Increasing the sustainability of copper electrorefining: Selective electrodeposition of antimony in the presence of bismuth from highly concentrated hydrochloric acid effluents

Abstract

Recovering critical materials from effluents of the copper electrorefining would improve the circularity and sustainability of this industry. In this task, selectivity is crucial to separate metals present in multi-component electrolytes and obtain added value products. Electrodeposition can be used to recover metals individually when their reduction takes place at different potentials. Moreover, the preferential deposition of a specific element can also be modulated under galvanostatic control. In this study, the recovery and separation of antimony and bismuth from highly concentrated hydrochloric acid solutions is investigated by means of voltammetry and electrodeposition. In potentiostatic mode, the preferential deposition of antimony takes place at − 0.25 VAg/AgCl, although a moderate selectivity is achieved. Under galvanostatic mode, at current densities below the limiting value (iL), the deposition of bismuth is almost prevented, and the selectivity factor for antimony reaches the highest values. These results prove the feasibility of a highly selective antimony recovery by electrodeposition. When the iL is exceeded, the selectivity towards antimony drops because more cathodic potentials are reached, which activate the deposition of bismuth and hydrogen evolution, thus decreasing the overall electrodeposition current efficiency. Upon an increase in the proportion of bismuth in the mixtures, high current densities also favor the deposition of this metal but decrease the contribution of hydrogen evolution reaction as compared to solutions with a higher proportion of antimony. Thus, the process can also be conducted at high electrodeposition current densities, yet at the cost of obtaining the product in the form of an alloy.