Efficient extraction of gold(I) from alkaline aurocyanide solution using green ionic liquid-based aqueous biphasic systems

Ionic liquid-based aqueous biphasic extraction is an environmentally benign technology for separation of various substances. In this study, aqueous biphasic systems (ABSs) consisting of 1-alkyl-3-methylimidazolium bromide ionic liquids (ILs) (alkyl = butyl, hexyl, and octyl) and phosphate-based salts were studied for extraction of gold(I) from alkaline aurocyanide solutions for the first time. The results indicated that gold(I) preferentially migrated into the IL-rich phase, achieving remarkable extraction efficiency up to 99.9%. The extraction mechanism of gold(I) was evaluated based on characterization by FT-IR spectroscopy, X-ray photoelectron spectroscopy. The results revealed the electrostatic interaction between gold(I) cyanide complex and IL was the main driving force for gold(I) partition. The migration of gold(I) into IL-rich phase was associated with an extraction mechanism by ion pair formation of [C(n)mim(+)]center dot[Au(CN)(2)(-)]. Furthermore, the microscopic structure of the IL-rich solution was also determined by transmission electron microscopy. It was found that the presence of [Au(CN)(2)(-)] anion induced the aggregation of ionic liquids. Finally, the gold present in IL-rich phase was successfully recovered by direct electrodeposition on a copper cathode. The proposed extraction strategy using IL-based ABSs is envisaged as potential platform for the green partition of gold(I) from alkaline aurocyanide solution. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.