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 Na2CO3-Na2SO4 mixture was added as flux. The feasibility of this process was detected from thermodynamic and experimental perspectives. The influence of Fe/SiO2 and CaO/SiO2, 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: WCoke = 15% WPb wastes, W Na 2 CO 3 / W Na 2 SO 4 = 0.7/0.3, Fe/SiO2 = 1.10, CaO/SiO2 = 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, NaFeS2, Fe2Zn3S5, and a little entrained Pb. The slag was a FeO-SiO2-CaO-Na2O quaternary melt.
Highlights
Today, large amounts of lead-containing wastes are produced in non-ferrous metallurgical industry [1,2,3], especially in Pb and Zn metallurgy fields, such as lead ash and lead slag generated in Pb/Zn smelting, lead anode slime, and lead sludge produced in the electrolytic refining.Other engineering fields [4,5,6] are sources of Pb-bearing substances, including lead scrap and lead paste separated from spent lead-acid batteries [7]
Purity of the crude lead was higher than 96.5%, and its main impurity was metallic Fe
While 92.4% Pb was directly recovered as crude lead, 98.8% Ag was enriched in the crude lead
Summary
Other engineering fields [4,5,6] are sources of Pb-bearing substances, including lead scrap and lead paste separated from spent lead-acid batteries [7] In many countries, these lead-bearing wastes are classified as hazardous waste due to the high toxicity of lead [8]. These lead-bearing wastes are classified as hazardous waste due to the high toxicity of lead [8] They are greatly detrimental to environment and human health if left untreated and abandoned directly to the environment [9,10]. These wastes generally contain considerable amounts of precious metals, such as gold (Au) and silver (Ag). Various lead wastes are potential resources for extracting lead and precious metals
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