Leaching behavior of silver sulfide in the sodium thiosulfate-copper sulfate-sodium metabisulfite system

The leaching of silver sulfide was performed for the first time from a novel copper-thiosulfate-metabisulfite solution. The effects of all leaching conditions, e.g., the concentrations of copper cations, thiosulfate, and metabisulfite, as well as temperature, pH, and leaching time on silver extraction from this novel leaching system were systematically investigated. Liquid samples were analyzed by atomic absorption spectrophotometry (AAS) to determine their silver content, and the remaining solid powder was then characterized by field-emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). Based on the results of leaching experiments, it was found that silver sulfide extraction efficiency could be enhanced to 97% with the addition of metabisulfite to the thiosulfate-copper leaching medium. It was revealed that silver extraction is kinetically controlled by diffusion from the product layer. The activation energies (E-a) of silver sulfide leaching and Cu2+ reactions were calculated to be 22.2 and 41.2 kJ/mol, respectively. Thus, the thiosulfate-copper-metabisulfite medium is introduced as an efficient leaching system for silver extraction.