Utilization of Gypsum Byproduct as Fuming Agent for Tin Smelting Slag

Pyrite is very commonly used as a source of sulfur for converting tin oxide from tin smelting slag or low-grade tin ore/concentrate into tin sulfide by means of a tin fuming process to increase the overall tin recovery in a tin smelting plant. The conversion of tin sulfide into tin oxide as final product of a tin fuming process produces sulfur dioxide, which is captured by spraying of calcium hydroxide, producing gypsum as the byproduct. To reduce the footprint of pyrite mining activity and to reduce the environmental impact, the recycling of sulfur from gypsum byproduct as a fuming agent to substitute pyrite was studied in this research. The FactSage (TM) thermodynamic software was applied to simulate the performance of tin fuming by addition of gypsum. The experiments were conducted in a muffle furnace for 1 h at 1100, 1200, and 1300 degrees C. The experimental results showed that a gypsum addition of 20% into tin smelting slag containing 10.44% Sn (S/Sn ratio = 1.3) yields a tin volatilization of 81.2% at 1200 degrees C. The addition of more gypsum lowers the degree of tin volatilization.