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

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 ([C(8)mim][Tf2N]) and trihexyltetradecylphosphonium chloride [P-6,P-6,P-6,P-14][C1]). Imidazolium-based [C(8)mim][Tf2N] shows a high selectivity for Pt(VI), whereas [P-6,P-6,P-6,P-14][C1] has a high extraction ability for both Pt(IV) and Pd(II). The addition of [P-6,P-6,P-6,P-14][C1] to [C(8)mim][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 [C(8)mim][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.