Cleaner extraction of lead from complex lead-containing wastes by reductive sulfur-fixing smelting with low SO 2 emission

Abstract

A novel and cleaner process for lead and silver recycling from multiple lead-containing wastes, e.g., lead ash, lead sludge, lead slag, and ferric sludge, by reductive sulfur-fixing smelting was proposed. In this process, coke and iron-containing wastes were employed as reductive agent and sulfur-fixing agent, respectively. A Na 2 CO 3 -Na 2 SO 4 mixture was added as flux. The feasibility of this process was detected from thermodynamic and experimental perspectives. The influence of Fe/SiO 2 and CaO/SiO 2 , composition of the molten salt, coke addition, smelting temperature, and smelting time on direct Pb recovery and sulfur-fixation efficiency were investigated. The optimal process conditions were determined as follows: W Coke = 15%W Pb wastes ,W Na2CO3 /W Na2SO4 = 0.7/0.3, Fe/SiO2 = 1.10, CaO/SiO 2 = 0.30, smelting temperature 1200 °C, and smelting time 2 h, where W represents weight. Under these optimum conditions, 92.4% Pb and 98.8% Ag were directly recovered in crude lead bullion in one step treatment, and total 98.6% sulfur was fixed. The generation and emissions of SO2 can be avoided. The main phases in ferrous matte obtained were FeS, NaFeS 2 , Fe 2 Zn 3 S 5 , and a little entrained Pb. The slag was a FeO-SiO 2 -CaO-Na 2 O quaternary melt.