Lead removal from tin chloride solution by barium sulfate and coprecipitation of (BaxPby)(SO4)2 for the processing of PbSn 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 (Ba_xPb_y)(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 (Ba_xPb_y)(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⁻.