Separation of Ag and Cu from Their Aqueous Thiosulfate Complexes by UV-C Irradiation

Abstract

In recent years, there has been renewed interest in the use of thiosulfate as a substitute for cyanide in silver leaching. Copper thiosulfate leaching without ammonia was applied to extract silver from silver sulfide, resulting in the production of Ag–Cu polymetallic thiosulfate complexes in solutions. It is necessary to separate Ag–Cu polymetallic thiosulfate complexes with the purposes of silver recovery and copper recycling. In this paper, the feasibility study on the use of UV-C irradiation to separate Ag–Cu polymetallic thiosulfate complexes was investigated based on the different photosensitivity of silver and copper. First, a kinetic study on the photolysis of silver and copper thiosulfate complexes by UV-C was investigated, indicating that the reactions follow first-order kinetics. The rate constant reactions were calculated, and it decreased with solution concentrations. On the other hand, the photoproducts of the silver and copper thiosulfate complexes were characterized by XRD and XPS in order to confirm the phase and chemical composition. It indicated that the silver photoproducts are Ag2S, S, Ag and the copper photoproducts are Cu2S, CuS, CuO, Cu, S. Finally, the four-step continuous separation of Ag–Cu polymetallic thiosulfate complexes by UV-C irradiation was investigated. The silver component was recovered with the accumulated recovery ratio of 97%, and the copper component was recycled with the accumulated recycle ratio of 51%, which made it possible for silver recovery and copper recycling.