Possibilities and limitations in separating Pt(iv) from Pd(ii) combining imidazolium and phosphonium ionic liquids

Abstract

An investigation on a process designed for separating Pt(IV) and Pd(II) dissolved in acidic aqueous solution containing HCl using two ionic liquids, 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([OMIM][NTf₂]) and trihexyltetradecylphosphonium bromide (Cyphos 102), is presented. To this end, the single extraction of platinum in [OMIM][NTf₂] has been investigated as a function of the initial concentration of Pt(IV) ions dissolved in 1 M HCl. The distribution coefficient for Pt(IV), present in water as a PtCl₆²⁻ anion, decreases with the concentration of Pt(IV). The extraction of Pd(II) towards [OMIM][NTf₂] or Cyphos 102 as a function of the concentration of HCl in the aqueous phase is also reported. Pd(II), present as PdCl₄²⁻ in water, is not extracted using [OMIM][NTf₂]. On the other hand, the distribution coefficients of Pd(II) using Cyphos 102 are above 2000. In this ionic liquid, Pd(II) is extracted as a PdBr₄²⁻ anion. Separation of Pt(IV) from Pd(II) was then carried out starting from aqueous phases containing 1 M HCl and various initial concentrations of Pt(IV). The influence of the number of extraction steps using [OMIM][NTf₂] on the extraction of Pt(IV) was also studied. Unlike the results obtained from single extraction experiments of Pt(IV), consecutive extraction of Pt(IV) in water using [OMIM][NTf₂] does not improve significantly the extraction of this metal ion. The second step of the extraction process carried out using Cyphos 102 leads to the quantitative extraction of Pd(II) and Pt(IV) remaining in the aqueous phase.