Search

A non-cyanide lixiviant for gold dissolution, cupric chloride, was studied. The work used a rotating disk electrode technique to investigate the dissolution reaction mechanism and kinetics of gold dissolution in concentrated chloride (3 M) solution with cupric ion concentration in the range 0.02–1.0 M and temperature 65–95 °C. A reaction mechanism including a disproportionation step of Au(I) is proposed. Increase in the gold dissolution rate was found to be proportional to temperature and cupric ion concentration up to 0.5 M. The dissolution rate was observed to decrease with cupric ion concentration of 1.0 M. A mechanistic kinetic model was developed to study the rate-controlling steps in the dissolution process. Uncertainties in the model parameters of the mechanistic kinetic model were studied with Markov chain Monte Carlo (MCMC) methods. The modeling results showed that the gold dissolution is mainly under mixed control, where both the intrinsic surface reaction and mass transfer have an effect on the overall dissolution rate. [ABSTRACT FROM AUTHOR]

The leaching behavior of copper sulfides in concentrated cupric chloride solution at 95 °C and at ambient pressure was studied in order to scrutinize the leaching behavior of a single bornite and four different chalcopyrite concentrates obtained from various mines around the world. The highest chalcopyrite oxidation was achieved with the highest pyrite content in the concentrate, suggesting galvanic effect on chalcopyrite dissolution. It was found that iron and copper from chalcopyrite did not dissolve into the solution in an equal ratio, as expected. A significant amount of copper precipitated at pH ≤ 1.4. This study showed that chalcopyrite chloride leaching, in the absence of oxygen purging, leads to covellite precipitation. The mineralogical studies on a leach residue established that the precipitated copper was a secondary covellite (CuS). Leaching of bornite rich concentrate did not increase acidity and no equally strong copper precipitation was observed at pH = 2.1. [ABSTRACT FROM AUTHOR]

Abstract: This study was conducted as part of the development of a novel process for copper recovery from copper sulfide concentrates by chloride leaching, simultaneous cuprous oxidation and cupric solvent extraction to transfer copper to a conventional sulfate electrowinning circuit, and hematite precipitation to reject iron. The kinetics of cuprous and ferrous oxidation by oxygen and cupric solvent extraction were studied as a function of reaction time, stirring rate, oxygen pressure and extractants. The concentration of Cu(I)+Fe(II) decreased linearly with reaction time while the copper extraction increased with reaction time. The rate of cuprous and ferrous oxidation increased with increasing stirring rate and it was proportional to the partial pressure of oxygen. The cuprous and ferrous oxidation by oxygen was enhanced with the addition of organic solution. During the simultaneous cuprous oxidation and cupric solvent extraction, the aqueous solution pH first decreased sharply with time, then remained constant and finally increased, which was determined by the generation of H+ ions (cupric and ferric solvent extraction) and consumption of H+ ions (cuprous and ferrous oxidation by oxygen). The iron extraction increased as the oxidation reaction generated more ferric ions and raised the pH to a higher value. Simultaneous cuprous oxidation and cupric solvent extraction is feasible to transfer copper to the conventional sulfate electrowinning circuit from a chloride leaching system. The optimum copper solvent extraction conditions in chloride solution were proposed. [Copyright &y& Elsevier]

Abstract: The nature of the redox potential in concentrated cupric chloride solutions where [NaCl]=280 g/L and [Cu2+]=10–40 g/L was studied at temperatures 25–85 °C for 49 days. The redox potential of the solution was studied as a function of solution storage time, temperature and initial cupric chloride concentration. Measured redox potential values varied in the range 0.56–0.75 V vs. Ag/AgCl, increasing with increasing total copper concentration and temperature. The rate of reduction of cupric to cuprous species was highest in the most concentrated solution and occurred in 5 days, with the concentration of copper species 40 g/L. The solutions having initial copper concentrations of 30, 20 and 10 g/L reached steady state after 20, 26 and 26 days, respectively. The standard electrode potential, E o, in concentrated cupric chloride solution was determined using the Nernst equation. The form of cuprous complex was proposed on the basis of the value of E o, since the cupric/cuprous standard electrode potentials divide clearly in two groups. The E o for redox couples, with cuprous present as a chloro-complex form, is a minimum of 0.3 V higher than the E o for redox pairs with uncomplexed cuprous ions. E o value for the redox pair existing in a HydroCopper® type environment was calculated to be −0.039 (±0.121) V vs. Ag/AgCl. This suggests that in a very concentrated cupric chloride solution without any additives, not all cuprous ions present are complexed with chlorides. [Copyright &y& Elsevier]

Abstract: This work presents a study of the leaching of chalcopyrite in acidic ferric chloride. Two chalcopyrite samples (natural chalcopyrite crystal and chalcopyrite concentrate) were leached under different conditions. The effects of stirring speed and temperature were investigated. It was found that agitation had a negative effect on copper recovery from chalcopyrite during the leaching process. This is explained by the fact that cupric chloride complexes are formed during the leaching process where cupric ion is considered as a stronger oxidant than ferric ion. Agitation sweeps away the cupric chloride complexes formed, whereas, under stagnant conditions cupric chloride complexes accumulate at the reaction interface causing enhanced dissolution of copper. The overall leaching reaction was found to be sensitive to temperature. The shrinking core model was fitted to the data and it was found that the leaching process was controlled by chemical reaction with activation energy of 69 kJ/mole. [Copyright &y& Elsevier]

Abstract: In this study we demonstrate the kinetics of Cu2+ reduction in concentrated cupric chloride solutions. Experiments were carried out near the boiling point of the solution ([NaCl]=280 g/l and [Cu2+]=1–40 g/l) at T =90 °C, atmospheric pressure, pH=2. Electrochemical methods such as cathodic polarization curves and cyclic voltammetry were used to investigate the cathodic reactions of copper complexes. To identify the nature and the rate-controlling steps of the reactions, rotating disk electrode (RDE) experiments were conducted. The chemical environment studied was similar to that of the Outokumpu HydroCopperTM process, which uses a cupric chloride solution to leach copper from the mineral chalcopyrite. The results suggest that the cathodic reactions are the reduction of [CuCl]+ to the complex [CuCl3]2−, the reduction of [CuCl3]2− to solid copper and hydrogen evolution. The diffusion coefficient and the unit rate constants for the solution species were calculated. The exchange current density and rate constant for electron transfer were also estimated. A simulation was made of the cathodic polarization curve and it was in good agreement with the experimental data. [Copyright &y& Elsevier]

Abstract: Platinum, a DSA (dimensionally stable anode) mesh and gold electrodes were investigated for use as redox potential sensors for the Outokumpu HydroCopper™ process. The redox potential was measured in a standard HydroCopper™ solution with constant pH, temperature and sodium chloride concentration. The concentration of cupric ions was varied in the range 0–40 g/dm3. The redox potential was observed to increase logarithmically with increasing cupric ion concentration and to decrease linearly with time. Platinum and DSA-type electrodes were found to be electrochemically inert and allowed the measurement of the redox potential. With the gold the corrosion potential of the electrode was measured. [Copyright &y& Elsevier]

Abstract: Outokumpu HydroCopper™ technology was developed by Outokumpu Research. It is a novel copper production method based on the efficient leaching properties of cupric chloride solutions. The leaching is operated at atmospheric pressure, near the boiling point of water in a stirred reactor and the pH is kept between 1.5 and 2.5. In the present work, an electrochemical study of the dissolution behaviour of chalcopyrite, the most common copper mineral, was made in a concentrated sodium chloride solution (250 g/L) with cupric ion concentrations varied in the range 0.09–26.6 g/L. The effects of pH (1–3) and temperature (70–90 °C) were also measured. The rotating disk electrode technique was used to determine the rate-controlling step in the leaching process. The increase in the dissolution rate was observed to be proportional to the increase in the temperature and to the cupric ion concentration with [Cu2+]>9 g/L. With [Cu2+]<9 g/L, the cupric ion concentration did not affect the leaching rate. In order to investigate the reaction products of the chalcopyrite dissolution, the electrodes were analysed by scanning electron microscopy. The results suggested that iron oxides, hydroxides and chlorides gathered on the chalcopyrite surface at higher pHs. At lower pHs, chalcopyrite passivated and a sulfur-rich layer was detected on the surface. [Copyright &y& Elsevier]

This paper shows a mechanism for recovering cupric chloride salts from spent etchant solution used in printing circuits industry. The tested solution is an ammoniacal copper solution containing 135 g/L Cu ion with minor impurity. Copper is present as the square planar cupprammine complex. The separation method involved decomposition of the cupprammine complex in two ways, The first by hydration, and the second by acidification using concentrated HCl . The mechanism of separation proceeds by second-order bimolecular substitution reactions. Results are explained in the light of a model which assumes that successive intermediate copper compounds are formed, which were identified and separated. The final product was pure cupric chloride crystals free of ammonium ions meeting the standard specification assigned for printing industry. Parameters affecting efficiency of the method such as solution pH, dilution, addition of acid and temperature have been investigated. Maximum extent of extraction amounted to 99%. [Copyright &y& Elsevier]

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, [Fe 3+ /Cu 2+ = 0.02–1.0 M, [Cl − = 1–5 M, pH = 0.0–2.0, and ω cyc = 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. • T , [Fe 3+ /Cu 2+ , [Cl − , and pH affects OCP and redox potential in chlorides solutions. • OCP, redox potential, and Au dissolution were all higher in ferric chloride solution. • Positive correlation between OCP, redox potential, and Au dissolution has been found. • Redox potential measurements can be used as a way to estimate Au dissolution rates. [ABSTRACT FROM AUTHOR]

The use of seawater in heap leaching of secondary copper sulfide minerals is a feasible alternative to freshwater in regions with limited freshwater supply. Seawater contains high concentrations of chloride ions that facilitate the formation of cupric/cuprous chloride complexes. The cupric ions formed can serve as an oxidizing agent for chalcocite oxidation. Even though copper leaching in chloride media has been well studied, most of the kinetics data were collected under uncontrolled leaching conditions. In this study, we modelled chalcocite leaching kinetics in chloride media using leaching data collected under fully-controlled pH and solution potential. Specifically, we carried out leaching tests with high-purity chalcocite sample in jacketed reactors to quantify the effects of chloride concentration, cupric concentration, particle size, and temperature on the copper extraction rate. The experimental results show that increases in chloride concentration and temperature remarkably enhanced the leaching rate; chalcocite leaching was insensitive to the initial cupric chloride concentration. Using the leaching data collected, we derived two individual kinetic models to describe the first and second stage of chalcocite leaching. This study provides fundamental kinetic models for predicting the performance of chalcocite leaching in cupric chloride for heap leach operations that intend to use seawater. • Chalcocite leaching in cupric chloride media occurred in two stages. • Kinetics models were obtained for each stage of chalcocite leaching. • First stage leaching was controlled by chloride diffusion through the liquid film. • Second stage leaching was controlled by chemical reaction process. • Second stage leaching was sensitive to temperature with a high activation energy. [ABSTRACT FROM AUTHOR]