Hydrometallurgy Of Zinc Purification Residue - Cobalt And Nickel Slag Selective Dissolution Study

The selective acid leaching of cobalt and nickel residue generated in the process of ZnSO₄ purification is studied in this paper, which will provide a fundamental basis for the industrial leaching and utilization of cobalt and nickel residue. The main conclusions are as follows:1. The particulate of cobalt and nickel residue is determined to be surrounded structure. Metal zinc was in the core, and cobalt or nickel generated by displacement reaction was covered outside. After stacking the residue for some time, partial Zn, Co and Ni were oxidized by the oxygen in the air. As a result, a layer of oxidation film was formed and surrounded at the surface of the particulate;2. The selective acid leaching was introduced to dispose the cobalt and nickel residue at the condition of pH≥3.5 during the leaching process and pH≥4.0 at the end of the reaction. The experiments showed that leaching rate of zinc was 95% approximately, the Co and Ni less than 10%, so Co and Ni were enriched in the solid phase, and were separated from the zinc effectively. Therefore, the selective acid leaching is suitable for the cobalt and nickel residue disposal;3. At the room temperature, the selective acid leaching of cobalt and nickel residue is the first order reaction, and the constant rate k^* was determined to be 0.5617 min^-1;4. The investigations indicate that when cobalt electrode is used to indicate the concentration of Co²⁺, the pH of solution system must be lower than 2.0. The application of cobalt electrode to leaching experiments of cobalt and nickel residue at the pH of 2.0 showed that, after leaching reaction for a little while, the electrode potential indicated by cobalt electrode increased gradually, which suggested that the concentration of Co²⁺ was increasing continuously, which was just consistent with the fact that cobalt and nickel residue was continuously dissolved into cobalt ion. Therefore, cobalt electrode could be used to qualitatively indicate the cobalt ion changes during the acid leaching process of cobalt and nickel residue.