Lead removal from tin chloride solution by barium sulfate and coprecipitation of (BaxPby)(SO4)2 for the processing of Pb[sbnd]Sn smelter slag

Abstract

Owing to the characteristics of mineral paragenesis (equilibrium sequence of mineral phases), the hydrochloric acid leach liquors of Sn ores and Sn-containing waste materials typically contain large amounts of Pb. In this study, barium sulfate coprecipitation was employed to efficiently remove Pb from a tin chloride solution. The lead removal efficiency, reaction mechanism, and limitations were investigated by varying the Cl− and SO42− concentrations. The results showed that the structural formula of the precipitates was (BaxPby)(SO4)2 (x + y = 2), and its solubility product was in the range of 1 × 10−12–1 × 10−13, indicating that Pb2+ and Ba2+ were more easily precipitated in the form of complex salts. In addition, thermodynamic analysis revealed that when the Cl− concentration was <1 mol/L in the Pb2+–Sn2+–Cl−–H2O system, [Pb2+] and [PbCl+] were the primary species. These positively charged species were readily adsorbed onto the surface of BaSO4 via electrostatic forces, resulting in a significant increase in the Pb content of (BaxPby)(SO4)2. Therefore, the Pb removal efficiency significantly improved as Cl− concentration decreased. The lead removal mechanism involves a combination of adsorption and replacement processes. Based on the aforementioned fundamental study, a method involving dechlorination and coprecipitation was proposed to remove lead from an acid leaching solution of Kaldo slag. With the dechlorination via distillation, the Pb removal efficiency could reach 99.9% at 1 mol/L Cl− and 0.5 mol/L SO42−.