Synthesis of temperature-responsive ionic liquids and study on the behavior and mechanism of Au(III) extraction from hydrochloric acid solutions

For sustainable development and environmental protection, recovery of critical metals, especially for gold, from secondary resources, has recently attracted substantial attention. In this work, two novel temperature-responsive ionic liquids (TRILs), [EA-TMEDA][Tf2N](2) and [EA-TMHDA][Tf2N](2), were designed and firstly synthesized for Au(III) extraction from hydrochloric acid medium. The optimum extraction conditions for Au(III) were selected by optimizing the amount of extractant, acidity and other factors. In optimal conditions, TRILs showed excellent extraction performance for Au(III), which could reach 97.5% with [EA-TMEDA][Tf2N](2) and 91% with [EA-TMHDA][Tf2N](2), respectively. They also exhibited great selectivity in multi-metal solution such as Cu(II), Mn(II) and Co(II). The thermomorphic behaviors were investigated around the upper critical solution temperature (UCST) by the characterization methods of variable-temperature H-1 NMR and dynamic light scattering (DLS). The extraction mechanism was also determined as anion exchange mechanism through the maximum metal loading experiments, UV-vis, FT-IR and C-13 NMR characterization. In addition, Au(III) could be almost completely stripped by C2H2O4 from the loaded IL phase and there was no significant reduction in efficiency after 5 cycles. Hence, the new TRILs offered outstanding extraction performance for the greener and sustainable extraction of Au(III), and will have broad application prospects in the extraction field.