Recovery of gold from hydrochloric medium by deep eutectic solvents based on quaternary ammonium salts

In this paper, 3 kinds of hydrophobic deep eutectic solvents were screened out for gold recovery due to their low viscosity, which were constructed by ionic liquids: [N-3333]Br, [N-4444]Br and [N-8881]Br and N-hexanoic acid. Anion exchange mechanism during the extraction process was proposed through the combination of UV-vis and FT-IR. Subsequently, the extraction behaviors under different conditions, such as: salinity (NaCl/NaBr), acidity and Au(III) concentration were investigated and discussed. N-8881-Br-acid showed the best extraction ability: it showed the 96.8% extraction efficiency on 1 mM Au(III) solution, compared with N-4444-Br-acid (around 93% on 0.6 mM) and N-3333-Br-acid (around 91% on 0.6 mM). Besides that, the N-8881-Br-acid showed the better salinity resistance among 3 DESs. The extracted Au (III) in the DESs phase was easily and completely stripped by applying 1 mL 0.1 g/mL NaBH4, and each extraction ability maintained after 5 turns of extraction cycle experiments. Since the excellent behaviors showed in the multi-metal selective extraction and extraction cycle experiments, the N-8881-Br-acid was regarded as the most potential system for gold recovery from HCl medium. Furthermore, its operating conditions combination: operating temperature and vibration time were optimized to 19 degrees C and 13 mM by applying response surface methodology (RSM). Under optimized conditions combination and given A/O = 1:1, the complete extraction procedure only needs two theoretical stages with a tiny amount (similar to 5%) of Au(III) left, which is indicated by drawing Mccabe-Thiele diagram.