Extraction and Separation of Pt and Pd by an Imidazolium-Based Ionic Liquid Combined with Phosphonium Chloride

Abstract

Extraction and separation of Pt(IV) and Pd(II) from a hydrochloric acid solution was examined with a mixture of undiluted ionic liquids, 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide ([C₈mim][Tf₂N]) and trihexyltetradecylphosphonium chloride ([P_6,6,6,14][Cl]). Imidazolium-based [C₈mim][Tf₂N] shows a high selectivity for Pt(VI), whereas [P_6,6,6,14][Cl] has a high extraction ability for both Pt(IV) and Pd(II). The addition of [P_6,6,6,14][Cl] to [C₈mim][Tf₂N] improved the extraction efficiency for Pt and the separation factor between Pt and Pd also increased. This improvement was attributed to the presence of Cl⁻ being more hydrophilic than Tf₂N⁻ in the [C₈mim][Tf₂N] extraction phase. Stripping of the metals was possible with HNO₃ solution without any degradation of the ionic liquid extraction phase. The ionic liquid mixture was shown to be reusable for at least five extraction cycles.