On the Use of Pseudo-Protic Ionic Liquids to Extract Gold(III) from HCl Solutions

Solvent extraction of gold(III) from HCl media using pseudo-protic ionic liquids (PPILs) dissolved in toluene as the extractant phase is investigated. Three PPILs are generated from the reaction of commercially available amines and 1 M HCl solution and named as pri-NH₂H⁺Cl^- (derived from the primary amine Primene 81R), sec-NHH⁺Cl^- (derived from the secondary amine Amberlite LA2) and ter-NH⁺Cl^- (derived from the tertiary amine Hostarex A327). In the above structures, -NH₂H⁺Cl^-, -NHH⁺Cl^- and -NH⁺Cl^- represented the active groups (anion exchangers) of the respective PPIL. In the case of gold(III) extraction, the experimental variables investigated included the equilibration time (2.5-30 min), temperature (20-60 °C), HCl concentrations (1-10 M) in the aqueous phase, gold(III) concentration (0.005-0.05 g/L) in this same phase, and PPILs concentrations in the organic phase. From the experimental data, and using the Specific Interaction Theory, the interaction coefficients (ε) for the pair AuCl₄^-, H⁺ are estimated for the systems involving the three PPILs. Gold(III) is recovered from the metal-loaded organic phases using sodium thiocyanate solutions, and from these, gold is finally recovered by the precipitation of zero-valent gold (ZVG) nanoparticles.