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][Tf 2 N] 2 and [EA-TMHDA][Tf 2 N] 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][Tf 2 N] 2 and 91% with [EA-TMHDA][Tf 2 N] 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 1H 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 13C NMR characterization. In addition, Au(III) could be almost completely stripped by C 2 H 2 O 4 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. Cycling recovery of Au(III) by temperature-responsive ionic liquids. [Display omitted] • Novel temperature-responsive ionic liquids were firstly synthesized and used for Au(III) extraction. • The water-ILs systems displayed adjustable thermomorphic behaviors. • The thermomorphic behaviors were investigated by the variable-temperature 1HNMR and dynamic light scattering (DLS). • [EA-TMEDA][Tf 2 N] 2 and [EA-TMHDA][Tf 2 N] 2 showed the excellent Au(III) extraction ability from secondary resources without adding organic solvents. • Au(III) was stripped by H 2 C 2 O 4 solution and maintained 5 cycles of extraction tests. [ABSTRACT FROM AUTHOR]