Oxidation Of Chalcopyrite Research Articles

DFT study and electrochemical investigation of Fe3+ion interaction on chalcopyrite (0 0 1)-S and M (M = Cu, Fe) surfaces: A thermodynamic insights

Ferric sulfate is a common oxidant of chalcopyrite leaching in an acidic medium, and the oxidation of chalcopyrite in the presence of ferric (Fe3+) ion increases copper extraction. In this work, the effect of ferric ion on chalcopyrite leaching is investigated by electrochemical analysis (cyclic voltammetry and linear sweep voltammetry methods) and density functional theory study. According to the cyclic voltammetry data, the presence of ferric ion showed the positive effect on the anodic and cathodic reactions to reduce the non-faraday region. Moreover, the Tafel plots revealed that the inactive region was removed by the presence of ferric ion with increasing corrosion current density. The reaction free energy value, resulting in the density of corrosion current, was related to the coulombic reaction of electroactive species (Fe3+ ion) with the surface. Subsequently, Fe3+ ion interaction with the (001)-S and (001)-M surfaces (M = Fe and Cu) of chalcopyrite was studied by using the density functional theory calculations. The computational data indicated that the Fe3+ ion interaction on chalcopyrite surfaces was favorable. In order, the presence of sulfur atoms decreased the coordination of the surface cations lead to more reactivity of surfaces. Thermodynamic data from computational and electrochemical studies showed that the interaction of Fe3+ ion with surfaces of chalcopyrite is a spontaneous reaction. The value of free energy for the ferric ion interaction in the presence of pyrite was obtained −17/8 kJ/nonindicated positive effect of pyrite on the reaction with increasing the reduction rate of Fe3+ ion.

Hydrometallurgical Recovery of Cu and Zn from a Complex Sulfide Mineral by Fe3+/H2SO4 Leaching in the Presence of Carbon-Based Materials

Chalcopyrite, the main ore of copper, is refractory in sulfuric media with slow dissolution. The most commonly employed hydrometallurgical process for the oxidation of chalcopyrite and copper extraction is the sulfuric acid ferric sulfate system The main objective of the present work is to study the use of cheap carbon-based materials in the leaching of copper and zinc from a sulfide complex mineral from Iberian Pyrite Belt (IPB). The addition effect of commercial charcoal (VC) and two magnetic biochars (BM and HM) that were obtained by pyrolysis of biomass wastes was compared to that of commercial activated carbon (AC). The experimental results performed in this work have shown that the presence of carbon-based materials significantly influences the kinetics of chalcopyrite leaching in the sulfuric acid ferric sulfate media at 90 °C. The amount of copper and zinc extracted from IPB without the addition of carbon-based material was 63 and 72%, respectively. The highest amount of extracted zinc (>90%) was obtained with the addition of VC and AC in IPB/carbon-based material ratio of 1/0.25 w/w. Moreover, it is possible to recover more than 80% of copper with the addition of VC in a ratio 1/0.25 w/w. Moreover, an optimization of the properties of the carbon-based material for its potential application as catalyst in the leaching of metals from sulfide is necessary.

A novel hydrometallurgical treatment for the recovery of copper, zinc, lead and silver from bulk concentrates

Nowadays sulphide ores exploitation is undergoing some troubles, which are hindering the treatment through traditional routes. Bulk flotation followed by a novel hydrometallurgical process can dodge these difficulties. In this work, an integral hydrometallurgical process consists of two ferric leaching steps, followed by a hot brine leaching stage, is proposed to recover target metals from a bulk sulphide concentrate (2.9% Cu, 7.4% Zn, 2.5% Pb, 67 ppm Ag and 37.2% Fe). In the first ferric leaching step, sphalerite, galena and copper secondary sulphides are dissolved and, in the second leaching step, a silver salt is added in order to catalyse chalcopyrite oxidation. If silver salt is added at the beginning of the process, sphalerite passivation is observed, and therefore zinc recovery is not possible. However, when catalytic leaching is performed after a previous ferric leaching, copper and zinc recoveries higher than 95% are achieved. The leached concentrate (0.3% Cu, 0.8% Zn, 3.3% Pb, 1438 ppm Ag, 38.0% Fe and 6.6% S0), is treated by a hot brine leaching. When hot brine leaching is performed at high pulp density, elemental sulphur removal is necessary to recover all silver added as a catalyst. Extractions higher than 95% for Zn, Cu and Pb are achieved as well as the total recovery of catalyst. The proposed process is silver surplus; therefore, this agent can be recirculated.

New insights on the role of lattice-substituted silver in catalytic oxidation of chalcopyrite

The present study investigates, for the first time, the effect of Ag doping on chalcopyrite oxidation. Oxidation kinetics were studied by comparing the electrochemical oxidation of synthetic pure and Ag-doped (8 ppm Ag) chalcopyrite in sulfuric acid solutions without and with Fe3+. Results showed that Ag doping increased the chalcopyrite oxidation rate by 56% (0.62 × 10−6 to 0.97 × 10−6 A/cm2) and 177% (0.97 × 10−6 to 2.69 × 10−6 A/cm2) in sulfuric acid solutions without and with Fe3+, respectively. Anodic polarization tests displayed three peaks corresponding to different active-passive behaviors during chalcopyrite oxidation. The first peak between the open circuit potential to 0.65 V was associated with Ag: it presented a peak current density of 10 × 10−6 and 80 × 10−6 A/cm2 for pure and Ag-doped chalcopyrite, respectively. Electrochemical impedance spectroscopy demonstrated that charge transfer resistance and passive layer resistance decreased when Ag was present in the chalcopyrite lattice.

Effect of Chloride Ions on the Electrochemical Oxidation of Chalcopyrite at 340 °C and 21 MPa

Understanding the oxidative mechanisms of chalcopyrite in various hydrothermal fluids is of great significance to improve copper extraction and to model the geochemical cycling of copper, iron, and sulfur. This paper investigated the effect of NaCl on the electrochemical oxidation of chalcopyrite at 340 °C and 21 MPa using polarization curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. The experimental results showed that NaCl can promote chalcopyrite leaching. As NaCl concentration increases, the protective property of the oxidation layer degraded. In the absence of NaCl, the oxidation layer that consisted of CuSn, (n ≥ 1), probably with some Fe2O3 and Fe(OH)3 and also in the presence of NaCl, Fe2O3, is the principal oxidation product. More rapid ionic diffusion and further chemical reaction contributed to the improvement of chalcopyrite dissolution with increasing NaCl concentration. A dissolution mechanism is proposed in this paper to explain the chalcopyrite leaching processes which is dependent on NaCl concentration.

Intensified Bioleaching of Copper from Chalcopyrite: Decoupling and Optimization of the Chemical Stage

A one-stage process for the bioleaching of copper from chalcopyrite has a low leaching rate compared to the conventional smelting, pressure oxidation, and roasting routes, thus reducing the economic viability of the process. It is, therefore, crucial to optimize the process and the associated rate-influencing factors to make it competitive with the traditional, proven technologies. A strategy to intensify the extraction process is the decoupling of the chemical and biological stages, which expands the attainable region for the optimization of the variables. In the present research, the decoupled optimization of the chemical stage in the copper bioleaching of a chalcopyrite ore from the Iranian Sungun mine at East Azerbaijan was investigated. The factors affecting the rate of oxidation of chalcopyrite were determined and optimized with a (realistic) priori prepared bio-related medium. The optimized variables included the reaction temperature of 70 °C, the ore particle size of 0.65 μm, pH of 1.8 in the leaching solution, ferric ion concentration of 0.1 of the stoichiometric value (0.0022 mol per gram of chalcopyrite), and redox potential ~406 mV. Overall, the effect of redox potential on the extraction rate was the most pronounced such that the leaching rate was increased by about three times in the potential range of 401.0–405.8 mV relative to other ranges.

Chalcopyrite leaching in acid media: a review

In the modern practice of copper production, more and more attention is paid to the possibility of treating low-percentage sulfide ores that cannot be treated with conventional procedures (crushing, grinding, flotation). In addition to this, the processes of obtaining copper from complex sulfide concentrates, which cannot undergo pyrometallurgical processing, are increasingly being investigated. Extraction of copper from such raw materials is in most cases achieved by applying leaching procedures.
 Since chalcopyrite (CuFeS2) is by far the most abundant copper sulfide mineral, a large portion of the research is focused on studying the behavior of chalcopyrite in the leaching process, because processes of copper extraction from increasingly poor raw materials may be created using results of these studies. In addition, the main objective of this research is examining the kinetics and mechanism of chalcopyrite oxidation under the influence of various oxidants (O2, Fe3 +, H2O2, chlorate ions, etc.) and at the same time obtaining data necessary for the development of copper production process that could satisfy increasingly stringent technological, economic and environmental criteria.
 The paper presents the existing knowledge of the chalcopyrite leaching procedure and phenomena that accompany chalcopyrite oxidation in acidic sulfate and chloride solutions.

Oxidation of chalcopyrite in air-equilibrated acidic solution: Inhibition with phenacyl derivatives

Abstract The effects of 4-(2-hydroxyphenyl)-2-(morpholin-4-yl)-1,3-thiazole (Pr02), 1-(3,5-dibromo-2-hydroxyphenyl)- 1-oxoethan-2-yl-N,N-diethyldithiocarbamate (Pr04) and 1-(5-bromo-2-hydroxy-3-methylphenyl)-1-oxoethan-2-yl-O- ethyl xanthate (Pr06) on the aqueous oxidation of chalcopyrite (CuFeS2) in air-equilibrated solution at a temperature of 25 °C and a pH of 2.5 were studied. The effects were investigated by using potentiodynamic polarization, electro- chemical impedance spectroscopy (EIS), scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) analysis, aqueous batch experiments, Fourier transform infrared (FTIR) spectroscopy, Raman scattering and quantum chemical calculations. It is found that the anodic current densities decrease in the order of EtOH > Pr02 > Pr04 > Pr06. These results, along with those of the EIS measurements, show that Pr02, Pr04 and Pr06 are effective anodic inhibitors of chalcopyrite aqueous oxidation. Both Raman scattering and FTIR spectroscopy indicate that the elemental sulfur, polysulfide and ferric oxyhydroxides that form on the surface of the mineral are not responsible when it comes to the aqueous oxidation inhibition of chalcopyrite. Quantum chemical calculations show that the adsorption of the tested compounds on the chalcopyrite surface is energetically favorable and so, it can explain the inhibiting effects that were observed.

Kinetics of Pyrite Oxidation in Simulated Mine Tailings Pond Conditions

Pyrite oxidation is the predominant source of acid mine drainage (AMD), which is one of the severe environmental impacts of mining. AMD destroys flora and fauna in the nearby ecosystem, and it causes grave health problems to the people. To further the understanding and help in the mitigation of AMD, this electrochemical study investigates the effect of the type and concentration of oxidant, and the presence of impurity (chalcopyrite) to the rate of pyrite oxidation, while simulating the conditions in tailings ponds. Open Cell Potential (OCP) and Electrochemical Impedance Spectroscopy (EIS) analysis were done using a three-electrode cell set-up, which is composed of a pyrite rotating disc electrode (RDE), mercury/mercurous sulfate reference electrode in saturated potassium sulfate, and a platinum counter electrode, with a sulfuric acid working electrolyte. Polarization resistance obtained after fitting an electrical circuit to the EIS data was related to the rate of pyrite oxidation, while OCP was used to describe its oxidation mechanism. It was found out that the oxidation of pyrite by ferric ions preferentially occurred rather than by dissolved oxygen. The parameter setting with the lowest relative oxidation rate were: electrolyte with no ferric addition, and with nitrogen purging; and RDE with 10 % chalcopyrite addition. Reaction orders calculated for the effect of ferric ions and dissolved oxygen were equal to 1; but ferric has a higher slope value in the plot. Presence of chalcopyrite in the RDE caused the preferential oxidation of chalcopyrite instead of the pyrite due to their galvanic interaction. To minimize pyrite oxidation, ferric and dissolved oxygen concentration should be minimized, and chalcopyrite impurities should be increased. Keywords: Electrochemical Impedance Spectroscopy, Acid Mine Drainage, Kinetics, Rotating-Disc Electrode, Pyrite

A scanning electrochemical microscopy (SECM) study of the interfacial solution chemistry at polarised chalcopyrite (CuFeS2) and chalcocite (Cu2S)

Chalcopyrite (CuFeS2) passivation during hydrometallurgical copper extraction is attributed to multiple competing mechanisms that are still not completely understood. Here we have studied the interfacial solution chemistry in situ at polarised chalcopyrite and chalcocite, using scanning electrochemical microscopy (SECM). It was observed that the copper species detected at an ultramicroelectrode (UME) positioned at the mineral:solution interface vary between the two minerals, and are dependent upon both the potential of the mineral and the polarisation time. Cu species formed in the presence of sulfide, derived from incomplete oxidation of chalcopyrite, are observed on the UME tip positioned above chalcopyrite under conditions where passivation may occur, in contrast to Cu(II) in the presence of sulfate under conditions where leaching is facile. Only Cu(II) in the presence of sulfate is observed at the interface of chalcocite. These observations via interfacial voltammetry provide experimental support to mechanistic studies on chalcopyrite leaching, and provide new information to complement previous in situ studies which have mostly focused on interfacial solids.

Kinetic Evolution of Chalcopyrite Thermal Degradation under Oxidative Environment

The oxidative degradation kinetics of chalcopyrite have been studied by thermogravimetric analysis (TGA). The obtained data are necessary for the kinetic description of the flash fusion process, which can contribute to the optimization of the smelting process in copper extractive metallurgy. Activation energy (Ea) evolutions of the involved processes have been determined by several isoconversional methods; in this sense, the chalcopyrite oxidation processes could be adequately described, among studied models (E1641–16, Ozawa–Flynn–Wall, Kissinger–Akahira–Sunose and Friedman), by the Kissinger–Akahira–Sunose kinetic model. Using this method, Ea and A values are found to be very dependent on the conversion. Under lower conversion levels, higher Ea and A values have been calculated with respect to that found for medium and higher conversion levels.

Distinct Roles of Acidophiles in Complete Oxidation of High-Sulfur Ferric Leach Product of Zinc Sulfide Concentrate.

A two-step process, which involved ferric leaching with biologically generated solution and subsequent biooxidation with the microbial community, has been previously proposed for the processing of low-grade zinc sulfide concentrates. In this study, we carried out the process of complete biological oxidation of the product of ferric leaching of the zinc concentrate, which contained 9% of sphalerite, 5% of chalcopyrite, and 29.7% of elemental sulfur. After 21 days of biooxidation at 40 °C, sphalerite and chalcopyrite oxidation reached 99 and 69%, respectively, while the level of elemental sulfur oxidation was 97%. The biooxidation residue could be considered a waste product that is inert under aerobic conditions. The results of this study showed that zinc sulfide concentrate processing using a two-step treatment is efficient and promising. The microbial community, which developed during biooxidation, was dominated by Acidithiobacillus caldus, Leptospirillum ferriphilum, Ferroplasma acidiphilum, Sulfobacillus thermotolerans, S. thermosulfidooxidans, and Cuniculiplasma sp. At the same time, F. acidiphilum and A. caldus played crucial roles in the oxidation of sulfide minerals and elemental sulfur, respectively. The addition of L. ferriphilum to A. caldus during biooxidation of the ferric leach product proved to inhibit elemental sulfur oxidation.

Redox potential-dependent chalcopyrite leaching in acidic ferric chloride solutions: Leaching experiments

The redox potential dependence of chalcopyrite leaching was investigated in acidic ferric chloride solutions using a specially designed batch leaching experimental setup that accurately determined and monitored changes of solution redox potential with time. The concentration ratio of ferric (Fe3+) to ferrous (Fe2+) ions and leaching rate-redox potential relationship were then determined from measured redox potential data assuming chalcopyrite oxidation with Fe3+ occurred stoichiometrically. A distinct peak was observed in the leaching rate vs. redox potential plot; that is, the leaching rate increased with increasing redox potential, reaching a (local) maximum (i.e., the peak rate) at a certain redox potential (i.e., the peak redox potential) followed by the gradual decrease in leaching rate at higher redox potentials. For example, in the experiment performed at [Cu2+] = [Fe2+] = 0.01 kmol m−3 in HCl (0.1 kmol m−3) at 343 K, the rate continuously increased with increasing redox potential, reaching the fastest rate of 9.7 × 10−8 mol s−1 g−1 (peak rate) at 0.442 V (peak redox potential). After passing this redox potential peak, the rate started to decrease, slowing down to 2.9 × 10−8 mol s−1 g−1 at 0.487 V. Using this setup, the effects of temperature and solution composition (Cu2+, Fe3+ and HCl concentrations) on the peak rate and peak redox potential were investigated. The results showed that the peak rate increased with increasing temperature, decreased with increasing HCl and Fe3+ concentrations but was not strongly affected by Cu2+ concentration. In comparison, the peak redox potential was less dependent on the temperature and concentrations of HCl and Fe3+. Although the role of Cu2+ was apparently not crucial in the occurrence of the peak rate, it exerted a relatively strong influence on the peak redox potential; that is, the peak redox potential increased with increasing Cu2+ concentration. Based on these results, an empirical equation for the relationship between peak redox potential and Cu2+ concentration was derived.

The interaction of Ag+ with synthetic chalcopyrite in the presence of Fe3+ and Cu2+ in sulfuric acid solutions

Silver (Ag+) and cupric (Cu2+) ions are known to be catalysts for oxidation of chalcopyrite (CuFeS2) in acid solutions. The present study investigates the interaction between Ag+ and Cu2+ with synthetic chalcopyrite under oxidative conditions in acidic ferric (50 mM Fe3+) sulfate solutions. After addition of Ag+ (e.g. concentration 20 mg/L) to solutions containing Cu2+, the oxidation rate of chalcopyrite increased from 1.08 × 10−6 to 12.65 × 10−6 A/cm2. In contrast, addition of 5 and 50 mM Cu2+ to solutions containing Ag+ decreased the chalcopyrite oxidation rate from 20.79 × 10−6 to 12.65 × 10−6 and 19.50 × 10−6 A/cm2, respectively. Oxidative chalcopyrite leaching tests results were in good agreement with those of the electrochemical tests above. X-ray photoelectron spectroscopy showed higher insensitivity of Ag 3d in leaching residue containing Cu2+ than residue without Cu2+. S 2p spectra analysis indicated the highest percentage of the disulfide form when leached in the Fe3+-Cu2+-Ag+ system, which suggests a synergistic effect of Cu2+ and Ag+ in the conversion of monosulfide to disulfide in chalcopyrite.

Bacterially-mediated supergene alteration and redistribution of copper in mineralised rocks at the Salobo IOCG deposit, Brazil

The primary ore at the giant Salobo iron oxide copper-gold (IOCG) deposit in Brazil is dominated by magnetite and Fe-rich silicates, with minor (~1%) disseminated Cu-Fe sulphides and a distinctive absence of pyrite. Supergene Fe-silicate and sulphide oxidation has been mediated by bacteria, commonly within micrometre-scale acidic environments, but silicate-dominated acid neutralisation has maintained ambient circumneutral pH. Supergene Cu mobility has been controlled by the highly localised Fe-dominated biogeochemical processes, with Cu redistribution on the micrometre to metre scales and negligible supergene Cu enrichment. Silicates, especially the phyllosilicates biotite and chlorite, have variably altered to the clay minerals vermiculite and/or smectite, and ultimately to kaolinite. Leaching of Mn, Fe, Mg and Si accompanied silicate alteration, with minor addition of Cu to clay mineral structures and along cleavage planes. Iron mobilised by bacterial oxidation processes initially precipitated as ferrihydrite (with up to ~10 wt% Cu). Most Cu and Mn, mobilised in localised acidic environments, were precipitated nearby (metre scale) at circumneutral pH and reflect the immediate supergene biogeochemical environments: Cu-carbonates, pseudomalachite, chrysocolla, and Cu-Mn oxides (= “copper wad”). The early stages of these natural supergene processes were simulated in laboratory leaching studies using a range of fresh rocks inoculated with an endemic iron-oxidising strain of Acidithiobacillus ferrooxidans previously cultured from the Salobo site. Bacterially-mediated precipitation of ferrihydrite, commonly Cu-bearing, in these experiments strongly resembles that seen in the natural outcrops. These leaching experiments confirmed the effectiveness of silicate-dominated acid neutralisation, especially when accompanied by bornite oxidation, which is also acid-consuming. In contrast, chalcopyrite oxidation is acid-producing and leads to more effective localised Cu mobility in solution. Our combination of field and laboratory observations at the Salobo IOCG deposit shows that the biogeochemical environment dominated by Fe-silicates with little sulphides, typical for these systems, has led to an entirely different style of supergene Cu redistribution from that seen at many other Cu deposits, such as chalcopyrite and pyrite-rich porphyry copper deposits, where substantial supergene Cu enrichment has occurred.

Stable sulphur and oxygen isotopes as indicators of sulphide oxidation reaction pathways and historical environmental conditions in a Cu–W–F skarn tailings piles, south-central Sweden

Improved remediation strategies or predictive modelling of acid mine drainage (AMD) sites, require detailed understanding of the sulphide oxidation reaction pathways, as well as pollutant-source characterisation. In this study, ore minerals, solids and water-soluble fractions of an oxidising Cu–W–F skarn tailings in Yxsjöberg, Sweden, were chemically and isotopically (δ34S and δ18O) characterised to reveal sulphate (SO42−) sources, sulphide oxidation reaction pathways and historical environmental conditions in the tailings. δ34S was additionally used to trace the weathering of danalite [(Fe,Mn,Zn)4Be3(SiO4)3S], a rare and unstable sulphur-bearing silicate mineral containing high concentrations of beryllium (Be) and zinc (Zn). Eighteen subsamples from a drill core of the tailings were subjected to batch leaching tests to obtain water-soluble fractions, which reflected both existing pore-waters and easily-soluble secondary minerals. The tailings were categorised into three geochemical zones: (i) oxidised zone (OZ), (ii) transition zone (TZ) and (iii) unoxidised zone (UZ), based on prevailing pH, elemental concentrations and colour. The upper OZ (UOZ) showed a sharp depletion of sulphur (S) and relatively higher δ18OSO4 values (−3.0 to +0.1‰) whereas the underlying lower OZ (LOZ) showed S accumulation and lower δ18OSO4 values (−4.6 to −4.2‰). The higher δ18OSO4 suggested the role of atmospheric oxygen, O2 (as oxidant), contribution of evaporated rainwaters and/or evaporation in the upper zones of the tailings. The lower δ18OSO4 values were indicative of ferric iron (Fe3+) as oxidant and the possible incorporation of 16O into SO42− during its formation, most probably from snow melt or depleted rainwater. The δ34SSO4 values in the OZ (+2.3 to +2.4‰) suggested SO42− from pyrrhotite oxidation in the UOZ which has been subsequently mobilised to the LOZ. Low δ34S fractionation (+0.2 to +1.9‰) between SO42− in the OZ and pyrrhotite, as well as the low δ18OSO4 values in the LOZ suggested the complete oxidation of pyrrhotite by Fe3+, signalling that previously, a low pH (<3) prevailed in the tailings. Mineralogical observations confirmed that pyrrhotite was completely oxidised in the UOZ, with the formation of hydrous ferric oxides (HFOs) coatings. The observed current high δ18OSO4 and pH (3.9–4.5) values in the UOZ were attributed to decreased oxidation rate and silicate buffering, limiting the availability of aqueous Fe3+ and subsequent formation of HFOs. The δ34SSO4 signatures of the water-soluble SO42− in the TZ and UUZ suggested the dissolution of gypsum which precipitated from a leachate from the weathering of danalite in the UOZ. In the middle UZ, the δ34SSO4 (−0.8 to +0.6‰) and δ18OSO4 (−1.8 to −1.0‰) signatures corresponded to SO42− from a mixture of pyrite, pyrrhotite and chalcopyrite oxidation by O2 at the LOZ (i.e. oxidation front). Negative δ34S fractionation values (−3.0 to −1.6‰) between these minerals and the water-soluble SO42− were attributed to the potential formation of intermediate S species, due to the partial oxidation of the sulphides. Consequently, the S accumulation in the LOZ could be due to the likely formation of the intermediate S species and secondary pyrite identified in this zone. The lower UZ coincided with the groundwater table and registered consistent negative δ34SSO4 (−2.6 to −1.8‰) and δ18OSO4 (−7.6 to −4.4‰) values. These signatures were hypothesised to be controlled by SO42− from the mineralisation of organic S in peat underneath the tailings and/or H2S oxidation, with possible contribution from sulphide oxidation in the tailings. This study highlights the usefulness of δ34S and δ18O as tracers of geochemical processes and environmental conditions that have existed in the tailings.

New insights into the surface relaxation and oxidation of chalcopyrite exposed to O2 and H2O: A first-principles DFT study

In order to unravel the oxidation mechanism(s) of chalcopyrite (CuFeS2) surfaces, the surface anisotropy of CuFeS2 was investigated under both dry and aqueous atmospheres through a fundamental density functional theory (DFT) study. Results showed that the CuFeS2 (112) surface was the preferred cleavage surface, rather than the commonly-assumed (001) surface. Iron oxides were formed when contacting with either molecular O2 or dissociated O atoms, but sulfoxy species were only formed in the presence of dissociated O atoms, exposing Cu atoms on the S-terminated (001) and (112) surfaces. This indicates that strong oxidation conditions are beneficial to CuFeS2 oxidation and the release of metals into solution. In addition, CuFeS2 was preferentially oxidized by O2 prior to the adsorption of H2O under an aqueous condition with both H2O and O2. The H2O adsorbed on the O-oxidized surface further promoted CuFeS2 oxidation, resulting in the formation of a hydrophilic surface, rather than the naturally hydrophobic surface. This study has unveiled, for the first time, the mechanisms of the oxidation of the most stable and reactive CuFeS2 (112) and (001) surfaces under both dry and aqueous environments at an atomic level, with potential applications in CuFeS2 flotation and leaching processes.

The electrochemistry of chalcopyrite in alkaline solutions

This paper summarizes the results of a study of the anodic characteristics of chalcopyrite in alkaline hydroxide and carbonate solutions. The cathodic reduction of oxygen, peroxide and hypochlorite have also been investigated as possible oxidants in a two-stage process for the heap leaching of chalcopyrite under alkaline conditions.Mixed potential measurements of chalcopyrite in alkaline solutions showed that the reactivity of the common oxidants is in decreasing order hypochlorite > peroxide > oxygen >> chlorate.Anodic oxidation of chalcopyrite involves active oxidation at low potentials followed by a passivation peak and transpassive oxidation at higher potentials. The kinetics of oxidation is favoured by increasing pH in both hydroxide and carbonate solutions. The formation of solid products of oxidation does not prevent continued oxidation for up to 18 h at potentials below the peak. Coulometric measurements suggest that both thiosulfate and sulfate ions are produced by oxidation in sodium hydroxide solutions while thiosulfate is the main product in carbonate and bicarbonate solutions.At potentials close to the mixed potentials, the rate of reduction of hypochlorite is approximately first-order in hypochlorite concentration and is greater at low hydroxide ion concentrations. The rate of the cathodic reduction of peroxide is also greater at lower pH values but is complicated by the surface catalysed disproportionation of peroxide to water and oxygen.Rates of oxidation of chalcopyrite by both hypochlorite and peroxide in sodium hydroxide solutions have been estimated. The rates in hypochlorite are an order of magnitude greater than those in peroxide solutions and are of the same order of magnitude as those previously measured for the dissolution of chalcopyrite in ammoniacal solutions with copper(II) ions as the oxidant.

Effect of surfactant on the growth and activity of microorganisms in a heap bioleaching system

The presence of surfactants in the lixiviant solution has the potential to improve solution penetration into small pores and cracks of large ore particles by decreasing surface tension, thereby enhancing access of lixiviant to internal mineral grains and associated metal recovery from low grade sulphide ores. The effect of surfactants on the growth and activity of microorganisms implicated in bioleaching must also be considered, because of the microorganisms’ principal role in the regeneration of leaching reagents and facilitating metal recovery from an ore. The effect of surfactant addition on ferrous ion oxidation and microbially-mediated leaching of chalcopyrite by a mixed thermophilic microbial culture was investigated using five non-ionic surfactants: Tween® 20, Tween® 80, Plurafac® LF 120, Plurafac® LF 600 and Lutensol® XL 90 at concentrations of 5, 10 and 20 mg L−1. The addition of 5 and 10 mg L−1 Tween® 20 showed no negative effect on microbial ferrous ion oxidation and chalcopyrite bioleaching. Further, its presence was observed to reduce the initial leaching lag time. Microbial ferrous ion oxidation was inhibited in the presence of 10 mg L−1 Plurafac® LF 120 while a partial inhibition was observed with 10 mg L−1 Lutensol XL 90. Plurafac® LF 600 at 5 and 10 mg L−1 and Tween® 80 at 10 mg L−1 inhibited microbial growth completely, and thereby leaching, hence precluding it from a role in bioleaching.

Iodide-assisted leaching of chalcopyrite in acidic ferric sulfate media

Chalcopyrite leaching in acidic ferric sulfate media at ambient temperature exhibits slow kinetics due to the formation of passivation layers on chalcopyrite surfaces. In this study, we investigated the use of potassium iodide to assist chalcopyrite leaching and proposed mechanisms by which iodide enhanced the leaching efficiency. The effect of ferric concentration, temperature and iodide concentration on chalcopyrite leaching was studied by factorial experimental design and statistical analysis of data using the analysis of variance (ANOVA) method. The addition of 0.5 g/L of potassium iodide to the leaching media containing Fe(III) resulted in the production of I2 and led to an increase of copper extraction by 47% at 50 °C. Controlled potential experiments highlighted an optimal potential window for leaching at 700–800 mV, thus suggesting that tri-iodide might play a significant role in leaching enhancement. Mineral liberation analysis (MLA) highlighted that elemental sulfur was the surface product generated from the oxidation of chalcopyrite. The rate parameters in the presence of KI were significantly higher, especially at lower temperature, and consistent with those observed for the H2SO4-I2 leaching media. The addition of potassium iodide into the leaching media led to a decrease of activation energy from 81.4 to 33.8 kJ/mol.