Selective separation of tin from tin-bearing middling via sulfur roasting

There is 3% ∼ $\sim$ 5% tin remaining in the Inner Mongolia tin-bearing middling obtained by flotation, which is a valuable secondary resource of tin. To effectively recover this tin, selective separation tin from tin-bearing middling by sulfide roasting using anhydrous gypsum (CaSO 4 ) as the sulfur agent was proposed in this study. The removal behaviors of tin during sulfur roasting were systematically investigated, including thermodynamic analysis, the effects of anhydrous gypsum, sulfur roasting temperature and time on the tin removal efficiency, and the mechanism model of separation of tin from tin-bearing middling during sulfide roasting. The results indicated that the cassiterite (SnO 2 ) was first transformed to Sn and then transformed to tin sulfide (SnS). Anhydrous gypsum could be recycled by exhausts absorption process in this work, which saved the sulfur agent for the whole separation process. In addition, arsenic was fixated in the residuals, which was beneficial for the separation of tin from tin-bearing middling. The removal efficiency of tin was 91.27% after sulfur roasting with 12.5 wt% CaSO 4 and 17.5 vol.% CO at 950 °C for 1 h.