Aqueous sulphur dioxide leaching of Cu, Ni, Co, Zn and Fe from smelter slag in absence of oxygen

Smelter slag and sulphur dioxide are waste products of non-ferrous pyrometa llurgical processes. Dissolution behaviour of Co, Cu, Fe, Ni and Zn from sm elter slag in aqueous sulphur dioxide was studied. Experiments were carried out in batch mode, under near ambient conditions. Under the conditions stu died, 81% Co, 60% Fe, 35% Ni and 68% Zn extraction were achieved within 3 h , while Cu behaved very differently. The initial dissolution of Cu was rapi d, but subsequent precipitation lowered its overall extraction. The precipi tation of Cu was more temperature sensitive than its dissolution. At 65 deg rees C all the dissolved Cu was precipitated in 2.5 h. The successive preci pitation was explained based on the solution chemistry of the Cu-Fe-S(IV) s ystem. Dissolution kinetics of the other metals were evaluated using the sh rinking core model. Diffusion through the product/ash layer appeared to be the rate controlling step. SEM-EDS analysis was used to characterize the sl ag and to confirm the existence of a product/ash layer after leaching.