Redox Controlled Chalcopyrite Leaching as a New Method for Copper Production

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Heap leaching of low-grade copper ore, combined with solvent-extraction/electro-winning, has become important in copper production, because of its low capital and operation costs, operational simplicity However, the process has not been fully successful, due to the extremely slow leaching kinetics of a common copper source, chalcopyrite (CuFeS_2). Chalcopyrite leaching is a redox process and the control of the redox potential determined by the concentration ration of oxidant ferric ion to reductant ferrous ion has been proposed to improve the leaching rate. In this study, the redox potential dependence of chalcopyrite leaching in sulfuric acid solutions and the factors affecting the potential dependence of the leaching were investigated to establish the redox controlled chalcopyrite leaching. Leaching and anodic-polarization experiments showed that coexistence of cupric and ferrous ions activate anodic dissolution of chalcopyrite, causing faster copper extraction at the potentials below a certain value (critical potential). The analysis of the AC impedance spectra for chalcopyrite electrode indicated that a high-resistance passive layer grows on the chalcopyrite surface without cupric and/or ferrous ions, and that coexistence of these ions causes a formation of another product layer and inhibits the passive layer growth at low potentials. These results are explained by a reaction model assuming the formation of intermediate Cu_2S due to chalcopyrite reduction and the subsequent oxidation of the Cu_2S. The critical potential corresponds to the redox potential of the Cu_2S formation and the predicted values matched with the experimental results, and the optimum redox potential for chalcopyrite dissolution is a function of cupric and ferrous ion concentrations. Effects of catalysts like silver ions and activated carbon on chalcopyrite leaching were also explained based on the above model.