Elemental Sulfur Layer Research Articles

(Electro)catalytic oxidation of sulfide and recovery of elemental sulfur from sulfide-laden streams

MnxOy coated over TiO2 nanotube array substrate was doped with Mo and polyaniline (PANI) and applied for electrochemical desulfurization of concentrated sulfide (HS−) solutions at basic pH, typical of biogas scrubbing solutions and industrial wastewater. Mo and PANI co-dopants significantly enhanced the anode activity towards sulfide oxidation and ensured its complete stability even in highly corrosive sulfide solutions (e.g., 200 mM HS−). This was due to the increased electrochemically active surface area, improved coating conductivity and reduced charge transfer resistance. The (electro)catalytic oxidation of HS− demonstrated robust performance with very limited impact of different operational parameters (e.g., dissolved oxygen, anode potential, HS− concentration). Due to the formation of elemental sulfur (S0) layer at the anode surface at basic pH, longer term anode usage requires its periodic removal. Chemical dissolution of S0 with toluene allows its rapid removal without affecting the anode activity, and easy recrystallization and recovery of pure sulfur.

Designer Cathode Additive for Stable Interphases on High-Energy Anodes.

Rechargeable lithium-based batteries built with high-energy anode materials (e.g., silicon-based and silicon-derivative materials) are considered a feasible solution to satisfy the stringent requirements imposed by emerging markets, including electric vehicles and grid storage, due to their higher energy density compared to contemporary lithium-ion batteries. The robustness of the solid electrolyte interphase (SEI) layer on high-energy anodes is critical to achieve long-term and stable cycling performances of the batteries. Herein, we propose a new type of designer cathode additive (DCA), i.e., an ultrathin coating layer of elemental sulfur on the cathode, for the in situ formation of a thin and robust SEI layer on various types of high-energy anodes. The DCA elemental sulfur undergoes simultaneous oxidation and reduction paths, forming lithium alkyl sulfate (R-OSO2OLi) and poly(ethylene oxide) (PEO)-like polymers on the anode surface. The as-formed R-OSO2OLi/PEO-modified SEI layer has good lithium cation (Li+) permeability to facilitate fast ion transportation across the interphases and superior elasticity to adapt to large volume changes, which is particularly effective for improving the cycling efficiency of high-energy anodes (e.g., ca. 14-35% increase in capacity retention for the silicon-carbon composite (SiC) or silicon-tin alloy (Si-Sn)||LiFePO4 cells). The present work opens a new avenue toward the practical deployment of high-energy rechargeable lithium-based batteries.

Nitric Acid Dissolution of Tennantite, Chalcopyrite and Sphalerite in the Presence of Fe (III) Ions and FeS2.

This paper describes the nitric acid dissolution process of natural minerals such as tennantite, chalcopyrite and sphalerite, with the addition of Fe (III) ions and FeS2. These minerals are typical for the ores of the Ural deposits. The effect of temperature, nitric acid concentration, time, additions of Fe (III) ions and FeS2 was studied. The highest dissolution degree of sulfide minerals (more than 90%) was observed at a nitric acid concentration of 6 mol/dm3, an experiment time of 60 min, a temperature of 80 °C, a concentration of Fe (III) ions of 16.5 g/dm3, and an addition of FeS2 to the total mass minerals at 1.2:1 ratio. The most significant factors in the break-down of minerals were the nitric acid concentration, the concentration of Fe (III) ions and the amount of FeS2. Simultaneous addition of Fe (III) ions and FeS2 had the greatest effect on the leaching process. It was also established that FeS2 can be an alternative catalytic surface for copper sulfide minerals during nitric acid leaching. This helps to reduce the influence of the passivation layer of elemental sulfur due to the galvanic linkage formed between the minerals, which was confirmed by SEM-EDX.

Hydrothermal Treatment of Arsenopyrite Particles with CuSO4 Solution.

The nature of the hydrothermal reaction between arsenopyrite particles (FeAsS) and copper sulfate solution (CuSO4) was investigated in this study. The effects of temperature (443–523 K), CuSO4 (0.08–0.96 mol/L) and H2SO4 (0.05–0.6 mol/L) concentrations, reaction time (1–120 min), stirring speed (40–100 rpm) and particle size (10–100 μm) on the FeAsS conversion were studied. The FeAsS conversion was significant at >503 K, and it is suggested that the reaction is characterized by the formation of a thin layer of metallic copper (Cu0) and elemental sulfur (S0) around the unreacted FeAsS core. The shrinking core model (SCM) was applied for describing the process kinetics, and the rate of the overall reaction was found to be controlled by product layer diffusion, while the overall process was divided into two stages: (Stage 1: mixed chemical reaction/product layer diffusion-controlled) interaction of FeAsS with CuSO4 on the mineral’s surface with the formation of Cu1+ and Fe2+ sulfates, arsenous acid, S0, and subsequent diffusion of the reagent (Cu2+) and products (As3+ and Fe2+) through the gradually forming layer of Cu0 and molten S0; (Stage 2: product layer diffusion-controlled) the subsequent interaction of CuSO4 with FeAsS resulted in the formation of a denser and less porous Cu0 and S0 layer, which complicates the countercurrent diffusion of Cu2+, Cu1+, and Fe2+ across the layer to the unreacted FeAsS core. The reaction orders with respect to CuSO4 and H2SO4 were calculated as 0.41 and −0.45 for Stage 1 and 0.35 and −0.5 for Stage 2. The apparent activation energies of 91.67 and 56.69 kJ/mol were obtained for Stages 1 and 2, respectively.

Leaching Chalcocite in Chloride Media—A Review

Chalcocite is the most abundant secondary copper sulfide globally, with the highest copper content, and is easily treated by conventional hydrometallurgical processes, making it a very profitable mineral for extraction. Among the various leaching processes to treat chalcocite, chloride media show better results and have a greater industrial boom. Chalcocite dissolution is a two-stage process, the second being much slower than the first. During the second stage, in the first instance, it is possible to oxidize the covellite in a wide range of chloride concentrations or redox potentials (up to 75% extraction of Cu). Subsequently, CuS2 is formed, which is to be oxidized. It is necessary to work at high concentrations of chloride (>2.5 mol/L) and/or increase the temperature to reach a redox potential of over 650 mV, which in turn decreases the thickness of the elemental sulfur layer on the mineral surface, facilitating chloride ions to generate a better porosity of this. Finally, it is concluded that the most optimal way to extract copper from chalcocite is, during the first stage, to work with high concentrations of chloride (50–100 g/L) and low concentrations of sulfuric acid (0.5 mol/L) at a temperature environment, as other variables become irrelevant during this stage if the concentration of chloride ions in the system is high. While in the second stage, it is necessary to increase the temperature of the system (moderate temperatures) or incorporate a high concentration of some oxidizing agent to avoid the passivation of the mineral.

Extraction of copper from chalcopyrite with potassium dichromate in 1-ethyl-3-methylimidazolium hydrogen sulfate ionic liquid aqueous solution

Developing new and sustainable leaching system with limited release of pollutant and low acid and energy consumption is a challenge for copper extraction from chalcopyrite. In this work, a hydrometallurgical process for chalcopyrite dissolution in 1-ethyl-3-methyl-imidazolium hydrogen sulfate ([EMIm]HSO4) media with potassium dichromate (K2Cr2O7) was developed, and the leaching behavior of chalcopyrite with various parameters, such as kinds of ionic liquids (ILs), concentrations of [EMIm]HSO4 and K2Cr2O7, stirring speed, leaching temperature, and particle size were discussed in detail. The result show that the most effective ILs medium for chalcopyrite dissolution was varied with the specific oxidant. The leaching rate of chalcopyrite was significantly enhanced by increasing temperature, concentrations of K2Cr2O7 and [EMIm]HSO4, and decreasing particle size, while it has little to do with the increasing of stirring speed. The maximum copper extraction yield of 90.2% was reached within 90 min under the following optimized conditions: 10 g/L of solid/liquid ratio, 10 vol% of [EMIm]HSO4 concentration, 0.1 M of initial K2Cr2O7 concentration, stirring speed of 200 rpm, the temperature of 70 °C and particle size of −45 µm. The leaching process of chalcopyrite in [EMIm]HSO4-K2Cr2O7 aqueous solution follows an empirical kinetic model 1-2/3x-(1-x)2/3=kdt with the apparent activation energy of 36.26 kJ/mol, which was limited by the diffusion through a protect layer of elemental sulfur and pyrite.

Dissolution mechanism of the oxidation process of covellite by ferric and ferrous ions

This study explores the influences of external iron ions on the dissolution behavior of covellite minerals at different temperatures. External iron ions can significantly accelerate covellite dissolution. The copper extraction of acid covellite leaching was less than 5%, while the addition of external iron ions (ferric or ferrous ions, Fe3+/Fe2+) effectively enhanced covellite dissolution. Covellite copper extraction with 0.1 mol/L Fe2+ was 25% at 303 K and 40% at 318 K after 18 days, and for leaching systems with 0.1 mol/L Fe3+, it was approximately 40% at 303 K and 60% at 318 K. The dissolution process of covellite with external iron ions can be divided into two stages. The dissolution kinetics at the first stage are controlled by the chemical reaction between iron ions and covellite, as the generated elemental sulfur has not yet blocked the covellite surface. Compared with ferrous ions, ferric ions further increase the dissolution rate of covellite, which is also suggested by the scanning electron microscopy analysis results. Additionally, Fe3+ accelerates the release of copper ions by effectively reducing the particle size of covellite. In the second stage (copper extraction >40%), the reaction kinetics shift to the mixed control of the surface chemical reaction with iron ions and diffusion due to the accumulation of an elemental sulfur layer on the surface. Although Fe2+ cannot directly oxidize covellite, the electron exchange between Fe2+ and oxygen is improved through the covellite mineral, which is attributed to its metallic properties. Then, the ferric ions generated in the above process gradually corrode covellite. In addition, the temperature rise can significantly accelerate the oxidation reaction process of iron ions with covellite by forming a more porous corrosive structure. Finally, leaching bacteria (Acidithiobacillus caldus and Leptospirillum ferriphilum) are proved to boost copper extraction from covellite by transforming Fe2+ into Fe3+ and eliminating surface elemental sulfur passivation. However, dense passivation layers inevitably form on the covellite surface at the end of bioleaching, which passivates the subsequent dissolution process.

Formation mechanisms of surface passivating phases and their impact on the kinetics of galena leaching in ferric chloride, ferric perchlorate, and ferric nitrate solutions

Hydrometallurgical leaching of Pb from galena is an environmentally friendly alternative to the traditional pyrometallurgical processing. Leaching produces secondary phases passivating the surface of galena and has a negative impact on the leaching rate and Pb extraction, yet a comprehensive understanding of surface passivation is lacking. Here we studied galena leaching in FeCl3, Fe(ClO4)3, and Fe(NO3)3 solutions, using the ex situ leaching-quenching-characterization method complemented by in situ synchrotron powder X-ray diffraction. We examined the effect of salt concentration (0.42 and 0.84 M), temperature (35–90 °C), time (up to 1440 h), solid-weight-to-fluid-volume ratio (0.5–50 g·L−1), and particle size (up to 355 μm) on the mechanisms and kinetics of galena leaching. The results show that leaching in FeCl3 was least effective due to precipitation of a cotunnite (PbCl2) layer on galena surface, and a layer of elemental sulfur on cotunnite, forming a core/mantle/shell structure (i.e., galena/cotunnite/sulfur), which restricted Pb extraction to less than 9%. Sulfur encapsulated PbCl2 and limited its dissolution even when the bulk solution remained undersaturated with respect to PbCl2. Leaching in Fe(ClO4)3 and Fe(NO3)3 solutions was more effective than in FeCl3, achieving 100% Pb extraction. Leaching in Fe(NO3)3 was fastest among the three iron salts. Porous elemental sulfur was the only secondary phase formed using Fe(NO3)3 and Fe(ClO4)3 and the leaching reactions follow the interface-coupled dissolution-reprecipitation mineral replacement mechanism. The effect of passivation was observed when the elemental sulfur layer reached ~20 μm thick. The activation energies calculated by the modified “time-to-a-given-fraction” method were 5.4–67.2 kJ·mol−1 for leaching with Fe(ClO4)3 and 11.4–56.8 kJ·mol−1 with Fe(NO3)3, indicating that leaching was controlled by surface reactions and phase boundary diffusion. This study provides new insights into the mechanisms controlling surface passivation due to the mineralogical and textural compositions of the passivating layers and the resulting leaching kinetics. It provides scientific bases for the development of heap and in situ leaching protocols for Pb extraction from galena ores.

The response of sulfur chemical state to different leaching conditions in chloride leaching of chalcocite

Heap chloride leaching of low-grade copper sulfides with the use of seawater has been proposed as a feasible alternative to address challenges associated with water scarcity and depletion of oxides. Our previous study of leaching kinetics showed that the leaching reaction slowed down in the second stage and the maximum copper extraction achieved at ambient temperature was around 70–80%. To uncover the reasons for the slowed-down leaching, we investigated the evolution of solid surface properties during leaching, particularly morphology and sulfur chemical state, and the responses of mineral surface properties to different leaching conditions using SEM-EDX and XPS techniques. The results showed that sulfur sequentially transformed from monosulfide S2− to disulfide S22−, and then to polysulfide Sn2− and elemental sulfur S0. Less elemental sulfur was present on the solid particle surfaces at high solution potentials, the removal of which by CS2 washing did not improve copper extraction. In contrast, at low solution potentials, a slight increase in copper extraction was associated with sulfur removal from the solid surfaces. These results led to the conclusion that the slow decomposition of polysulfide formed during leaching was responsible for the slow reaction at high solution potentials, whereas at low solution potentials, a combination of polysulfide decomposition and diffusion barrier by elemental sulfur layer was the reason for the slow dissolution. The effect of chloride was concluded to be important only at low solution potentials where the level of elemental sulfur crystallinity was lower.

The kinetics of enargite dissolution in chloride media in the presence of activated carbon and AF 5 catalysts

This paper pertains to the kinetics study of atmospheric dissolution of enargite in chloride media with and without the addition of two different catalysts: (1) granular coconut shell based activated carbon (AC), and (2) a novel carbon-based catalyst with the commercial name of AF 5 Lanxess Lewatit® (AF 5). Unlike AC or other catalysts, AF 5 is capable of collecting solid sulphur particles on its surface during the atmospheric leaching process, leaving behind insignificant elemental sulphur in the oxidative leaching residues.The addition of both AC and AF 5 considerably enhance the leaching efficiency. Only 70% of copper was recovered in 96 h at 90 °C without the catalyst addition. The copper recovery was increased to 92% and 96% in the presence of AC and AF 5 respectively, in the concentrate to catalyst weight ratio of 1:1. The Cu2+ ions are found to be the main oxidant in the enargite leaching procedure. It was shown that the diffusion of Cu2+ ions through the product layer on the partially-leached enargite particles is the controlling step of the leach process, and the addition of the AC and AF 5 catalysts did not change the process controlling mechanism. The shrinking core model (SCM) has been used as the general kinetic model to study the enargite leaching kinetics at different temperatures. Scanning electron microscopy images of the partially-leached minerals confirmed that no impermeable elemental sulphur layer was formed on the enargite surface.

添加 NaCl 提高黄铜矿的铜提取率

The addition of NaCl in the ammonium persulfate-APS (as an oxidant) leaching was investigated. APS has some advantages compared with conventional oxidants and its standard redox potential (E°) is 2.0 V. Effect of six parameters such as NaCl concentration, APS concentration, temperature, time, liquid–solid ration (L/S), and stirring speed on the leaching behavior was studied. Results showed that metals extraction increased with increasing of NaCl concentration, APS concentration, leaching temperature (up to 333 K), and L/S ratio. During oxidative leaching of sulfide minerals, the occurrence of elemental sulfur layer on particle surface is known as primary problem that causes low metal extraction. According to the results, the passivation effect of sulfur layer and low dissolution problems can be eliminated in the presence of chloride ions. Copper and iron extraction yields were obtained as 75% and 80%, respectively under leaching conditions as follows: APS concentration 250 g/L; NaCl concentration 150 g/L; time 180 min; temperature 333 K; stirring speed 400 r/min; and L/S 250 mL/g.

The mechanism of electrochemical dissolution of sphalerite in sulfuric acid media

The dissolution of sphalerite concentrate from Angouran mine was studied in 0.5M sulfuric acid solution by the application of carbon paste electrode at 22°C. Different electrochemical methods including cyclic voltammetry (CV), chronoamperometry and electrochemical impedance spectroscopy (EIS) were applied to study the behavior of the sphalerite. Results showed that the oxidation of sphalerite proceeds in the anodic potential range of open circuit potential (OCP) to 900mV vs. Ag/AgCl. At low anodic potential of 400mV vs. Ag/AgCl a sulfur−rich passive layer forms on the mineral surface. The predominant reaction on the electrode surface at 400mV vs. Ag/AgCl is oxidative sphalerite dissolution, in which zinc ions and elemental sulfur layer, as a passive layer, form through the electrochemical reaction. By increasing the potential to 550mV vs. Ag/AgCl the passive layer was partially dissolved. Further increase of the potential to 900mV vs. Ag/AgCl results in the complete dissolution of the passive film and active dissolution of sphalerite. The electrochemical oxidation of sphalerite and the formation and dissolution of its passive film were also studied by EIS. Afterwards, the EIS spectra were modeled by equivalent electrochemical circuit. Together, the EIS data and Raman spectroscopy results strongly supported the proposed mechanisms for the oxidative sphalerite dissolution through the anodic potential range.

The role of catalyst in the passivation of chalcopyrite during leaching

In this work, we present as investigation of chalcopyrite leaching under different leach conditions for how liquidation and surface of chalcopyrite study using Scanning Electron Microscopy (SEM) to determine the composition of the passivation layer in the surface of chalcopyrite. The study of chalcopyrite dissolution were in H2SO4 solution systems at pH of 1.2, with 5% chalcopyrite concentrate in redox potential of 460 mV at 90°C. The tests were directed to study on the leaching of chalcopyrite in ferric sulfate solution to extract copper with adding pyrite, silver and silver coated pyrite. In these approaches, achieved recoveries were different. The results showed that, in the present of pyrite, the presence of the elemental sulfur layer formed around the chalcopyrite particles which hindered the complete dissolution of copper in chalcopyrite. Also, in the presence of silver, no commercial process has been developed which successfully as a catalyst to recover copper from chalcopyrite. Because, the precipitation of argentojarosite, which forms during the leaching process, limits the availability of silver ion in solution which may act as a catalyst. But syndicate of silver and pyrite to form of silver coated pyrite, causes dissolution increase. However, in the presence of the pyrite coated by silver, leaching was very rapid for the duration of the test, and complete copper extraction was achieved within 10 hours.

Synchrotron-based XPS and NEXAFS study of surface chemical species during electrochemical oxidation of chalcopyrite

The surface chemical information of massive chalcopyrite electrode during electrochemical oxidation was studied by SXPS, NEXAFS and Raman spectroscopy. The electrochemical studies show that there was an activated region for chalcopyrite anodic dissolution between 550 and 630mV (vs. Ag/AgCl), accompanied by two passive regions nearby. The spectroscopic studies suggest a thin film of non-stoichiometric sulfur-rich layer formed in the first passive region, likely to be responsible for the passivation. In the active region, S22− species and covellite were also found, which could be the cause of the potential surge. When the potential was increased to 650mV, another passive region appeared. At the same time, S22− and covellite started to dissolve, leaving a highly metal deficient polysulfide and elemental sulfur layer on the chalcopyrite surface.

Kinetics of chemical leaching of chalcocite from low-grade copper ore: size-distribution behavior

Kinetics of the chemical leaching of chalcocite from a low-grade copper ore in a ferric sulfate medium was investigated using the constrained least square optimization technique. The experiments were carried out for different particle sizes in both the reactor and column at constant Eh, pH, and temperature. The leaching rate increased with increase in the temperature. About 50% of the Cu recovery was obtained after 2 hours of reactor leaching at 75 o C using the -0.5 mm size fraction. Also about 50% of the Cu recovery was obtained after 60 days of column leaching for the +4-8 mm size fraction. For the fine-particle leaching, the first leaching step was fast, and the rate controlling step was diffusion through the liquid film. The results obtained show that as the leaching proceeds, the chemical reaction control appears. Finally, accumulation of the elemental sulfur layer in the solid product together with the jarosite precipitate causes change in the controlling mechanism to solid diffusion. For the coarse-particle leaching, diffusion through the solid product appeared from the initial days of leaching.

Thermodynamic and XRD analysis of arsenopyrite biooxidation and enhancement of oxidation efficiency of gold-bearing concentrates

Gold found in ores may be associated with sulfidic minerals (mainly arsenopyrite and pyrite). The biooxidation of sulfidic minerals is a method to recover gold from these ores. In this study, the biooxidation of arsenopyrite was investigated, and a method to increase the biooxidation of sulfidic concentrates was proposed. It was demonstrated that thin sections of single crystals of arsenopyrite were oxidized more efficiently when a microbially produced Fe3+ containing solution was used than when solutions of Fe2(SO4)3 ·9H2O were used. In the latter case, the crystal structure of the elemental sulfur was markedly different from rhombic sulfur. Studies on the biooxidation of pure arsenopyrite and sphalerite indicated that a layer of elemental sulfur was formed on its surface. This product of biooxidation was identified as elemental sulfur with a β-modification similar to that of selenium. The microorganisms used in this study were demonstrated to alter the crystal structure of sulfur prior to the oxidation thereof, independent of the type of mineral.During the initial stages of the biooxidation of sulfidic minerals, the ferric iron destroys the bonds on the surface of the crystal lattice. The disrupted surface structure of the sulfides promotes the solubilization of ferrous iron and trivalent arsenic (for arsenopyrite) and enhances the electron flow from the surface to the solution; microbial enzyme systems subsequently transfer these electrons to molecular oxygen.The separation of biooxidation of gold-containing pyrite/arsenopyrite concentrates into the component chemical and biological steps makes it possible to conduct each of the steps under optimal conditions. The two-step oxidation was demonstrated to be significantly more efficient under batch conditions than the standard one-step biooxidation. The oxidation level of arsenopyrite increased from 76.6 to 93.3%.

The Adsorption of Gold, Palladium, and Platinum from Acidic Chloride Solutions on Mesoporous Carbons

Studies on the adsorption characteristics of gold, palladium, and platinum on mesoporous carbon (CMK-3) and sulfur-impregnated mesoporous carbon (CMK-3/S) evaluated the benefits/drawbacks of the presence of a layer of elemental sulfur inside mesoporous carbon structures. Adsorption isotherms collected for Au(III), Pd(II), and Pt(IV) on those materials suggest that sulfur does enhance the adsorption of those metal ions in mildly acidic environment (pH 3). The isotherms collected in 1 M HCl show that the benefit of sulfur disappears due to the competing influence of large concentration of chloride ions on the ion-exchanging mechanism of metal ions sorption on mesoporous carbon surfaces. The collected acid dependencies illustrate similar adsorption characteristics for CMK-3 and CMK-3/S in 1-5 M HCl concentration range. Sorption of metal ions from diluted aqueous acidic mixtures of actual leached electronic waste demonstrated the feasibility of recovery of gold from such liquors.

Atmospheric oxygen-rich direct leaching behavior of zinc sulphide concentrate

The leaching behavior of main metallic sulphides in zinc concentrate under atmospheric oxygen-rich direct leaching conditions was studied through mineralogical analysis. The results show that the sulphides dissolve obviously except pyrite. Based on the relationship between elemental sulfur and the residual sulphides in the leaching residue, the dissolution of sphalerite, chalcopyrite, covellite and galena is assumed to follow the indirect oxidation reactions, where the acidic dissolution takes place firstly and then the released H2S transfers from the mineral surface into bulk solution and is further oxidized into elemental sulfur. The interface chemical reaction is further supposed as the controlling step in the leaching of these sulphides. The direct electrochemical oxidation reactions are assumed to contribute to the dissolution of pyrrhotite, which is controlled by the diffusion through elemental sulfur layer.

A model for the zeta potential of copper sulphide

A model is proposed for the zeta-potential versus pH curve of Covellite (CuS). The classical Gouy–Chapman–Stern treatment of the adsorption of protons is applied to a model surface derived from the crystallographic data. The surface charges are obtained by an original adaptation of the concepts from the MUSIC model to a sulphide, i.e. the analysis of the chemical bonding in Pauling's electrostatic valence framework to derive partial surface charges. The authors develop a software for the fitting of pζ–pH curves using IPHREEQC for the calculation of the zeta potential at each pH point and Matlab to drive the calculation of the whole pH set and the optimisation of the parameters: capacitances of the double layer, site densities, charges and acidity constants. The model successfully reproduces the experimental data, considering only two sulphided surface sites: introduction of an elemental sulphur layer or consideration of hydroxyl surface sites is not required to explain the charging behaviour of Covellite when carefully precipitated under nitrogen.

Evaluation of processing options to avoid the passivation of chalcopyrite

The feasibility of two options to avoid the passivation of a chalcopyrite concentrate was evaluated in an oxidative process by ferric ion at 30°C. These options attempt to reduce the formation of a layer of iron precipitates, and sequentially inoculate the bacterium Acidithiobacillus thiooxidans to consume the elemental sulfur layer, without modifying the oxidizing power of the leaching solution.QEMSCAN analysis revealed a reduction in ferric compound precipitation over the mineral surface from 32% to 2% by mass by controlling the formation of precipitates. However, the increase in the rate of copper extraction was insignificant, increasing this only from 3.8% to 4.0% in 30days. The observed precipitates were mostly of type Fe-sulfates, with minor appearance of jarosite. In neither case, QEMSCAN analysis revealed formation of elemental sulfur on the mineral. Consequently, the inoculation of sulfur oxidizing bacterium A. thiooxidans in a controlled precipitation system produced no improvement in the extraction of copper.The leaching behavior fitted with the model of SCM (shrinking core model), indicating the formation of a layer of undetected compounds which exerts an effect on the diffusion of the leaching agent. Therefore, none of the options taken to avoid the passivation of chalcopyrite were successful, indicating that passivation occurs even in the absence of iron precipitation and the presence of sulfur oxidizing bacteria.