Membrane electrolysis for recovering Sb and Bi from elution solutions of ion-exchange resins used in copper electrorefining: A cyclic voltammetric study

Antimony (Sb) and bismuth (Bi), which have been considered critical raw materials by the European Commission, cause inconveniences to copper production when they are present as impurities in copper electrorefining solutions. Therefore, ion-exchange resins to extract Sb and Bi from copper-containing electrolytes have typically been applied; after the adsorption of the metals, the elution step is conducted with an HCl solution to desorb them. In the present study, a novel membrane electrolysis system with a cation-exchange membrane was proposed to extract Sb and Bi ions from the elution solution, and a cyclic voltammetric study was carried out to evaluate the influence of the most important operating parameters on the process performance, such as Sb, Bi and HCl concentration, dilution factor of the solution, the presence of thiourea as a complexing agent, the presence of iron as an impurity, and temperature. The obtained voltammograms indicated that the simultaneous presence of the metals in solution alters considerably their electrodeposition and oxidation pattern when compared to the solutions with pure metals. The reactions of electrodeposition of both metals are not electrochemically reversible and the diffusion control for bismuth is greater than that for antimony. The increase in the concentration of Sb affects its electrodeposition kinetically, whereas that of Bi is affected both kinetically and thermodynamically. The increase in HCl concentration disfavors the electrodeposition of both metals. Diluting the solution reduces the energy consumption and prolongs the membrane lifespan. Increasing the temperature reduces the cathodic potential to deposit the metals but favors the hydrogen evolution reaction. The presence of iron as an impurity does not affect the electrodeposition of both metals, whereas the use of thiourea as a complexing agent must be avoided because it impairs their electrodeposition.