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 pyrometallurgical processes. Dissolution behaviour of Co, Cu, Fe, Ni and Zn from smelter slag in aqueous sulphur dioxide was studied. Experiments were carried out in batch mode, under near ambient conditions. Under the conditions studied, 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 rapid, but subsequent precipitation lowered its overall extraction. The precipitation of Cu was more temperature sensitive than its dissolution. At 65 degrees C all the dissolved Cu was precipitated in 2.5 h. The successive precipitation was explained based on the solution chemistry of the Cu-Fe-S(IV) system. Dissolution kinetics of the other metals were evaluated using the shrinking core model. Diffusion through the product/ash layer appeared to be the rate controlling step. SEM-EDS analysis was used to characterize the slag and to confirm the existence of a product/ash layer after leaching.