Rate Of Chalcopyrite Dissolution Research Articles

Chalcopyrite leaching in ammonium chloride solutions under ambient conditions: Insight into the dissolution mechanism by XANES, Raman spectroscopy and electrochemical studies

Ammoniacal leaching solutions have been considered as an effective lixiviant for the oxidative dissolution of chalcopyrite. However, compared with the extensive studies of acidic chalcopyrite dissolution, the dissolution mechanism of chalcopyrite in ammoniacal solutions needs further understanding. In this study, the oxidative dissolution of chalcopyrite in ammonium chloride solutions under room temperature and pH 8.5 was studied by X-ray absorption near-edge spectroscopy (XANES), Raman spectroscopy and electrochemical impedance spectroscopy (EIS). Both batch leaching experiments and electrochemical studies showed that Cu(II) ions were more efficient than dissolved oxygen for chalcopyrite oxidation in ammonium chloride solutions. Leaching kinetics analysis showed that without the initial addition of Cu(II), chalcopyrite dissolution rate was controlled by two different stoichiometric chemical reactions: the initial and slow leaching stage controlled by dissolved oxygen; then predominated by Cu(II) rather than dissolved oxygen with a fast leaching rate when copper concentration exceeded a certain level (>0.12 g/L). Thiosulfate (S2O32−) rather than sulfate (SO42−) was confirmed as the primary soluble sulfur species produced during chalcopyrite dissolution. Decomposition of S2O32− in the presence of both O2 and Cu(II) resulted in the final stable product SO42− accompanied by the formation of other sulfur intermediate species, including S4O62− and SO32−. No evidence was found for the formation of elemental sulfur. Amorphous hematite (Fe2O3) and six-line ferrihydrite (5Fe2O3·9H2O) were the major components residing on the chalcopyrite surface, which were responsible for the slow dissolution rate at late stage. According to the present work, a model for the chalcopyrite dissolution mechanism in alkaline ammonium chloride solutions under ambient conditions is provided.

OPTIMIZATION OF CHALCOPYRITE GALVANIC LEACHING IN THE PRESENCE OF PYRITE AND SILVER AS CATALYSTS BY USING RESPONSE SURFACE METHODOLOGY (RSM)

In this research, dissolution of chalcopyrite concentrate is modelled and optimized using Response Surface Methodology (RSM). Also, effective parameters in the leaching process such as the amount of pyrite, silver ions, redox potential and initial concentration of acid are comprehensively studied. Central Composite Design (CCD) methodology is chosen as the design matrix to predict the optimum level of the parameters. In the next step, it will be proven that in the presence of silver ions, pyrite effectiveness is improved and also the chalcopyrite dissolution rate is increased considerably. Using the result of quadratic programming, a rotation speed of 1000 rpm, a pyrite/chalcopyrite mass ratio of 3:1, the amount of 150 ppm silver ion, a solution potential set point of 470 mV, at 800°C and 25 g/L initial acid concentration are the optimal level of the selected parameters wherein the maximum copper extraction with more than 95% in less than 10 hours can be accessible.

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+.

Is the growth of microorganisms limited by carbon availability during chalcopyrite bioleaching?

Microorganisms, which play a key role during mineral dissolution in bioleaching processes, require O2 to promote the oxidation processes of sulfide mineral dissolution and CO2 or more complex molecules as carbon source for cell growth. Preliminary models have been proposed for relating the microbial succession in bioleaching heaps with the activity of different CO2 fixation pathways. The increase of internal heap temperature during bioleaching improves the rate of chalcopyrite dissolution. However, it also negatively affects CO2 and O2 availability, consequently the microbial community changes and only the best adapted microorganisms are capable of growing under the limiting conditions. In this work we attempt to elucidate how microbiological succession proceeds in a semi-industrial bioleaching column test system, with emphasis in determining the identity of the microorganisms participating and the metabolic dynamics of carbon fixation pathways. In silico reconstruction of the carbon fixation metabolisms based on available genomes and the gene expression studies using microarray and RNA-seq were performed. The physicochemical conditions and the metallurgical parameters were also included in the analysis. Although the investigation is based on a non-homogeneous system - which leads to some seemingly contradictory data - the results showed a clear change in the structure of the microbial community as well as in the expression of pathways for CO2 fixation, as the column test progressed. These changes were directly related to two factors, the temperature inside column and the CO2 availability. The gene expression analyses confirmed the temporal distribution of microorganisms as a function of the temperature and the different pathways for CO2 fixation. The evidences obtained here support the fact that low CO2 availability becomes an important asset to the microbial population survival and growth promotion in the bioleaching environments. The determination of the expression level of the key genes is a good opportunity to improve a sound understanding of the high temperature bio-assisted heap leaching of chalcopyrite and to optimize the technology.

Chalcopyrite Dissolution at 650 mV and 750 mV in the Presence of Pyrite

The dissolution of chalcopyrite in association with pyrite in mine waste results in the severe environmental issue of acid and metalliferous drainage (AMD). To better understand chalcopyrite dissolution, and the impact of chalcopyrite’s galvanic interaction with pyrite, chalcopyrite dissolution has been examined at 75 °C, pH 1.0, in the presence of quartz (as an inert mineral) and pyrite. The presence of pyrite increased the chalcopyrite dissolution rate by more than five times at Eh of 650 mV (SHE) (Cu recovery 2.5 cf. 12% over 132 days) due to galvanic interaction between chalcopyrite and pyrite. Dissolution of Cu and Fe was stoichiometric and no pyrite dissolved. Although the chalcopyrite dissolution rate at 750 mV (SHE) was approximately four-fold greater (Cu recovery of 45% within 132 days) as compared to at 650 mV in the presence of pyrite, the galvanic interaction between chalcopyrite and pyrite was negligible. Approximately all of the sulfur from the leached chalcopyrite was converted to S0 at 750 mV, regardless of the presence of pyrite. At this Eh approximately 60% of the sulfur associated with pyrite dissolution was oxidised to S0 and the remaining 40% was released in soluble forms, e.g., SO42−.

Chalcopyrite leaching and bioleaching: An X-ray photoelectron spectroscopic (XPS) investigation on the nature of hindered dissolution

Chalcopyrite (CuFeS2) is both the most economically important and the most difficult copper mineral to (bio)leach. The main reason for the slow rate of chalcopyrite dissolution is the formation of a layer on the surface of the mineral that hinders dissolution, termed “passivation”. The nature of this layer is still under debate. In this work, the role of bacterial activity was examined on the leaching efficiency of chalcopyrite by mimicking the redox potential conditions during moderately thermophilic bioleaching of a pure chalcopyrite concentrate in an abiotic experiment using chemical/electrochemical methods. The results showed that the copper recoveries were equal in the presence and absence of the mixed culture. It was found that the presence of bulk jarosite and elemental sulphur in the abiotic experiment did not hamper the copper dissolution compared to the bioleaching experiment. The leaching curves had no sign of passivation, rather that they indicated a hindered dissolution. XPS measurements carried out on massive chalcopyrite samples leached in the bioleaching and abiotic experiments revealed that common phases on the surface of the samples leached for different durations of time were elemental sulphur and iron-oxyhydroxides. The elemental sulphur on the surface of the samples was rigidly bound in a way that it did not sublimate in the ultra-high vacuum environment of the XPS spectrometer at room temperature. Jarosite was observed in only one sample from the abiotic experiment but no correlation between its presence and the hindered leaching behaviour could be made. In conclusion, a multi-component surface layer consisting of mainly elemental sulphur and iron-oxyhydroxides was considered to be responsible for the hindered dissolution.

Galvanic Effect of Pyrite on Chalcopyrite Leaching in Sulfate-Chloride Media

Chalcopyrite concentrate and mixtures of pyrite/chalcopyrite were leached in H2SO4-NaCl-O2 solutions to assess the effect of pyrite on the chalcopyrite dissolution rate in this media. The results showed that the addition of pyrite increases the dissolution rate of chalcopyrite at short leaching times but the catalytic effect of pyrite decreases as the reaction progresses. Based on the experimental evidence, it was concluded that the presence of pyrite in the leaching of chalcopyrite in H2SO4-NaCl-O2 solutions enhances the dissolution of copper through a galvanic interaction between pyrite and chalcopyrite. Additions of ferrous sulfate also increase chalcopyrite leaching rate effectively.

Effect of initial pH on chalcopyrite oxidation dissolution in the presence of extreme thermophile Acidianus manzaensis

The influence of initial pH on the chalcopyrite oxidation dissolution at 65 °C was investigated by bioleaching and cyclic voltammetry experiments, and the oxidation products were investigated by XRD and Raman spectroscopy. Bioleaching results show that chalcopyrite dissolution rate increases with the decrease of the initial pH in chemical leaching, while the influence of initial pH on bioleaching is on the contrary. The presence of Acidianus manzaensis does not promote chalcopyrite dissolution under initial pH 1.0, which mainly results from serious inhibition of high acidity to the growth of Acidianus manzaensis. Electrochemical experiments results show that anodic oxidation currents of electrolyte with or without Acidianus manzaensis both increase with the increase of initial pH, and covellite and sulfur are detected on the electrode surface. The results confirm that chalcopyrite dissolution in chemical leaching is under the combined action of oxidation and non-oxidation of proton, with conversion of chalcopyrite to covellite and elemental sulfur.

Electrochemical simulation of redox potential development in bioleaching of a pyritic chalcopyrite concentrate

The majority of the world's copper reserves are bound in the sulphide mineral chalcopyrite (CuFeS2), but supply of the copper is hindered by the recalcitrance of chalcopyrite to (bio)leaching. The main reason for the slow rate of chalcopyrite dissolution is the formation of a layer on the surface of the mineral that hinders dissolution, termed “passivation”. The nature of this layer and the role of microorganisms in chalcopyrite leaching behaviour are still under debate. Moderately thermophilic bioleaching of a pyritic chalcopyrite concentrate was mimicked in an electrochemical vessel to investigate the effect of the absence and presence of microorganisms in copper dissolution efficiency. Data from the redox potential development during bioleaching was used to program a redox potential controller in an electrochemical vessel to accurately reproduce the same leaching conditions in the absence of microorganisms. Two electrochemical experiments were carried out with slightly different methods of redox potential control. Despite massive precipitation of iron as jarosite in one of the electrochemically controlled experiments and formation of elemental sulphur in both electrochemical experiments, the efficiencies of copper dissolution were similar in the electrochemical tests as well as in the bioleaching experiment. No passivation was observed and copper recoveries exhibited a linear behaviour versus the leaching time possibly due to the galvanic effect between chalcopyrite and pyrite. The data suggest that the main role of microorganisms in bioleaching of a pyritic chalcopyrite concentrate was regeneration of ferric iron. It was also shown that the X-ray photoelectron spectroscopy measurements on the residues containing bulk precipitates cannot be employed for a successful surface characterisation.

Chalcopyrite dissolution rate laws

Abstract Meta-analysis of 173 rate measurements from 21 publications was used to develop rate laws for chalcopyrite dissolution under environmentally relevant conditions. Multiple linear regression analysis of 28 data for nonoxidative chalcopyrite dissolution in the presence of O2 and Cl− produced the following rate law: r = 10 - 1.52 e - 28200 / RT [ H + ] 1.68 Here, r is the rate of chalcopyrite dissolution in units of mol m−2 s−1 where the surface area is expressed on a geometric basis. Multiple linear regression analysis of 36 data for chalcopyrite dissolution caused by reaction with Fe(III) in the presence and absence of O2 and Cl− produced the following rate law: r = 10 1.88 e - 48100 / RT [ H + ] 0.8 [ Fe ( III ) ] 0.42 Some data were excluded from these rate law models because they were inconsistent with the overall dataset and/or were relatively unconstrained. There were no published rate data that could be clearly identified as representing chalcopyrite dissolution caused by O2 oxidation alone. Although there are numerous reports that suggest that chalcopyrite dissolution rates are increased by the presence of Cl− in solution, the regression models documented that the effect of Cl− on dissolution was insignificant for this dataset. The rate laws developed in this work are most appropriate for characterizing chalcopyrite dissolution at low pH (⩽3), and will ultimately allow better modeling of acid, sulfate, Fe, and Cu release to the environment.

Chalcopyrite dissolution rate law from pH 1 to 3

Chalcopyrite dissolution kinetics in the pH range of 1 to 3 were studied by means of long-term flow-through experiments to obtain a dissolution rate law which can be coupled with reactive transport models to forecast Acid Rock Drainage. In the range of conditions under study, the rate of chalcopyrite dissolution is only slightly dependent on hydrogen ion activity, increasing with decreasing pH. The steady-state dissolution rates obtained in the present study were combined with earlier results presented by Acero et al. (2007a) to obtain the following expression for chalcopyrite dissolution rate law: where Rchalcopyrite is the chalcopyrite dissolution rate (mol m-2 s-1), aH+ is the activity of hydrogen ion in solution, R is the gas constant (kJ mol-1 K-1) and T is the temperature (K). This expression can applied through a wide range of environmental conditions similar to the ones found in systems affected by acid drainage. In agreement with earlier chalcopyrite kinetic studies, iron was released to solution preferentially over copper and sulfur, compared with the stoichiometry of the pristine mineral. Consistently, XPS examination of the samples showed that reacted surfaces were enriched in sulfur and copper (relative to iron) compared with the initial, pristine chalcopyrite surface. However, this surface layer does not exert any passivating effect on chalcolpyrite dissolution and the kinetics of the overall process in the long term seems to be surface-controlled.

Bioleaching of chalcopyrite by pure and mixed cultures of Acidithiobacillus spp. and Leptospirillum ferriphilum

Bioleaching is an economical method for the recovery of metals that requires low investment and operation costs. Furthermore, it is generally more environmentally friendly than many physicochemical metal extraction processes. The bioleaching of chalcopyrite in shake flasks was investigated with pure and mixed cultures of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Acidithiobacillus caldus, and Leptospirillum ferriphilum. The mixed cultures containing both iron- and sulfur-oxidizing bacteria were more efficient than the pure culture alone. The presence of sulfur-oxidizing bacteria positively increased the dissolution rate and the percentage recovery of copper from chalcopyrite. Mixed cultures consisting of moderately thermophilic L. ferriphilum and A. caldus leached chalcopyrite more effectively than mesophilic A. ferrooxidans pure and mixed cultures. The decrease of the chalcopyrite dissolution rate in leaching systems containing A. ferrooxidans after 12–16 days coincided with the formation of jarosite precipitation as a passivation layer on the mineral surface during bioleaching. Low pH significantly reduces jarosite formation in pure and mixed cultures of L. ferriphilum and A. caldus.

Kinetics of chalcopyrite dissolution at pH 3

The management of mine wastes and the quantitative forecast of Acid Rock Drainage ( ARD ) generation have aroused widespread interest. In order to be coupled with gas and water flux models, chalcopyrite dissolution kinetics at pH 3, at temperatures from 25 to 70 °C and at variable dissolved oxygen concentrations was studied in flow-through experiments. In the range of conditions under study, the rate of chalcopyrite dissolution is independent of the concentration of dissolved oxygen. This enables chalcopyrite to dissolve throughout the whole waste piles. The rise in temperature from 25 to 70 °C produces an increase of one order of magnitude in the chalcopyrite dissolution rate. As a result of this study, the following expression for chalcopyrite dissolution rate was obtained: \[\mathit{R_{chalcopyrite}} = 10^{{-}5.52{\pm}0.07}\mathit{e}^{\frac{{-}32{\pm}5}{\mathit{RT}}}\] where R chalcopyrite is the chalcopyrite dissolution rate (molm −2 s −1 ), R is the gas constant (kJmol −1 uK −1 ) and T is the temperature (K). In line with earlier studies carried out under different conditions, iron was released to solution preferentially over copper in all the experiments carried out. XPS examination of the samples showed that reacted surfaces were formed by phases enriched in sulfur and copper (relative to iron) compared with the initial, pristine chalcopyrite surface. However, these surface layers allow the progress of dissolution with out passivating the chalcopyrite surface. According to the apparent activation energy obtained (32±5 kJ mol − 1 ) and to the lack of rate variation with stirring, the chalcopyrite dissolution rate seems to be controlled by surface reactions and is independent of the non-stoichiometric surface layer.

Kinetics of chalcopyrite dissolution by hydrogen peroxide in sulphuric acid

The extraction of copper from a chalcopyrite concentrate by hydrogen peroxide in sulphuric acid solutions was studied. The influence of various parameters was investigated in order to elucidate the kinetics of chalcopyrite dissolution. It was determined that stirring speed had no effect on the rate of chalcopyrite dissolution, which suggested that reaction was not controlled by liquid-phase diffusion. Dissolution curves were found to conform to the surface reaction controlled shrinking core model, i.e., 1−(1− X) 1/3= k s t. Both the magnitude of the activation energy of 60 kJ/mol and the linear relationship between the rate constant and the inverse particle radius support the fact that dissolution is controlled by the surface reaction. Hydrogen peroxide had great influence on the rate of chalcopyrite dissolution; a reaction order of unity was calculated with respect to the concentration of this oxidant. Sulphuric acid also had influence on chalcopyrite dissolution, with a reaction order of 0.3 with respect to the acid concentration being established.

The role of iron-hydroxy precipitates in the passivation of chalcopyrite during bioleaching

The bioleaching of chalcopyrite in an acidic sulphate nutrient medium was investigated using Sulfobacillus thermosulfidooxidans, a moderately thermophilic iron- and sulphur oxidising bacterium. Copper release to solution was initially rapid but this slowed significantly after about SO hours. The decrease in chalcopyrite dissolution rate coincided with significant precipitation of jarosite on the mineral surface. Cultures of the moderately thermophilic acidophilic bacteria Acidimicrobium ferrooxidans, Sulfobacillus acidophilus and Sulfobacillus thermosulfidooxidans were grown in anaerobic media containing chalcopyrite passivated by jarosite. The moderate thermophiles used the ferric ion in the jarositic surface precipitate as a terminal electron acceptor in place of oxygen in the anoxic environment. Despite extensive bioreduction of the iron-hydroxy precipitates, it was found that the jarosite was not completely removed and that subsequent biooxidation of the treated concentrate achieved no significant increases in copper release compared with concentrate that had not been subjected to prior biooxidation or bioreduction.

The role of iron-oxidizing bacteria in stimulation or inhibition of chalcopyrite bioleaching

A series of bacterial and chemical leaching experiments were conducted to clarify contradictory reports in the literature regarding the role of bacteria in the bioleaching of chalcopyrite. Tests containing a high bacterial concentration showed inhibited leaching, even lower than non-inoculated controls. However, when bacterial cells were washed before inoculation, it was apparent that it was not the bacterial cells but rather the chemical species introduced with them that influenced the leaching rate. In addition, the results of comparative tests with 0.1 M ferrous sulphate or ferric sulphate showed that copper was leached from the ore 2.7 times faster in leach solutions containing ferrous ion, suggesting that ferric ions inhibit chalcopyrite dissolution. The results indicated that the chalcopyrite dissolution rate is strongly dependent on the reduction potential ( E h) in solution, and that this parameter is far more influential than the number or activity of bacterial cells. These results imply that the role of bacteria may only be stimulatory when the prevailing electrochemical conditions are also favourable.

Investigation of the kinetics of chalcopyrite oxidation by potassium dichromate

The kinetics of chalcopyrite oxidation by potassium dichromate in sulphuric acid were investigated. The effects of stirring rate, temperature, dichromate concentration, sulphuric acid concentration and particle size on the rate of chalcopyrite oxidation were examined. The activation energy is 48–54 kJ/mol, indicating that the rate of chalcopyrite oxidation is chemically controlled. The dichromate ion concentration had no effect on rate of chalcopyrite dissolution and, relative to sulphuric acid, an order of 0.80–0.92 was established. In addition, the effects of chloride, copper(() and iron(III) concentrations on the rate of chalcopyrite oxidation were investigated.

Cupric Chloride Leaching of Chalcopyrite

In a strong chloride solution the predominant cuprous, cupric, ferrous, and ferric chloride complexes are CuCl3 −2, CuCl+, CuCl2, FeCl2, and FeCl2 + respectively. The probable dissolution reaction for chalcopyrite in cupric chloride solution is CuFeS2 + 3CuCl+ + 11Cl−2 = 4CuCl3 −2 + FeCl2 + 2S The standard free energy change for this reaction at 25°C and unit activities is +43.84 kJ, indicating that the reaction is not thermodynamically feasible. The reaction becomes thermodynamically feasible at high chloride concentration when the ratio of cuprous to cupric copper in solution is less than about 1.9. When the cuprous to cupric ratio becomes larger than a critical value (dependent upon the operating conditions) the dissolution ceases because it is no longer thermodynamically feasible. Over the range 0.79–1.46 M Cu+2 and 2.82–6.21 M Cl− at 90°C, neither cupric nor chloride ion concentration influences the rate of chalcopyrite dissolution, which is directly proportional to mineral surface area. The activation energy for the reaction is 134.7 kJ/mole, and the rate controlling process is probably a step in the anodic reaction.

The effect of some impurities on the rate of chalcopyrite dissolution

Sintered disks of synthetic chalcopyrite were prepared with known amounts of various sulphide impurities. The disks were leached in acidified ferric sulphate solutions to determine the effect of the second phase on the rate of chalcopyrite dissolution. Experiments using inert impurities showed that the observed variations in the leaching rates were caused by the presence of the impurity and not by other effects. Chalcopyrite-cubanite mixtures behave almost additively; chalcopyrite-bornite mixtures dissolve slightly more rapidly than would be expected from their additive rates. The presence of pyrite, molybdenite or stibnite (which reacts to form pyrite) accelerates the chalcopyrite dissolution rate; the presence of galena retards its dissolution. High-iron sphalerite slightly retards the chalcopyrite dissolution but low-iron sphalerites behave erratically. These results are consistent with a galvanic corrosion mechanism except for the observed effects of molybdenite. Résumé Des pastilles frittées de chalcopyrite synthétique contenant des quantites connues de diverses impuretes sulfurées ont été préparées. Les pastilles ont été lixiviées dans des solutions acidifiées de sulfate ferrique afin de déterminer l'effet de la deuxième phase sur Ie taux de dissolution de la chalcopyrite. En utilisant des impuretés inertes, les expériences ont montré que les variations observées dans les taux de lixiviation sont causées par la présence de l'impureté et non par la présence de d'autres effets. Les mélanges de chalcopyrite-cubane se comportent de façon additive; ceux de chalcopyrite-bornite se dissolvent un peu plus rapidement que ce dont on aurait pu s'attendre de la sommation de leurs taux. La présence de pyrite, de molybdénite ou de stibine (laquelle réagit pour former la pyrite) accélère le taux de dissolution de la chalcopyrite; la presence de galène retarde sa dissolution. La sphalérite à haute teneur en fer retarde legerement la dissolution de la chalcopyrite; cette dissolution présente un comportement erratique pour les sphalérites à faible teneur en fer. Les résultats sont en accord avec le mécanisme de corrosion galvanique sauf pour les effets observés de la molybdénite.

The effect of some impurities on the rate of chalcopyrite dissolution

The effect of some impurities on the rate of chalcopyrite dissolution