculation cost and necessary parameter amount. It shows that semi-empirical models can considerably improve simulation accuracy where complex phase interactions are present.

Hydrothermal carbonization makes it possible to transform lignocellulosic biomass into hydrochar, a carbon-rich material that can be used as fuel. Hydrochar has less calorific value than standard coal but generates less ashes during combustion. This study is a pre-feasibility analysis carried out to evaluate technically-economically and environmentally the use of hydrochar as fuel or co-fuel in thermal power plants in Chile. Until now there are no reports about it. The proposal of this work was to study the replacement of coal with a fuel that uses the same equipment and processes in power generation but with less air emission and with an economically profitable change. The results suggest that a plant with a supply of 104 t/h of bituminous coal could be replaced between 18 and 37 t/h of hydrochar, with a reduction of 8 and 27% in NOx and SO₂ emissions, a reduction in 7 to 24% in ashes and a marginal increase in CO₂ emission. The proposed use of hydrochar was economically profitable, with internal rates of return of up to 40% and with cash flows that reached USD 22 million.

Electronic waste (e-waste) is the fastest-growing type of waste worldwide and contains significant levels of precious metals, rare earth elements, and basic elements that make it economically attractive. This type of waste presents a challenge in the metallurgical processing industry due to its heterogeneity, toxicity, and the environmental impact caused by its incorrect disposal by companies and individuals. Their treatment with traditional solvents that are environmentally unfriendly affects the recovery of metals. In addition the practical application, recovery and recycling of the ionic liquids (ILs) are topics that align with the circular economy context, which is imperative to address today. This study presents a comprehensive review of the use of ILs to recover metals from electronic waste, with an emphasis on the leaching stage. The advantages of using ILs in hydrometallurgy are their design properties and low toxicity, which would benefit the environment and human health. A simple economic evaluation is made to expand the use of ionic liquids in metal leaching. The physicochemical properties and their influence on the process according to the nature of the cation and anion are reported.

The resistance of kaolin aggregates to shearing in water clarification and recovery operations is a critical input in designing thickener feed wells. A recently formulated but already available criterion is used to determine the shear strength of flocculated kaolin aggregates. The flocculant is a high molecular weight anionic polyelectrolyte. The resistance of the aggregates is evaluated as a function of flocculation time, flocculant dosage, and water quality. The determination is based on a standardized experimental method. First, the time evolution of the average size of kaolin flocs is
measured when aggregates are exposed to incremental shear rates from a predetermined base value. Then, the results are fitted to a pseudo-first-order model that allows deriving a characteristic value of the shear rate of rupture associated with the upper limit of the strength of the aggregates. In seawater, at a given dose of flocculant, the strength of the aggregates increases with time up to a maximum; however, at longer times, the resistance decreases until it settles at a stable value corresponding to
stable aggregates in size and structure. A higher flocculant dosage leads to stronger aggregates due to more bridges between particles and polymers, leading to a more intricate and resistant particle network. In industrial water with very low salt content, the resistance of the kaolin aggregates
is higher than in seawater for the same dose of flocculant. The salt weakens the resistance of the aggregates and works against the efficiency of the flocculant. The study should be of practical interest to concentration plants that use seawater in their operations.
Keywords: kaolin flocculation; aggregate resistance; salinity; flocculation kinetic; shear rate

Wildfires generate large amounts of atmospheric pollutants yearly. The development of an emission inventory for this activity is a challenge today, mainly to perform the air quality modeling. There are accessible available databases with historical information about this source. The main goal of this study was to process the results of biomass burning emissions for the year 2014 from the Global Fire Assimilation System (GFAS). The pollutants studied were black carbon, organic carbon, and fine and coarse particulate matter. The inputs were pre-formatted to enter into the simulation software of the emission inventory. In this case, the Sparse Matrix Operator Kernel Emissions (SMOKE) was used, and the values obtained in various cities were analyzed. As a result, the spatial distribution of the forest fire emissions in the Southern Hemisphere was achieved, with the polar stereographic projection. The highest emissions were located in the African continent, followed by the northern region of Australia. Future air quality modeling at a local level could apply the results and the methodology of this study. The biomass burning emissions could add a better performance of the results and more knowledge on the effect of this source.

The temperature of the flame of copper concentrates was determined through spectral measurements by using an optical and infrared spectrometer, where the experimental data were adequately processed by the two-colour pyrometer method. Experiments were carried out in a drop-tube, and the furnace temperature was 773 K ensuring the ignition of
concentrates. This technique allowed an in-situ evaluation to be made of the effect of the oxygen content in the feed gas and the sulphur in the concentrate. Two intense peaks at 750 nm wavelength from spectral measurements may be explained by the oxidation of labile sulphur in concentrates. The flame temperature was between 1600 and 2100 K and
this increased with both oxygen concentration and S/Cu ratio. The direct study of emission spectra through unique measurement probes can help to have a more profound vision of what is happening with the concentrated particles subjected to flash combustion conditions. This work has special interests in the pyrometallurgical industry, presenting a critical lack of non-invasive techniques for monitoring and controlling the process.

In this study, an optimal sampling schedule was developed for leaching experiments with the objective of improving the confidence of the kinetic parameters. This study shows that there is an improvement in the confidence interval from uniform sampling and the method presented here. The optimal sampling times were determined by reducing the determinant of the covariance matrix associated with the kinetic constant, which can be expressed through the covariance matrix of the extracted fraction, X,X, used to generate a function to distribute the sampling times in the experiment. The method presented here requires minimal knowledge a priori of the system to be characterized. Only the kinetic expression for the system is required. The methodology was applied to a simulated case and experimental case study of ammoniacal leaching of copper slags. The simulations conducted indicated a lower value of the standard deviation of 1.40·10⁻⁴ min⁻¹ for optimized sampling times and a value of 1.78·10⁻⁴ min⁻¹ for uniform distribution. The experimental validation results indicated a reduction of the coefficient of variation for optimized experiments of 9.3 pct (less uncertainty) from 29.7 pct (uniform sampling) to 14.6 pct (optimized sampling). Thus, the methodology proposed here is successful in decreasing the uncertainty in laboratory leaching experiments.

Abstract: Mineral leaching is the key unit operation in metallurgical processes and corresponds to the dissolution of metals. The study of leaching is carried out in many areas, such as geology, agriculture and metallurgy. This paper provides an introduction to the theoretical background regarding the mathematical modelling of the leaching process of copper minerals, establishing an overall picture of the scientific literature on technological developments and the generation of representative mathematical and theoretical models, and indicating the challenges and potential contributions of comprehensive models representing the dynamics of copper mineral leaching.
Keywords: mathematical models; copper mineral leaching; CFD; leaching kinetics; metal extraction

Abstract:

Climate change is the world's greatest challenge today, the reason why it is urgent to optimize industrial processes and find new renewable energy sources. Hydrothermal carbonization (HTC) is one of the Waste-to-Energy technologies with greater projections due to its operative advantages. However, for its large-scale implementation, there are challenges related to the variability of the composition of the waste biomass and the seasonal and geographical availability. This research applied the Life Cycle Analysis methodology to evaluate the environmental impacts caused by three biomasses blends as raw material in the HTC process at laboratory scale. The blends analyzed considered different organic fractions of municipal solid waste (food and pruning) and sewage sludge. The results showed that blend 1 had a lower environmental impact for the case of production in the experimental laboratory level, compared with blends 2 and 3. This is mainly due to its greater calorific value and mass yield, which allows obtaining more hydrochar compared with the other blends, increasing the energy efficiency of the process. Also, between 87.94% and 98.00% of the energy reduction is required to obtain neutral impacts regarding the energy requirements in the experimental laboratory level scenario and the Chilean energy matrix. The processing of blends in HTC has excellent potential in a context where municipal solid wastes have been disposed in sanitary landfills or dumps, as in most emerging countries. Since this study incorporated data from the literature, future studies should perform an elemental analysis to provide experimental and differentiated data.

Abstract:

The reaction mechanisms in As and As-S systems during their oxidation and/or thermal decomposition are complex to describe due to the physicochemical characteristics of arsenic and its sulfides; the information highlighted in the literature was analyzed and correlated to determinate the predominant phases and reaction mechanisms during the thermal decomposition and oxidation of arsenic, in its elemental form and in sulfurate phases. As a result of this analysis, it was determined that the predominant phases are mainly composed of allotropies of arsenic, sulfides, and dimers. In addition, reaction mechanisms are provided that describe the behavior of arsenic and its sulfides during its thermal decomposition and oxidation.

Keywords: reaction mechanisms; arsenic sulfide; thermal decomposition; oxidation; roasting

Abstract: Due to the significant growth of the world population, the accelerated growth of economic industries in various countries, and improved living conditions, freshwater consumption has increased dramatically and is currently under critical pressure. Its good use and rationing are essential. Even though mining is an industry that consumes much less water than other industries, such as agriculture, surrounding communities are constantly questioned. This occurs mainly because
mining deposits are generally found in arid areas where freshwater is scarce, forcing government authorities to regulate water use in mining processes more severely. Faced with this scenario, the mining industry has innovated the use of seawater and wastewater from processes for its production processes. In addition, various projects are under development to construct desalination plants and water impulsion systems of the sea; therefore, it is expected that seawater and/or wastewater in
mining will continue to grow in the coming years. Among the main challenges faced in the use of these water resources in mining is: (i) the close relationship that exists between the use of seawater and energy consumption, transferring the problem of water scarcity to a problem of energy cost overruns; (ii) generation of greater integration between the use of water and sustainable energy; and (iii) brine management is economically expensive and technically challenging and, therefore,
most desalination plants discharge untreated brine directly into the sea, causing an environmental impact. On the other hand, regarding the use of these water resources in leaching processes, there are very positive results for the dissolution of copper from sulfide minerals, where the wastewater from desalination plants presents better results than seawater due to its higher concentration of chloride ions, allowing it to work at higher redox potential values in order to increase copper dissolution. This manuscript is a bibliographic review in which finally, it is concluded that it is feasible to incorporate wastewater from water desalination plants in heap leaching processes for copper sulfide ores, as long as the cost of transfer from water desalination plants to mining sites can be supported.
Keywords: seawater; wastewater; reject brine; leaching; copper mining

Abstract: In the face of a series of global challenges caused by the dependence on fossil fuels, such as the greenhouse effect, energy shortage and air pollution, the development and utilization of hydrogen energy is considered a promising solution. Currently, hydrogen production methods mainly include thermochemical reactions, water electrolysis, biological or plasma processes. Among those alternatives, thermochemical hydrogen production has attracted much attention in recent years, particularly by water-gas shift and steam methane reforming reactions. Improving the hydrogen production efficiency of these reactions is a subject of widespread concern, including the use of inorganic membrane reactors, which have high thermal stability, high mechanical strength and chemical stability. Membranes are used to separate hydrogen generated during thermochemical reactions in-situ. They can not only significantly improve hydrogen production efficiency via Le Chatelier's principle but also significantly increase hydrogen purity. This article summarizes the studies that employed inorganic membranes based on palladium, silica, and zeolite molecular sieve, to separate hydrogen in-situ, and discusses their respective advantages and disadvantages to enhance hydrogen production from thermochemical reactions.

Keywords: Hydrogen separation Inorganic membrane Steam methane reforming Water gas shift.

Abstract: Complex gangues and low-quality waters are a concern for the mining industries, particularly in water shortage areas, where the closure of hydric circuits and reduction in water use are essential to maintain the economic and environmental sustainability of mineral processing. This
study analyzes the phenomena involved in the water recovery stage, such as sedimentation of claybased tailings flocculated with anionic polyelectrolyte in industrial water and seawater. Flocculation sedimentation batch tests were performed to ascertain the aggregate size distribution, the hindered settling rate, and the structure of flocs expressed through their fractal dimension and density.
The aggregates’ properties were characterized by the Focused Beam Reflectance Measurement (FBRM) and Particle Vision Microscope (PVM) techniques. The impact of the type of water depends on the type of clay that constitutes the suspension. For quartz/kaolin, the highest performance was
obtained in industrial water, with bigger aggregates and faster settling rates. However, the tailings composed of quartz/Na-montmorillonite reversed this trend. The type of water impacted the efficiency of primary-particle aggregation. The trials in industrial water generated a portion of nonflocculated particles, which was observed through a bimodal distribution in the unweighted chordlength distribution. This behavior was not observed in seawater, where a perceptible fraction of non-flocculated particles was not found. The additional cationic bonds that offer seawater favor finer primary-particle agglomeration for all tailings types.

Keywords: seawater flocculation; clay-based tailings; kaolin and Na-montmorillonite; fractal aggregates; mineral processing

Current challenges in froth flotation are the presence of complex gangues and the use of lowquality waters, such as seawater. In this scenario, the recovery of molybdenum minerals is difficult, mainly due to the hydrophobic faces’ physicochemical changes. In the present study, the natural floatability of pure molybdenite was analyzed by using microflotation assays, and hydrophobicity was measured by performing contact-angle measurements. The impact of two clays, kaolin (nonswelling) and Na-montmorillonite (swelling), was studied. The behavior in freshwater and seawater at pH 8 was compared, considering the current condition of the Cu/Mo mining industries, which use seawater in their operations. The presence of clays lowered the natural floatability of molybdenite precisely because they adhere to the surface and reduce its contact angle. However, the intensity with which they cause this phenomenon depends on the type of water and clay. Kaolin strongly adheres to the valuable mineral in both freshwater and seawater. For its part, Na-montmorillonite does it with greater intensity in a saline medium, but in freshwater, a high concentration of phyllosilicate is required to reduce the hydrophobicity of molybdenite. The clays’ adherence was validated by scanning electron microscopy (SEM) analysis.
Keywords: seawater flotation; molybdenite; kaolin; Na-montmorillonite

Abstract: This article presents the assessment of four different 3D-printed rectangular waveguide structures using highly conductive filaments, operating from 8 GHz to 40 GHz. The waveguides are evaluated in terms of the high-frequency transmission losses and are fabricated by using a highly conductive filament with a fused filament 3D printer. A smoothing treatment based on chloroform is used on the waveguides in order to reduce the roughness introduced by the 3D printing process. The measurement results confirm that the high-frequency transmission losses are reduced with this posttreatment, having a higher impact in higher frequencies, in which a reduction of around a 65% with respect to the nominal value is achieved.

Abstract:

The air pollution has impacted for years the population and the ecosystem in the industrial area located in Quintero, Puchuncavi, and Concon counties, the coastal area of Central Chile. In this study, we used the WRFSMOKE-CMAQ model system to evaluate the photochemical modeling of PM10, PM2.5, and O3. The industrial and the residential wood combustion sources were the main contributors of particulate matter, sulfur dioxide and volatile organic compounds. The small diurnal temperature cycle, the high relative humidity and the low wind
speed profiles exposed the meteorological condition of the coastal lows during the period of analysis. The daily average concentrations for PM10 and PM2.5 ranged from 24.03 to 50.10 μg/m3 and 15.60–21.95 μg/m3 for
observed registries; meanwhile, the simulated results were in the range of 22.71–40.62 μg/m3 and 5.49–17.29μg/m3, respectively. The omission of missing sources in the emission inventory and the default values in the
boundary condition could be one of the reasons on the underprediction obtained. The best performance for O3 occurred in the Quintero and Sur stations, located near industrial sources with high NOx and VOC emissions. In the industrial complex, PM10 and PM2.5 concentrations were 10–30 μg/m3 lower when the industrial emissions were shut down and a negligible difference was observed when the residential wood combustion emissions were not considered. Future air quality modeling must be performed in the same region for other periods like the Summer season. Also, the emission inventory from all sources needs to be accurate with more accurate temporal profiles.

Abstract: The detection and classification of heavy metals is a growing need to guarantee the quality of process water in different industries. However, the official methodologies to evaluate the presence of these contaminants require samples pre-processing, making them time-consuming and expensive; these elements do not allow online monitoring. For this reason, new technologies are required for online monitoring and evaluation. In this work, a new methodology is presented for the detection and classification of different heavy metal ions such as: As, Pb and Cd. Commercial graphite sensors modified with 2D molybdenite were used applying an electroanalytical technique of square wave voltammetry. Subsequently, signal processing based on pattern recognition and machine learning methods was carried out. This classification methodology includes the following steps: data display and arrangement, dimensionality reduction through the t-distributed stochastic neighbor embedding (t-SNE) method, which serves as feature extraction, and the support vector machines (SVM) method as a classifier. The validation is carried out with a data set of 118 aqueous samples. Leave one out cross-validation (LOOCV) was used to obtain classification accuracy. The results showed a classification accuracy of 98.31% with only two errors of the experimental validation with this data set. It is concluded that this methodology is a useful tool for detecting the presence of these ions in aqueous samples with MoS2-2D.

Abstract:

In areas where access to water for mineral processing is limited, the direct use of seawater in processing has been considered as an alternative to the expense of its desalination. However, efficient flotation of copper sulfides from non-valuable phases is best achieved at a pH > 10.5, and raising the pH of seawater leads to magnesium precipitates that adversely affect subsequent tailings dewatering. Seawater pre-treatment with lime can precipitate the majority of magnesium present, with these solids then being removed by filtration. To understand how such treatment may aid tailings dewatering, treated seawater (TSw) was mixed with raw seawater (Rsw) at different ratios, analyzing the impact on the flocculated settling rate, aggregate size as measured by focused beam reflectance measurement (FBRM), and vane yield stress for two synthetic clay-based tailings. A higher proportion of Tsw (10 mg/L Mg2+) led to larger aggregates and higher settling rates at a fixed dosage, with FBRM suggesting that higher calcium concentrations in Tsw may also favor fines coagulation. The yield stress of concentrated suspensions formed after flocculation decreased with higher proportions of Tsw, a consequence of lower flocculant demand and the reduced presence of precipitates; while the latter is a minor phase by mass, their high impact on rheology reflects a small particle size. Reducing magnesium concentrations in seawater in advance of use in processing offers advantages in the water return from thickening and subsequent underflow transport. However, this may not require complete removal, with blending Tsw and Rsw an option to obtain acceptable industrial performance.

Keywords: rheology; clay-based tailings; treated seawater; flocculation

Abstract: Residual biomass is a low-cost raw material, although it must overcome some limitations such as its low calorific value, seasonal availability, and high humidity, which reduces its quality as a fuel. Hydrothermal Carbonization (HTC) is an operation that increases the
energy density of raw biomass, obtaining a final solid (hydrochar) with higher calorific value and hydrophobic properties. This work studies the drying process of the hydrochar obtained from Pinus radiata sawdust in an indirect rotary dryer. The process was modeled by the Schlunder and Mollekopf penetration model. The fit obtained with the experimental data €
indicates an acceptable performance. The mass transfer coefficient varied between 69.4 and 131.7 W/m2
K (average solid temperature) and from 83.9 to 165.8 W/m2
K (100 C as solid temperature). The mixing number (Nmix) determined was between 19.19 and 24.39, comparable to that reported in the literature. The significant effects on the process were heating steam pressure and the turning speed of the drum. Finally, through a response surface analysis, the optimum nondimensional drying rate value was determined: Vsec ¼ 0.0040 kg H2O/kgdb
s.

Abstract: Currently, the high demand for copper is in direct contrast with the decrease in the mineral grade and, more significantly, the concerns regarding the environmental impact that arise as a result of processing such low-grade materials. Consequently, new mineral processing concepts are needed.
This work explores the chemical dissolution of chalcopyrite concentrate at ambient pressure and moderate temperatures in a deep eutectic solvent. Copper and iron are dissolved without changing their oxidation state, without solvent pH change, and stabilized as a chloride complex with no
evidence of passivation. Chemical equilibria of the metallic chloride complexes limit the dissolution, and the step that is rate-controlling of the kinetics is the interdiffusion of species in the solvent. The chemical mechanism may involve initial chloride adsorption at positive sites of the solid surface, pointing out the importance of surfaces states on chalcopyrite particles. A model based on a shrinking particle coupled with pseudo-second-order increase in the liquid concentration of copper describes
the dissolution kinetics and demonstrates the importance of the liquid to solid ratio. Iron and copper can be recovered separately from the solvent, which highlights that this concept is an interesting alternative to both redox-hydrometallurgy and pyrometallurgy to obtain copper by the processing of chalcopyrite concentrate.
Keywords: copper metallurgy; chalcopyrite; deep eutectic solvent; choline chloride ethylene glycol; non-redox leaching; dissolution kinetics; copper chloro-complex

Abstract:

One of the challenging tasks in tailings management is dealing with clay-based minerals, which create constant problems, especially in pumping thickened slurries. For their treatment, a broad range of additives has been
tested in situ, where sodium triphosphate has shown some successful preliminary advantages due to its ability to disperse particles. This work aims to evaluate the adsorption capacity of sodium triphosphate in kaolinite from atheoretical molecular approach that combines quantum calculations and molecular dynamics simulation. First, triphosphate was parameterized from quantum calculations (QM) to obtain the force field that describes the system using molecular dynamics (MD) simulation. Then, MD simulations described the behavior of triphosphate in saline solutions.
The results indicated that triphosphate can self-aggregate and even more in the presence of NaCl salts. The adsorption of triphosphate on kaolinite surfaces was stable and formed mainly sodium-mediated bridge-type
interactions between the charged groups. The adsorption was favorable when the triphosphate concentration increased, but in the presence of NaCl, it increased only up to concentrations of 0.06 M. These latter results can
be attributed to the tendency to form aggregate over the interaction with kaolinite.

Abstract:

The impact of shear rate on the structural properties of aggregates obtained during the flocculation of clay-based tailings with an anionic polyacrylamide was analyzed. The effects generated in industrial water (IW) and seawater (SW) were compared. Flocculation-sedimentation batch tests were performed to know aggregate size distribution, hindered settling rate, and internal structure of flocs expressed through their fractal dimension. The aggregate properties were characterized by the Focused Beam Reflectance Measurement (FBRM) and Particle Vision Microscope (PVM) techniques.
The aggregate size distribution showed a bimodal behavior, where a portion of the particles does not flocculate properly unless the shear rate increases during flocculation. On the other hand, the size and quantity of coarse aggregates strongly depend on the mixing intensity. The use of seawater led to a reduction in the size of aggregates. It is suggested that this is a result of polymer coiling, which leads to a decreased ability to form
polymeric bridges and thus less particle capture.
The fractal dimension of aggregates shows that while the shear rate increases, the aggregates are less compact, with structures possibly more open and further away from a solid spherical body. The greatest reduction
occurred in industrial water, related to the larger size of the structures in a low salinity environment.

Abstract:

A two-parameter model was applied to describe the activity coefficient for a culture medium, and, compared with Henry’s law for water, Henry's law fitted to experimental data, the extended UNIQUAC model, and experimental data obtained from an experimental setup system, consisting of a liquid culture media Thiobacillus (ATCC 290) with hydrogen sulfide (H2S), dimethyl sulfide (DMS), methyl mercaptan (MM), and dimethyl disulfide (DMDS), separately. The R2 and R2 adj coefficients obtained from the analysis show that Henry's Law for water gives lower or null determinations than Henry’s Law adjusted. Adjusted Henry’s Law shows lower determination coefficients than the two-parameter model (with differences in R2 adj between 0.69% and 3.64%), except for DMS (R2 adj = 95.88% for adjusted Henry’s Law and R2 adj = 94.00% for two-parameter model). The extended UNIQUAC model presents lower determinations than the other models for all compounds except H2S. On the other hand, this species has the worst comparative fits in all the models reviewed, even when Henry's law was adjusted, which may be associated with its effective solubility in the complex culture medium where the study was carried out. The ANOVA test for model discrimination shows that, for H2S, MM, and DMDS, the two-parameter model significantly represents better the liquid-vapor distribution for such components, precisely when the gas concentration was upper 300 [ppm]. In complex culture media very different from pure water, adjusted models to describe the liquid-vapor equilibrium are necessary due to the high deviations compared to pure water. In the case of the culture medium, using Henry's Law is not sufficient to describe the equilibrium for H2S, MM, and DMDS.
Keywords−− activity coefficient; culture medium; partition coeffic

Abstract:

It is of interest to study the use of copper tailings as a raw material to generate geopolymers due to the exorbitant amounts of existing tailings deposits, which also produce different risks to nearby communities. Therefore, using this industrial waste as construction material would result in several environmental and economic benefits. Due to the above, it is necessary to perform laboratory tests that account for the relevant variables to obtain fresh geopolymer pastes with good consistency,
and to obtain hardened geopolymers with good mechanical strength. This report gives an account of the experimental work carried out in the laboratory of the CIMS Sustainable Mining Research Center of the Engineering Consulting Company JRI, exposing the preliminary results observed in the generation of geopolymers by means of seven different methods using copper tailings and NaOH.
Of the seven methods evaluated in the laboratory, it was observed that two of them deliver better results from a qualitative point of view, where the influence of the curing stage stands out, reflecting that temperature is one of the critical variables for the formation of geopolymers based on copper
tailings and NaOH. The best means to work the mixtures should be studied to optimize the solubility of the NaOH and, therefore, the dissolution of the aluminosilicates in the tailings.
Keywords: copper tailings geopolymers; geopolymer generation; mechanical strength; curing temperature

Abstract:

Geopolymers are created by mixing a source of aluminosilicates, which can be natural or by-products from other industries, with an alkaline solution. These materials based on by-products from other industries have proven to be a less polluting alternative for concrete production than ordinary Portland cement (OPC). Geopolymers offer many advantages over OPC, such as excellent mechanical strength, increased durability, thermal resistance, and excellent stability in acidic and alkaline environments. Within these properties, mechanical strength, more specifically compressive strength, is the most important property for analyzing geopolymers as a construction material. For this reason, this study compiled information on the different variables that affect the compressive strength of geopolymers, such as Si/Al ratio, curing temperature and time, type and concentration of alkaline activator, water content, and the effect of impurities. From the information collected, it can be mentioned that geopolymers with Si/Al ratios between 1.5 and 2.0 obtained the highest compressive strengths for the different cases. On the other hand, high moderate temperatures (between 80 and 90 ◦C) induced higher compressive strengths in geopolymers, because the temperature favors the geopolymerization process. Moreover, longer curing times helped to obtain higher compressive strengths for all the cases analyzed. Furthermore, it was found that the most common practice is the use of sodium hydroxide combined with sodium silicate to obtain geopolymers with good mechanical strength, where the optimum SS/NaOH ratio depends on the source of aluminosilicates to be used. Generally speaking, it was observed that higher water contents lead to a decrease in compressive strength. The presence of calcium was found to be favorable in controlled proportions as it increases the compressive strength of geopolymers, on the other hand, impurities such as heavy metals have a negative effect on the compressive strength of geopolymers.

Keywords: Si/Al ratio; curing; impurities; water/solids ratio; compressive strength

Abstract:

Seawater treated with lime and sodium carbonate in different proportions to reduce magnesium and calcium contents is used in flocculation and sedimentation tests of artificial quartz and kaolin tailings. Solid complexes were separated from water by vacuum filtration, and factors such as lime/sodium carbonate ratio, kaolin content, flocculation time, and flocculant dose are evaluated. The growth of the aggregates was captured in situ by a focused beam reflectance measurement (FBRM) probe. Solid magnesium and calcium complexes are formed in raw seawater at pH 11, impairing the performance of flocculant polymers based on polyacrylamides. The results show that the settling rate improved when the treatment’s lime/sodium carbonate ratio increased. That is, when a greater removal of magnesium is prioritized over calcium. The amount of magnesium required to be removed depends on the mineralogy of the system: more clay will require more significant removal of magnesium. These results respond to the structural changes of the flocs, achieving that the more magnesium is removed, the greater the size and density of the aggregates. In contrast, calcium removal does not significantly influence flocculant performance. The study suggests the necessary conditions for each type of tailing to maximize water recovery, contributing to the effective closure of the water cycle in processes that use seawater with magnesium control.

Keywords: tailings flocculation; seawater; calcium and magnesium removal; lime; sodium carbonate.

Abstract:

Process design procedures under uncertainty result in stochastic optimization problems whose resolution is complex due to the large uncertainty space, which hinders the application of optimization approaches, as well as the establishment of relationships between input and output variables. On the other hand, supervised machine learning (SML) offers tools with which to develop surrogate models, which are computationally inexpensive and efficient. This paper proposes a procedure based on modern design of experiments, deterministic optimization, SML tools, and global sensitivity analysis (GSA) to reduce the size of the uncertainty space for stochastic optimization problems. The proposal is illustrated with a case study based on the stochastic design of flotation plants. The results reveal that surrogate models of stochastic formulation enable the prediction of the structure, profitability parameters, and metallurgical parameters of designed flotation plants, as well as reducing the size of the uncertainty space via GSA and, consequently, establishing relationships between the input and output variables of the stochastic formulation.

Keywords: stochastic optimization; supervised machine learning; global sensitivity

Abstract:

Most developing countries lack sufficient legal and management infrastructure to dispose of urban solid waste (USW). The continuous increase of USW generation requires evaluating different treatments for developing countries based on the life cycle assessment methodology to compare the environmental impact by reducing greenhouse gases and leachate. Hydrothermal carbonization (HTC) and gasification processes are presented as potential solutions for USW treatment due to their effi- ciency in producing energy for local requirements. This study aimed to compare both technologies for Temuco and Padre Las Casas cities in Southern Chile that show severe air pollution and USW management problems. The results indicated that gasi- fication had a better environmental performance than HTC when the conversion of 1 ton of organic fraction USW was analyzed. However, since HTC achieved higher energy efficiency, it had a lower environmental impact than gasification, considering the production of 1 MWh. For a definitive choice of the technology to be used, it is necessary to compare other variables, including economic and social aspects, to pro- vide a holistic perspective.

Abstract:

Pyrite (FeS2) is known as a sulfide that provides energy for various pyrometallurgical processes (fusion and conversion). There are several studies related to the evaluation of pyrite oxidation mechanisms at high temperatures, obtaining discrepancies in the products generated. In our work, the novelty of our research would be to obtain the thermochemical oxidation mechanism of FeS2 by using conventional thermogravimetric methods. The oxidative roasting of pyrite from 550 to 800°C was analyzed for an oxygen concentration of 5.07 to 28.06 kPa of oxygen and particle size between 12.3 to 33.8 microns. The results showed that the pyrite proceeded by sequential roasting: first, it produced an intermediate compound, pyrrhotite (Fe7S8), which was later oxidized to generate hematite (Fe2O3), both stages validated by weight loss of the sample as well as by analysis by DRX. Each stage had a different roasting speed as it was also influenced differently by different parameters. The temperature and particle size favored the rate of pyrrhotite generation, and the oxygen concentration favored the rate of hematite formation. The first-order kinetic equation ln (1-XPy) represented the roasting of the first stage (FeS2 → Fe7S8), with a calculated activation energy of 70.1 kJ/mol. The order of reaction was 0.5
concerning the partial pressure of oxygen and inversely proportional to the initial particle radius.
Keywords: pyrite, pyrrhotite, roasting, kinetics

Abstract:

Polymers have interesting physicochemical characteristics such as charge density, func‐ tionalities, and molecular weight. Such attributes are of great importance for use in industrial pur‐ poses. Understanding how these characteristics are affected is still complex, but with the help of molecular dynamics (MD) and quantum calculations (QM), it is possible to understand the behavior of polymers at the molecular level with great consistency. This study was applied to polymers de‐ rived from polyacrylamide (PAM) due to its great use in various industries. The polymers studied include hydrolyzed polyacrylamide (HPAM), poly (2‐acrylamido‐2‐methylpropanesulfonate) (PAMPS), polyacrylic acid (PAA), polyethylene oxide polymer (PEO), and guar gum polysaccha‐ ride (GUAR). Each one has different attributes, which help in understanding the effects on the pol‐ymer and the medium in which it is applied along a broad spectrum. The results include the con‐ formation, diffusion, ion condensation, the structure of the water around the polymer, and intera‐ tomic polymer interactions. Such characteristics are important to selecting a polymer depending on the environment in which it is found and its purpose. The effect caused by salinity is particular to each polymer, where polymers with an explicit charge or polyelectrolytes are more susceptible to changes due to salinity, increasing their coiling and reducing their mobility in solution. This natu‐ rally reduces its ability to form polymeric bridges due to having a polymer with a smaller gyration radius. In contrast, neutral polymers are less affected in their structure, making them favorable in media with high ionic charges.

Keywords: soluble polymers; flocculation; salinity; molecular dynamic; ion adsorption

Abstract:

Heap leaching is a firm extractive metallurgical technology facilitating the economical processing of different kinds of low-grade ores that are otherwise not exploited. Nevertheless, regardless of much development since it was first used, the process advantages are restricted by low recoveries and long extraction times. It is becoming progressively clear that the selection of heap leaching as an appropriate technology to process a specific mineral resource that is both environmentally sound and economically feasible very much relies on having an ample understanding of the essential underlying mechanisms of the processes and how they interrelate with the specific mineralogy of the ore body under concern. This paper provides a critical overview of the role of gangues and clays minerals as rate-limiting factors in copper heap leaching operations. We aim to assess and deliver detailed descriptions and discussions on the relations between different gangues and clays minerals and their impacts on the operational parameters and chemical dynamics in the copper heap leaching processes.

Keywords: hydrometallurgy; leaching; gangues; clays minerals; heap leaching; agglomeration

Abstract:

Uptake of precious metal ions from low concentrate solutions by immobilized powder of eggshell membrane (ESM) in a matrix of alginate was investigated. This novel sorbent material is able to uptake simultaneously precious metals (Pt, Au, Pd) and base metals (Cu) by the different constituents of this sorbent. The take up of precious metal ions is by the ESM’s functional groups and of copper ions is by the alginate matrix. The uptake of precious metal ions is pH-dependent; negligible uptake at pH 0.5, however at pH 4.0 the uptake reached 1.2, 1.6 and 2.4 mmol g^–1 for Pt, Au and Pd, respectively. The uptake fitted a kinetic of pseudo second order, with diffusion of ions through the sorbent material being the controlling step, which was supported by an extremely low activation energy. A selective stripping of Au and Cu was achieved by an appropriate mineral acid sequence.

On a examiné l’absorption d’ions de métaux précieux à partir de solutions à faible concentration à l’aide de poudre immobilisée de membrane de coquille d’oeuf (ESM) dans une matrice d’alginate. Le réseau complexe de fibres protéiniques d’ESM n’est pas déformé par un broyage cryogénique et un processus ultérieur d’immobilisation. Ce nouveau matériau absorbant est capable d’éliminer simultanément les métaux de base comme le cuivre et les métaux précieux comme le platine, l’or et le palladium. Les ions sont captés sélectivement par les différents constituants de ce sorbant. L’absorption des métaux précieux complexes se fait par les groupes fonctionnels de l’ESM et celle des ions de cuivre, par la matrice d’alginate. L’absorption du métal précieux complexe est un procédé dépendant du pH; à un pH aussi bas que 0.5, il n’y a presque pas d’absorption. Cependant, au pH de 4, l’absorption atteint des valeurs autour de 1.2, 1.6 et 2.4 mmol g^–1 pour le platine, l’or, et le palladium, respectivement, à 25°C. On a ajusté ces absorptions à une cinétique de pseudo deuxième ordre, la diffusion des ions à travers le matériau absorbant étant l’étape de contrôle, qui était supportée par une énergie d’activation extrêmement faible d’environ 1.6, 1.1, et 1.3 J mol^–1 pour Pt, Au et Pd, respectivement. Ces constatations suggèrent un processus physique d’adsorption impliqué dans l’absorption. On a effectué une évaluation préliminaire de l’absorption et extraction de la colonne pour une solution ayant un mélange d’ions d’or et de cuivre. Une extraction sélective des ions était possible en utilisant une séquence appropriée d’acides minéraux. En premier, on a obtenu l’extraction du cuivre en utilisant de l’acide sulfurique, ensuite on utilise de l’acide chlorhydrique pour extraire l’or, obtenant une solution acide riche en sulfate de cuivre et une autre solution d’acide de chlorure riche en or.

Abstract:

Due to the increase in the amount of copper sulphide minerals processed through concentra- tion processes and the need to improve the efficiency of these production processes, the development of theoretical models is making an important contribution to generating a better understanding of their dynamics, making it possible to identify the optimal conditions for the recovery of minerals, the impact of the independent variables in the responses, and the sensitivity of the recovery to variations in both the input variables and the operational parameters. This paper proposes a method for modeling, sensitizing, and optimizing the mineral recovery in rougher cells using a discrete event simulation (DES) framework and the fitting of analytical models on the basis of operational data from a concentration pilot plant. A sensitivity analysis was performed for low, medium, and high levels of the operative variables and/or parameters. The outcomes of the modeling indicate that the optimum mineral recovery is reached at medium levels of the flow rate of gas, bubble size, turbulence dissipation rate, surface tension, Reynolds number of bubble, bubble–particle contact angle, superficial gas velocity and gas hold-up in the froth zone. Additionally, the optimal response is reached at maximum levels of particle size and density and at minimum levels of bubble speed, fluid kinematic viscosity and fluid density in the sampled range. Finally, the recovery has an asymptotic behavior over time; however, the optimum recovery depends on an economic analysis, examining the marginalization of the response over time in an operational context.

Keywords: flotation process; analytical models; discrete event simulation; dynamic systems

Abstract:

This work aimed to achieve partial nitrification (PN) in a Sequencing Moving Bed Biofilm Reactor SMBBR with zeolite as a biomass carrier by using sulfide pulses in the presence of organic matter as an inhibitor. Two conditions were evaluated: sulfide (HS−) = 5 mg S/L and vvm (air volume per liquid volume per minute, L of air L−1 of liquid min−1) = 0.1 (condition 1); and a HS− = 10 mg S/L and a vvm = 0.5 (condition 2). The simultaneous effect of organic matter and sulfide was evaluated at a Chemical Oxygen Demand (COD) = 350 mg/L and HS− = 5 mg S/L, with a vvm = 0.5. As a result, using the sulfide pulse improved the nitrite accumulation in both systems. However, Total Ammo- nia Nitrogen (TAN) oxidation in both processes decreased by up to 60%. The simultaneous presence of COD and sulfide significantly reduced the TAN and nitrite oxidation, with a COD removal yield of 80% and sulfide oxidation close to 20%. Thus, the use of a sulfide pulse enabled PN in a SMBBR with zeolite. Organic matter, together with the sulfide pulse, almost completely inhibited the nitri- fication process despite using zeolite.

Keywords: sulfide doses; NOB inhibition; organic matter; AOB inhibition; zeolite

Abstract:

The Global Emissions Initiative (GEIA) stores and offers global datasets of emission inventories developed in the last 30 years. One of the most recently updated global datasets covering anthropogenic source emissions is the Copernicus Atmosphere Monitoring Service (CAMS). This study applied NetCDF Command Operator (NCO) software to preprocess the anthropogenic sources included in the CAMS datasets and converted those files as an input in the Sparse Matrix Operator Kerner Emissions (SMOKE) model for future air quality modeling. As a result, six steps were applied to obtain the required file format. The case of the central coast in Chile was analyzed to compare the global database and official reports for the on-road transport sector. As a result, some differences were shown in the most populated locations of the domain of analysis. The rest of the zones registered similar values. The methodology exposed in this report could be applied in any other region of the planet for air quality modeling studies. The development of global datasets such as CAMS is useful for hemispheric analysis and could bring an estimation on the mesoscale. It represents an opportunity for those locations without official reports of non-updated data.

• This study applied NCO commands available for the preprocessing of the CAMS dataset files.
• The emissions and temporal profile registered in CAMS datasets must be compared to official reports oftransport sectors.
• The development of global datasets such as CAMS is useful for hemispheric analysis and could bring an estimation on the mesoscale.

Abstract:

The in-situ ore fragmentation and probability of occurrence of hang-ups at draw points are the most significant factors on the performance of block cave mining. In this study we develop a hybrid methodology to study the uncertainty in the block geometry in the context of blockiness variable and hang-up frequency at a cave mine. This hybrid approach is based on the combination of geostatistical simulation, probabilistic discrete fracture network, geometrical and topological characterization of the fracture networks and supervised Poisson regression models. Our results and hybrid predictive models provide guidance on the systematic characterization of the fractured rock mass at a cave mine for its design, evaluation of production rates, and for risk evaluation purposes. This study can serve as a reference for the rock block geometry analysis in other related fields.

Abstract:

Chile is the world's leading copper producer (28.3%) and maintains approximately 23.0% of current global reserves. Chile is faced with a significant risk posed by its collection of the most unsustainable and antiquated smelter operations among major copper producers worldwide. Moreover, forecasts also indicate a trend toward higher proportions of copper sulphide ores that carry high impurities, especially arsenic. To achieve the planned pro- duction increases, improve competitiveness in the global market, and reduce reliance on international smelting capacities, Chile must make significant and justifiable investment into new and/or existing smelting operations through equipment modernization. The required investment for upgrades may be on the order of billions of dollars.

This review analyzes current roadblocks faced by the Chilean copper smelters and potential solutions according to environmental, economic and strategic factors. Recent advances in smelting technologies have focused on flash and bath smelting; despite a general trend toward flash furnace systems, recent bath furnace methods (e.g. China's SKS- BBS) are equally promising, particularly for varying and complex feeds. Strategic policies should focus on regionalized, non-integrated custom smelters, which can handle ores from a variety of sources while reducing overall operating costs. The government must play a fundamental role to incentivise the investments necessary to develop new smelter oper- ations and upgrade existing infrastructure. With a large portion of copper concentrate exports coming from privately owned mines, synergistic efforts with industry partners will be crucial to increase overall smelting capacity and position Chile as a global leader in the smelting of copper concentrates.

Abstract:

Uncertainty in industrial processes is very common, but it is particularly high in the grinding process (GP), due to the set of interacting operating/design parameters. This uncertainty can be evaluated in different ways, but, without a doubt, one of the most important parameters that characterise all GPs is the particle size distribution (PSD). However, is the PSD a good way to quantify the uncertainty in the milling process? This is the question we attempt to answer in this paper. To do so, we use 10 experimental grinding repetitions, 3 grinding times, and 14 Tyler meshes (more than 400 experimental results). The most relevant results were compared for the weight percentage for each size (WPES), cumulative weight undersize (CWU), or the use of particle size distribution models (PSDM), in terms of continuous changes in statistical parameters in WPES for different grinding times. The probability distribution was found to be changeable when reporting the results of WPES/CWU/PSDM, we detected the over-/under-estimation of uncertainty when using WPES/CWU, and variations in the relationships between sizes were observed when using WPES/CWU. Finally, our conclusion was that the way in which the data are analysed is not trivial, due to the possible deviations that may occur in the uncertainty process.

Keywords: experimental uncertainty analysis; batch grinding

Abstract:

A simple criterion is proposed to quantitatively estimate the resistance of aggregates based on incremental mechanical shear disturbances. Aggregate strength can be affected by the hydrodynamic conditions under which flocculation occurs; therefore, an experimental method is standardized to determine the resistance of aggregate structures that are formed under defined conditions of salinity (NaCl 0–0.1 M), mixing time (3 min), and mean shear rate (G = 273 s⁻¹). Kaolin particles were flocculated in saline solutions with an anionic flocculant of high molecular weight. The method involves increasing the mean shear rate (G = 0–1516 s⁻¹). Each increment represents a new experiment that starts from the base of 273 s⁻¹. Target aggregates are increasingly fragmented as mechanical disturbance increases. The monotonic relationship between the mean shear rate increments (ΔG) and the final size of the aggregates is used for a quantitative estimate of the resistance of the target aggregates since this resistance underlies this relationship. The evolution of aggregate size is analyzed by the Focused Beam Reflectance Measurement (FBRM) method, which may capture the chord length distribution on concentrated slurries. To estimate and compare the resistance of the target aggregates in solutions with different salinities, a pseudo-first-order model that describes the rupture degree as a function of shear rate increments obtains the characteristic shear rate. The rupture percentage is reached with considerably lower agitation increments at higher salinity than at low salinity. This criterion is expected to help improve the efficiency of solid–liquid separation processes, especially in plants operating with seawater, be it raw or partially desalinated. 

Keywords: kaolin flocculation; aggregate strength; salinity; flocculation kinetic; flocculation mechanism

Abstract: Computing intelligence is an important branch of artificial intelligence, and its techniques have been applied successfully in different research fields, such as mineral processing. These techniques include metaheuristic al- gorithms (MAs), which have been used to address difficult optimization problems. In this line, MAs have been proposed as an alternative to exact algorithms for designing flotation circuits, since the latter exhibit an extremely slow convergence even for moderately small instances. However, the MAs implemented in the liter- ature to design flotation circuits are generally not validated or compared to other MAs to guarantee the quality of the solutions obtained. In this work, we present a methodology for developing, validating, and comparing MAs to design flotation circuits to full scale. The methodology is described considering the Tabu search algorithm, Differential Evolution Algorithm, and Particle Swarm Optimization, and their hybridizations. To improve the performance of MAs, we consider aspects such as competitive coevolution and one-dimensional and two- dimensional chaotic maps. The results reveal that the methodology provides algorithms that exhibit a good relationship between the execution time and the quality of the results.

Abstract:

This research aims to analyze the impact of sodium tripolyphosphate (STPP) as a rheological modifier of concentrated kaolin slurries in seawater at pH 8, which is characteristic of copper sulfide processing operations. The dispersion phenomenon was analyzed through chord length measurements using the focused beam reflectance measurement (FBRM) technique, complementing size distributions in unweighted and square-weighted modes. The reduction of the rheological properties was significant, decreasing from 231 Pa in a reagent-free environment to 80 Pa after the application of STPP. A frequency sweep in a linear viscoelastic regime indicated that by applying a characteristic dosage of 0.53 kg/t of STPP, the pulp before yielding increases its phase angle, which increases its liquid-like character. Measurements of the chord length verified the dispersion of particles, which showed an apparent increase in the proportion of fine particles and a reduction of the coarser aggregates when STPP was applied. Measurements of the zeta potential suggested that the high anionic charge of the reagent (pentavalent) increases the electrostatic repulsions between particles, overcoming the effect of cations in seawater. The results are relevant for the mining industry, especially when the deposits have high contents of complex gangues, such as clays, that increase the rheological properties. This increases the energy costs and water consumption needed for pumping the tailings from thickeners to the tailing storages facilities. The strategies that allow for the improvement of the fluidity and deformation of the tailings generate slack in order to maximize water recovery in the thickening stages.

Keywords: clays; seawater; sodium tripolyphosphate; particle dispersion; yielding; viscoelasticity

Abstract:

The rise in the electronics industry has impacted the environment through the large volumes of waste that are improperly disposed of and the growing demand for precious and rare metals from natural sources. Leaching of copper, cobalt, gold, and silver from printed circuit boards of waste cellular phone has been carried out using imidazolium cation-based ionic liquids (ILs). For the studied metals, the obtaining of selective leaching obtained is reported for the first time, where acidic ionic liquids ([Bmim]HSO4 and [Hmim]HSO4) leached copper and cobalt, while basic ionic liquids ([Bmim]Cl and [Bmim]Br) extracted gold and silver. The effect of temperature has been studied by testing at 60 and 80 °C, where the highest extraction was obtained at the lowest temperature. The concentration of the ionic liquid was also studied through a test without ionic liquid and then varying from 20 to 60%, where at higher concentration the extraction is more efficient ratifying the use of ionic liquids as leaching solutions for metals. Ionic liquids have demonstrated the ability to leach metal ions as the primary reagent in the leaching solution. The following extraction percentages were obtained for each metal: 86.2% copper, 99.5% cobalt, 40.8% gold, and 44.6% silver.

Keywords e-waste · Ionic liquids · Printed circuit boards · Leaching

Abstract:

Chilean mining is one of the main productive industries in the country. It plays a critical role in the development of Chile, so process planning is an essential task in achieving high perfor- mance. This task involves considering mineral resources and operating conditions to provide an optimal and realistic copper extraction and processing strategy. Performing planning modes of op- eration requires a significant effort in information generation, analysis, and design. Once the oper- ating mode plans have been made, it is essential to select the most appropriate one. In this context, an intelligent system that supports the planning and decision-making of the operating mode has the potential to improve the copper industry’s performance. In this work, a knowledge-based decision support system for managing the operating mode of the copper heap leaching process is presented. The domain was modeled using an ontology. The interdependence between the variables was en- capsulated using a set of operation rules defined by experts in the domain and the process dynamics was modeled utilizing an inference engine (adjusted with data of the mineral feeding and operation rules coded) used to predict (through phenomenological models) the possible consequences of var- iations in mineral feeding. The work shows an intelligent approach to integrate and process opera- tional data in mining sites, being a novel way to contribute to the decision-making process in com- plex environments.

Keywords: intelligent recommendation systems; heap leaching; planning modes of operation

Abstract:

The effect of Na2SO3 as a pyrite depressant in NaCl and KCl saline media and the presence of kaolinite were evaluated by zeta potential tests. Chalcopyrite was also included in the study, because pyrite usually accompanies this mineral. Subsequently, the floatability results of both minerals in the NaCl solution were optimized based on the design of experiments (DoE). The Box–Behnken DoE was applied considering the percentage of kaolinite (X1), collector dose (X2), and depressant dose (X3) as factors. The results were modeled using artificial neural networks (ANNs) to construct contour plots and to determine the optimal conditions. In particular, maximization of the mass recovery of chalcopyrite and minimization of that of pyrite were sought. The particle swarm optimization algorithm was used as an optimization technique. The results indicated that the optimal conditions to maximize the floatability of chalcopyrite were kaolinite 6.85%, collector dose 3.58 × 10–3 mol/dm3, and depressant dose 3.49 × 10–5 mol/dm3. On the contrary, the optimal conditions to minimize the floatability of pyrite were 5% kaolinite, collector dose 5 × 10–4 mol/dm3, and depressant dose 6.4 × 10–5 mol/dm3. Under these conditions, the mass recoveries of chalcopyrite and pyrite were 66.1% and 14.0%, respectively. The results also indicated that the presence of kaolinite negatively affects the flotation of chalcopyrite, while the effect of Na2SO3 is not significant. In general, the findings suggest that Na2SO3 is a viable alternative to consider as a pyrite depressant in saline environments.

Keywords: Na2SO3, IPETC, clays; flotation, saline solution, artificial neural networks 

Abstract: Ionic liquids are applicable in the recovery of valuable products, remotion of polluting agents, and used in many CO2-capture techniques. In this work, high-pressure vapor-liquid equilibria of twenty-one binary mixtures of light hydrocarbons + IL has been modelled with Peng-Robinson/Stryjek-Vera equation of state applying Wong-Sandler mixing rules and van Laar model for the gamma-phi approach and Perturbed Chain-Statistical Associating Fluid Theory equation of state for the phi-phi approach. Critical properties were determined using a group contribution method. Adjustable characteristic pure component parame- ters were obtained using predicted vapor pressures and saturated liquids densities values. Experimental data, obtained from literature, were subjected to thermodynamic consistency area test. For the thermody- namic modelling, adjustable parameters were fitted between predicted and experimental bubble pressure. Van Laar and interaction parameters were regarded as temperature-dependent. Results obtained for both models, in terms of the main deviations between experimental and calculated pressures, were reasonably satisfactory.

Abstract:

Abstract: Molecular dynamic simulations of polyacrylic acid polyelectrolyte (PAA) analyzed its interaction with the main minerals that make up characteristic tailings of the mining industry, in this case, quartz, kaolinite, and montmorillonite. The simulations were carried out with the package Gromacs 2020.3. The interaction potentials used were General AMBER Force Field (GAFF) for PAA and CLAYFF-MOH for mineral surfaces. The SPC/E model described water molecules and Lennard-Jones 12-6 parameters adjusted for SPC/E model were used for Na+ and Cl− ions. The studied systems were carried out at pH 7, obtaining stable adsorption between the PAA and the studied surfaces. Interestingly, the strongest adsorptions were for montmorillonite at both low and high salt concentrations. The effect of salinity differs according to the system, finding that it impairs the absorption of the polymer on montmorillonite surfaces. However, a saline medium favors the interaction with quartz and kaolinite. This is explained because montmorillonite has a lower surface charge density and a greater capacity to adsorb ions. This facilitated the adsorption of PAA. It was possible to identify that the main interaction by which the polymer is adsorbed is through the hydroxyl of the mineral surface and the COO−Na+ complexes. Molecular dynamics allows us to advance in the understanding of interactions that define the behavior of this promising reagent as an alternative for sustainable treatment of complex tailings in highly saline environments.

Keywords: polyacrylic acid; clays; adsorption; molecular dynamic simulation; saline environment

Abstract:

Response surface methodology has been applied in numerous studies using polynomial models despite some of them exhibit poor correlation coefficient R2, which implies an incorrect optimization. In this work, a methodology for obtaining response surfaces when a small data set is available and its behavior is complex is presented. The methodology consists of four steps. First, the classic experimental design is used for obtaining a data set. Second, using the experimental results from a design of experiment, the classical kriging is employed for estimating properties at unsampled locations. Third, a response surface is obtained by training an artificial neural network using the kriging-estimated data set, and a hybrid algorithm based on differential evolution and backpropagation algorithms. The verification of the model is accomplished with the experimental data set. Fourth, the uncertainty quantification is utilized for studying the behavior of the response against uncertainties, which guarantee the robustness of the model developed. The methodology was applied to three cases, considering verification, validation, and uncertainty quantification. The results indicate that the proposed methodology is robust, and it provides more stable response surfaces than the approaches commonly used for polynomials and artificial neural networks. As a result, better optimal conditions are attained.

KEYWORDS: Response surface methodologyclassical krigingartificial neural networksuncertainty quantificationhybrid algorithm

Abstract:

The purpose of this work was to analyze the requirements for the operational feasibility of flotation systems as well as the effects of the selection of flotation equipment and metal price uncertainty. A procedure based on mathematical optimization and uncertainty analysis was im- plemented to achieve this aim. The optimization included flotation and grinding stages operating under uncertainty, whereas the uncertainty analysis considered the Monte Carlo method. The results obtained indicate a small number of optimal flotation structures from the economic point of view. Considering the relationship between the economic performance and metallurgical parameters, we established that these structures exhibited favorable conditions for operating under uncertainty. Such conditions were proportional to the percentages representing each structure in the optimal set; i.e., a higher percentage of a structure implied a greater capacity to face operational and metal price changes. The set of optimal structures included configurations implementing cell banks, flotation columns, or both, indicating the influence of the flotation equipment type on the optimal structures. We also established the influence of metal price on the number of optimal structures. Therefore, the results obtained allowed us to separate the design of the flotation systems into two stages: first, a set of optimal structures exhibiting favorable conditions for facing uncertainty is determined; second, the optimal operation is established via resilience/flexibility approaches after the previous determination of the equipment design parameters.

Keywords: design; flotation systems; uncertainty analysis; selection of equipment; grinding

Abstract:

The low grade of copper deposits and the use of the froth flotation process have caused excessive tailing production. In recent years, experts have looked for new alternative methods to improve this situation. Black copper minerals are abundant resources not exploited by large-scale copper mining and possess high Mn concentrations. On the other hand, manganese nodules are submarine resources and show high concentrations of Cu, Ni, Fe, and, mainly, Mn. However, both mineral resources are refractory to conventional leaching processes, and so a reducing agent is necessary for their treatment. We studied the use of tailings obtained from the flotation of foundry slags with a high content of Fe3O4 as reducing agents at different MnO2/tailings ratios and H2SO4 concentrations. Mn dissolution was compared in marine nodule and black copper minerals samples.
It was found that higher Mn dissolutions are obtained from marine nodules, likely due to the acid consumption created by Cu dissolution from black copper minerals. The remnant elements in manganese nodules were leached under an oxidant condition.
Keywords: leaching; reducing agent; MnO2

Abstract:

This review aims to understand the environmental impact that tailings produce on the land and marine ecosystem. Issues related to flora, fauna, and the environment are revised. In the first instance, the origin of the treatment and disposal of marine mining waste in Chile and other countries is studied. The importance of tailings’ valuable elements is analyzed through mineralogy, chemical composition, and oceanographic interactions. Several tailings’ treatments seek to recover valuable minerals and mitigate environmental impacts through leaching, bioleaching, and flotation methods. The analysis was complemented with the particular legislative framework for every country, highlighting those with formal regulations for the disposal of tailings in a marine environment. The available registry on flora and fauna affected by the discharge of toxic metals is explored. As a study case, the “Playa Verde” project is detailed, which recovers copper from marine tailings, and uses phytoremediation to neutralize toxic metals. Countries must regularize the disposal of marine tailings due to the significant impact on the marine ecosystem. The implementation of new technologies is necessary to recover valuable elements and reduce mining waste.

Keywords: underwater tailing dumps; environmental impact; mining waste.

Abstract:

Usually, the concentration of minerals is carried out with a set of flotation and grinding units. Most of the modeling strategies for the flotation and grinding stages have followed separate developmental paths. This paper presents a strategy based on using flotation studies to model flotation and grinding via an integrated approach. The methodology, which is an approximate method that allows one to study of the effects of grinding on flotation circuits, is applied to a copper sulfide mineral with appropriate results. Given its nature, the application of this method will help preliminary studies on the design, improvement, and simulation of flotation circuits. The major advantages of this method are its simplicity and low cost. Thus, the main contribution of this work is a new strategy to model grinding for integration into the modeling of flotation circuits. This new strategy can be extended to other concentration technologies that include grinding.

Abstract:

The accelerated growth in global demand for Manganese coincides with the continuing depletion of high-gradeores on the earth’s surface. This element is essential for diverse markets such as steel production, dietary additives, fertilizers, cells, fine chemicals, and some chemical reagents. Interestingly, there are large mineral reserves in the ocean’s depths, where marine nodules are an attractive option due to their high manganese content (between 16 and 24%). The dissolution of MnO2 from manganese nodules needs a reducing agent. Iron is a feasible alternative with a low cost and can even be recycled from scrap or industrial waste like smelting slag, tailings, or scrap steel. This paper provides a comprehensive review of Manganese acid-reducing processes from 2+0 0 marine nodules using different iron-reducing agents that include FeS2, Fe , Fe , Fe2O3, and Fe3O4. Fe has displayed the best performance in terms of dissolution kinetics and Mn extraction. This review further confers the chemistry and reactions involved in the reductive leaching and stresses the critical parameters that could be considered for optimization. In this sense, the concentration of reducing agent and temperature are highlighted as the most influential, making other parameters (e.g., particle size, stirring speed, acid concentration, and leaching time) almost irrelevant. Finally, it0is concluded that the best way to extract Mn from marine nodules is to reuse steel scraps, working with high Fe /MnO2 ratios (2/1), low concentrations of sulfuric acid (0.1 mol/L), and short times (5 min), achieving extractions of 90%.

Abstract:

Black carbon (BC) has been measured in Antarctica's air, and its global warming effect can potentially speed up the ice melting in the most solid water reservoir of the planet. However, the primary responsible sources are not well evidenced in this region. The dispersion of black carbon emissions from the Southern Hemisphere was conducting using atmospheric chemical transport model and we compared the results with satellite registries from March 1st to April 30th in 2014. The emission inventory considered the anthropogenic and biomass burning emissions from global datasets. The largest and most populated cities in Southern Hemisphere showed the higher emission of BC. As a result, the average daily concentrations of atmospheric BC were around 4 ng/m3 in most regions of Antarctica ac- cording to its pristine characteristics. We analyzed fifteen relevant sites in coastal zones of Antartica and some peaks registered by the satellite records were not replicated by model outputs and it was mainly associated with the lack of emissions. Finally, we made simulations in the same period without biomass burning emissions and we observed decreased concentrations of BC in the range of 20–50%. As a result, we show that the black carbon transportation from the continental land to the polar region took place in 17–24 days during the Austral summer and the biomass burning emissions were the primary source. Black Carbon deposition in Antarctica is not permanent, but the uncon- trolled emissions from Southern Hemisphere can increase its transportation to the white continent and make its ac- cumulation during the period when the weak polar vortex occurs.

Abstract:

The scarcity of water resources for mining activities drives the search for new low-quality water sources such as well-water and seawater. Seawater was found to be a promising alternative, but it may pose significant op- erational challenges, for example, when it needs to be recovered from the tailings in thickening stages for subsequent recycling. This is mainly explained by the high saline environment and colloidal magnesium pre- cipitates that are generated at highly alkaline conditions. In this work, we use molecular dynamics (MD) si- mulations to understand the affinity of the flocculant with colloidal magnesium precipitates and the main mi- nerals that make up a mining tailing such as quartz and kaolinite. The results are contrasted with the in-situ characterization of aggregates through the Focused Beam Reflectance Measurement (FBRM). Through X-ray diffraction, it was found that the magnesium precipitates are mainly composed of brucite crystals. The MD results allowed to explain the experimental results, mainly when solid magnesium precipitates appear at high pH, where the flocculant loses its effectiveness sharply. This is related to the undesired association among the flocculant with brucite. The adsorption is mainly carried out by the interaction between the deprotonated oxygen from the acrylic group of the polymer and the oxygen from the hydroxide of the brucite surface. There is also a significant contribution of hydrogen bonding between nitrogen from the acrylamide group and oxygen from the hydroxide.

Abstract:Stabilization of synthetic clay-rich tailings in seawater with sodium polyacrylate (NaPA) has been studied by measurements of yield stress, viscoelastic moduli, zeta potential, and particle chord length distribution. The tailings are kaolin-quartz and sodium montmorillonite-quartz mixtures in seawater at pH 8 at which all surfaces are anionic. The yield stress of both tailings decays exponentially with the dose of NaPA. Reducing the initial value of yield stress to a preset fraction (1-1/e) requires 52 g/ton NaPA for kaolin-quartz and 31 g/ton NaPA for montmorillonite-quartz tailing. At these dosages, in the linear viscoelastic range, both tailings respond similarly to the presence of NaPA, increasing their liquid-like character and suspension stability. The stabilizing action of NaPA is supported by a slight increase of the negative zeta potential and a clear shift of the particle size distribution to the finer sizes. The underlying stabilizing mechanism involves steric-electrostatic repulsion of the clay particles. These results suggest an alternative to improve the management of clay-rich tailings in processes that use raw seawater at natural pH.

Abstract: This work studied the mechanisms governing the electrode processes along with the structure and impact of the passivation layer on the electro-generation of ferrate using three low-cost sacrificial iron materials: mild steel (MS), grey cast iron (GCI) and white cast iron (WCI) electrodes in highly alkaline media. Cyclic voltammetry studies showed that the mechanisms controlling the electrode reactions depend on its alloy composition as it influences the iron species formed in the passivation layer. The presence of silicon in the GCI electrode reduced the stability of the latter, significantly enhancing the ferrate electro-generation due to the persistence of γ-FeOOH in the passivation layer. The instability/dissolution of this layer contributed to a 54%-higher generation of ferrate with GCI when compared to the other electrodes, reaching a maximum titre of 37 mM of ferrate in 10 M NaOH solution with a current efficiency of 45% and the lowest specific energy consumption of 8 kWh kg⁻¹.

Abstract: The unique properties of ionic liquids (ILs) drive the growing number of novel applications in different industries. The main features of ILs are high thermal stability, recyclability, low flash point, and low vapor pressure. This study investigated pure chalcopyrite dissolution in the presence of the ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate, [BMIm]HSO4, and a bromide-like complexing agent. The proposed system was compared with acid leaching in sulfate media with the addition of chloride and bromide ions. The results demonstrated that the use of ionic liquid and bromide ions improved the chalcopyrite leaching performance. The best operational conditions were at a temperature of 90 ◦C, with an ionic liquid concentration of 20% and 100 g/L of bromide.

Keywords: leaching; chalcopyrite; ionic liquid; bromide

Abstract: Chalcocite (Cu₂S) has the fastest kinetics of dissolution of Cu in chlorinated media of all copper sulfide minerals. Chalcocite has been identified as having economic interest due to its abundance, although the water necessary for its dissolution is scarce in many regions. In this work, the replacement of fresh water by sea water or by reject brine with high chloride content from desalination plants is analyzed. Additionally, the effect of adding MnO₂ from available manganese nodules in vast quantities at the bottom of the sea is studied. Reject brine shows better results than sea water, and the addition of MnO₂ to the brine significantly increases the kinetics of chalcocite dissolution in a short time. H₂SO₄ concentration is found to be irrelevant when working at high concentrations of chloride and MnO₂. The best results, 71% Cu extractions in 48 h, are obtained for reject brine, 100 mg of MnO₂ per 200 g of mineral and H₂SO₄ 0.5 mol/L. The results are expected to contribute to a sustainable process of dissolution of chalcocite by using the reject brine from desalination plants.

Keywords: sulfide leaching; chalcocite dissolution; desalination; reject brine; replace water; sustainability

Abstract: Anthocyanins from maqui (Aristotelia chilensis) and blackberry (Rubus glaucus) were used as light harvesters to improve the photocatalytic activity of titanium dioxide in visible light. Anthocyanins from both species were obtained using high-frequency ultrasound-assisted liquid-liquid extraction with methanol. Mixtures of anthocyanins were developed to study their effectiveness in the visible light/TiO₂ reaction for the oxidation of aniline blue. For this purpose, stainless-steel foams were covered with TiO₂ and anthocyanin and characterized by SEM. Different samples were fabricated by varying the ratio of the two anthocyanins in the mixture (100, 75, 50, 25 and 0 vol% of maqui-anthocyanin (delphinidin)). The mixtures of 25 vol% anthocyanin from maqui and 75 vol% anthocyanin from blackberry had higher total anthocyanin content and better photocatalytic activity in visible light: degradation of aniline blue was 40% at pH 7, 56% at pH 3 and 95% at pH 3 with the injection of oxygen for 2 h in comparison with TiO₂-foam/UV light, which yielded values of 13% at pH 7 and 73% at pH 3 with and without the addition of oxygen. Natural dyes that are low-cost and environmentally friendly substances are shown to be capable of improving the visible-light photocatalytic activity of TiO₂. 

Keywords: titanium dioxide; visible light photocatalysis; aniline blue; anthocyanins; maqui; blackberry

Abstract: Universities must focus the training process of their students to integrate theoretical and scientific rigor and academic exigency with the requirements of the work environment. Competency-based curricular designs have been consolidated to integrate knowledge, practices, and attitudes, with a focus on achieving significant learning. Because of this, the monitoring and evaluation of competencies and learning outcomes is relevant to meet these objectives. The processes of continuous improvement and quality assurance focus on these monitoring and evaluation systems. However, despite the relevance of this, in university practice, evaluations do not directly consider the monitoring of learning outcomes and competencies. Because of this, this research proposes the Design of Assessment System for Learning Outcomes and Competences in Engineering Programs, to know the progress and achievement obtained by students in this perspective.

Keywords – learning outcomes,competency-based education, monitoringsystem,engineering education

Abstract: Ionic liquids (ILs) have been reported to have an enhanced absorption capacity for SO₂ compared to that of traditional molecular solvents. This work evaluated the effect of water content in a 1-butyl-3-methyl imidazolium chloride [bmim][Cl] solution on the absorption of a diluted gas stream under dynamic conditions in a packed-bed column and analyzing chemical changes by FT-IR spectroscopy. For aqueous IL solutions, the absorption behavior shown a first fast-chemical reaction related to the SO_2–sulfite–bisulfite water equilibrium followed by physical absorption. The whole process is not limited by mass transfer. Conversely, in low water-content IL, the SO₂ interacts directly with the cation and absorption capacity is highly improved. In this case, mass transport limitations were detected as a consequence of high viscosity. For diluted IL solutions, only partial isothermal desorption could be reached by changing the solution pH. No desorption is obtained for highly concentrated solutions. The water content has a positive effect in reducing mass transfer limitation; however, changes the mechanism of absorption and reduce the capture capacity. The chemistry involved in aqueous IL capture of SO₂ seems to be analogous to amine-based technology; however, the non-volatility and thermal/chemical stability of the [bmim][Cl] allow minimize the generation of atmospheric and liquid phase pollutants during the absorption operation.

Keywords: 1-Butyl-3-methyl imidazolium chloride, bisulfite, desorption, gas absorption, ionic liquids, sulfur dioxide

Abstract: Modeling the global markets is complicated due to the existence of uncertainty in the information available. In addition, the lithium supply chain presents a complex network due to interconnections that it presents and the interdependencies among its elements. This complex supply chain has one large market, electric vehicles (EVs). EV production is increasing the global demand for lithium; in terms of the lithium supply chain, an EV requires lithium-ion batteries, and lithium-ion batteries require lithium carbonate and lithium hydroxide. Realistically, the mass balance in the global lithium supply chain involves more elements and more markets, and together with the assortment of databases in the literature, make the modeling through deterministic models difficult. Modeling the global supply chain under uncertainty could facilitate an assessment of the lithium supply chain between production and demand, and therefore could help to determine the distribution of materials for identifying the variables with the highest importance in an undersupply scenario. In the literature, deterministic models are commonly used to model the lithium supply chain but do not simultaneously consider the variation of data among databases for the lithium supply chain. This study performs stochastic modeling of the lithium supply chain by combining a material flow analysis with an uncertainty analysis and global sensitivity analysis. The combination of these methods evaluates an undersupply scenario. The stochastic model simulations allow a comparison between the known demand and the supply calculated under uncertainty, in order to identify the most important variables affecting lithium distribution. The dynamic simulations show that the most probable scenario is one where supply does not cover the increasing demand, and the stochastic modeling classifies the variables by their importance and sensibility. In conclusion, the most important variables in a scenario of EV undersupply are the lithium hydroxide produced from lithium carbonate, the lithium hydroxide produced from solid rock, and the production of traditional batteries. The global sensitivity analysis indicates that the critical variables which affect the uncertainty in EV production change with time.

Keywords: lithium; batteries; electric vehicles; supply chain; demand; uncertainty

Abstract: Some databases report global emissions of certain pollutants. Emissions Database for Global Atmospheric Research (EDGAR) project is one of these, which also records emissions by sources. In this study, the emissions of black and organic carbon and fine particulate matter from the EDGAR database were used as an input to process it in the Sparse Matrix Operator Kernel Emissions (SMOKE) model. We showed the spatial distribution of the fraction of black and organic carbon in particulate matter from each source in the Southern Hemisphere. Also, we extracted these ratios for several cities in the domain of analysis. The results and methodology of this study could improve the emission inventories with bottom-up methodology in areas without information located at Southern Hemisphere. Also, it could be relevant to obtain better performance in air quality modeling at the local level for decision-making on climate change and health effects.

Abstract: A population balance model described the flocculation of clay-based mining tailings in treated seawater with reduced magnesium content. For the treatment, 0.06 M of lime was added to the liquor, generating solid magnesium complexes that were subsequently removed by vacuum filtration. Magnesium content varied between 10–1440 ppm when mixing raw seawater with treated seawater. The aggregate size was analysed by the Focused Beam Reflectance Measurement (FBRM) technology. The model follows the dynamics of the aggregation-rupture and it provides a good approximation to the temporal evolution. A decrease in collision efficiency was implemented as an indicator of the polymer depletion, describing the size reduction. Lower magnesium content makes larger aggregates with a higher fractal dimension, but an increase in the concentration of clays reduces both the size of aggregates and the fractal dimension, indicating more open and porous structures, with higher permeability to the passage of fluid. The model efficiently illustrates the experimental data, with R-square (R²) greater than 0.9 and Goodness of Fit (GoF) greater than 95% in most cases, wherein the fitting parameters allowed for analysing the impact of magnesium and clays on the collision efficiency, collision frequency, and fragmentation rate. The model is predictive with few parameters, and it is potentially a powerful tool for water management optimisation. 

Keywords: treated seawater; magnesium removal; tailings flocculation; clays; population balance models

Abstract: Global warming is one of the most significant issues of today. Carbon dioxide is the primary contributor to climate change, and is mainly formed by the energy sector; thus, it is imperative to expand the total decarbonisation of this industry. Another global concern is the high demand and low supply of critical metals due to the constant growth of technological advances. These elements are essential for the manufacturing of advanced technology, green technology, and emerging industries. Currently, there is global tension and unrest over how the critical metals market is developing, with one example regarding China, which has an apparent monopoly on the mining, refining, and technical expertise associated with rare earth elements. China currently provides approximately 90% of the production of rare earth elements, causing conflicts with the European Union, the USA, and Japan due to their dependence on these raw materials. Another controversial case is the production of cobalt in the Democratic Republic of the Congo, which dominates in the global production (60% of the world’s production of Co). Despite this, the Democratic Republic of the Congo is one of the poorest countries in the world. The constant depletion of high-grade minerals from the Earth's surface forces the search for new alternative sources of the critical metals. The abundance of minerals within the sea is of relevance, with large deposits of marine nodules, ferromanganese crusts, and massive polymetallic sulphides. These are of great interest to the mining industry, as it is estimated that the largest reserves of various critical metals are found on the seabed, in addition to the largest reserves of cobalt, nickel, and manganese, and a considerable amount of rare earth elements. The exploitation of mineral resources from the seabed by the company Deep Sea Mining Finance Limited (DSMF) is currently being developed, which might promote the expansion of this market throughout the world. The wealth of minerals in the seabed may be a solution to the shortage of critical metals in the market, may decrease political tensions between countries worldwide, and may promote the large-scale deployment of renewable energy.

Abstract: In developing countries, there is a relevant problem related to air pollution caused by the indiscriminate use of residual biomass and the disposal of Municipal Solid Waste. Currently, various technologies (biological, thermal, thermochemical, among others) are available to valorize them. This review shows a current summary of two technologies: hydrothermal carbonization and gasification. The first one has been considered as a Waste to Energy technology capable of providing a solid, that can be used as a fuel, with higher calorific value and lower moisture and ash content than raw residual biomass. On the other hand, gasification generates syngas used as fuel or in the generation of electricity. During the last decade, most of the studies focused on hydrothermal carbonization of Municipal Solid Waste in contrast to gasification. However, the integration of those technologies has not even had the same interest. This study analyzed in-depth the product characteristics and the associated costs for both processes, including from transportation to obtaining the final product. Both promising Waste to Energy alternatives can result in Municipal Solid Waste disposal cost savings and environmental impact reductions. Nevertheless, research combining technologies must be enhanced in order to develop sustainable systems.

Abstract: The use of firewood and other biomass-based fuels have generated severe environmental pollution problems due high particulate matter emissions. Additionally, developing countries face considerable challenges in aspects related to the final disposal of organic waste in sanitary landfills that are already overflowed, and that constitutes a serious problem. In the last years, the search for alternative energy sources based on organic waste valorization has gained popularity. For waste biomass conversion, Hydrothermal Carbonization (HTC) has some advantages: low process temperatures required and the ability to work with biomass of different compositions and high moisture. Two groups of urban waste were considered in this investigation: 1) organic fraction of municipal solid waste (OFMSW) and 2) digested sludge (DS) from a water treatment plant. An Experimental Design was developed to study the effect of the blend composition with different OFMSW:DS ratios, reaction time (0.5 and 1 h) and temperature (190 and 220 ºC) on the Mass Yield (MY), the Higher Heating Value (HHV), Energy Densification Ratio (EDR) and Energy Yield (EY). The response equations had an average determination coefficient (R2 ) of 0.95 with an RMSE of 5.9 %. The results showed that temperature was the most significant variable on the MY (-9.8 %) and the HHV (+8.7 %). Blend 2, with a greater amount of pruning waste, had higher MY and HHV. Blend 1 had the highest percentage of food waste and sludge, and, therefore, the highest MY values. The energy yield determined for the three mixtures was about 80 %, indicating that HTC is a feasible technology for the recovery of municipal waste biomass and sludge

Abstract: A conceptual design of an industrial production plant for activated carbon was developed to process 31.25 tons/day of industrial waste nutshells as the raw material and produce 6.6 ton/day of activated carbon using steam as an activation agent. The design considered the cost of the main equipment, the purchase price of the nutshells, basic services, and operation. A sensitivity analysis was developed, considering the price of the finished product and the volume of raw material processing varied up to ±25%. Furthermore, the total annual cost of the product was determined based on the production of 2100 tons/year of activated carbon. Two cash flows were developed and projected to periods of 10 years and 15 years of production, using a tax rate of 27%, a low discount rate (LDR) of 10% per year, and without external financing. For a 10-year production project, the net present value (NPV) was USD 2,785,624, the internal return rate (IRR) 21%, the return on investment (ROI) 25%, and the discounted payback period (DPP) after the fifth year. Considering a project with 15 years of production, the NPV was USD 4,519,482, the IRR at 23%, the ROI 24%, and the DPP after the fifth year of production.

Keywords: economic evaluation; production cost; nutshell waste; activated carbon

Abstract: Given the active growth of emerging technology industries, it has become essential to have large quantities of critical metals to meet the current demand. In the Chilean mining industry, there is a depletion of high-grade mineral ores, and there is hence a need to increase production levels in the copper industry and diversify its market by extracting other elements. One of the strategies is to foster the production of lithium batteries, but the manufacture requires reserves of cobalt (Co) and manganese (Mn). Currently, Co reserves are not being exploited in Chile, and Mn production is almost negligible. This is due to the apparent shortage of high-grade ores on the land surface of the country. Given this scenario, the seabed manganese nodules are presented as a good alternative due to their high average grades of Co and Mn, which in turn would allow the growth of strategic value-added industries including lithium battery production. Chile’s current environmental regulations prevent the exploitation of marine resources. However, given technological advances worldwide, both in collection mechanisms and extractive processes, in addition to the needs generated from the future strategic plans, leads us to think about a project to exploit manganese nodules locally. 

Keywords: manganese nodules; cobalt; manganese; Chilean marine deposits

Abstract:The cell potential of the cell containing two ion-selective electrodes (ISE), Na-ISE |NaClO4 (m), PEG 4000 (Y), H2O (100-Y) | ClO4-ISE has been measured at temperatures of (288.15, 298.15, and 308.15) K as a function of the weight percentage Y of PEG 4000 in a mixed solvent at a 1 Mpa and the standard state for measured activity coefficients will be a solution of the salt in pure water. Y was varied between (0 and 25) wt.% in five-unit steps and the molality of the electrolyte (m) was between 0.05 mol kg-1 and almost saturation. The values of the standard cell potential were calculated using routine methods of extrapolation together with extended Debye- Hückel and Pitzer equations. The results obtained produced good internal consistency for all the temperatures studied. Once the standard electromotive force was determined, the mean ionic activity coefficients for NaClO4, the Gibbs energy of transfer from the water to the PEG 4000-water mixture, and the primary NaCl hydration number were calculated.

Keywords: NaClO4; PEG 4000; Cell potential; Ion-selective electrode; Activity coefficient

Abstract: The regrinding of some streams within flotation circuits, to liberate valuable mineral attached to gangue, is a common practice. However, the methodologies proposed for flotation circuit design based on optimization, usually, do not consider regrinding. This work analyzes the effect of the uncertainty in flotation and regrinding stages on the design of flotation circuits via mathematical optimization. We postulate that there are few optimal circuit structures when regrinding is included in the design problem under uncertainty. Two methods of proof are used to confirm the postulated hypothesis: proof by construction and proof by exhaustion. Results obtained allow us to confirm the hypothesis, which allows separating the design of the flotation circuits into two steps. First, a set of optimal structures are determined. Second, the equipment design parameters and operating conditions are determined through simulation and laboratory tests.

Abstract: Copper oxide minerals composed of carbonates consume high quantities of leaching reagent. The present research proposes an alternative procedure for malachite leaching (Cu2CO3(OH)2) through the use of only compound, ammonium hydroxide (NH4OH). Preliminary studies were also carried out for the dissolution of malachite in an acid system. The variables evaluated were solution pH, stirring rate, temperature, NH4OH concentration, particle size, solid/liquid ratio and different ammonium reagents. The experiments were carried out in a stirred batch system with controlled temperatures and stirring rates. For the acid dissolution system, sulfuric acid consumption reached excessive values (986 kg H2SO4/ton of malachite), invalidating the dissolution in these common systems. On the other hand, for the ammoniacal system, there was no acid consumption and the results show that copper recovery was very high, reaching values of 84.1% for a concentration of 0.2 mol/dm3 of NH4OH and an experiment time of 7200 s. The theoretical/thermodynamic calculations indicate that the solution pH was a significant factor in maintaining the copper soluble as Cu(NH3)42+. This was validated by the experimental results and solid analysis by X-ray diffraction (XRD), from which the reaction mechanisms were obtained. A heterogeneous kinetic model was obtained from the diffusion model in a porous layer for particles that begin the reaction as nonporous but which become porous during the reaction as the original solid splits and cracks to form a highly porous structure. The reaction order for the NH4OH concentration was 3.2 and was inversely proportional to the square of the initial radius of the particle. The activation energy was calculated at 36.1 kJ/mol in the temperature range of 278 to 313 K.

Abstract: The development of heterogeneous Fenton-based electrochemical advanced oxidation processes is important for the removal of organic pollutants at industrial level in the near future. This work reports the application of heterogeneous photoelectro-Fenton (HPEF) with UVA light as an enhanced alternative to the more widespread heterogeneous electro-Fenton (HEF) process. The treatment of the antibiotic cephalexin using chalcopyrite as a sustainable catalyst was studied using an undivided IrO₂/air-diffusion cell. XPS analysis showed the presence of Fe(III), Cu(I) and Cu(II) species on the surface. The amount of Fe²⁺ ions dissolved upon chalcopyrite exposure to continuous stirring and air bubbling was proportional to chalcopyrite content. In all cases, the occurrence of pH self-regulation to an optimum value near 3 was observed. The HEF and HPEF treatments of 100 mL of 50 mg L⁻¹ cephalexin solutions with 0.050 M Na₂SO₄ have been studied with 1.0 g L⁻¹ chalcopyrite at 50 mA cm⁻². Comparative homogeneous EF and PEF with dissolved Fe²⁺ and Cu²⁺ catalysts were also performed. HPEF was the most effective process, which can be mainly explained by the larger production of homogeneous and heterogeneous OH and the photodegradation of the complexes formed between iron and organics. The effect of applied current and catalyst concentration on HPEF performance was assessed. Recycling experiments showed a long-term stability of chalcopyrite. Seven initial aromatics and six cyclic by-products of cephalexin were identified, and a plausible degradation route that also includes five final carboxylic acids is proposed.

Abstract: The pH of the seawater was raised with lime before it was used into the process, generating solid precipitates of magnesium that were removed by vacuum filtration. Then this treated seawater was applied to improve the flocculation of clay-based tailings in a highly alkaline environment (pH 11).

Tailings settling assays were conducted by using a PTFE 30 mm turbine type stirrer with an in-situ floc size characterisation utilising the Focused Beam Reflectance Measurement (FBRM) and Particle Vision Measurement (PVM) techniques. After mixing the pulp with the flocculant, the sample was settled, registering the evolution of the mudline and turbidity of the supernatant liquid. When operating with direct seawater at pH 11, magnesium complexes arise that impairs the flocculant performance. The polymer loses selectivity for the particles, causing weak aggregation and low settling rates. However, by diminishing the magnesium content before the seawater is incorporated into the process, the flocculant was able to bridge the particles and achieve a promising flocculation response. Microscopic characterisation of aggregates showed that these were larger and denser, improving the sedimentation rates considerably. The proposed research provides a new strategy to advance in tailings management issues for the mining industry, focusing on plants that use seawater in their operations.

Abstract: This work analyzes the relationship between short-term exposure to fine particulate matter and its incidence of respiratory and cardiorespiratory diseases. It involved the socioeconomic status of the population distributed in representative areas of Santiago de Chile, the capital city of Chile. The data used were collected from monitoring stations of fine particulate matter concentrations, classification of cardio-respiratory diseases, and the annual age distribution of the population in the representative areas of this megacity. Also, morbidity and mortality data and the distribution of the forecast of health by geographic zones within the Metropolitan Region were variables of input. The relative risk results showed that the level of risk from exposure to air pollution is not defined solely by the level of exposure to the pollutant when crossing the information considered. Therefore, the age distribution or quality of life of the population will define the susceptibility of this, being able to increase the risk of becoming ill or dying by being exposed to air pollution. This work showed that the exposed results serve as input data for the realization of studies in this area, regarding the cost-benefit that would be obtained by reducing pollutant emissions to the atmosphere, as well as valuable information to develop better air quality management policies.

Abstract: Black coppers are mineraloids with a high content of Cu and Mn. These have an amorphous crystalline structure that makes them refractory to conventional leaching processes. For this reason, these mineral resources are not incorporated in industrial leaching heap processes and are taken to dumps. In the present study, an agglomerate pretreatment process incorporating NaCl is evaluated, and a curing stage, followed by acid-reducing leaching for Cu and Mn dissolution from a high-grade black copper mineral. For this, an experimental design was developed both to evaluate the impact of the dependent variables on the response, to generate analytical models that represent the copper and manganese recoveries under the set of sampled conditions. The models indicate that the curing time and the NaCl concentration have a primary effect on the recovery of both elements. In contrast, the optimization model suggests that the optimal operating levels are reached at relatively high levels of time (>130 h) and of NaCl concentration (>22 kg/t). 

Keywords: exotic minerals; black copper; chloride reduction; pretreatment; modeling

Abstract: In pyrometallurgical processes refining copper, the main source of loss in the conversion stage is from slag. This paper reports on research work treating converter slag containing high percentages of copper (36 wt%) using ammonium hydroxide at room temperature. Variables analyzed are solution pH, agitation, temperature, NH₄OH concentration and particle size. Results showed that the hydronium ion resulting from ammonium hydroxide dissociation was the main oxidant of copper compounds in slag, such as CuO, Cu₂O and Cu, with the exception of CuFeO₂. The particles contain a large amount of microcracks (porosity) in their refractory structure (analyzed by compositional image capture (BSE)). Thus, the diffusion of the leaching solution through the microcracks making contact with the copper oxides would be allowed. Leaching mechanisms were corroborated by X-ray diffraction and scanning electron microscopy analysis. Increasing temperature and NH₄OH concentration while decreasing particle size obtained higher copper recoveries, reaching values of 84.8%. Under the same conditions, the main impurity (iron) was minimal (<2%). Solution pH also affected slag leaching. Agitation of the solution positively affected the rate of copper extraction. Leaching kinetics of the leaching solution through the porosity formed in the slag was analyzed under the intraparticle diffusion model. The reaction order was 1.2 with respect to the concentration of ammonium hydroxide and the model was inversely proportional to the square of the particle radius. The activation energy obtained was 42.3 kJ/mol for temperature range 283 to 333 K.

Keywords: converter slag; ammonia leaching; microcracks; kinetics

Abstract: Studying the dissolution of chalcocite allows to understand the behavior of the most abundant secondary sulfide ore in copper deposits, while digenite (Cu1.8S) and other intermediate sulfides (Cu2−xS) are often associated with chalcocite. The most common mechanism of dissolution is by two stages, and chloride ions benefit the kinetics of dissolution. In this study, a pure chalcocite mineral (99.9% according to XRD (X-Ray Diffraction) analysis) is leached in chloride media using NaCl and wastewater as the sources of chloride. Magnetic leaching tests are performed at 65, 75, and 95 °C, using a particle size between −150 and + 106 μm. Chloride concentration and leaching time are the main variables. A substantial dissolution of chalcocite was obtained with 0.5 M H2SO4, 100 g/L of chloride and a leaching time of 3 h. The apparent activation energy (Ea) derived from the slopes of the Arrhenius plots was 36 kJ/mol. The XRD analysis proves the presence of elemental sulfur (S0) as the main component in the leaching residue. No significant differences in copper extraction were detected when using 100 g/L of chloride ion or wastewater (39 g/L).

Keywords: sulfide leaching; desalination water; reusing water; waste water

Abstract: Covellite is a secondary copper sulfide, and it is not abundant. There are few investigations on this mineral in spite of it being formed during the leaching of chalcocite or digenite; the other investigations on covellite are with the use of mineraloids, copper concentrates, and synthetic covellite. The present investigation applied the surface optimization methodology using a central composite face design to evaluate the effect of leaching time, chloride concentration, and sulfuric acid concentration on the level of copper extraction from covellite (84.3% of purity). Copper is dissolved from a sample of pure covellite without the application of temperature or pressure; the importance of its purity is that the behavior of the parameters is analyzed, isolating the impurities that affect leaching. The chloride came from NaCl, and it was effectuated in a size range from –150 to +106 μm. An ANOVA indicated that the leaching time and chloride concentration have the most significant influence, while the copper extraction was independent of sulfuric acid concentration. The experimental data were described by a highly representative quadratic model obtained by linear regression (R2 = 0.99) 

Keywords: sulfide leaching; ANOVA; secondary sulfide; CuS

Abstract: Experimental assays and mathematical models, through population balance models (PBM), were used to characterize the particle aggregation of mining tailings flocculated in seawater. Three systems were considered for preparation of the slurries: i) Seawater at natural pH (pH 7.4), ii) seawater at pH 11, and iii) treated seawater at pH 11. The treated seawater had a reduced magnesium content in order to avoid the formation of solid complexes, which damage the concentration operations. For this, the pH of seawater was raised with lime before being used in the process—generating solid precipitates of magnesium that were removed by vacuum filtration. The mean size of the aggregates were represented by the mean chord length obtained with the Focused beam reflectance measurement (FBRM) technique, and their descriptions, obtained by the PBM, showed an aggregation and a breakage kernel had evolved. The fractal dimension and permeability were included in the model in order to improve the representation of the irregular structure of the aggregates. Then, five parameters were optimized: Three for the aggregation kernel and two for the breakage kernel. The results show that raising the pH from 8 to 11 was severely detrimental to the flocculation performance. Nevertheless, for pH 11, the aggregates slightly exceeded 100 µm, causing undesirable behaviour during the thickening operations. Interestingly, magnesium removal provided a suitable environment to perform the tailings flocculation at alkaline pH, making aggregates with sizes that exceeded 300 µm. Only the fractal dimension changed between pH 8 and treated seawater at pH 11—as reflected in the permeability outcomes. The PBM fitted well with the experimental data, and the parameters showed that the aggregation kernel was dominant at all-polymer dosages. The descriptive capacity of the model might have been utilized as a support in practical decisions regarding the best-operating requirements in the flocculation of copper tailings and water clarification. 

Keywords: copper tailings; enhanced flocculation; water recovering; magnesium removal; population balance model; seawater flocculation

Abstract: The fluid phase behavior of liquid–liquid equilibrium (LLE) is an important piece of the separation processes in chemical engineering, mainly for solvent extraction or liquid–liquid extraction. In this work, experimental studies were carried out in the LLE of a ternary system composed of water, ethanol, and ethyl acetate at four different temperatures at atmospheric pressure. A two-step procedure was done for each temperature in the experimental stage. First, the construction of the binodal curve of the ternary system, and second, the determination of the tie-lines (LLE). For the tie-lines, because the configuration of the binodal curve and the refractive index of the liquid phases at equilibrium were known, their compositions were determined. The LLE experimental data were evaluated through the method developed by Marcilla and collaborators. The gamma–gamma approach was used for the modeling, by using the analytical solutions of groups (ASOG), the nonrandom two-liquids (NRTL), and the universal quasichemical (UNIQUAC) models. Results of the thermodynamic modeling were compared with the experimental values, and the deviations of the compositions of the lighter phase were very low for the thermodynamic models used.

Abstract: Using deterministic values of input variables is desirable for process design. However, some of these input variables may present uncertainty, which may drive the designed process to unwanted responses and, consequently, generating large economic damages. This manuscript proposes a methodology for avoiding the scenario earlier described. The methodology considers three steps: (1) deterministic process design, (2) elimination of non-influential input variables using global sensitivity analysis, and (3) classification of the influential input variables using least squares support vector machines (LS-SVM) classifier, whose parameters are tuned through particle swarm optimization (PSO). The proposed methodology was applied in the design of mineral concentration circuits. The results show that the elimination of non-influential input variables from training data helps to improve the accuracy and to prevent the overfitting of LS-SVM classifier. The methodology allows classifying input variables and knowing what combinations will drive the designed process to unwanted conditions. Thus, the proposed methodology could be useful for fault detection and diagnosis in large size processes operating under uncertainty.

Keywords: Least squares support vector machines, Particles swarm optimization, Hybrid kernel, Global sensitivity analysis, Process design, Flotation, Fault detection

Abstract: Optical backscattering (OBS) signal values were used to evaluate the flocculation of kaolin slurries and seek the implications of using seawater. Two anionic flocculants were applied to kaolin suspensions at several dosages and in water of varying pH and electrolyte concentration. An OBS height scan method was used to estimate the degree of aggregation, supernatant quality, and solids concentration of the sediments. The residual solids of the supernatant depended of the extent of particle coagulation before flocculant was added, where the pH and salinity displayed a significant impact on flocculation. The OBS results were highly sensitive to the presence of fine particles, which was estimated in parallel from the focused beam reflectance measurements (FBRM.) In seawater, without flocculant added, the samples had increased root-mean-square scattering (F_rms) values and larger final sediment volume than samples prepared in water with lower electrolyte concentration. This indicates a higher initial state of aggregation of the particles in seawater. Then, the aggregation degree was best linked to the square-weighted chord length distribution of the FBRM data, which intensifies the sensitivity to coarse aggregates. 

Keywords: clays; seawater flocculation; optical backscattering; aggregation state; polyelectrolyte

Abstract: Studying the dissolution of chalcocite allows to understand the behavior of the most abundant secondary sulfide ore in copper deposits, while digenite (Cu1.8S) and other intermediate sulfides (Cu2−xS) are often associated with chalcocite. The most common mechanism of dissolution is by two stages, and chloride ions benefit the kinetics of dissolution. In this study, a pure chalcocite mineral (99.9% according to XRD (X-Ray Diffraction) analysis) is leached in chloride media using NaCl and wastewater as the sources of chloride. Magnetic leaching tests are performed at 65, 75, and 95 °C, using a particle size between −150 and + 106 μm. Chloride concentration and leaching time are the main variables. A substantial dissolution of chalcocite was obtained with 0.5 M H2SO4, 100 g/L of chloride and a leaching time of 3 h. The apparent activation energy (Ea) derived from the slopes of the Arrhenius plots was 36 kJ/mol. The XRD analysis proves the presence of elemental sulfur (S0) as the main component in the leaching residue. No significant differences in copper extraction were detected when using 100 g/L of chloride ion or wastewater (39 g/L).

Keywords: Sorption kinetics, Pre-combustion capture, Post-combustion capture, Gas-solid reaction

Abstract: Hoy en día, el análisis de sensibilidad (AS) es una metodología comúnmente utilizada para identificar parámetros importantes que determinan el comportamiento del modelo. El AS de un modelo permite determinar cómo las incertidumbres en las respuestas del modelo (salidas) se pueden asignar a los valores de los parámetros del modelo (variables de entrada). La literatura relacionada indica que hay varios métodos para realizar el AS. Este trabajo aborda la evaluación comparativa de cuatro métodos ampliamente utilizados para el AS global (ASG): Sobol-Jansen, Sobol-Baudin, Sobol-Owen y Sobol 2007, basados en el concepto de perfil de desempeño introducido por Dolan y Moré (2002) y la extensión hecha por Mahajan et al. (2012). Para evaluar estos métodos, se consideró un conjunto de 21 modelos y sus variaciones, los cuales corresponden a diversas aplicaciones en ingeniería química (tales como lixiviación, red de distribución de agua, molienda, circuito de flotación, entre otros). Estas comparaciones muestran que, aunque los cuatro métodos ASG basados en la descomposición de la varianza demostraron ser bastante estables, el método Sobol-Jansen presentó el mejor rendimiento, ya que es el primero en realizar ASG en el 83% de los modelos considerados y mantiene un alto rendimiento hasta el 100%.

Palabras clave: Análisis de sensibilidad global, incertidumbre, método de Sobol, sensibilidad paramétrica, índices de desempeño.

Abstract: Developing carbon capture and storage (CCS) technology is a promising route to tackle the rising level of atmospheric carbon dioxide (CO2). Capturing CO2 at high temperature by solid sorbents is attractive in both pre-combustion and post-combustion scenarios. This paper highlights the importance of CO2 sorption kinetics and reviews the published research available on the calcium-based sorbents, magnesium-based sorbents, layered double hydroxide sorbents and alkali ceramic-based sorbents. Insights are provided into the main factors affecting the CO2 sorption kinetics such as reaction and mass transfer mechanism, material microstructures and reaction operating conditions. Finally, a few possible research gaps are identified and recommendations for future research are proposed.

Keywords: Sorption kinetics, Pre-combustion capture, Post-combustion capture, Gas-solid reaction

Abstract: The effect of magnesium chloride as an additive of hydrothermal carbonization (HTC) of lignocellulosic biomass (Pinus radiata sawdust) was studied. The HTC tests were carried out at fixed conditions of temperature and residence time of 220 °C and 1 h, respectively, and varying the dose of magnesium chloride in the range 0.0–1.0 g MgCl₂/g biomass. The carbonized product (hydrochar) was tested in order to determine its calorific value (HHV) while using PARR 6100 calorimeter, mass yield by gravimetry, elemental analysis using a LECO TruSpec elemental analyzer, volatile matter content, and ash content were obtained by standardized procedures using suitable ovens for it. The results show that using a dose of 0.75 g MgCl₂/g biomass results in an impact on the mass yield that was almost equal to change operating conditions from 220 to 270 °C and from 0.5 to 1 h, without additive. Likewise, the calorific value increases by 33% for this additive dose, resulting in an energy yield of 68%, thus generating a solid fuel of prominent characteristics.

Keywords: hydrothermal carbonization; waste to energy; additives; lignocellulosic biomass; magnesium chloride

Abstract: Multiphase systems are important in minerals processing, and usually include solid–solid and solid–fluid systems, such as in wet grinding, flotation, dewatering, and magnetic separation, among several other unit operations. In this paper, the current trends in the process system engineering tasks of modeling, design, and optimization in multiphase systems, are analyzed. Different scales of size and time are included, and therefore, the analysis includes modeling at the molecular level (molecular dynamic modeling) and unit operation level (e.g., computational fluid dynamic, CFD), and the application of optimization for the design of a plant. New strategies for the modeling, design, and optimization of multiphase systems are also included, with a strong focus on the application of artificial intelligence (AI) and the combination of experimentation and modeling with response surface methodology (RSM). The integration of different modeling techniques such as CFD with discrete element simulation (DEM) and response surface methodology (RSM) with artificial neural networks (ANN) is included. The paper finishes with tools to study the uncertainty, both epistemic and stochastic, based on uncertainty and global sensitivity analyses, which is present in all mineral processing operations. It is shown that all of these areas are very active and can help in the understanding, operation, design, and optimization of mineral processing that involves multiphase systems. Future needs, such as meso-scale modeling, are highlighted.

Keywords: computational fluid dynamic; molecular dynamics; density functional theory; discrete element simulation; smoothed particle hydrodynamics; flotation; grinding; response surface methodology; machine learning; artificial neural networks; support vector machine; hydrocyclone; global sensitivity analysis; uncertainty analysis

Abstract: This work evaluates a continuous biomass hydrothermal carbonization process through modeling and steady state simulation using the UniSim Design process simulator. The reactive process was divided into four stages: biomass hydrolysis, intermediate compounds degradation, aromatics formation, and polymerization process, which make it possible to obtain the solid product or hydrochar. Pure biomass types and their mixtures were compared, considering hydrochar and carbon yields, H/C, and O/C ratios, and their deviation from the batch process. The results of hydrochar yield indicated that biomass with high cellulose content can perform satisfactorily in the proposed model. In addition, the possibility of carrying out the process in reactive stages together with the recirculation of liquid product, allowed a greater yield with respect to the batch process. It is concluded that the proposed model improves the characteristics of the obtained hydrochar compared to its crude biomass, achieving lower proportions of hydrogen and oxygen in the solid product.

Keywords: Biomass, Computer simulation, Hydrothermal carbonization, Hydrochar

Abstract: Most copper minerals are found as sulfides, with chalcopyrite being the most abundant. However; this ore is refractory to conventional hydrometallurgical methods, so it has been historically exploited through froth flotation, followed by smelting operations. This implies that the processing involves polluting activities, either by the formation of tailings dams and the emission of large amounts of SO2 into the atmosphere. Given the increasing environmental restrictions, it is necessary to consider new processing strategies, which are compatible with the environment, and, if feasible, combine the reuse of industrial waste. In the present research, the dissolution of pure chalcopyrite was studied considering the use of MnO2 and wastewater with a high chloride content. Fine particles (−20 µm) generated an increase in extraction of copper from the mineral. Besides, it was discovered that working at high temperatures (80 °C); the large concentrations of MnO2 become irrelevant. The biggest copper extractions of this work (71%) were achieved when operating at 80 °C; particle size of −47 + 38 µm, MnO2/CuFeS2 ratio of 5/1, and 1 mol/L of H2SO4. 

Keywords: dissolution; CuFeS2; chloride media; manganese nodules

Abstract: A population balance model is used to describe the flocculation of tailings particles in aqueous salt solutions. The synthetic tailings, composed of quartz and kaolin particles, are flocculated in a jar at a constant shear rate where in-situ FBRM determines the size of the aggregates. The model follows the dynamics of aggregation and breakage processes and provides a good approximation to the temporal evolution of aggregate size. The fractal and permeable nature of the aggregates are considered, while the depletion of the collision efficiency allows describing the initial growth of aggregates and subsequent size reduction. The numerical solution requires five parameters, which are obtained by minimizing the difference between experimental size data and model predictions. A specific aim is to study the effect of magnesium hydroxide that is formed at pH ca. 10, and its interaction with flocculant, on the flocculation kinetics parameters. At pH ≥ 10 the aggregates grow less due to the presence of the magnesium hydroxide gel that surrounds quartz, kaolin and flocculant. The fractal dimension is quite stable at pH < 10 with a representative value of 2.7, typical of a clustered network, although in the presence of magnesium at pH ≥ 10 the fractal dimension of the aggregates is only 2.2, typical of Gaussian chains. Tailings aggregates in the presence of hydroxide are smaller and weakly three-dimensional and therefore contribute little to the settling velocity. The aggregation and breakage parameters are largely constant for a particulate system which composition remains unchanged over a pH range, and if the composition changes, for example by precipitation of magnesium hydroxide, then the aggregation parameters are different but close to constant.

Keywords: Clay tailings, Bridging flocculation, Magnesium hydroxide, Population balance modelling, Seawater

Abstract: Oxidized black copper ores are known for their difficulty in dissolving their components of interest through conventional methods. This is due to its non-crystalline and amorphous structure. Among these minerals, copper pitch and copper wad are of great interest because of their considerable concentrations of copper and manganese. Currently, these minerals are not incorporated into the extraction circuits or left untreated, whether in stock, leach pads, or waste. For the recovery of its main elements of interest (Cu and Mn), it is necessary to use reducing agents that dissolve the present MnO2, while allowing the recovery of Cu. In this research, the results for the dissolution of Mn and Cu from a black copper mineral are exposed, evaluating the reducing effect of NaCl for MnO2 through pre-treatment of agglomerate and curing, and subsequently leaching in standard condition with the use of a reducing agent (Fe2+). High concentrations of chloride in the agglomerate process and prolonged curing times would favor the reduction of MnO2, increasing the dissolution of Mn, while the addition of NaCl did not benefit Cu extractions. Under standard conditions, low Mn extractions were obtained, while in an acid-reducing medium, a significant dissolution of MnO2 was achieved, which supports the removal of Cu. 

Keywords: agglomerate; copper pitch; copper wad; curing; pre-treatment

Abstract: The application of guar gum for pyrite depression in seawater flotation was assessed through microflotation tests, Focused Beam Reflectance Measurements (FBRM), and Particle Vision Measurements (PVM). Potassium amyl xanthate (PAX) and methyl isobutyl carbinol (MIBC) were used as collector and frother, respectively. Chemical species on the pyrite surface were characterized by Fourier-transform infrared spectroscopy (FTIR) spectroscopy. The microflotation tests were performed at pH 8, which is the pH at the copper sulfide processing plants that operate with seawater. Pyrite flotation recovery was correlated with FBRM and PVM characterization to delineate the pyrite depression mechanisms by the guar gum. The high flotation recovery of pyrite with PAX was significantly lowered by guar gum, indicating that this polysaccharide could be used as an effective depressant in flotation with sea water. FTIR analysis showed that PAX and guar gum co-adsorbed on the pyrite surface, but the highly hydrophilic nature of the guar gum embedded the hydrophobicity due to the PAX. FBRM and PVM revealed that the guar gum promoted the formation of flocs whose size depended on the addition of guar gum and PAX. It is proposed that the highest pyrite depression occurred not only because of the hydrophilicity induced by the guar gum, but also due to the formation of large flocs, which could not be transported by the bubbles to the froth phase. Furthermore, it is shown that an overdose of guar gum hindered the depression effect due to redispersion of the flocs.

Keywords: seawater flotation; pyrite depression; guar gum; FBRM

Abstract: A population balance model (PBM) is used to describe flocculation of particle tailings in seawater at pH 8 for a range of mixing intensities. The size of the aggregates is represented by the mean chord length, determined by the focused beam reflectance measurement (FBRM) technique. The PBM follows the dynamics of aggregation and breakage processes underlying flocculation and provides a good approximation to the temporal evolution of aggregate size. The structure of the aggregates during flocculation is described by a constant or time-dependent fractal dimension. The results revealed that the compensations between the aggregation and breakage rates lead to a correct representation of the flocculation kinetics of the tailings of particles in seawater and, in addition, that the representation of the flocculation kinetics in optimal conditions is equally good with a constant or variable fractal dimension. The aggregation and breakage functions and their corresponding parameters are sensitive to the choice of the fractal dimension of the aggregates, whether constant or time dependent, however, under optimal conditions, a constant fractal dimension is sufficient. The model is robust and predictive with a few parameters and can be used to find the optimal flocculation conditions at different mixing intensities, and the optimal flocculation time can be used for a cost-effective evaluation of the quality of the flocculant used.

Keywords: clay-based copper tailings; fractal dimension; mixing intensity; population balance model; seawater flocculation

Abstract: Enargite ore (Cu₃AsS₄) is generally processed via pyrometallurgy, with high temperatures that release toxic arsenic (As_xO_y) and sulfur (SO_x) gases. In seeking alternatives that avoid production of noxious gases, this paper discusses batch leaching experiments of mineral mixtures of enargite and pyrite (Cu₃AsS₄ and FeS₂), agitated under ammoniacal media (NH₄OH) using sodium persulfate (Na₂S₂O₈) as an oxidant. The results showed that almost complete leaching of enargite (98%) could be obtained due to the elimination of passivation (S°) by the action of the oxidant. With the help of a deep thermodynamic study and with DRX analysis, it was possible to establish the reaction mechanisms of dissolution of enargite with persulfate in an ammoniacal media. Leaching action selected for enargite, not affecting pyrite present. Enargite leaching can be represented under a heterogeneous kinetic model of reactant diffusion through a porous layer formed at reaction time. Orders of reaction 2.0 and 1.5, for persulfate and ammonium hydroxide concentrations, respectively, were established. Activation energy was calculated at 45.0 kJ/mol. Consecutive evaluations showed that metals present (Cu and As) could be precipitated with sodium sulfide and sodium hydrosulfide at 99% yields, thus generating a solution rich in ammonia that can be re-used in leaching.

Keywords: enargite, Sodium persulfate, Ammonium hydroxide, Leaching, Passivation

Abstract: The declining grades of copper ore associated with the additional processing of clay-based minerals and the use of seawater are problems that copper mining companies are currently facing, where froth flotation and tailing management operations become challenging for operators. In both cases, the detrimental effect is intensified by the presence of calcium and magnesium ions in seawater and their precipitation under alkaline conditions. This research proposes a partial seawater desalination treatment to improve the flotation and thickening performance in clay-containing ore. The proposed seawater treatment promotes the removal of calcium and magnesium ions using carbon dioxide gas and a sodium hydroxide solution. Flotation tests were conducted in a batch cell using synthetic minerals composed of mixtures of chalcopyrite, kaolin, and quartz. Meanwhile, tailings settling assays were performed in a PTFE 30 mm turbine type stirrer with an in-situ characterization of aggregates (using a focused beam reflectance measurement (FBRM) probe). The results showed an improvement in flotation and flocculation performance when tests were carried out with treated seawater at pH > 10.5, where the copper recovery increased from 82% to 95%, compared to seawater without salt removal; meanwhile, the settling rate of flocculated tailing increased from 5.0 m/h to 11.5 m/h. As expected, the sedimentation outcomes showed a clear relationship with the aggregate size. In this context, the partial seawater desalination treatment could be a promising alternative to face the challenges generated by clays and seawater for copper mining companies.

Keywords: Seawater, flotation, Flocculation, Calcium and magnesium removal, Clays, Chalcopyrite

Abstract: Sulfur compounds are removed from petroleum by the addition of sodium hydroxide at a very high concentration. As a result, a residue called spent soda or spent caustic is generated, being extremely aggressive to the environment. In this work, the chemical properties of this residue are described in detail. The sodium hydroxide remains that have not reacted, sulfur compounds, and organic matter are the primary pollutants reported. Additionally, the main characteristics of the methods of treatment used to reduce them are described. This review comes from comprehensive and updated research and bibliographic analysis about the investigation on the topic. The advantages and disadvantages of the different treatment methods are highlighted. We established some criteria to set out when assessing the application of each one of these treatments is considered. 

Keywords: biological processes; electrochemical processes; oxidation processes; petroleum; phenols; sulfides

Abstract: Response surface methodology has been applied in numerous studies using polynomial models despite some of them exhibit poor correlation coefficient R2R2, which implies an incorrect optimization. In this work, a methodology for obtaining response surfaces when a small data set is available and its behavior is complex is presented. The methodology consists of four steps. First, the classic experimental design is used for obtaining a data set. Second, using the experimental results from a design of experiment, the classical kriging is employed for estimating properties at unsampled locations. Third, a response surface is obtained by training an artificial neural network using the kriging-estimated data set, and a hybrid algorithm based on differential evolution and backpropagation algorithms. The verification of the model is accomplished with the experimental data set. Fourth, the uncertainty quantification is utilized for studying the behavior of the response against uncertainties, which guarantee the robustness of the model developed. The methodology was applied to three cases, considering verification, validation, and uncertainty quantification. The results indicate that the proposed methodology is robust, and it provides more stable response surfaces than the approaches commonly used for polynomials and artificial neural networks. As a result, better optimal conditions are attained.

Keywords: Response surface methodology, classical kriging, artificial neural networks, uncertainty quantification, hybrid algorithm

Abstract: The scope of this work is to determine the effect of initial acidity and electric field intensity on the Electrokinetic Remediation of manganese and zinc from mine tailings from a Chilean copper mine. To achieve this objective, experiments were carried out focusing on the effect of the applied electric field (1 and 2 V cm⁻¹), the H₂SO₄ concentration during pretreatment (1 and 2 mol L⁻¹) and the interaction between these factors in manganese and zinc concentration. From the obtained results, manganese and zinc can be removed from the analyzed tailings, with the maximum net removal 31.88% and 17.95%, respectively. The enhancement of electromigration was proven by an Analysis of Variance with a significance level of 10% for the soluble and total metal concentration in the cathodic zone, where total concentration was increased to 24% and 11% for zinc and manganese, respectively.

Keywords: Electric field, Soil remediation, Electrokinetic remediation, Mine tailings, Heavy metal removal

Abstract: Con el objetivo de aumentar la concentración de sólidos de sedimentos de un relave minero, se utilizó agua de mar con cantidades reducidas de calcio y magnesio. Los experimentos se efectuaron considerando un relave sintético, compuesto por cuarzo y caolinita, y utilizando un floculante aniónico de alta masa molecular. El agua de mar generó un comportamiento eficiente al trabajar a pH < 9. Sin embargo, a mayor alcalinidad la concentración de sólidos del sedimento se redujo sustancialmente. Examinando los principales iones por separado se encontró que el magnesio, y en menor medida el calcio, son los principales responsables de reducir la eficiencia del proceso, producto de la formación de complejos MgOH⁺/CaOH⁺ y precipitados de Mg(OH)₂. Por este motivo, al utilizar el agua de mar con concentraciones reducidas de calcio y magnesio se logró aumentar considerablemente la concentración de sólidos, ofreciendo una alternativa eficaz para operar a condiciones altamente alcalinas.

Palabras clave: agua de mar; arcillas; calcio y magnesio; espesadores; relaves

Abstract: Hydrothermal carbonization (HTC) is a thermochemical technology of biomass conversion that has some advantages: lower operating temperature than other technologies, ability to process biomass with high moisture content and generation of a final product with a higher calorific value than the original biomass and with hydrophobic characteristics. This study evaluated the influence of temperature, time, biomass blend, nature and dose of additive in the HTC process. The response variables were mass yield (MY) and higher heating value (HHV), generating a total of 128 experiments that were grouped in 8 complete factorial designs (24 ). Pressed olive (OLV), oat husks (AV), Pinus radiata sawdust (AS), and raps seeds (RPS) were used as raw biomass. MY and HHV had an R2 above 0.90 using the response equations of Experimental Design. Results indicate that temperature was the main effect in both responses, since it produced a decrease of MY between 5 and 10 %, and an increase of HHV between 1.5 and 2.2 MJ / kg. Use of additives did not significantly improve the energy yield. On the other hand, addition of a ‘more reactive’ biomass with increasing temperature achieved an important improvement in the HHV value. It is a positive fact because the studied biomass presents strong seasonal and geographical availability.

The design of a flotation circuit based on optimization techniques requires a superstructure for representing a set of alternatives, a mathematical model for modeling the alternatives, and an optimization technique for solving the problem. The optimization techniques are classified into exact and approximate methods. The first has been widely used. However, the probability of finding an optimal solution decreases when the problem size increases. Genetic algorithms have been the approximate method used for designing flotation circuits when the studied problems were small. The Tabu-search algorithm (TSA) is an approximate method used for solving combinatorial optimization problems. This algorithm is an adaptive procedure that has the ability to employ many other methods. The TSA uses short-term memory to prevent the algorithm from being trapped in cycles. The TSA has many practical advantages but has not been used for designing flotation circuits. We propose using the TSA for solving the flotation circuit design problem. The TSA implemented in this work applies diversification and intensification strategies: diversification is used for exploring new regions, and intensification for exploring regions close to a good solution. Four cases were analyzed to demonstrate the applicability of the algorithm: different objective function, different mathematical models, and a benchmarking between TSA and Baron solver. The results indicate that the developed algorithm presents the ability to converge to a solution optimal or near optimal for a complex combination of requirements and constraints, whereas other methods do not. TSA and the Baron solver provide similar designs, but TSA is faster. We conclude that the developed TSA could be useful in the design of full-scale concentration circuits. 

Keywords: design; flotation circuits; Tabu-search algorithm; multispecies

Abstract: The effect of alkali metal chlorides on the viscoelastic behavior and yielding properties of silica suspensions was studied through creep-recovery and dynamic oscillatory tests with stress control. Then, the viscoelasticity of the pulps was correlated with the silica zeta potential, aggregate size, and the percentage of cations adsorbed on the surface of the ore. The results indicate that larger cations are more prone to adhere to the silica surface, which increases the number of ionic bonds that bind the particles. This generates stronger particle networks and a greater agglomeration of particles, especially those smaller than 10 µm. As the size of the bare cations increases, the rheological response provides higher values of yield stress, complex viscosity, and viscoelastic moduli, but in turn, pulps undergo minor deformations under the application of stress. Dynamic oscillatory tests suggest structural changes, with the phase angle following the inverse relationship with the bare cation size, indicating that the liquid-like character of the pulps increases as the size of the cations increase. 

Keywords: Hofmeister series; oscillatory dynamic tests; rheology; saline medium; silica pulp; viscoelasticity

Abstract: This research aimed to identify the copper ion removal mechanism when using protonated dry alginate beads. This mechanism was explained through ion exchange between Cu ions and the protons from the functional groups of the alginate beads. Copper removal increased with stirring velocity, reaching values of 97.5 mg g-1 (97.5×10-3 kg/kg of PDAB) of dry alginate at 200 rev min-1, at a solution pH of 6.0 and a run time of 360 min. For the lowest level of copper concentrations, at 10 mg dm-3 (10×10-6 kg dm-3), full removal was attained. The removal kinetics was represented by a pseudofirst order model. A value of 0.0131 min-1 was found for the velocity constant. Under equilibrium conditions, the experiment data was fit to the Langmuir adsorption model, and the highest removal values were 270.3, 222.2 (222.2×10-3 kg/kg of PDAB) and 49 mg g-1 (49×10-3 kg/kg of PDAB) for pH values of 5.0, 3.5 and 2.5, respectively. These are higher than most sorbents used in the literature for copper removal. Increased temperature leads to higher Cu removal. The activation energy was calculated at 9.3 kJ mol-1 for the temperature range of 283 to 343K. Observations using SEM and composition measurements of the alginate cross-section taken by EDS showed a uniform distribution of the copper concentration through the structure of the alginate beads, independent of the solution pH, contact time and temperature. 

Keywords: Removal mechanism, copper ions, alginate beads, pseudo-first order kinetics model, activation energy

Abstract: Dissolution kinetics of digenite (Cu9S5) was studied in Fe3+-H2SO4-NaCl media. The temperature range for the study was between 297 and 373 K (24 and 100°C), with a ferric concentration between 0.0100 and 0.0806 mol/dm3, a sulfuric acid concentration of 0.05 to 1.5 mol/dm3 and a NaCl concentration of 1.5 to 5 mol/dm3. Agitation speed and particle size were also studied. Results indicate that the dissolution mechanisms of digenite occurs in two stages: i) generation of covellite (CuS) with the formation of cupric ion (Cu2+) and ii) dissolution of covellite (CuS) with copper production in the system, as well as amorphous sulfur (S°). The second stage occurred very slowly compared to the first stage, the above variables studied directly affected the second stage. Temperature, Fe3+ and H2SO4 concentration positively affected dissolution of covellite formed (second stage), while the presence of NaCl did not increase dissolution of Cu9S5 or CuS. Results showed that stirring speed had an important role in the dissolution rate of CuS. Dissolution kinetics was analyzed using the model of diffusion through the porous layer. Covellite dissolution reaction order was 2.3 and 0.2 with respect to the concentration of ferric and sulfuric acid, respectively, and the rate was inversely proportional to particle size. The calculated activation energy was 36.1 kJ/mol, which is a typical value for a reaction controlled by diffusion in the porous layer at temperature between 297 and 373 K (24 and 100°C). 

Keywords: dissolution kinetics, digenite, covellite, diffusion

Abstract: Converter slags are by-products of pyrometallurgical processing of copper concentrates in Chile, which contain significant amounts of copper (close to 40.0% in the material considered here), converting them from a passive material (material that is not feasible to process) to an active material (it can be processed). This study analyses column leaching of converter slag with the use of ammonium hydroxide. A preliminary analysis was carried out on acid leaching (in an agitated system). Later, in ammonia medium, several variables were assessed, including particle size and NH₄OH concentration, as well as different grades of acid purity to adjust the pH of the leaching solution. The experiments were carried out in 1.2 m high columns with a cross-section diameter of 7.5 × 10⁻² m, using 2.0 kg of slag. The results show that using an acid system (i.e. ordinary leaching), reagent consumption reached 473.9 kg H₂SO₄/ton of slag, with copper recovery of only 50.8% and Fe recovery of over 67.0%. On the other hand, using an ammonia system, the recovery values reached 87.7% for Cu, with almost no impurities, with reagent consumption of 3.8 kg H₂SO₄/ton of slag. The working pH was 10.5. These recovery levels are due to the leaching of Cu₂O and Cu° from the converter slag. When using an acid contaminated with impurities to adjust the pH, the copper extraction rate was increased. The impurities of antimony, bismuth and arsenic are not significant. The copper in pregnant solution (PLS) obtained was put into contact with NaSH to generate hydrated chalcanthite (CuSO₄·5H₂O) with a high grade of purity, while the remaining solution can be returned to the leaching stage due to its high level of ammonia content. 

Keywords: Column leaching, Converter slag, Grade C acid, Precipitation with NaSH

Abstract: The handling of large gas volumes containing low SO₂ concentrations is still a challenge for the industry. Here is possible to identify an opportunity for a cleaner production by using novel solvents such as ionic liquids (ILs) specially biodegradables Deep Eutectic Solvents (DES) as an alternative of amine-based absorbents which are volatile and easily degrades and may produce further contamination and health hazard. The present work analyses the performance of four DESs were under dynamic conditions (in a packed-bed column) for SO₂ absorption. The results were compared with the absorption capacities published for the same DESs under static conditions identifying essential differences to consider in a large-scale implementation. At low SO₂ partial pressure (600 ppm), chemical absorption becomes the most important mechanism, and thus, the chemical nature of the DES determines the absorption capacity. DESs containing amine groups showed superior absorption, and between the thiourea- and urea-containing DESs, the former exhibited the best performance, which was not related to its viscosity nor its initial solution pH but rather to the chemical interaction of functional groups in the DES promoting ionic interaction with generated sulphites.

Keywords: Ionic liquids, Deep eutectic solvents, Choline chloride, Sulphur dioxide, Gas absorption, Packed bed column

Abstract: Mining effluents contain cobalt ions that can damage humans and flora. However, this metal also has high commercial value when recovered. The objective of this research work was to recover cobalt (Co2+) from diluted solutions using a biosorbent, specifically protonated dry alginate beads (PDAB). Experimental work was carried out in batch from an initial concentration of 22×10-6 kg dm-3 Co2+ and 80 mg alginate. Variables such as agitation, pH solution, experimental time, isotherm values, and temperature were analyzed. Maximum cobalt recoveries were obtained at pH values above 5.0, reaching 60.6×10-3 kg kg-1 of PDAB. Cobalt recovery occurred with ion exchange mechanisms from alginate carboxyl group proton release. Experimental data had excellent fit with both the Lagergren kinetic model (pseudo-first order) and the Langmuir isotherm model. As temperature increased, cobalt recovery increased. The calculated activation energy was 12.8 kJ mol-1. Compositional measurements obtained by scanning electron microscope and energy-dispersive X-ray spectroscopy for alginate crosssections showed uniform distributions of cobalt concentrations throughout the spherical alginate structure, independent of solution pH, contact time, or temperature. Furthermore, elution gave significant cobalt re-extraction (98.2%) and demonstrated PDAB reusability. 

Keywords: recovery mechanism, cobalt ions, alginate beads, kinetic adsorption model, elution

Abstract: In this study, the viscoelastic properties of quartz and kaolin suspensions in seawater were analysed considering two distinct conditions: pH 8 and 10.7. Creep and oscillatory sweep tests provided therheological parameters. An Anton Paar MCR 102 rheometer (ANAMIN Group,Santiago, Chile)was used with a vane-in-cup configuration, and the data were processed with RheoCompassTM Lightsoftware(ANAMINGroup,Santiago,Chile). The out comes were associated with the formation of solid species principally composed of magnesium precipitates. The magnesiumin solution reduced in the presence of quartz (68 wt %), from 1380 to 1280 mg/L. Since the difference was not large regarding the solid-free seawater, the disposition of solid complexes at pH 10.7 was expected to be similar. The jump in pH caused both yield stress and viscoelastic moduli to drop, suggesting that the solid precipitates diminished the strength of the particle networks that made up the suspension. For the kaolin slurries (37 wt %), the yield stress raised when the pH increased, but unlike quartz, there was significant adsorption of magnesium cations. In fact, the concentration of magnesium in solution fell from 1380 to 658 mg/L. Dynamic oscillatory assays revealed structural changes in both pulps; in particular, the phase angle was greater at pH 8 than at pH 10.7, which indicates that at more alkaline conditions, the suspension exhibits a more solid-like character. 

Keywords: viscoelasticity; quartz; kaolin; seawater; magnesium precipitates

Abstract: This research aims to analyse the effect of sodium polyacrylate on the rheological behaviour of kaolin pulps in seawater by means of rheograms and dynamic oscillatory assays. Then, the rheological properties were associated with zeta potential and particle aggregation/dispersion phenomena. Seawater raised the rheological properties compared to distilled water, generating an evident non-Newtonian behaviour, characterised by the appearance of yield stress, followed by a shear-thinning behaviour. This occurred because the high concentration of electrolytes compresses the ionic cloud that surrounds the particles' surfaces, overcoming the electrostatic repulsions, but besides, the seawater counterions (like Mg and Na) contribute to forming cationic bridges between the anionic particles. The addition of sodium polyacrylate did not induce significant alterations on the zeta potential; however, this formed a steric stabilisation where chord length measurements showed a greater presence of fine particles and fewer kaolin aggregates. The yield stress significantly diminished after polymer addition, while the viscoelastic modules and complex viscosity indicate that sodium polyacrylate reduces the strength of the particle networks that make up the slurry, but in turn, the phase angle indicates increase in its solid-like character. 

Keywords: Kaolin, Seawater, Sodium polyacrylate, Steric stabilisation, Rheology, Viscoelasticity

Abstract: The water activities of unsaturated solutions of potassiumperchlorate + poly(ethylene glycol) + water at 298.15, 308.15 and 318.15 K and densities and viscosities at 288.15, 298.15 and 308.15 K were measured experimentally. The concentration range of the solutions was from 0.2 to 0.8 mass % of poly(ethylene glycol) with an average molecular weight of 4000 and from 0.25 to 1.25 mass % of KClO₄. The water activity data show that in the PEG–salt–water system, KClO₄ has a significant effect on the water activities and the vapour pressures; a slight increase in water activities with increasing temperature was also observed. Density and viscosity decrease as temperature increases and both properties increase as KClO₄ and PEG-4000 concentrations increase. The electrolyte and polymer non-random two liquid models, extended for the representation of water activity, excess molar volume and dynamic viscosity, were applied. Good agreement between the experimental and correlated data was obtained, since for the ternary system, the average absolute deviations calculated at all temperatures studied for the water activity, density and viscosity were 0.0067, 0.72 and 2.91%, respectively. 

Keywords: Thermodynamic and transport properties, Electrolyte solutions, Polymer, NRTL model

Abstract: This work evaluates the hydrothermal carbonization (HTC) process as a method to upgrade the quality of biomass residues to be used as fuels in gasification or combustion processes. Seven residues from Chilean biomass were characterized thermochemically before and after being processed by HTC. Additionally, the kinetics of devolatilization and combustion were studied. HTC produces biomass with lower ash content, higher carbon content and higher heating value than the original biomass. Herbaceous wastes showed lower heating values (LHV) around 20% higher after HTC process, while increases around 10% in woody and agroindustrial wastes and corn (even being herbaceous wastes) were observed. The chlorine values obtained after HTC indicate the possibility of using the herbaceous, woody and industrial wastes studied as fuels without chlorine related problems. The activation energy (E_a) values from cellulose and hemicellulose decomposition were higher after HTC process, while lower E_a values from lignin decomposition were found. The combustion characteristic temperatures, ignition temperature (T_i), peak temperature (T_p), and burnout temperature (T_b), were delayed towards higher temperatures with HTC process for all residues. Moreover, the reactivity (R) and combustibility index (S) were lower after HTC, indicating slower combustion for the samples after HTC. Finally, the results show that HTC is a promising process to homogenize the kinetic parameters and the combustion behavior of the samples, thus increasing the interchangeability of the samples in combustion or gasification systems. 

Keywords: Hydrothermal carbonization, Hydrochar properties, Combustion behavior, Pyrolysis kinetics, TGA, Biomass residues

Abstract: This article studies the mechanisms of electrochemical production of ferrate (VI) using a boron-doped diamond (BDD) electrode. Ferrate was synthesized using different current densities, electrolysis time and concentrations of Fe(NO₃)₃, FeSO₄, FeCl₃ and FeCl₂. The ferrate generation rate was highly affected by the initial concentration and the type of iron salt. The results suggest that diffusion is the controlling mechanism at the BDD electrode. However, for iron salts with oxidation state +2, electron charge also takes place. Cyclic voltammetries showed that the oxidation peak that correlated with ferrate generation is close to the potential where •OH radicals occur. This indicates that a direct electron transfer from the BDD and an indirect oxidation through •OH radicals influenced the generation of ferrate. Although Fe(NO₃)₃ and FeSO₄ oxidation does not perform as well as iron chloride salts in the generation of ferrate, they do not form chlorate and perchlorate. This study demonstrates that it is possible to produce a powerful oxidant that could be used for water treatment purposes without generating toxic by-products. 

Keywords: Electrosynthesis, Cyclic voltammetry, Ferrate, Boron doped diamond

Abstract: The implications of physical conditions of the feedwell on the rheological properties of synthetic copper tailings, flocculated in seawater, were analysed. The mixing intensity of flocculation was related to the structural characteristics of the aggregates, and the outcomes were linked to the yield stress of the pulp sediments. Tailings settling assays were conducted by using a 30 mm turbine type stirrer with an in-situ aggregate size characterisation. The structural characteristics of the aggregates were determined by using the focused beam reflectance measurement (FBRM). After a mixing time between the pulp and the flocculant, the sample was allowed to settle for 2.5 h, where the variation of the sediment height was minimal. The sediment was gently removed and subjected to rheological characterisation. The yield stress was measured on an Anton Paar MCR 102 rheometer (ANAMIN Group, Santiago, Chile), with a vane-in-cup configuration. The mixing intensity was related to the characteristics of the aggregates, and the outcomes were linked to the yield stress of the flocculated pulp sediments. More aggressive hydrodynamics deteriorated the structure of the aggregates, promoting the reduction of both its size and the fractal dimension. This brought direct consequences on the rheological properties of the sediments: at higher mixing level, the yield stress was lower. The explanation lies in the structural changes of the aggregates, where at a fixed mixing rate, the yield stress presented a seemingly exponential increase over the fractal dimension. Additionally, correlations were found between the rheological properties with settling rate and aggregate size.

Keywords: seawater; copper tailings; rheology; fractal aggregates; thickening

Abstract: The deposits of Fe-Mn, in the seabed of the planet, are a good alternative source for the extraction of elements of interest. Among these are marine nodules, which have approximately 24% manganese and may be a solution to the shortage of high-grade ores on the surface. In this investigation, an ANOVA analysis was performed to evaluate the time independent variables and MnO2/reducing agent in the leaching of manganese nodules with the use of different Fe reducing agents (FeS2, Fe2+, Fe0 and Fe2O3). Tests were also carried out for the different reducing agents evaluating the MnO2/Fe ratio, in which the Fe0 (FeC) proved to be the best reducing agent for the dissolution of Mn from marine nodules, achieving solutions of 97% in 20 min. In addition, it was discovered that at low MnO2/Fe ratios the acid concentration in the system is not very relevant and the potential and pH were in ranges of −0.4–1.4 V and −2–0.1 favoring the dissolution of Mn from MnO2.

Keywords: MnO2; acid media; ANOVA; dissolution

Abstract: The dissolution kinetics of synthetic molybdite (MoO₃) in a potassium hydroxide (KOH) medium was studied by varying the system temperature, KOH concentration, and particle size. Additionally, the effects of the stirring rate and different reagents such as barium hydroxide (Ba(OH)₂), calcium hydroxide (Ca(OH)₂), and sodium hydroxide (NaOH) were also evaluated. The experiments were performed in a reactor with controlled temperature and agitation. The results indicated that the dissolution reaction mechanism of molybdite generates potassium molybdate (K₂MoO₄) without intermediate compounds. Temperature (6–80 °C), KOH concentration (0.0005–0.025 mol/L), and particle size (5–40 μm) positively affected the dissolution of molybdite. The maximum Mo recovery was 67.5% in 0.25 h for 80 °C and 0.01 mol/L KOH. At the lowest temperature (6 °C), which is near the freezing point of water (0 °C), a substantial amount of Mo was recovered (17.8% in 45 min). The kinetics equation describing the molybdite dissolution in a KOH environment indicated that diffusion occurs through the porous layer. The activation energy was calculated to be 47.81 kJ/mol. A reaction order of 1.0 with respect to KOH concentration was obtained and was found to be inversely proportional to the squared particle size. The kinetics equation was obtained. The dissolution of molybdite resulting from the oxidation of a molybdenite concentrate (MoS₂) led to a low molybdenum recovery, which was primarily caused by the consumption of KOH by impurities such as CaCO₃ and Cr(MO₄)₃.

Keywords: molybdite dissolution, kinetics, potassium hydroxide

Abstract:A short-time and low-cost synthesis route was used to produce large lateral size (from 2 to 15 μm) from monolayers to few layers of graphene by a two-step process of electrochemical exfoliation with a deep eutectic solvent in a mixture with water that can be reused, and ultrasonic bath. The graphene was characterized by SEM, TEM, AFM, Raman and electrochemical activity. During the electrochemical exfoliation, high expanded graphene particles were obtained and these were dispersed in a mixture of water with 5%wt ethylene glycol by an ultrasonic bath in order to complete the exfoliation process. An enhancement of the electrical conductivity of these dispersions was obtained with the increase of graphene concentration, 0.38 mg/mL, which best result was achieved with 30 wt% water and a DC voltage of 10 V. It was possible to add a conductive layer to a glass substrate with the graphene obtained and Tyndall effect was observed.

KEYWORDS: graphene, deep eutectic solvent, electrochemical exfoliation, expanded graphite

Abstract:Pharmaceuticals have low biodegradability and can retain their chemical structure for long periods of time leading to an accumulation in the environment causing irreversible changes. Electrochemical oxidation has been proved to be an environmentally friendly and economically viable solution for bio-refractory of organic molecules as well as for the disinfection of wastewaters. This paper aims to evaluate the performance of specific energy consumption for a given reduction of toxic organic compound loads in a continuous flow bipolar packed-bed electrochemical reactor and compare this with a classical parallel plate reactor. The energy cost for both the parallel plate and bipolar electrochemical reactors are similar (around 1.6 kWh m^-3) lower than other advanced oxidation process reported in literature. However, the bipolar configuration is particularly suitable for low conductivity waste water and/or for avoiding the formation of organochloride compounds in a chloride rich wastewater.

Keywords: electroxidation, advanced oxidation process, tin oxide electrode, pharmaceutical compounds, bipolar electrochemical reactor, Diclofenac

Abstract:ZnO nanorod arrays were prepared by electrodeposition from a zinc nitrate precursor on seed layers of the oxide fabricated by spin coating on fluor-tin-oxide (FTO) covered glass substrates. The morphological, structural, and optical properties of the arrays were analyzed by scanning electronic microscope, X-ray diffraction, and ultraviolet-visible spectroscopy. The nanorods were used as electron transport material in CH3NH3PbI3-xClx sensitized perovskite solar cells that were characterized by X-ray diffraction. The performance of the cells was investigated using current-voltage measurements. They showed an open circuit voltage of 0.85 V, a short-circuit current of 6.8 mA cm-2 ,a fill factor of 0.46 and 2.4% power conversion efficiency under 1 sun of illumination.

Abstract:Dew harvesting can be a supplementary source of freshwater in semiarid and arid areas. Several experiments on small-scale dew condensers (usually of 1 m²) have been carried out in many places in the world; however, few experiments have been conducted on large-scale collectors integrated into buildings. This work aims to assess one year of dew water harvesting in Combarbalá (Chile) using a painted galvanised steel roof as collecting surface. The roof (36 m²) was coated with a high-infrared-emissivity paint containing aluminosilicate minerals (OPUR, France). Dew measurements were conducted daily from September 2014 to August 2015. The dew yield and its relationship with meteorological variables were analysed. The results show that despite the low nocturnal relative humidity throughout the year (average: 48%), dew collection occurred on 56.1% of the recorded days. The daily average collection rate was 1.9 L d⁻¹, with a maximum of 15 L d⁻¹. The maximum daily dew yield is correlated strongly with relative humidity and correlated weakly with air temperature and wind speed. Considering the same rooftop can collect dew and rain, it was estimated that over one year dew water could contribute to roughly 8.2% of the total water collected, considering both sources.

Keywords: atmospheric water, dew collection, radiative cooling, water resources

Abstract:The use of various electrolyte materials in a lithium ion battery must be studied under stable electrochemical conditions; therefore, the LiClO₄ activity coefficients in water at the temperatures described in this work are the result of an electrochemical cell (ISE): Na-ISE|LiClO₄(m)|ClO₄-ISE. For this study, the determination of activity coefficients was carried out using the Pitzer and Debye–Hückel equations to represent the relationship between log γ and molality. For the system used with the electrochemical cell, it has good the behavior of mean ionic activity coefficients of LiClO₄ for all temperatures, and at a temperature of 298.15 K, there is good agreement between the experimental data and the data in the literature.

Abstract: Cuprite is a difficult oxide to leach under acidic conditions (for the maximum extraction of 50%). In this research, the feasibility of leaching cuprite in an ammoniacal medium was studied. The working conditions addressed here were the liquid/solid ratio (120:1–400:1 mL/g), stirring speed (0–950 r/min), temperature (10–45 °C) and NH₄OH concentration (0.05–0.15 mol/L). In addition, different ammoniacal reagents (NH₄F and (NH₄)₂SO₄) were analyzed. The experiments were performed in a 2 L reactor with a heating mantle and a condenser. The most important results were that the maximum leaching rate was obtained at pH 10.5, 0.10 mol/L NH₄OH, 45 °C, 4 h, 850 r/min and a liquid/solid ratio of 400:1, reaching a copper extraction rate of 82%. This result was related to the non-precipitation of copper in solution by the formation of copper tetra-amine. The liquid/solid ratio and stirring speed were essential for increasing the cuprite leaching. The maximum leaching rate was achieved at higher temperatures; however, significant copper leaching rate occurred at temperatures near the freezing point of water (17.9% over 4 h). Increasing NH₄OH concentration and decreasing particle size increased the cuprite leaching rate. The two ammoniacal reagents (NH₄F and (NH₄)₂SO₄) had low extraction rate of copper compared with NH₄OH. The kinetic model representing cuprite leaching was a chemical reaction on the surface. The order of the reaction with respect to the NH₄OH concentration was 1.8, and it was inversely proportional to the radius of the ore particles. The calculated activation energy was 44.36 kJ/mol in the temperature range of 10–45 °C.

Keywords: leaching, cuprite, ammonium hydroxide, copper tetra-amine, reaction kinetics

Abstract: The effect of bubble accumulation on anodic potential and current in the conversion of Fe²⁺/Fe³⁺ under porous electrodes (316L, ε = 78.73, a_e = 11 150 m² m⁻³) is studied. It was observed that when the electrolyte flow is under 2 mL s⁻¹ and the electrode thickness (L) is greater than 0.62 mm, the coalescence of bubbles blocks the electrode, thereby reducing the electroactive area and increasing the electrical resistance, which produces elevation and important oscillations in anodic potential. For higher flows between 8 and 16 mL s⁻¹, the potential tends to be uniform over time. The average measurement of anodic potential indicated that for working conditions of I = 0.1 A, L = 0.64 mm, the flow increases from 2 to 8 mL s⁻¹, reducing the average anodic potential value by 35%, while for I = 0.5 A, L = 1.86 mm, flow of 2 and 16 mL s⁻¹ reduces the average anodic potential by approximately 11%.

KEYWORDS: Porous electrode, parallel volumetric cell, potential and current distribution

Abstract:The quality of Education in Chile is a controversial topic which has been in the public debate in the last several years. To ensure quality in graduate programs, accreditation is compulsory. The current article presents a model to improve the process of self-regulation. The main objective was to design a Model of Quality Assurance for Postgraduate Programs in order to constitute a theoretical, mathematical and informatics reference that would optimize the processes of self-regulation, self-evaluation and accreditation of master and doctorate programs from the Universidad Católica de la Santísima Concepción, Chile. This descriptive research is based on a mixed methods approach. The proposal was intended through theoretical and empirical references related to the accreditation systems. The analysis process was conducted with key informants, and the informatics instrument was created and validated through expert judgment. After the analysis, the model was optimized considering the expert’s suggestions. As a result of the optimization process, a matrix of eight dimensions was obtained and it is available online in order to be used by the heads of postgraduate programs. Finally, a model with four main stages was achieved in order to install a self-regulation and a self-evaluated culture that leads to accreditation as evidence of the quality of postgraduate programs.

Keywords: quality of education, digital technologies, online platform, benchmark of quality, postgraduate programs

Abstract: The present mini-review focuses on recent applications of ionic liquid (IL) and deep eutectic solvents (DES) in biphasic oxidations where the oxidizing agent corresponds to the hydrogen peroxide. Biphasic reactions are accomplished when the substrate presents low or moderate solubility in aqueous (polar) systems and/or when separation of products and by-product is an issue. The properties of the IL and DES, allows to intensify reaction activity. On the other hand, the high chemical stability of the ionic solvents allows the use of the hydrogen peroxide minimizing the solvent degradation and unwanted byproducts. The experimental evidence presented in this work show that IL and DES can be used as co-catalysts, catalysts and solvents achieving enhanced yields and conversions. The process advantages, in terms of reduction of volatile solvents improve the safety and the use of the oxidizing agent, implying the possibility of new process improvements to be developed in the future.

Abstract: The use of deep eutectic solvent (DES)/water mixtures were explored for the selective enzymatic synthesis of α‐monobenzoate glycerol (α‐MBG) from glycerol and benzoic acid as substrates. Experiments were performed with four DES, three of them containing choline chloride (ChCl), combined with urea (URA), glycerol (GLY), and ethylene glycol (ETA) (in all cases ChCl/HBD 1:2 mol ratio), and another one formed with methylammonium chloride and glycerol (MA/GLY 1:3 mol ratio). The best conversions (99 %) were achieved with immobilized lipase B from Candida antarctica (CAL‐B) when ChCl/GLY was used as the solvent and the substrate at the same time. The use of water as a cosolvent (8 % v /v ) led to a significant decrease in the viscosity of the DES, and full conversions were then reached. Reusability studies of the biocatalyst revealed a 37 % decrease in activity after the first batch, but the activity remained mostly constant for the rest of the cycles.

Abstract: Food fermentations are important to obtain different products such as bread, beer, mead, wine, yogurt, among other. The rate of fermentation is generally monitored by the measurement of simple variables like pH, Brix, titratable acidity and volume increase (in case of bread’s dough). Isothermal microcalorimetry has been used to evaluate bacterial growth in medical, clinical, environmental and food fields. This work aims to show the potentiality of isothermal microcalorimetry as a tool for monitoring different fermentations. Yogurt fermentations were performed on 100 mL milk in isothermal conditions at 45°C with types of pasteurized milk (cow and goat), fermented by two activated commercial yogurt starters (with a different combination of Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus and a dose of 0.4 % w/v). Apricot juice fermentations were performed on 4 mL glass vials (15 Bx, pH 4.5) in isothermal conditions at 15°C with six different type of commercial yeasts (Saccharomyces cerevisiae with a dose of 0.3 % w/v). Dough fermentations were performed on 4mL Hastelloy vials in isothermal conditions at 30°C with different flours (wheat, cornstarch, teff, commercial gluten free mixture and buckwheat) and commercial bread yeast (Saccharomyces cerevisiae with a dose of 1.0 % w/w). All fermentations evaluated show a different behaviour for heat flow and accumulated heat: (1) for yogurt has a strong influence related to kind of milk as well as starter used. (2) for apricot juice has a strong influence related to kind of yeast used as well as its concentration. (3) for dough has a strong influence related to kind of flour used as well as the inclusion of wheat flour. These results confirm isothermal calorimetry can be combined with other techniques in order to be useful for monitoring different industrial fermentations and evaluating changes in formulation and process

Abstract: Electroanalysis is applied to study reactions that involves oxidations and reductions. Currently, there are different studies that report electroanalysis used to determine food quality, classification, and evaluation of different types of contaminants or adulterants as well as to quantify different nutrients and functional compounds of interest; however, there are few applications of these techniques for the evaluation of productive processes over time. Mead is one of the oldest and most traditional alcoholic beverages and its production is regulated according to the initial must (water content, honey and other raw materials) and final product physicochemical characteristics. Normally alcoholic honey must fermentation is usually monitored by using traditional techniques such as pH, acidity, Brix, density, and others such as liquid and gas chromatography, Proton Transfer Reaction – Mass Spectrometry as well as electronic nose and tongue. There are different studies related to mead fermentation that report yeast selection, effect of nitrogen sources, immobilization, addition of different flavour enhancers such as spices and fruits, among others. In this work some of traditional techniques and electroanalysis were applied to evaluate mead fermentation process during time for mead production at 25°C for 30 days. It was found that it is possible to follow during time alcoholic fermentation by using commercial sensors and techniques such as cyclic and square wave voltammetry, because there is a relationship to sugars consumption during fermentation, as well as to organic acids generation, converting electroanalysis in a useful tool to evaluate fermentative processes.

Abstract: La miel es utilizada como edulcorante natural. El origen botánico o geográfico de las mieles se establece mediante análisis
palinológico y sensorial. El uso de técnicas rápidas como la nariz electrónica puede ser una alternativa para la clasificación de
mieles. En este estudio se validaron los parámetros operativos de una nariz electrónica comercial para determinar el perfil del olor
de miel. Se utilizó un diseño compuesto central con cinco factores, tres niveles y 28 ensayos, variando la cantidad de muestra (1, 2 y
3g), la temperatura de incubación (30, 40 y 50°C), el tiempo de incubación (10, 20 y 30min), el flujo de gas (50, 150 y 250mL/min)
y el tiempo de inyección (100, 200 y 300 s). La nariz comercial contaba con diez sensores. La repetibilidad se evaluó con un
coeficiente de variación de 10%. Se utilizó la metodología de superficie de respuesta y se encontraron las siguientes condiciones: 3g
de muestra, incubación a 50°C por 17min, flujo de gas de 100mL/min y tiempo de muestreo de 150s. Finalmente, estos parámetros
se utilizaron para analizar 19 muestras de miel, las cuales se clasificaron según sus perfiles de olor, demostrando así que puede ser
una herramienta útil para clasificar mieles.

Palabras clave: Miel, nariz electrónica, validación y perfil olfativo.