Processing of anode slime with deep eutectic solvents as a green leachant

This paper describes an efficient process of recovering valuable metals from a copper anode slime sample using green chemicals such as choline chloride (ChCl) based deep eutectic solvents (DESs). The leaching agents include ChCl-urea, ChCl-ethylene glycol, ChCl-urea-ethylene glycol and ChCl/urea-deionized water in a 1:2, 1:2, 1:0.5:1.5, and 1:1 ratio, respectively. Prior to leaching experiments, chemical and mineralogical characterization of copper anode slime was performed. Considerable amount of precious metals was detected in the copper anode slime by chemical analysis. The main phases of copper anode slime detected by XRD and SEM/EDX analysis were namely Cu2O, SnO2, and, PbSO4. After leaching experiments, 97% of copper was recovered from the copper anode slime using ChCl-urea under an optimum condition at 95 degrees C of reaction temperature, 4 h reaction duration and, 1/25 g/mL solid/liquid ratio. The results showed that 91% of silver was extracted from the anode slime under the optimum condition with ChCl-urea DES composition, 95 degrees C reaction temperature, 48 h reaction duration, and 1/10 solid/liquid ratio. Gold was not leachable in the experiment using ChCl based DES with hydrogen bonding reagents such as urea and ethylene glycol. Moreover, the results revealed that PbSO4 was very soluble in DES prepared by ChCl and urea.