Oxidation of copper sulfides in aqueous ammonia

A.O. Filmer

The oxidative leaching of CuS and Cu2S in aqueous ammonia containing ammonium sulfate was investigated under milder temperatures and oxygen pressure than those conventionally used in hydrometallurgical processes. Emphasis was placed on understanding the chemistry of sulfide leaching in aqueous ammonia but whenever possible the results were related to practical situations. Elemental sulfur was discovered as a kinetically stable reaction product of the oxidative ammoniacal leaching of copper sulfide. The effects of reaction variables, temperature, oxygen pressure and reagent concentrations, on both the kinetics of copper extraction and the yield of elemental sulfur were studied. Results were explained in terms of a postulated mechanism of copper sulfide oxidation (figure 1). (Consult page ii for figure 1). Copper sulfide is initially oxidized to a copper polysulfide [(CUyS) y < 1] intermediate which can then either thermally decompose to form sulfur and copper sulfide or be further oxidized to copper ions and soluble sulfur-oxygen species. The sulfur formed from CuS is liable to further oxidation, with its stability being critically dependent on the leaching conditions. The kinetics of copper extraction from samples of synthetic Ci^S and CuS were studied, fast and an intermediate similar to CuS is formed. The initial copper extraction from CU2S is This reacts more slowly to solubilize the copper and generate elemental sulfur, sulfate and other soluble sulfur-oxygen species. An empirical rate equation k [p 02] 0.45 [nh3] 0.7 for the oxidation of CuS in aqueous ammonia was obtained. The reactions of copper sulfide in aqueous ammonia were also studied electrochemically. These studies were related to both the formation of elemental sulfur and the extraction of copper during oxidative leaching of copper sulfides in aqueous ammonia. The chemistry of leaching of copper sulfides was applied to a copper sulfide byproduct of Western Mining Corporation's Kwinana Nickel Refinery. A mild oxidative leach of the material in aqueous ammonia was proposed as the initial step of a refining process. The chemistry of copper, sulfur, nickel, cobalt, palladium, gold and silver was followed through each stage of the proposed process, and recovery procedures were suggested for these elements.

Oxidation of copper sulfides in aqueous ammonia

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