Selective Leaching of Cadmium from Cold Filter Cake Using Green Deep Eutectic Solvent Choline Chloride-Oxalic Acid

Deep eutectic solvents (DESs) are a class of new solvents with good compatibility and biodegradability that have been used for dissolving various metals. In this study, the ability of different DESs, including choline chloride-urea, choline chloride-ethylene glycol, choline chloride-citric acid, choline chloride-maleic acid, choline chloride-malonic acid, and choline chloride-oxalic acid, was investigated for dissolving cold filter cake (CFC). Among the solvents used, choline chloride-oxalic acid almost completely dissolved cadmium (97.47%) at a pulp density of 20 g/L. However, it dissolved < 50% of zinc and almost no nickel. As the pulp density increased to 200 g/L, only cadmium was dissolved with < 3% dissolution of zinc and nickel. Therefore, that was chosen as a suitable solvent for the selective leaching of cadmium from CFC. The effects of time and temperature parameters were also investigated, which showed that even at shorter times (5 min) and lower temperatures (50 degrees C), a significant portion of cadmium (over 80%) was dissolved. Kinetic studies showed that the rate-controlling step of the dissolution process of cadmium from CFC in choline chloride-oxalic acid solvent was a chemical reaction with an activation energy of 51.52 kJ/mol.