Advanced Heap-leaching for Chalcopyrite

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Heap-leaching has become important in copper production: over 20% of copper in the world is now produced at open pit mines of porphyry copper deposits through this method. In this method, copper in low-grade oxide and secondary sulfide ores is extracted into sulfuric acid solutions, and the extracted copper is recovered by solvent-extraction and electro-winning methods. However, the leaching rate of chalcopyrite (CuFeS_2), a major copper mineral in the deepest parts of the deposits, is very slow, and the development of advanced heap-leaching methods for this mineral is an object for copper hydrometallurgy in the future.One factor affecting the leaching rate of chalcopyrite is the redox potential determined by the concentration ratio of Fe^<3+> to Fe^<2+> in the solution: the leaching rate increases when increasing the redox potential to reach a maximum at an optimum redox potential, and then decreases at higher redox potentials. This study investigated the effect of redox potential con … More trol on chalcopyrite leaching rates.Shaking flask leaching experiments and electrochemical experiments were carried out to clarify factors affecting the redox potential dependence of chalcopyrite leaching, and the results indicates that the optimum redox potential is a function of the cupric and ferrous ion concentrations. Based on the experimental results and theoretical considerations of the leaching mechanism, a computer simulation model was developed and the optimum leaching conditions for chalcopyrite were determined. The simulated results agree with the results of column leaching experiments using a chalcopyrite powder sample supported on inert silica host rocks: About 80% of copper was extracted from the chalcopyrite in 100 days when the chemical composition and redox potential of solution were controlled. This extraction rate is comparable to the rate in the conventional heap-leaching operation for secondary copper sulfides, indicating that the redox potential control established here is effective for chalcopyrite leaching. Less