Behavior, mechanism and equilibrium studies of Au(iii) extraction with an ionic liquid [C4-6-C4BIm]Br2

Abstract

The first gemini-type benzimidazole ionic liquid ([C₄-6-C₄BIm]Br₂) with two sites of action was synthesized and applied for gold extraction. The effects of [C₄-6-C₄BIm]Br₂ concentration, initial gold(III) concentration, acidity, and the loading capacity of [C₄-6-C₄BIm]Br₂ were examined in detail. It was found that [C₄-6-C₄BIm]Br₂ has excellent extraction ability for obtaining high purity gold. The anion exchange mechanism between [C₄-6-C₄BIm]Br₂ and Au(III) was proved by Job's method and ¹H NMR and FTIR spectroscopy. Quantum chemical calculations were carried out to prove the mechanism theoretically. The extraction equilibrium process was modeled using Langmuir and Freundlich isotherms. Thermodynamic parameters ΔH, ΔG and ΔS indicated that the extraction process was exothermic and spontaneous. The pseudo-second-order kinetic model well fitted the experimental data (R = 0.99). In addition, [C₄-6-C₄BIm]Br₂ has high selectivity for Au(III) compared to other base metals. In summary, [C₄-6-C₄BIm]Br₂ has great application prospects in industry due to its excellent characteristics such as low cost, easy availability, and high extraction capacity.