Recovery of cobalt and zinc from the leaching solution of zinc smelting slag

Abstract

Zinc smelting slag belongs to hazardous solid waste. Traditional pyrometallurgical or hydrometallurgical technology for treating zinc smelting slag focuses on zinc extraction but neglects cobalt recovery. With increasing cobalt demand and soaring cobalt price, recovering cobalt from zinc smelting slag not only helps alleviate resource shortage, but also improves the economic efficiency of zinc smelting slag recovery. In this study, a facile method for combination of recycling cobalt and zinc from the leaching solution of zinc smelting slag based on step-by-step removal of impurities and precipitation of cobalt processes was developed. First, impure iron ion was removed from acid leaching solution through the Fenton reaction by adding H2O2 and controlling the pH. The iron removal rate could reach 99%, and the content could be reduced to less than 1 mg/l. And then, copper and cadmium ions in the solution were extracted with zinc powder by cementation, and the removal rate reached 99%, reducing the content of copper and cadmium to 1 and 5 mg/l, respectively. Finally, cobalt was recovered by adding sodium ethyl xanthate. Almost 100% cobalt precipitation efficiency was obtained in this process under the optimum conditions of 8 g/l sodium ethyl xanthate, 1 g/l K2MnO4, pH 4, 55 °C, and 5 h. After precipitation, the cobalt ion concentration of the solution decreased to less than 1 mg/l, and a pure zinc solution with a concentration of 114.5 g/l was obtained. 88% cobalt and 98% zinc were recovered in the entire separation and purification processes.