Dissolution Of Chalcopyrite Research Articles

Enhancing chalcopyrite leaching by tetrachloroethylene-assisted removal of sulphur passivation and the mechanism of jarosite formation

Chalcopyrite (CuFeS2) is the primary ore mineral for copper, but leaching of this mineral under atmospheric conditions is slow due to the formation of surface passivating phases such as elemental sulphur and jarosite. Here, we studied chalcopyrite leaching in a sulphuric acid solution at 75 °C and 750 mV (relative to the standard hydrogen electrode), and found that after adding 20 vol% of tetrachloroethylene (TCE) into the leaching solution, elemental sulphur was dissolved from chalcopyrite and surface passivation was removed at the early stage of leaching. The removal of surface sulphur significantly enhanced the leaching rate by approximately 600% compared with TCE-free leaching. However, adding dimethyl sulfoxide (DMSO) did not improve the leaching rate. At the later stage of leaching, the increasing concentrations of Fe3+ from the dissolution of chalcopyrite and K+ possibly from the dissolution of minor amount of gangue minerals resulted in the precipitation of a potassium jarosite layer on the surface of chalcopyrite. The jarosite shell did not passivate TCE-free leaching due to its porous structure. However, in the case of leaching with TCE, elemental sulphur filled the pores, and the jarosite shell became nearly impermeable, resulting in passivation after 80% copper extraction. This study demonstrates a way for effective removal of sulphur passivation at the early stage of chalcopyrite leaching by adding sulphur dissolving solvent such as TCE, but to prevent jarosite formation at the later stage of leaching, it is necessary to keep the concentrations of Fe3+ and K+ at low levels.

Kinetics of Chalcopyrite Leaching by Hydrogen Peroxide in Sulfuric Acid

In ores, chalcopyrite is usually associated with other sulfide minerals, such as sphalerite, galena, and pyrite, in a dispersed form, with complex mineralogical structures. Concentrates obtained by flotation of such ores are unsuitable for pyrometallurgical processing owing to their poor quality and low metal recovery. This paper presents the leaching of chalcopyrite concentrate from the location “Rudnik, Serbia”. The samples from the flotation plant were treated with hydrogen peroxide in sulfuric acid. The influences of temperature, particle size, stirring speed, as well as the concentrations of hydrogen peroxide and sulfuric acid were followed and discussed. Hence, the main objective was to optimize the relevant conditions and to determine the reaction kinetics. It was remarked that the increase in temperature, hydrogen peroxide content, and sulfuric acid concentration, as well as the decrease in particle size and stirring speed, contribute to the dissolution of chalcopyrite. The dissolution kinetics follow a model controlled by diffusion, and the lixiviant diffusion controls the rate of reaction through the sulfur layer. Finally, the main characterization methods used to corroborate the obtained results were X-ray diffraction (XRD) as well as qualitative and quantitative light microscopy of the chalcopyrite concentrate samples and the leach residue.

Effect of pyrite on the electrochemical behavior of chalcopyrite at different potentials in pH 1.8 H2SO4

Chalcopyrite is the most abundant, but also one of the most refractory, copper sources. One way to enhance chalcopyrite’s electrochemical dissolution is by mixing it with pyrite. To understand how and to what extent pyrite affects chalcopyrite’s electrochemical dissolution at different potentials, the electrochemical behaviors of chalcopyrite, pyrite, and chalcopyrite–pyrite couples in pH 1.8 H2SO4 were studied by potentiodynamic and electrochemical impedance spectroscopy. Potentiodynamic curves showed their different electrochemical reaction states and electrode surface characteristics. From open-circuit potential to 470 mV (vs saturated calomel electrode), chalcopyrite–pyrite was passivated with Cu1− xFe1− yS2 [Formula: see text]; from 470 to 580 mV, trans-passive dissolution occurred, and in the passive region, Cu1− xFe1− yS2 transformed into Cu1− x− zS2; from 580 to 700 mV was an active region; and a pseudo-passive region was formed with CuS when the potential was above 700 mV. The smaller charge transfer resistance and passive resistance, as well as the smaller inductive relaxation, revealed how and to what extent the coupled pyrite accelerated the electrochemical dissolution of chalcopyrite.

Combined effects of jarosite and visible light on chalcopyrite dissolution mediated by Acidithiobacillus ferrooxidans

Although jarosite and visible light are important factors for the formation of acid mine drainage (AMD), the effects of combined jarosite and visible light on chalcopyrite biodissolution have not been explored until now. In order to fill this knowledge gap, the combined effects of jarosite and visible light on chalcopyrite dissolution mediated by Acidithiobacillus ferrooxidans were investigated. The results indicated that jarosite and visible light could significantly accelerate chalcopyrite biodissolution, thus releasing more copper ions, iron ions and producing more acid. This in turn suggests enhanced generation of AMD under these conditions. Biodissolution results, mineral surface morphology, mineralogical phase and elemental composition analyses revealed that the promotion of chalcopyrite dissolution by additional jarosite and visible light was mainly attributed to the acceleration of ferric iron/ferrous iron cycling and the inhibition of the formation of a passivation layer (jarosite and Sn2−/S0) on the surface of chalcopyrite. This study provides a better understanding of the effects of jarosite and visible light on chalcopyrite biodissolution. In the future, the influences of jarosite and visible light on chalcopyrite dissolution should be considered in AMD evaluation to ensure reliability.

New insights into chalcopyrite leaching enhanced by mechanical activation

Mechanical activation has been applied prior to leaching to improve copper extraction from chalcopyrite. Results showed that 86% copper was extracted within 2 h from chalcopyrite ground with sodium chlorite at 500 rpm, at pH 1.0 (sulfuric acid) and 348 K, greater than from leaching of unground (4.5% copper extraction) and ground chalcopyrite without sodium chlorite (13.5% extraction). Size reduction, structural modification and phase transformation were suggested as three mechanisms for improved copper extraction rate, with the last mechanism found to be dominant. Two leaching steps were proposed, for the first time, for chalcopyrite ground with sodium chlorite, including the first stage primarily determined by the dissolution of copper chlorite formed via a solid state reaction during grinding with chalcopyrite and the second stage dominated by the dissolution of unconverted chalcopyrite. This study suggests that grinding of chalcopyrite with sodium chlorite is beneficial to highly efficient copper extraction from chalcopyrite.

Comparative study on chalcopyrite bioleaching with assistance of different carbon materials by mixed moderate thermophiles

Abstract The catalysis of four carbon materials including artificial graphite (AG), carbon black (CB), activated carbon (AC) and carbon nanotube (CN) on chalcopyrite bioleaching by mixed moderate thermophiles was comparatively investigated. In AC and AG added bioleaching groups, low solution pH and suitable redox potential values, high total iron and ferric iron concentrations, and large number of adsorbed bacteria were obtained, resulting in high copper extractions. CB and CN inhibited the growth of bioleaching bacteria and led to the low bioleaching efficiency. X-ray diffraction analysis showed that jarosite and sulfur film were the main components of passivation layer with the addition of AG and AC, but did not hinder the dissolution of chalcopyrite. Microbial community structures of free and attached cells in AC and AG added groups changed dramatically compared with mixed moderate thermophiles. The sulfur-oxidizing bacteria of A. caldus S1 strain dominated the microbial community (93%−98%) at the end of bioleaching. The iron-oxidizing bacteria of L. ferriphilum YSK only accounted for low percentage (1%−2%).

The electrochemical behaviour of enargite in ammoniacal solutions. I. Anodic reactions

The leaching of enargite in acidic solutions is known to be particularly slow and, as in the case of chalcopyrite, the use of alternative lixiviants has been extensively studied. In particular, the use of ammoniacal solutions has been a focus due to the faster kinetics in such media. However, there have not been any fundamental studies of the electrochemistry of enargite in such solutions. A fundamental study has therefore been made of the electrochemical behaviour of enargite in both ammonium sulfate and ammonium chloride solutions at pH values from 8 to 10 and comparisons have been drawn with the behaviour of chalcopyrite under similar conditions. Mixed potential measurements have shown that copper(II) is an effective oxidant for enargite in ammoniacal solutions and the potential region in which enargite is oxidised have been defined. Voltammetry under various conditions has shown that partial passivation also occurs in such solutions and that the anodic behaviour in chloride solutions is similar to that in sulfate. Potentiostatic measurements at potentials in the region of the mixed potentials in copper(II) solutions have been used to derive pseudo-steady-state curves that reveal Tafel-like behaviour with slopes of approximately 120 mV/decade suggesting a one-electron rate determining step. A first-order dependence of the rate of anodic dissolution on the ammonia concentration has been derived from this data. Coulometric measurements suggest that thiosulfate is the main product of anodic oxidation under these conditions. The relative rates of dissolution of chalcopyrite and enargite in ammoniacal solutions have been estimated using mixed potential theory that show that enargite dissolves more rapidly than chalcopyrite in such systems.

Dissolution and Passivation of Chalcopyrite during Bioleaching by Acidithiobacillus ferrivorans at Low Temperature

Our knowledge on the dissolution and passivation mechanisms of chalcopyrite during bioleaching at low temperature has been limited to date. In this study, an Acidithiobacillus ferrivorans strain with high tolerance to heavy metals and UV radiation was used for chalcopyrite bioleaching. At 6 °C, no apparent precipitate was detected on the mineral surface after bioleaching using a scanning electron microscope (SEM). X-ray diffraction (XRD) revealed that the ore residue contained only chalcopyrite and quartz. X-ray photoelectron spectroscopy (XPS) analysis revealed that the content of S0 on the mineral surface remained low and the ratio of SO42− decreased from 46.7% to 20.9%, but the amount of Sn2− increased from 10.4% to 21.4% after bioleaching. Expression of five critical iron- and sulfur-oxidation genes during bioleaching was analyzed using quantitative real-time PCR. The gene rusA had higher expression in the mid-log phase than in the stationary phase but hdrA and cyoC1 showed an opposite trend. All genes had higher expression at 6 °C than at 28 °C, so as to compensate for the decline in the enzyme activities. The study revealed that polysulfide was the most plausible passivating substance at 6 °C, and the strain can maintain the iron- and sulfur-oxidation activities during low-temperature bioleaching.

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.

Catalytic mechanism of silver in the oxidative dissolution process of chalcopyrite: Experiment and DFT calculation

In this work, combined techniques were utilized to interpret the catalytic mechanism of Ag+ ions in sulfuric acid-ferric sulfate system of chalcopyrite. Density functional theory (DFT) calculations indicated the favorable adsorption of Ag+ ions on reconstructed (001)-S and (112)-S surfaces of chalcopyrite, and confirmed the possibility of silver sulfide and sulfur vacancy formations. XPS analysis further indicated the formation of silver sulfide on chalcopyrite surface. Electrochemical analysis showed that silver catalyzed chalcopyrite dissolution by enhancing the electrochemical reactivity. In addition, the incorporation of silver atoms into the chalcopyrite surface might cause a major distortion in its structure and accelerated the diffusion rate of copper atoms mainly because of that the Cu+ ionic radius is much smaller than that of Ag+. As a consequence, the accumulation of passivating species was prevented and the adverse effect of passivation layer mainly consisting of polysulfide and metallic oxides was reduced, thus resulting in high dissolution kinetics. According to the present work, a model for interpreting catalytic mechanisms of Ag+ in chalcopyrite dissolution is provided.

An XAS study of silver species evolution in silver-catalysed chalcopyrite bioleaching

The catalysing effect of Ag+ or Ag nanoparticle (AgNp) on chalcopyrite (bio)leaching at 30 °C was studied in this paper, and the change of Ag speciation was investigated by Ag K-edge X-ray Absorption Near-edge Spectroscopy (XANES). The solution studies indicate that the addition of 0.2% Ag (fraction of Ag to chalcopyrite) can effectively improve the dissolution of chalcopyrite in both bioleaching and chemical leaching. Further increasing the silver concentration to 1% only marginally increase the rate of chalcopyrite dissolution compared with the rate with 0.2% Ag added. No obvious difference has been found between the catalytic effect of Ag+ and AgNp (Silver Nanoparticle). XRD studies indicate the formation of jarosite, elemental sulfur in both bioleaching and chemical leaching. However, the speciation of Ag in the residual cannot be confirmed by XRD analysis. Ag k-edge XANES spectra show that Ag+ or AgNp have completely changed to Ag2S within 7 days in both bioleaching and chemical leaching process. In-situ XANES analysis shows that the Ag+ or AgNp changed to Ag2S very rapidly in the absence of Fe3+. In contrast, AgCl was firstly detected with the presence of 3 g/L Fe3+, which only partially changed to Ag2S in about 36 h, which is likely because the stability of Ag2S was decreased by Fe3+.

Electrochemical Behaviour of Chalcopyrite in Chloride Solutions

Due to the depletion of oxidized copper ores, it necessitates the need to focus on metallurgical studies regarding sulphide copper ores, such as chalcopyrite. In this research, the electrochemical behaviour of chalcopyrite has been analysed under different conditions in order to identify the parameters necessary to increase the leaching rates. This was carried out through cyclic voltammetry tests at 1 mV/s using a pure chalcopyrite macro-electrode to evaluate the effect of scan rate, temperature, and the addition of chloride, cupric, and ferrous ions. Lastly, the feasibility of using seawater for chalcopyrite dissolution was investigated. An increase in the sweep rate and temperature proved to be beneficial in obtaining highest current densities at 10 mV/s and 50 °C. Further, an increase of chloride ions enhanced the current density values. The maximum current density obtained was 0.05 A/m2 at concentrations of 150 g/L of chloride. An increase in the concentration of cupric ions favoured the oxidation reaction of Fe (II) to Fe (III). Finally, the concentration of chloride ions present in seawater has been identified as favourable for chalcopyrite leaching.

The electrochemistry and kinetics of the oxidative dissolution of chalcopyrite in ammoniacal solutions. Part II – Cathodic reactions

The cathodic reduction of copper(II) and oxygen on the surface of chalcopyrite have been studied in ammonia-ammonium sulphate using cyclic voltammetry and chrono-amperometry. The predominant cathodic reaction in the oxidative dissolution of chalcopyrite in ammoniacal solutions has been established to be that of the reduction of copper (II). The rate of the cathodic reaction is inversely dependent on the total ammonia concentration and although the tetra-ammine copper(II) ion is the most dominant species under these conditions, it is suggested that the tri-ammine complex is the most electroactive under these conditions. It was shown that both the reduction of copper(II) and oxidation of copper(I) occur simultaneously at potentials close to the mixed potentials of chalcopyrite under the conditions of this study and apparent mass transfer limitations observed on the reaction were concluded to be due the outward migration of the product of Cu(I) ions from the mineral surface.

Paddlewheelite, a New Uranyl Carbonate from the Jáchymov District, Bohemia, Czech Republic

Paddlewheelite, MgCa5Cu2[(UO2)(CO3)3]4·33H2O, is a new uranyl carbonate mineral found underground in the Svornost mine, Jáchymov District, Bohemia, Czech Republic, where it occurs as a secondary oxidation product of uraninite. The conditions leading to its crystallization are complex, likely requiring concomitant dissolution of uraninite, calcite, dolomite, chalcopyrite, and andersonite. Paddlewheelite is named after its distinctive structure, which consists of paddle-wheel clusters of uranyl tricarbonate units bound by square pyramidal copper “axles” and a cubic calcium cation “gearbox.” Paddle wheels share edges with calcium polyhedra to form open sheets that are held together solely by hydrogen bonding interactions. The new mineral is monoclinic, Pc, a = 22.052(4), b = 17.118(3), c = 19.354(3) Å, β = 90.474(2)°, V = 7306(2) Å3 and Z = 4. Paddlewheelite is the second-most structurally complex uranyl carbonate mineral known after ewingite and its structure may provide insights into the insufficiently described mineral voglite, as well as Cu–U–CO3 equilibrium in general.

A strategy to accelerate the bioleaching of chalcopyrite through the goethite process

Theoretically, controlling redox potential to a relatively low value and inhibiting jarosite formation on the chalcopyrite surface would be an effective strategy to accelerate the bioleaching of chalcopyrite. In this work, using limonite as seed crystals, the effects of the goethite precipitation process on the bioleaching of chalcopyrite were studied for the first time. The bioleaching results showed that the addition of limonite controlled the redox potential in an appropriate range and promoted chalcopyrite dissolution through the removal of ferric (Fe3+) ions. X-ray diffraction and scanning electron microscope analyses indicate that limonite significantly induced the goethite precipitation process and inhibited the production of jarosite. We conclude that promoting the goethite precipitation process with limonite is an effective strategy in accelerating the bioleaching process of chalcopyrite.

The electrochemistry and kinetics of the oxidative dissolution of chalcopyrite in ammoniacal solutions: Part I – Anodic Reactions

The oxidative dissolution of chalcopyrite in aqueous solutions is an electrochemical process. Such processes can be evaluated as coupled anodic and cathodic reactions using electrochemical techniques. The chalcopyrite dissolution reaction has been studied in ammonia-ammonium sulphate solutions using potentiostatic and potentiodynamic methods. Anodic current densities in the vicinity of the mixed potential have been found to increase with an increase in total ammonia (NH3 + NH4+) from 1 M to 3 M, and the order of reaction was found to be 1st order with respect to ammonia. The reaction was found to be zero order with respect to [OH−] at a pH between 9 and pH 10. An analysis of the Tafel slopes suggested an average charge transfer coefficient of 0.61. The rate controlling step was concluded to be a single electron transfer reaction, which supports the formation of a copper depleted intermediate surface that is rapidly oxidised in subsequent electron transfer reactions. The anodic sweeps and constant potential tests did not support the formation of a passivating surface deposit on the oxidising chalcopyrite surface.

A Sulfur K-Edge XANES and Raman Study on the Effect of Chloride Ion on Bacterial and Chemical Leaching of Chalcopyrite at 25 °C

In the present study, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray absorption near edge structure (XANES) spectroscopy, and Raman spectroscopy were used to investigate the effect of chloride ions on chalcopyrite bioleaching and chemical leaching at 25 °C. The leaching results show that the addition of chloride ions suppressed the dissolution of chalcopyrite in both chemical and bacterial leaching. In chemical leaching, the solution redox potential in the experiment without Cl− stayed in a range more suitable for chalcopyrite dissolution compared with experiments with Cl−. In bioleaching, the bacteria activity was suppressed by Cl− leading to low dissolution rates of Cu. Surface morphology and chemical speciation studies confirmed the formation of potassium jarosite on the surface of the chalcopyrite leach residues. In addition, S K-edge XANES indicated the formation of trace amount of elemental sulfur and covellite on the mineral surfaces.

Intensified bioleaching of chalcopyrite by communities with enriched ferrous or sulfur oxidizers

The chalcopyrite bioleaching by enriched ferrous or sulfur oxidizers was investigated. The bioleaching was also intensified three times by the enriched communities. The results indicated that copper recoveries extracted by the enriched ferrous and sulfur oxidizers (Fe-O and S-O) were 38.87% and 43.13%, compared with that by the original community (35.35%). The positive effects of re-introducing S-enriched community to Fe-O and S-O groups were observed with copper extraction rates up to 41.67% and 46.45%. CCA indicated that the community dynamics intensified by S-enriched community was closer to that of the no re-inoculated one, but the Fe-enriched community drove a great fluctuation. A mechanism model for S-enriched community intensifying chalcopyrite bioleaching was proposed. More sulfur oxidizers in community slowed down jarosite formation and maintained lower ORP, which was propitious to chalcopyrite dissolution. Meanwhile, they accelerated S0 decomposition and decreased pH, which promoted acid leaching of chalcopyrite at a low cost.

Influence of seawater and discard brine on the dissolution of copper ore and copper concentrate

It is well known that the Chilean mining industry is facing a shortage of water resources for the sustainable operation not only of existing plants but also of future projects. In addition, the depletion of oxide ores and those containing secondary sulfide copper will leave chalcopyrite ores as the main source of copper for future plants. To assure a sustainable hydrometallurgy plant, alternative water resources such as seawater and discard brine from desalination plants should be used together with a leaching process that can enhance the dissolution of chalcopyrite. This paper reports a study on the dissolution kinetics of finely ground copper oxide ore, chalcopyrite ore, and chalcopyrite concentrate leached in shake flasks, agitated reactors and columns using seawater and discard brine as the leaching solution. The type of chloride solution did not affect the dissolution of the copper oxide mineral. Regardless of the chloride solution used in the leaching test stirred at room temperature, the chalcopyrite dissolution did not exceed 4%, but increased to 90% when the temperature was increased to 50 °C. Column leaching of chalcopyrite ore with a P80 of 5 mm achieved a maximum dissolution of 43% of copper using discard brine at ambient temperature. The results show that curing time of the packed bed before the commencement of column irrigation and intermittent irrigation during leaching appeared to be important parameters to enhance dissolution of copper. Less irrigation time and more resting time can be beneficial for an industrial-scale heap leach plant.

Study on catalytic mechanism of silver ions in bioleaching of chalcopyrite by SR-XRD and XANES

Ag+ is one of the efficient and recoverable catalysts to improve chalcopyrite bioleaching. Because of the complexity of the surface reaction during chalcopyrite bioleaching, there is still controversy on catalytic mechanism of Ag+ in improving dissolution of chalcopyrite. In the present study, we studied the catalytic effect of Ag+ on bioleaching of chalcopyrite by extreme thermophile Acidianus manzaensis. Based on synchrotron radiation X-ray diffraction (SR-XRD) and X-ray absorption near edge structure (XANES) spectroscopy, the relevant iron and sulfur speciation of leaching residues was analyzed. Bioleaching experiments showed that copper extraction was significantly promoted by adding Ag+, and the optimum concentration of Ag+ was 0.05% (mass fraction of Ag+ to chalcopyrite). SR-XRD and XANES analyses showed that, during bioleaching in the presence of 0.05% of Ag+ and in the absence of Ag+, the intermediates S0, jarosite and secondary minerals (chalcocite, bornite and covellite) were formed. The linear combination fitting of XANES spectra further revealed that the addition of silver ions remarkably promoted the formation of bornite and covellite, while had no effect on formation of chalcocite, indicating that bioleaching of chalcopyrite should be catalyzed by Ag+ with promoting the generation of bornite and its conversion to covellite. This model suggested that the rapid formation of bornite like species contributed to positive effect of Ag+ on chalcopyrite bioleaching, while the accumulation of covellite slowed leaching rate at the end period of chalcopyrite bioleaching.