Amino Acid Ionic Liquid Two-Phase System: Construction and Its Application for Green Gold Recovery from E-waste...

Although gold extraction from electronic waste using thiosulfate is a highly promising approach, the recovery of gold from thiosulfate leaching solutions still poses a significant challenge. To enable more environmentally friendly gold recycling, aqueous two-phase systems (ATPSs) composed of guanidinium amino acid ionic liquids (TMG-AA ILs) and phosphates were developed for extracting gold from thiosulfate-leached solutions of electronic waste. Key parameters affecting Au(I) extraction were systematically investigated, including the types and concentrations of TMG-AA ILs and inorganic salts, initial gold concentration, temperature, and reaction time. The findings indicate that the Au(I) complex preferentially partitions into the TMG-AA IL-rich phase, achieving an extraction efficiency of up to 99.0% under the optimized conditions. The extraction mechanism of Au(I) was elucidated through comprehensive characterizations including Fourier transform infrared spectroscopy, nuclear magnetic resonance, and X-ray photoelectron spectroscopy. Driven by electrostatic interactions, gold thiosulfate migrates into the IL-rich phase, where it undergoes anion exchange with amino acid anions and forms ion pairs with guanidinium cations in the TMG-AA ILs. Extraction experiments using thiosulfate leachate from discarded circuit boards confirmed that the IL-ATPS exhibits high selectivity for gold with negligible extraction of other metal ions. The loaded IL phase can be effectively regenerated via stripping with a KSCN solution. In five consecutive extraction-stripping cycles, the results of the first three cycles showed that the gold extraction efficiency slightly decreased from 98.7 to 90.0% and the stripping efficiency decreased from 84.7 to 82.3%, which confirmed the good recyclability of the AA IL-ATPS system.