Effect of suspension potential on the oxidation rate of copper concentrate in a sulfuric acid solution
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I.
INTRODUCTION
C H A L C O P Y R I T E is one of the most difficult minerals to leach, and much effort has been expended to gain an understanding of the mechanism of oxidative leaching. Thus, Yu, Hansen, and Wadsworth 1 studied the oxidation rate of chalcopyrite in sulfuric acid suspension under different pressures of oxygen. Munoz, Miller, and Wadsworth 2 and Dutrizac 3 investigated the mechanism of ferric sulfate and ferric chloride leaching in acid solution, while Beckstead, et al. 4 and Pawlek 5 showed that the oxidation rate was dependent on particle size and was greatly accelerated by ultrafine grinding by means of an attritor. Murr and Hiskey 6 further investigated the effect of particle size and also studied the effect of dislocation density on the oxidation rate in dichromate solution. Dutrizac 7 compared the ferric chloride leaching behavior of 11 chalcopyrite samples from different locations. If we consider leaching to be an electrochemical process, then the rate of oxidation would be expected to be dependent on the potential difference between the surface of the particles and the solution. The semiconducting properties of the particles would also be expected to have some bearing as would properties of the leach solution such as temperature, pH, and the concentrations of reactants and products. In some situations solid products have been shown to accumulate at the interface and retard the rate. 2'8 Oxidation in suspension differs in some respects from an electrode reaction. Firstly, it is not possible to measure directly or to control the potential difference between the suspended particles and the solution. This makes it difficult to compare directly leaching reactions and the electrode processes. Secondly, the semiconducting properties of pulverized minerals are different from those of massive minerals, 9 and the properties of the former vary during oxidation. 10 In the present study the problem of the potential difference in suspension was partly overcome by conducting the experiments with a constant redox potential in the solution. This potential is henceforth referred to as the susHIROSHIKAMETANI, Head, and AIKO AOKI, Semor Researcher, are with First NonferrousProcess MetallurgyLaboratory, Process Metal-
lurgy Dlvtslon, NationalResearchInstitutefor Metals, Tokyo 153, Japan. Manuscnpt submitted July 24, 1984. METALLURGICALTRANSACTIONSB
pension potential. Evidence is presented to show that the oxidation rate of chalcopyrite is highly dependent on suspension potential.
II.
EXPERIMENTAL
A. Material
The copper concentrate came from the Kosaka Mine of the Dowa Mining Co. Ltd. in Japan. It was normal production material whose chemical and calculated mineralogical composition are shown in Table I. The high concentrations of Zn, Pb, and Fe reflect the nature of the original ore, namely, a complex sulfide ore called Kuroko (black ore), in which chalcopyrite, pyrite, sphalerite, galena, gypsum, baryte, etc. are present as a mixture of finely intergrown crystals. To ensure liberation, the ore is finely
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