Chelyabinsk Zinc Plant PJSC, Chelyabinsk, Russia:

V. V. Geraskin, Lead Process Engineer at the Engineering Centre, e-mail: vdg@zinc.ru
D. V. Chemeryazev, Supervisor at the Zinc Electrolysis Facility
D. A. Nelyubin, Deputy Head of the Operations Department

This paper describes the results of a laboratory study and a series of pilot tests that aimed to determine how the zinc powder particle size influences the process of cobalt removal from zinc sulphate solution. In the process flow of Chelyabinsk Zinc Plant, zinc powder is used to remove impurities (such as copper, cadmium, cobalt, nickel, arsenic, antimony, etc.) from sulphate solutions by cementation. The data on impurities cementation that can be found in the literature, as well as the outcomes of the laboratory study suggest that, with all the other parameters being constant, the optimum consumption of zinc powder is defined by its specific surface area, which is determined by the particle size. Zinc powder with the average particle size of ~30 μm is normally used in industry to remove cobalt and nickel from zinc sulphate solutions. Such zinc powder is produced on site by spraying liquid zinc. Antimony in the form of Sb₂O₃, as well as copper ions contained in copper sulphate solution are used as activating agents in the cementation process. Chelyabinsk Zinc Plant conducted a laboratory study, in which samples of zinc powder with the average particle sizes of 10, 20 and 30 μm were used for the cementation of cobalt from zinc sulphate solution. The findings indicate that zinc powder would become more active as the average particle size would get smaller. Due to high activity of finer zinc powder, a decreased consumption of reagents and the cementation agent itself can be achieved with the process duration remaining constant, and the cementation deposit resolution rate can be lowered. Thus, depending on the size of the zinc powder used, the consumption of antimony could be decreased by 2 to 3.5 times and that of copper — by 2.5 to 10 times. The results of the laboratory study have been verified in the course of pilot cementation tests when cobalt was removed from zinc sulphate solution in a flow mode using finely dispersed zinc powder (with the average particle size of 20 μm). A 22% reduction in the consumption of zinc powder was achieved in real-life environment, which implies a constantly changing flow and chemical composition of the solution. The consumption of activating agents was also lowered — that of Cu²⁺ by 43% and that of Sb₂O₃ by 55%.

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