Recovery of antimony and bismuth from tin anode slime after soda roasting–alkaline leaching

Abstract

In this study, a combined process of Na2S leaching and NaCl-H2SO4 leaching was developed to extract antimony and bismuth from tin anode slime after soda roasting–alkaline leaching. The optimal conditions for the extraction of antimony have been established as: Na2S concentration of 0.7 mol/L, temperature of 85 °C, liquid-to-solid ratio (L/S) of 14:1, and leaching time of 120 min. Under the conditions, more than 98% of antimony was extracted from tin anode slime, wherein the antimony was converted to liquid sodium thioantimonate, which was then converted into Na3SbS4(H2O)9 crystal via evaporation-crystallization; for this process, the recovery of antimony reached 93.83% at 50% evaporation rate, and the crystallization rate of antimony was 95%. The residue obtained was subjected to NaCl-H2SO4 leaching. About 94.94% of bismuth was extracted under the optimum conditions: H2SO4 concentration of 1 mol/L, NaCl/H2SO4 mole ratio of 2.5:1, L/S of 12:1, temperature of 80 °C, and leaching time of 120 min. The leach solution was then hydrolyzed and precipitated to form BiOCl, which showed a precipitation rate of 95.91% and Bi recovery of 91.12% at the hydrolysis pH of 2.4.