Equilibrium and mechanism studies of gold(I) extraction from alkaline aurocyanide solution by using fluorine-free ionic liquids

Solvent extraction based on ionic liquids is generally considered to be an environmentally benign and effective technology for gold(I) recovery. The aim of this work is to study gold(I) extraction from aurocyanide solution using fluorine-free ionic liquids [A336][SCN], [A336][MTBA] and [A336][Mal]. Various factors that affect gold(I) extraction (including concentration of ionic liquids, equilibrium pH, concentration of the modifier tributyl phosphate (TBP), reaction time and initial concentration of gold in an aqueous solution) were studied and optimized. The results indicate that the three Aliquat 336-based ionic liquids all exhibit excellent behaviors for gold(I) extraction. More than 99.8% of gold(I) can be extracted from the aqueous phase into the ionic liquid phase. The gold-loaded ionic liquids were characterized using infrared spectroscopy and mass spectrometry to study the extraction mechanism of gold(I). The results revealed that extraction of gold(I) into the ionic liquid phase was based on an exchange reaction between the anion Au(CN) ₂ ⁻ in aqueous solution and the anion SCN⁻ in ionic liquid [A336][SCN]. The logarithmic relationship between distribution coefficient and TBP concentration indicates that two TBP molecules are involved in the formation of the extracted complex. The extracted complex was determined to be A336⁺·Au(CN) ₂ ⁻ ·2TBP. In addition, the gold(I)-loaded ionic liquids can be efficiently stripped using NH₄SCN, 2-methylthiobenzoic acid and methyl maltol. The results establish that Aliquat 336-based ionic liquids have potential application prospects in gold(I) recovery from cyanide solutions.