Hydrometallurgical process for recovery of cobalt from zinc plant residue

A hydrometallurgical process has been developed for the recovery of cobalt from a zinc plant residue. The residue contains a great quantity of active carbon and zinc sulfate. In addition, it contains naphthol derivative complexes with cobalt, nickel, iron, copper, and other metals. The process consists of the following six major unit operations: (1) washing: 0.5 mol L−1 sulfuric acid, L/S ratio of 10:1, 75 °C, 30 min; (2) roasting and leaching: first, roasting at 800 °C, then sulfation roasting at 250 °C, followed by roasting at 550 °C, lixiviating with water, L/S ratio of 7–8:1, 95 °C, 3 h; (3) precipitation of iron and manganese: first at pH 3.5, 95 °C, 1 h, then pH 4–4.5, 95 °C, with dropwise addition of 10% ammonium persulfate solution; (4) separation of zinc, cadmium, and copper by anion-exchange resin: 2 mol L−1 chloride ion, pH=4, where copper was first reduced to monovalence at a Na2SO3/Cu2+ weight ratio of 2.7:1 and pH 4.5; (5) separation of nickel by selective extraction of cobalt: 25% P507 in sulfonated kerosene, pH 4–6, O/A ratio of 1.6:1, stripping with 3 mol L−1 hydrochloric acid, O/A ratio of 1:1.5; (6) precipitation of cobalt: pH 1–1.5, (NH4)2C2O4/Co2+ weight ratio of 3.3:1. After roasting at 700 °C, pure cobalt oxide with cobalt in excess of 74% was obtained. The total recovery of cobalt was found to be approximately 94%.