Purification of zinc sulfate solutions from chloride ions using bismuth hydroxosulfate

Abstract

ABSTRACT An efficient, simple and lowcost method for purification of zinc sulfate solutions from chloride ions by precipitation with bismuth hydroxosulfate BiOHSO4∙H2O was proposed. Chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the solid obtained. The studied parameters were reaction temperature, pH, concentrations of zinc sulfate and chloride, and the molar ratio between BiOHSO4∙H2O and chloride. Under optimal conditions, the chloride removal efficiency reached 94.5–95.8% and the residual concentration of Cl− in the purified solution was 65–85 mg/L, which meets the requirements for zinc electrolysis and allows the production of special high-grade zinc. Compared with the commonly used approaches, the method proposed has the advantages such as a higher degree of purification of zinc electrolyte, the short period of time required for the BiOCl precipitation (1 hour) and good filterability. Apart from that, the consumption of the precipitant is close to the stoichiometric molar ratio, which makes the purification process cost-effective.