Separation and recovery of tin and copper from tin refining sulfur slag using a new process of airtight sulfuration – Vacuum distillation

Abstract

Sulfur slag is a high-value hazardous waste produced during the refining process of crude tin. To reduce the emission of wastewater, harmful gas, and hazardous residue, a theoretical and experimental investigation was carried out to develop a new process for converting metal to metal sulfide that utilizes physical differences (saturated vapor pressure) for separation. Here, a sulfur slag processing approach based on airtight sulfuration-vacuum distillation is proposed. In this paper, the Gibbs free energies of the sulfuration reaction of tin and cuprous sulfide and the decomposition reaction of copper sulfide are calculated, the saturated vapor pressure of each substance is analyzed, and the composition of the products is predicted. By adding sulfur to sulfur slag, the composition of the substances in the slag was regulated, and efficient separation of tin and copper was achieved based on the difference in volatility of the compounds. The optimum sulfur addition amount, sulfuration temperature and time, and volatilization temperature and time were investigated using airtight sulfuration and vacuum distillation experiments. The results show that tin and cuprous sulfide were thoroughly sulfurated when 20 g sulfur was added, the airtight sulfuration temperature was 573 K, and the holding time was 4 h. Stannous sulfide volatilizes violently above 941 K and volatilizes completely at 1273 K. The purities of stannous sulfide and cuprous sulfide obtained by the airtight sulfuration-vacuum distillation experiment were 99.02% and 99.30%, respectively. The direct recovery rates of tin and copper were 99.93% and 99.91%, respectively. The removal rate of copper in the volatiles was 99.84%, and the removal rate of tin in the residue was 99.96%. The method thoroughly separated tin and copper from sulfur slag, significantly reducing the environmental and economic costs compared to those of the traditional process.