Tuning the Selectivity of Carboxylic Acid–Based Eutectic Solvents for the Dissolution and Electrochemical Separation of Metal Oxides

Extracting metals from natural resources and recovering from waste materials with less-hazardous solvents is essential for sustainable technological advancements. The commonly employed method utilizes harsh chemicals for metal dissolution and the ensuing separation. In this study, we examined the potential of eutectic solvents (types III and IV) as alternative media for the selective dissolution of metals and metal oxides and their subsequent electrochemical separation. Notably, type III eutectics composed of betaine:acetic acid and triazole:lactic acid exhibited excellent solubility for cobalt oxide (24.1 g·L–1) and copper oxide (30.5 g·L–1), respectively. In comparison, the type IV eutectic mixture of Ca(NO3)2·4H2O:acetic acid demonstrated the highest conductivity and lowest viscosity with solubility for both copper oxide (6.1 g·L–1) and metallic copper (5.4 g·L–1 from an electronica used electronic circuit). Using a Ca(NO3)2·4H2O:acetic acid mixture, copper was selectively dissolved from a waste printed circuit board and subsequently electrodeposited onto a nickel electrode. These findings highlight the tunability of DESs for the selective recovery of metals from electronic waste, offering a promising approach for sustainable metal recycling and resource recovery.