A study on pyro-hydrometallurgical process for selective recovery of Pb, Sn and Sb from lead dross

This study is to propose a pyro-hydrometallurgical process for recovering Pb, Sn, and Sb from lead dross (LD), incorporating stages of roasting, leaching, and precipitation. The LD, containing 67.2% of Pb, 4.0% of Sn, and 1.4% of Sb, was first roasted at 750 °C for 2 h to oxidise the sulphide metals. Approximately 90% of Pb was oxidised from the first roasting. The LD was second roasted by mixing with 95% H₂SO₄ for sulphatising at 300 °C for 3 h to break the complex oxide structure of the oxyplumboromeite (Pb₂Sb₂O₇). After the two-step roasting process, over 99% of Pb was oxidised and Sb was separated. The calcine obtained was desulphurised by 2 M Na₂CO₃ solution for insoluble PbSO₄ to PbCO₃ for selective leaching. The residue was then leached in 2.5 M HNO₃ at 50 °C for 3 h and over 99% of Pb dissolved into the solution while Sn and Sb remained in the solid residue. The Pb containing solution was neutralised at pH 8 using 2 M Na₂CO₃ and over 99% Pb was precipitated as PbCO₃ and Pb hydroxides. A residue containing Sn and Sb was leached in 7 M NaOH at 95 for 1 h and over 99% Sn was leached selectively. Sn in the solution was precipitated at pH 7 using 2 M H₂SO₄ as SnO₂. Sb was recovered as Sb₂O₃ in solid reside from Sn leaching. The overall recovery rates of Pb, Sn, and Sb from the LD were 99.5%, 95.4%, and 86.3%, respectively. The proposed process is expected to contribute to recycling Pb and other metal values from LD by minimising hazardous waste emissions.