Cupric Chloride Leaching Research Articles

Electro-hydrometallurgical chloride process for selective gold recovery from refractory telluride gold ores: A mini-pilot study

The current paper introduces for the very first time recently invented electrodeposition-redox replacement (EDRR) method in continuous leaching-recovery-solution purification process. The mini-pilot study reveals that longer duration of the EDRR process is beneficial as it increases gold recovery per stage and decreases the specific energy consumption of the EDRR. This extraordinary behavior is postulated to be inherent to the EDRR process, as during the EDRR the cathode surface is gradually transformed from stainless steel surface to gold(±copper) surface, thus increasing process performance with time. In addition, gold concentration of 1 mg/L in the PLS was established as the minimum concentration required for efficient operation of the EDRR process.Gold extraction from ore to solution throughout the pilot test reached up to ca. 90%, whereas in reference cyanidation test only 64% of gold was dissolved. Overall, after 150 h of pilot experiment, 83% of dissolved gold was recovered from solution on the cathode, resulting in 68.5% holistic recovery of gold from ore. Furthermore, process simulation model was built, and it suggested that closed-loop operation of cupric chloride leaching – EDRR recovery – copper precipitation process can recover in total over 84% of gold from refractory telluride ore to the cathode product, providing further evidence of true potential of EDRR in sustainable gold extraction.

Direct Cupric Chloride Leaching of Gold from Refractory Sulfide Ore: Process Simulation and Life Cycle Assessment

ABSTRACT A simulation-based life cycle assessment was conducted to compare the impacts of different cyanide-free chloride processing routes for refractory ores to determine whether one-stage leaching of gold from the ores could be advantageous over chloride leaching after conventional pressure oxidation from an environmental perspective. It was shown that both leaching conditions and the refractoriness of the ore strongly affect the environmental impacts of the process. The global warming potential in the direct leaching route was determined to vary between 7.7–17.0 t CO2-eq for 1 kg gold/Au. Prerequisites for the sustainable application of the direct leaching process are suggested.

Process simulation based life cycle assessment of cyanide-free refractory gold concentrate processing – Case study: Cupric chloride leaching

The development of cyanide-free gold leaching methods is becoming increasingly important due to the treatment of complex ores, where treatment by cyanidation is not economically viable. Cupric chloride leaching provides an alternative leaching process to replace cyanidation. A detailed simulation of refractory gold concentrate processing by cupric chloride leaching is presented in this study. The simulation with mass and energy balances was built to be used as life cycle inventory data to evaluate the environmental impacts of the development stage cupric chloride process. Three cases, the Base Case (125 g/L Cl-), Mild Case (50 g/L Cl-), and Extremely Mild Case (20 g/L Cl-), were investigated in two flowsheet options. Loss of gold to wash waters was observed in the Flowsheet 1 cases, and therefore Flowsheet 2, with the recirculation of wash water to solvent extraction, was developed and investigated in order to achieve higher gold recovery. The gold extraction improved from around 85% to 99%. Chemical consumption (NaCl, NaBr, CuCl2) was greatly affected by the leaching conditions, higher concentrations consuming more initial chemicals. In milder conditions, efficient recycling of chlorides could be obtained in the process, and no addition of NaCl was required. In the Extremely Mild Case, the chloride concentration was close to sea water conditions (20 g/L), where sea water could be used to provide chlorides for the process, and the effluent waters could be disposed of in the sea after purification. The global warming potential was estimated to be 12.5 t CO2-e/kg Au in chloride leaching and was further decreased to 10.6 t CO2-e/kg Au in the mildest conditions (20 g/L Cl-). The milder chloride leaching conditions (20 g/L Cl- and 50 g/L Cl-) were shown to decrease the acidification potential, eutrophication potential, and water depletion.

Kinetics of cupric leaching of pyrite in 4 M NaCl solutions

ABSTRACT Cupric chloride leaching is an attractive alternative for the treatment of pyritic refractory gold ores. In this context, the kinetics of pyrite dissolution was studied in cupric chloride solutions containing 4 M NaCl. Pyrite leaching experiments were conducted in a stirred tank reactor for 250 h. The effect of temperature was evaluated at 45°C, 60°C and 75°C, while the effect of [Cu (II)] was evaluated with solutions containing 0.054, 0.252 and 0.512 M. The results showed that the increase in temperature and [Cu (II)] improved the rate of pyrite dissolution. The fraction of pyrite oxidised to sulphate ranged from 52% to 75%. Sulphate formation correlated well with the number of holes and cracks formed on leached pyrite particles. The kinetics of pyrite dissolution fitted well to the shrinking core model with chemical reaction control (T ≤ 60°C and [Cu (II)] ≤ 0.054 M) or mixed control (T > 60°C and [Cu (II)] > 0.054 M). The activation energy was 73.102 kJ/mol and the dependence of [Cu (II)] was proportional to .

Effect of redox potential and OCP in ferric and cupric chloride leaching of gold

The research presented contributes to the global goal of responsible production by providing robust tools for the optimization of gold dissolution in cyanide-free gold leaching solutions, which represent emerging non-toxic gold technologies. In the current study, gold dissolution was investigated in ferric and cupric chloride solutions. The effect of the redox potential on the open circuit potential (OCP) and dissolution rate of gold was investigated experimentally in the parameter range of T = 25–95 °C, [Fe3+/Cu2+] = 0.02–1.0 M, [Cl−] = 1–5 M, pH = 0.0–2.0, and ωcyc = 2500 RPM. A high rotational speed was chosen to minimize the effects of limited mass transfer rate. The aim was to provide tools for estimating the gold dissolution rate in ferric and cupric chloride solutions, using the solution properties. The results showed that redox potentials, OCPs, and dissolution rates were constantly higher in ferric chloride solutions compared to corresponding cupric chloride solutions. The multilinear regression models for redox potential showed that a rise in temperature and oxidant concentration increased the redox potential in both ferric and cupric chloride solutions. However, an increase in the chloride concentration decreased the redox potential in ferric chloride solutions, whereas the effect was the opposite in cupric solutions. A rise in the pH value increased the redox potential in ferric solutions, but this was found to be an insignificant variable in cupric chloride leaching within the investigated parameter range. The redox potential had a positive correlation with OCP and the logarithm of the gold dissolution rate in both investigated systems. The results suggest that, in the chloride leaching systems examined, the solution properties can be used to determine the redox potential, and furthermore, the redox potential can be used to estimate the gold dissolution rate. This study provides an experimentally verified tool for the robust estimation of the gold dissolution rate in chloride systems.

Features affecting the cupric chloride leaching of gold

The current study investigated gold dissolution in cupric chloride solution, which is one of the most promising alternatives to replace cyanide, although not yet in operation on industrial scale. In this paper, the gold dissolution reaction rate and mechanism were studied by varying the process variables of temperature (28–95 °C), cupric concentration (0.02–1.0 M), chloride concentration (1–5 M), rotational speed (100–2500 RPM), and pH (0.5–2.0). The parameters affecting either the anodic or cathodic reaction, or both, were identified for the first time to the best of the authors’ knowledge in this wide range and with these parameter intervals. Tafel and linear polarization methods as well as cyclic voltammetry were used for pure gold with both rotating disk and stationary gold electrodes. An increase in the gold dissolution rate was observed with an increase in temperature, chloride concentration, and rotational speed. Additionally, an increase in cupric concentration ([Cu2+] = 0.02–0.75 M) promoted the gold dissolution rate, whereas the gold dissolution rate decreased with [Cu2+] from 0.75 to 1.0 M. The conditions for maximizing the gold dissolution rate in cupric chloride solution were concluded to be T > 55 °C, [Cu2+] = 0.5–0.75 M, [Cl−] = 5 M, and pH = 1.0 and the highest gold dissolution rate (2.9 · 10−4 mol m−2 s−1) was achieved at 95 °C with [Cu2+] = 0.5 M, [Cl−] = 5 M, pH = 1.0, and ωcyc = 2500 RPM. The pH was shown not to affect the gold dissolution rate at all, but only to affect the solubility of the oxidant. It was suggested that gold dissolved as aurous species in the conditions of this study, although the increase in chloride concentration promoted the dissolution of gold as both, auric and aurous, species.The reaction mechanism was interpreted using mixed potential theory. An increase in temperature was shown to promote only the cathodic reduction of cupric ion to cuprous at lower temperatures (28–55 °C); however, both the anodic gold dissolution reaction and cathodic cupric reduction reaction were enhanced at higher temperatures (65–95 °C). The cathodic reaction was also enhanced with an increase in cupric concentration (0.02–0.5 M), whereas the anodic reaction was promoted when the cupric concentration was increased from 0.5 to 0.75 M. When the cupric concentration was increased from 0.75 to 1.0 M, the cathodic reaction rate decreased. However, the reason for the decrease in the cathodic reaction rate was not clear. An increase in chloride concentration enhanced the cathodic reaction in the investigated range (1–5 M), whereas an increase in rotational speed (i.e., improved mass transfer) increased the anodic gold dissolution rate, specifically at low rotational speeds.

Electrochemical recovery of minor concentrations of gold from cyanide-free cupric chloride leaching solutions

Abstract Despite of being the most common hydrometallurgical process for extraction of gold from ores and concentrates, cyanide leaching is blamed for its hazardous impact on environment and human health. These concerns have given a rise for alternative cyanide-free technologies, such as cupric chloride leaching. However, the state-of-art processes for gold recovery from chloride solutions are facing issues of high reagent consumption and poor selectivity. This article describes an innovative method for recovery of minor concentrations of gold from hydrometallurgical solutions by repetitive Electrochemical Deposition-Redox Replacement (EDRR) cycles. In contrast to conventional carbon-in-leach/resin-in-leach technologies or solvent extraction, the proposed electrochemical method does not require addition of any chemicals in the process and remarkably selective gold recovery can be achieved from concentrated cupric solution by tailoring the process parameters. A number of electrochemical experiments was performed in order to identify the process variables affecting the Au recovery. Results indicate that so called cut-off potential and deposition time were the EDRR parameters having the strongest impact on gold recovery at fixed concentration of Cu and Au ions. The Au content in the metal deposit after 250 EDRR cycles exceeded 75% and the Au:Cu ratio has increased by a factor of 1000, from 1:340 in the solution up to 3.3:1 in the final product. X-ray photoelectron spectroscopy analysis of the cathode surface confirmed full replacement of sacrificial copper with gold. Obtained results prove that the EDRR method can be efficiently used for the recovery of trace amounts of gold from cupric chloride solutions used for cyanide-free gold leaching.

Cupric chloride leaching (HCl–CuCl2–NaCl) of metals from waste printed circuit boards (WPCBs)

The leaching of metals from waste printed circuit boards (WPCBs) in cupric chloride solutions (HCl–CuCl2–NaCl) was studied. Effects of initial concentration of cupric (8–157mM Cu2+), chloride (0.7–2.0M NaCl), temperature (20–80°C), solids ratio (1–15w/v) and air/oxygen (1L/min) on the leaching of copper as well as other metals (i.e. Fe, Ni, Ag, Pd and Au) were investigated. The findings have shown that increasing the initial concentration of Cu2+ leads to a significant enhancement in the metal extractions. At Cu2+ concentrations of ≥79mM, high extractions (i.e. ≥98%) for copper, nickel and iron were obtained over 120min. An increase in the concentration of chloride (i.e. from 0.7M to 2M Cl−) decreased the extraction of copper by up to 40% at 60min due to the decrease in the activity of free Cu2+. Rising the temperature from 20°C to 80°C resulted in a 1.38-fold increase in the copper extraction at 120min. The activation energy (Ea) for leaching of copper was calculated to be ≈41kJ/mol, indicative of a chemically controlled leaching reaction. Air/oxygen (1L/min) was supplied for the regeneration of Cu2+, which improved the extraction of all the metals monitored. Increasing the solids ratio (1–15w/v) adversely affected the leaching process with no copper extraction at 15w/v. However, the extraction of metals (Cu, Ni, Ag and Pd) substantially ameliorated in the presence of oxygen. The current study have shown that copper, palladium, nickel and silver can be readily extracted from WPCBs in cupric chloride leaching where the extraction of gold is very limited.

Leaching of complex sulphide concentrate in acidic cupric chloride solutions

The chemical analysis of a complex sulphide concentrate by emission spectrometry and X-ray diffraction shows that it contains essentially copper, lead, zinc and iron in the form of chalcopyrite, sphalerite and galena. A small amount of pyrite is also present in the ore but does not be detected with X-ray diffraction. The cupric chloride leaching of the sulphide concentrate at various durations and solid/liquid ratios at 100 °C shows that the rate of dissolution of the ore is the fastest in the first several hours, and after 12 h it does not evolve significantly. If oxygen is excluded from the aqueous cupric chloride solution during the leaching experiment at 100 °C, the pyrite in the ore will not be leached. The determination of principal dissolved metals in the leaching liquor by flame atomic absorption spectrometry, and the chemical analysis of solid residues by emission spectrometry and X-ray diffraction allow to conclude that the rate of dissolution of the minerals contained in the complex sulphide concentrate are in the order of galena >sphalerite>chalcopyrite.

Effect of NaCl concentration and particle size on chalcopyrite leaching in cupric chloride solution

The paper summarizes results of investigation on the effect of NaCl addition to the acidified cupric chloride leaching solution as well as the effect of the particle size (surface area) of chalcopyrite on the kinetics leaching. While NaCl addition has a definitely positive effect on the leaching rate, the effect of particle size is almost negligible. The experiments conducted under this investigation showed good agreement with the opinion stated in the literature that the major effect of NaCl presence results from the formation of complexes. The negligible effect of chalcopyrite particle size on the leaching kinetics suggests that, at least for the metal recovery obtained in our experiments, the chalcopyrite particles do not become covered by the solid layer that would slow down the reaction.

Studies on Processing of an Alnico Scrap

This paper presents the results of research and development work on processing of alnico scrap, a secondary resource of nickel and cobalt, generated during the manufacturing of alnico magnets. The scrap contains 8–10% nickel, 10–12% cobalt, 32–50% of iron, 8–10% aluminium, 2% copper and remaining silica. Various processes such as acid leaching, aqueous chlorine leaching, salt roasting and cupric chloride leaching were studied in detail. Of these cupric chloride leaching was found to be most effective with respect to recovery and purity. It has been possible to obtain pure nickel and cobalt salts by cupric chloride leaching of the scrap, solvent extraction and precipitation of the salts. The overall recovery by the above process was almost 99%.

Studies on Processing of an Alnico Scrap

This paper presents the results of research and development work on processing of alnico scrap, a secondary resource of nickel and cobalt, generated during the manufacturing of alnico magnets. The scrap contains 8-10% nickel, 10-12% cobalt, 32-50% of iron, 8-10% aluminium, 2% copper and remaining silica. Various processes such as acid leaching, aqueous chlorine leaching, salt roasting and cupric chloride leaching were studied in detail. Of these cupric chloride leaching was found to be most effective with respect to recovery and purity. It has been possible to obtain pure nickel and cobalt salts by cupric chloride leaching of the scrap, solvent extraction and precipitation of the salts. The overall recovery by the above process was almost 99%.

The leaching of sulphide minerals in chloride media

Recent studies on the ferric chloride and cupric chloride leaching of chalcopyrite, galena and sphalerite are reviewed. Although the chloride leaching of chalcopyrite concentrates has been proven at the demonstration plant scale, the leaching reaction is difficult. In contrast, galena dissolves rapidly in FeCl 3 media, and both the leaching rate and lead solubility increase significantly with increasing chloride concentration. The hydrometallurgical treatment of lead concentrates seems to be technically feasible. The sphalerite leaching rate is strongly affected by its solid solution iron content, and leaching processes for iron-rich zinc concentrates could probably be developed. The importance of intermediate sulphide phases and insoluble reaction products on the leaching of sulphides is discussed. In addition, it is postulated that at least part of the elemental sulphur reaction product is formed via the oxidation of dissolved H 2S. The ability of chloride leaching processes to generate elemental sulphur while leaving pyrite largely unaffected makes them especially useful for the treatment of pyritic complex sulphides. Thus, recent chloride leaching technologies for complex sulphides are also reviewed.

Equilibria associated with cupric chloride leaching of chalcopyrite concentrate

The leaching of chalcopyrite in aqueous cupric chloride solutions is treated with a thermodynamic model which incorporates the equilibria associated with the formation of various cupric, cuprous and ferrous chloride complexes. The precipitate from a refluxing slurry of elemental sulfur and aqueous cuprous and ferrous chlorides contained predominantly covellite (CuS) and a small amount of pyrite (FeS 2). Mössbauer spectra indicate that there was no chalcopyrite formation. Cupric chloride leaching experiments on both chalcopyrite concentrate and cupric sulfide indicated that the extent of cuprous ion formation in these aqueous cupric chloride solutions is controlled by the thermodynamics of the equilibrium: CuS+Cu 2+⇌ 2 Cu ++S 0 Conditions which favor the desired complete reduction of cupric ion are discussed.

Cupric chloride leaching of model sulfur compounds for simple copper ore concentrates

To learn more about the leaching characteristics of simple copper ore concentrates, the leaching behavior of cupric sulfide (CuS) and cuprous sulfide (Cu2S) was studied. These compounds serve as model compounds for covellite and chalcocite, respectively. With aqueous saline cupric chloride solutions above 100 °C, dissolution of both compounds is rapid, but does not proceed to completion on a stoichiometric basis. The course of the leaching can be explained with a solution model based on thermodynamic considerations and recognition of certain side reactions. The model is based on consideration of the complexes formed by various ionic species in solution and their effect on the observed extent of reaction near equilibrium. The leaching process was found to be enhanced by elevated temperatures, high chloride concentrations, and acidity. Limited leach times also were found to be advantageous. At dilute copper concentrations, leaching reactions could be driven closer to completion than with higher concentrations, as predicted by the model. For process reasons, it is desirable to convert all copper (II) in solution to copper (I). Routes for accomplishing this are reviewed.

Cupric chloride leaching of a complex copper/zinc/lead ore

A complex Cu/Zn/Pb ore from Cayeli, Turkey, was reacted with cupric chloride solutions under different conditions. Energies of activation were calculated for dissolution of copper (37 kJ mol −1), iron (33 kJ mol −1, zinc (26 kJ mol −1) and lead (7.5 kJ mol −1, values which indicate diffusion control of the reaction, probably through the sulphur layer formed round each particle. Particle size/leaching relationships corroborated microscopic assessments and indicated that chalcopyrite dissolved at a very low rate. Calculation of Fe:Cu ratios of metal leached showed considerable dissolution of pyrite from finely-ground ( d 1 2 ≈ 3−5 μ m ) ore. Examination of residues using SEM X-ray fluorescence line scan techniques revealed little attack of large pyrite crystals, suggesting that fine pyrite particles in complex relationship with the sphalerite and chalcopyrite were dissolving.

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.