Extraction and separation on Au(III) and Pt(IV) from HCl media using novel piperazine-based ionic liquid as an ionic exchanger

Abstract

Selective recovery of gold and platinum from secondary resources is of great significance under the crisis of resource shortage. Hence, the optimal extractant 1-(2-(dimethylamino) ethyl)-4-methyl-piperazin bis(trifluoromethylsulfonyl)imide ([C6-Et-TMEDA-PIP][Tf2N]2) was synthesized and screened out from five piperazine-based ionic liquids (ILs) to construct an IL-water system for Au(III) and Pt(IV) extraction. ILs have high hydrophobicity and low viscosity at room temperature, which can be used as both extractant and hydrophobic phase. The effects of IL dosage, metal concentration and acidity on the extraction efficiency were investigated. Under the optimal conditions, the extraction efficiency of 98.5% (Au(III)) and 97.5% (Pt(IV)) can be achieved. The anion exchange mechanism was verified through the combination of Ultraviolet visible spectroscopy (UV–vis), Nuclear magnetic spectra (NMR) and quantum chemical calculations. Besides that, the two-factor optimization of the extractant dosage and HCl concentration was carried out by Response surface methodology (RSM), and the effective separation of Au(III) and Pt(IV) was successfully achieved. Au(III)/ Pt(IV) was extracted into the IL phase as [Et-TMEDA-PIP+][AuCl4-] and can easily be stripped by reduction to Au(0)/Pt(Ⅱ) with H2C2O4/CS(NH2)2-HCl, and each extraction ability maintained after 5 turns of extraction cycle experiments. Since the excellent behaviors showed in the multi-metal selective extraction and cycle experiments, the [C6-Et-TMEDA-PIP][Tf2N]2 was regarded as the most potential system for Au(III) and Pt(IV) recovery from HCI medium.