Selective leaching of base metals from copper smelter slag

A novel hydrometallurgical method was developed to selectively extract base metal values, such as cobalt, zinc, and copper from copper smelter slag at atmospheric pressure. It involves leaching with sulfuric acid and sodium chlorate oxidant and neutralization with calcium hydroxide for better and faster filtration of the precipitate. It significantly decreases or avoids the adverse effects of silica and iron(III) oxides on recycling or extracting target value metals. Four key parameters were explored in this new approach, namely, sulfuric acid consumption, amount of sodium chlorate, reaction temperature and reaction time. Calcium hydroxide was one of most critical factors to precipitate silica and iron(III) oxides before filtration. Once all these four parameters were optimized, the overall extraction and recovery of cobalt, zinc and copper was 98%, 97%, and 89% respectively, while the extraction of silicon and iron was only 3.2% and 0.02%, respectively. This hydrometallurgical process, almost completely recovers the valuable metals of cobalt, copper and zinc from the copper smelting slag without roasting. The proposed leaching method is simple, economical and competitive to operate, so it is readily applicable in industry.