Chelyabinsk Zinc Plant PJSC, Chelyabinsk, Russia:
E. V. Golubeva, Lead Process Engineer at the Engineering Centre, e-mail: evg@zinc.ru
P. V. Fedotkin, Supervisor at the Waste Treatment Facility

This paper describes the results of a laboratory study that looked at reactant treatment of highly mineralized solutions resultant from carbonization of lead sulphate cake at Chelyabinsk Zinc Plant aimed at arsenic removal. The salts contained in the solutions mainly include sodium sulphates; they also contain smaller amounts of chloride, arsenic, calcium and magnesium ions, as well as ions of heavy metals. Apart from the process parameters, the concentration of impurity metals in the solution after carbonization is governed by their concentration in the primary product — i.e. lead sulphate cake, which is the product of hydrometallurgical processing of Waelz fumes from zinc- and lead-containing materials. Zinc- and lead-containing copper middlings are the main source of arsenic in the lead cake. This research work also encompassed development of a recycling process for solutions after carbonization to stop them from being discharged with waste water. The process includes concentration by evaporation and crystallization, which results in the production of condensate (which is reused in the normal process) and a salt mixture or a commercial grade of sodium sulphate salt (GOST 6318–77, type А, grade 2). A review of literature and the conducted study indicate that the most appropriate purification technique may include precipitation of arsenic with iron (III) sulphate in the presence of an oxidizer, which produces a not easily soluble compound of iron arsenate. The laboratory study helped determine the optimum amount of reagents to be used, as well as the reaction temperature and time. Arsenic can be extracted from the carbonization solutions as a highpurity solid product, which can be processed in a Waelz kiln. If arsenic should be removed from the process solutions and the relevant purification degree can only be determined after one has determined the composition of the obtained sodium sulphate salts and the product’s hazard category. These findings can be used by producers in order to develop recycling processes for sulphate solutions with similar compositions.

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