Leaching of silver sulfide with copper sulfate-tartrate-thiosulfate solutions

Abstract

Due to the high toxicity of cyanide, researchers are trying to find an environmentally friendly and sustainable leaching process for precious metals. Thiosulfate is considered one of the most promising alternative leaching systems. Nevertheless, a traditional thiosulfate leaching solution generally consists of copper sulfate and ammonia, in which copper sulfate acts as oxidant and ammonia acts as copper ion stabilizer. However, ammonia is another toxic reagent. For this reason, a novel and eco-friendly system of copper sulfate-tartrate-thiosulfate was investigated for silver sulfide leaching in this work. The effects of rotation speed, temperature, initial pH, copper sulfate, tartrate and thiosulfate concentrations and different atmospheres on the dissolution rate of Ag₂S were examined. The process of silver sulfide dissolution is controlled by chemical reactions with an apparent activation energy of 43.49 kJ/mol. The reaction orders of silver sulfide leaching with respect to copper sulfate, tartrate, and thiosulfate concentrations in copper sulfate-tartrate-thiosulfate solutions are 0.491, 1.366, and 0.916, respectively. A detailed dissolution route of Ag₂S was proposed based on XRD analysis of intermediate products such as Ag₃CuS₂, AgCuS and (Ag, Cu)₂S. XPS analysis indicated that elemental sulfur was determined to be the final oxidant product of sulfur ions from Ag₂S.

Keywords

silver sulfide / tartrate / thiosulfate / leaching

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