Reduction smelting on bismuth oxide residue in FeO-SiO2-CaO ternary slag system

Reduction smelting of the bismuth oxide residue from pressure leaching of bismuth sulfide was investigated in the FeO-SiO2-CaO ternary slag system. The results show that all the recovery ratios of Bi, Ag, Cu and Pb increase with the increase of reductive coal proportion, reaction temperature and time, while too much reductive coal would help Fe enter metal phase; CaO/SiO2 and FeO/SiO2 of the chosen slag system should be 0.5-0.75 and 1.25-1.75, respectively, for the reason that the slag system has the optimum mobility and is beneficial for the recovery of metals. The corresponding optimum conditions are determined as follows: the added coal proportion is 7% of the leaching residue, CaO/SiO2 mass ratio in the chosen slag system is 0.5 and FeO/SiO2 is 1.5, the reaction temperature is 1300 °C and the reaction time is 40 min. Under the above conditions, the recovery ratios of Bi, Ag, Cu and Pb are 99.6%, 99.8%, 97.0% and 97.3%, respectively.