Producción científica

Año 2020:

Leaching Chalcopyrite with an Imidazolium-Based Ionic Liquid and Bromide

Trabajo de investigación desarrollado por el Dr. Pedro Robles.  Publicado en la revista Minerals.

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

Assessment of the Supply Chain under Uncertainty: The Case of Lithium

Trabajo de investigación desarrollado por el Dr. Freddy Lucay. Publicado en la revista Minerals

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.

 

Black and organic carbon fractions in fine particulate matter by sectors in the South Hemisphere emissions for decision-making on climate change and health effects

Trabajo de investigación desarrollado por el Dr. Ernesto Pino y Dr. Samuel Carrasco, Publicado en la revista Environmental Science and Pollution Research.

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.

Improving the Flocculation Performance of Clay-Based Tailings in Seawater: A Population Balance Modelling Approach

Trabajo de investigación desarrollado por el Dr. Pedro Robles Publicado en la revista Minerals

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. 

 

Seabed mineral resources, an alternative for the future of renewable energy: A critical review

Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en la revista Ore Geology Reviews.

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.

Valorization of Municipal Solid Waste using Hydrothermal Carbonization and Gasification: A review

Trabajo de investigación desarrollado por el Dr. Ernesto Pino Publicado en la revista Chemical Engineering Transactions

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.

An Experimental Study for Municipal Organic Waste and Sludge Treated by Hydrothermal Carbonization

Trabajo de investigación desarrollado por el Dr. Ernesto Pino Publicado en la revista Chemical Engineering Transactions

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

Design, Cost Estimation and Sensitivity Analysis for a Production Process of Activated Carbon from Waste Nutshells by Physical Activation

Trabajo de investigación desarrollado por el Dr.Marcelo León, Dr. Javier Silva y Dr. Samuel Carrasco. Publicado en la revista Processes

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.

 

Manganese Nodules in Chile, an Alternative for the Production of Co and Mn in the Future—A Review

Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en la revista Minerals

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. 

 

Activity Coefficients of NaClO4 in (PEG 4000 + H2O) Mixtures at (288.15, 298.15 and 308.15) K.

Trabajo de investigación desarrollado por el Dr. Jaime Morales. Publicado en la revista Iranian Journal of Chemistry and Chemical Engineering

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.

The effect of regrinding on the design of flotation circuits

Trabajo de investigación desarrollado por el Dr. Freddy Lucay. Publicado en la revista Minerals Engineering.

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.

Mechanism and Kinetics of Malachite Dissolution in an NH4OH System

Trabajo de investigación desarrollado por el Dr. Álvaro Aracena y Javiera Pino. Publicado en la revista Metals

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.

 Treatment of antibiotic cephalexin by heterogeneous electrochemical Fenton-based processes using chalcopyrite as sustainable catalyst

Trabajo de investigación desarrollado por el Dr. Carlos Carlesi Publicado en la revista Science of The Total Environment

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.

Enhancing the sedimentation of clay-based tailings in seawater by magnesium removal treatment

Trabajo de investigación desarrollado por el Dr. Pedro Robles.  Publicado en la revista Separations and Purification Technology.

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.

Effect of socioeconomic status on the relationship between short-term exposure to PM2.5 and cardiorespiratory mortality and morbidity in a megacity: the case of Santiago de Chile

Trabajo de investigación desarrollado por el Dr. Ernesto Pino y Dr. Samuel Carrasco .  Publicado en la revista Air Quality Atmosphere And Health

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.

Optimization of Cu and Mn Dissolution from Black Coppers by Means of an Agglomerate and Curing Pretreatmens

Trabajo de investigación desarrollado por el Dr. Pedro Robles.  Publicado en la revista Metals

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). 

 

Ammoniacal System Mechanisms for Leaching Copper from Converter Slag

Trabajo de investigación desarrollado por el Dr Álvaro Aracena. Publicado en la revista Metals

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.

 

Leaching of pure chalcocite in a chloride media using waste twaer at high temperature

Trabajo de investigación desarrollado por el Dr. Pedro Robles.  Publicado en la revista Metals

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 leachingdesalination waterreusing waterwaste water

Statistical Study for Leaching of Covellite in a Chloride Media

Trabajo de investigación desarrollado por el Dr. Pedro Robles.  Publicado en la revista Metals

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)

 

Reducing the Magnesium Content from Seawater to Improve Tailing Flocculation: Description by Population Balance Models

Trabajo de investigación desarrollado por el Dr. Pedro Robles.  Publicado en la revista Metals

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. 

An LS-SVM classifier based methodology for avoiding unwanted responses in processes under uncertainties

Trabajo de investigación desarrollado por el Dr. Freddy Lucay  Publicado en la revista Computers and Chemical Engineering

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

Thermodynamic behavior of the phase equilibrium of ethyl acetate+ethanol+water systems at atmospheric pressure: Experiment and Modeling

Trabajo de investigación desarrollado por el Dr. Pedro Robles.  Publicado en la revista Journal of Cheemical nd Engeneering Data

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.

Analysis of kaolin flocculation in seawater by optical backscattering measurements: Effect of flocculant management and liquor conditions

Trabajo de investigación desarrollado por el Dr. Pedro Robles.  Publicado en la revista Minerals

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 (Frms) 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. 

Recent advances on kinetics of carbon dioxide capture using solid sorbents at elevated temperatures

Trabajo de investigación desarrollado por el Dr. Gianni Olguín. Publicado en la revista Applied Energy

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

Performance profiles for benchmarking of global sensitivity analysis algorithms

Trabajo de investigación desarrollado por el Dr. Freddy Lucay Publicado en la Revista Mexicana de Ingeniería Química

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.

Recent advances on kinetics of carbon dioxide capture using solid sorbents at elevated temperatures

Trabajo de investigación desarrollado por el Dr. Gianni Olguín. Publicado en la Revista Applied Energy

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

Experimental Study on Hydrothermal Carbonization of Lignocellulosic Biomass with Magnesium Chloride for Solid Fuel Production

Trabajo de investigación desarrollado por los Drs. Javier Silva, Ernesto Pino y Samuel Carrasco. Publicado en la Revista Processes

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.

 

Trends in Modeling, Design, and Optimization of Multiphase Systems in Minerals Processing

Trabajo de investigación desarrollado por el Dr. Freddy Lucay Publicado en la Revista Minerals

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 dynamicmolecular dynamicsdensity functional theorydiscrete element simulationsmoothed particle hydrodynamicsflotationgrindingresponse surface methodologymachine learningartificial neural networkssupport vector machinehydrocycloneglobal sensitivity analysisuncertainty analysis

Modeling and simulation of a continuous biomass hydrothermal carbonization process

Trabajo de investigación desarrollado por los Drs. Samuel Carrasco, Ernesto Pino y Javier Silva. Publicado en la revista Chemical Engineering Communications.

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

Analysis of the flocculation process of fine tailings particles in saltwater through a population balance model

Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en la revista Separation and Purification Technology

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

Leaching Chalcopyrite with High MnO2 and Chloride Concentrations

Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en la Revista Metals.

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: dissolutionCuFeS2chloride mediamanganese nodules

Reducing-Effect of Chloride for the Dissolution of Black Copper

Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en la Revista Metals.

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: agglomeratecopper pitchcopper wadcuringpre-treatment

Depression of Pyrite in Seawater Flotation by Guar Gum

Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en la Revista Metals.

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.

Describing Mining Tailing Flocculation in Seawater by Population Balance Models: Effect of Mixing Intensity

Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en la Revista Metals.

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.

Partial seawater desalination treatment for improving chalcopyrite floatability and tailing flocculation with clay content

Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en la Revista Minerals Engineering 

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

Enargite leaching under ammoniacal media with sodium persulfate and consecutive precipitation of As/Cu with Na2S/NaHS

Trabajo de investigación desarrollado por el Dr. Álvaro Aracena. Publicado en la Revista Hydrometallurgy

Abstract: Enargite ore (Cu3AsS4) is generally processed via pyrometallurgy, with high temperatures that release toxic arsenic (AsxOy) and sulfur (SOx) 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

Characteristics and Treatment of Wastewater from the Mercaptan Oxidation Process: A Comprehensive Review

Trabajo de investigación desarrollado por el Dr. Ernesto Pino Cortés. Publicado en la Revista Process 

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. 

Modeling of the Complex Behavior through an Improved Response Surface Methodology

Trabajo de investigación desarrollado por el Dr. Freddy Lucay. Publicado en la Mineral Processing and Extractive Metallurgy Review.

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.

Año 2019:

Electrokinetic remediation of manganese and zinc in copper mine tailings 

Trabajo de investigación desarrollado por el Dr. Álvaro Aracena y el Dr. Rodrigo Ortiz. Publicado en Journal of Hazardous Materials.

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

Remoción de Calcio y Magnesio en Agua de Mar para Mejorar la Concentración de Sólidos en la Descarga de Espesadores

Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en Información Tecnológica.

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

 Performance Evaluation of Biomass Blends with Additives Treated by Hydrothermal Carbonization

Trabajo de investigación desarrollado por los Drs. Ernesto Pino y Samuel Carrasco. Publicado en Chemical Engineering Transactions.

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.

Design of Flotation Circuits Using Tabu-Search Algorithms: Multispecies, Equipment Design, and Profitability Parameters

Trabajo de investigación desarrollado por el Dr. Freddy Lucay. Publicado en Revista Minerals

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

Analysis of Silica Pulp Viscoelasticity  in Saline Media: The Effect of Cation Size 

Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en Revista Metals.

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

Uptake of copper ion using protonated dry alginate beads from dilute aqueous solutions 

Trabajo de investigación desarrollado por el Dr. Álvaro Aracena. Publicado en Physicochemical Problems of Mineral Processing 

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

Dissolution kinetics of secondary covellite resulted from digenite dissolution in ferric/acid/chloride media 

Trabajo de investigación desarrollado por el Dr. Álvaro Aracena. Publicado en Physicochemical Problems of Mineral Processing 

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

Converter slag leaching in ammonia medium/column system with subsequent crystallisation with NaSH 

Trabajo de investigación desarrollado por el Dr. Álvaro Aracena. Publicado en Revista Hidrometallurgy

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

Greener gas capture in deep eutectic solvents aqueous solutions: Performance in a dynamic condition

Trabajo de investigación desarrollado por lo/as Drs. Carlos Carlesi y Dreidy Vásquez. Publicado en Journal of Cleaner Productions

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

    Recovery of cobalt ions from diluted solutions by means of protonated dry alginate beads 

    Trabajo de investigación desarrollado por el Dr. Álvaro Aracena. Publicado en Physicochemical Problems of Mineral Processing 

    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

    Viscoelasticity of Quartz and Kaolin Slurries in Seawater: Importance of Magnesium Precipitates

    Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en Revista Metals.

    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

    Analysis of sodium polyacrylate as a rheological modifier for kaolin suspensions in seawater 

    Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en Applied Clay Science

    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

    Measurement and modelling of water activity, density and viscosity of the KClO4 + poly(ethylene glycol) + H2O system at various temperatures

    Trabajo de investigación desarrollado por el Dr. Jaime Morales. Publicado Journal of Molecular Liquids

    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

    Effect of hydrothermal carbonizationon the properties, devolatilization, and combustion kinetics of Chilean biomass residues 

    Trabajo de investigación desarrollado por el Dr. Ernesto Pino. Publicado Revista Biomass and Bioenergy

    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 (Ea) values from cellulose and hemicellulose decomposition were higher after HTC process, while lower Ea values from lignin decomposition were found. The combustion characteristic temperatures, ignition temperature (Ti), peak temperature (Tp), and burnout temperature (Tb), 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

    Unravelling the mechanisms controlling the electro-generation of ferrate using four iron salts in boron-doped diamond electrodes

    Trabajo de investigación desarrollado por la Dra. Macarena Cataldo. Publicado en Journal of Electroanalytical Chemistry

    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

    Copper Tailing Flocculation in Seawater: Relating the Yield Stress with Fractal Aggregates at Varied  Mixing Conditions

    Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en Revista Metals.

    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

    Leaching Manganese Nodules in an Acid Medium and Room Temperature Comparing the Use of Different Fe Reducing Agents 

    Trabajo de investigación desarrollado por el Dr. Pedro Robles. Publicado en Revista Metals.

    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

    Año 2018:

    Dissolution kinetics of molybdite in KOH media at different temperatures

    Trabajo de investigación desarrollado por el Dr. Álvaro Aracena. Publicado en Science Direct

    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

    Large scale cathodic exfoliation of graphite using deep eutectic solvent and water mixture

    Trabajo de investigación desarrollado por el la Dra. Dreidy Vásquez, Dr. Álvaro Aracena y Dr. Carlos Carlesi. Publicado en Fullerenes, Nanotubes and Carbon Nanostructures

    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.

    Bipolar Packed-bed Electrochemical Reactor for the Degradation of Diclofenac; a Bio-refractory Organic Compound

    Trabajo de investigación desarrollado por el la Dr Jaime Morales, Dr. Álvaro Aracena y Dr. Carlos Carlesi. Publicado en Periodica Polytechnica Chemical Engineering

    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
     

    Electrodeposition of ZnO Nanorods as Electron Transport Layer in a Mixed Halide Perovskite Solar Cell

    Trabajo de investigación desarrollado por Ana Burgos, Rodrigo Schrebler, Gustavo Cáceres, Humberto Gómez. Publicado en International Journal of Electrochemical Science

    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.

    Roof-integrated dew water harvesting in Combarbalá, Chile

    Trabajo de investigación desarrollado por el Dr. Danilo Carvajal y el Dr. Alvaro Aracena. Publicado en Journal of Water Supply: Research and Technology-Aqua 

    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.

    Thermodynamic Study of LiClO4 Activity Coefficients in Aqueous Solution at (288.15, 298.15, and 308.18) K

    Trabajo de investigación desarrollado por el Dr. Jaime Morales y el Dr. Carlos Carlesi. Publicado en Journal of Chemical and Engeneering Data

    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.

    Leaching of cuprite through NH4OH in basic systems

    Trabajo de investigación desarrollado por el Dr. Alvaro Aracena y Dr. Danilo Carvajal. Publicado en Science Direct

    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

    Bubble formation effect over the potential and current during functioning of 316 L stainless steel
    porous electrode in a parallel volumetric cell

    Trabajo de investigación desarrollado por el Dr. Robinson Constanzo. Publicado en Canadian Metallurgical Quarterly

    Abstract: The effect of bubble accumulation on anodic potential and current in the conversion of Fe2+/Fe3+ under porous electrodes (316L, ε = 78.73, ae = 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 electrodeparallel volumetric cellpotential and current distribution

    Año 2017:

    Quality Assurance for Postgraduate Programs: Design of a Model Applied on a University in Chile

    Trabajo de investigación desarrollado por el Dr. Eduardo Meyer Aguilera. Publicado en International Review of Research in Open and Distance Learning

    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

    Applications of Liquid/Liquid Biphasic Oxidations by Hydrogen Peroxide with Ionic Liquids or Deep Eutectic Solvents

    Trabajo de investigación desarrollado por el Dr. Carlos Carlesi y Dr. Jaime Morales Publicado en ChemPlusChem 

    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.

    Water as Cosolvent: Nonviscous Deep Eutectic Solvents for Efficient Lipase-Catalyzed Esterifications

    Trabajo de investigación desarrollado por el Dr. Carlos Carlesi. Publicado en Chemestry Europe.

    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 % /) 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.

    Microcalorimetry as a Tool for Monitoring Food Fermentations

    Trabajo de investigación desarrollado por Dra. Martha Cuenca. Publicado en Semantic Scholar.

    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

    Electroanalysis applied to monitor mead fermentations

    Trabajo de investigación desarrollado por Dra.Martha Cuenca. Publicado en Chemical Engineering Transactions 

    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.

    Validación de la técnica de nariz electrónica para la determinación del perfil olfativo de miel de abejas

    Trabajo de investigación desarrollado por Dra. Martha Cuenca. Publicado en Chemical Engineering Transactions 

    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.