Industrial symbiosis: High purity recovery of metals from Waelz sintering waste by aqueous SO₂ solution

Sintering operation in the production of Zn, Cd, and Pb by Waelz process produces a powdery waste containing mainly (about 70%) ZnO, CdO, and PbO. The waste may be referred to as Waelz sintering waste (WSW). The aim of this study is to develop a process for the separation and recovery of the metals from WSW with high purities. The process is based on the dissolution of the WSW in aqueous SO₂ solution. The research reported here concentrated on the effect of some important operational parameters on dissolution process. The parameters investigated and their ranges were as follows: SO₂ gas flow rate (V); 38-590 ml/min, stirring speed (W); 100-1000 rpm, reaction temperature (T); 13-60 °C, reaction time (t); 1-16 min, and solid-liquid ratio (S/L); 0.1-0.5 g/ml. The results showed that the dissolution rate increased with increasing W, V, and S/L and decreasing T. The best dissolution conditions were found to be V = 325 ml/min, W = 600 rpm, t = 6 min, T = 21 °C, and S/L = 0.1 g/ml. Separation of Zn from Cd involved precipitation of ZnSO₃ from a mixture solution. The best pH level for the precipitation was observed to be 6. © 2007 Elsevier B.V. All rights reserved.