A Cyclic Voltammetry Study on the Electrodeposition of Antimony from Oxaline (Choline Chloride–Oxalic Acid) Deep Eutectic Solvent

Deep eutectic solvents (DESs) have emerged as sustainable alternatives to strong acids and bases, with oxaline, a mixture of oxalic acid and choline chloride, being one of the most studied. Its high metal-dissolving capacity makes it a promising eco-friendly solvent for recovering critical raw materials. One key application is the recovery of antimony (Sb) from secondary sources, as conventional methods rely on highly acidic HCl, which is toxic and corrosive. This study systematically evaluates via cyclic voltammetry the use of oxaline as a potential solvent for the electrochemical recovery of Sb. Results show that oxaline adsorbs on the Pt electrode, an effect intensified by the presence of Sb. The Sb3+ reduction peak and the hydrogen evolution region occur at more widely separated potentials in the oxaline medium than in HCl, allowing operation over a broader potential range while minimizing potential damage to the electrodeposit caused by secondary reactions. However, the high viscosity of oxaline and the diffusion-controlled nature of the process limit the rate of Sb reduction. High operating temperatures increase the peak current density of Sb deposition but also result in thin Sb deposits. Despite these challenges, DESs represent a viable alternative to HCl if their viscosity-related limitations can be overcome.