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

Abstract

Abstract 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 [Cnmim+]•[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.