Recovery of Crude Silver and Valuable Metals from Tin Anode Slime

Tin anode slime is a by-product of the crude tin electrolytic refining process. This study investigated a process to separate silver and valuable metals by sulfidation vulcanization roasting, and vacuum distillation was proposed by exploiting the physical difference (saturated vapor pressure) of metal sulfides. The Gibbs free energies of sulfidation reactions were calculated, and the saturated vapor pressures of raw materials and sulfides were analyzed. An experiment of vulcanization roasting and vacuum distillation determined the optimum vulcanization and volatilization temperatures. The results show that under the best experimental conditions, the direct recovery rate of silver obtained by vulcanization roasting and vacuum distillation is 98.98%. The silver content in crude silver is 39.07%. Cu-Ni-Sn alloy, tin, antimony and bismuth sulfides were obtained from residues and volatiles, respectively. These results are beneficial for the recycling of industrial waste and the development of a green economy.