The role of association of ions in ionic liquid/molecular solvent mixtures on metal extraction

Abstract

Several mixtures of butyl acetate (BA) and an ionic liquid (1-methyl-3-octylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [C₁C₈Pyrro][NTf₂], 1-octyl-pyridinium bis(trifluoromethylsulfonyl)imide, [C₈Pyr][NTf₂], 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide, [C₁C₄Im][NTf₂] or 1-octyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide, [C₁C₈Im][NTf₂]) have been characterized by measuring density, viscosity and conductivity, from pure BA to pure ILs at 298.15 K. The ionicity of these mixtures has been determined on the basis of electrical conductivity and NMR spectroscopy. IR spectra of these mixtures were used to examine the interactions between ions. In parallel, Pt(IV) was extracted from the acidic aqueous phase towards mixtures of BA and [C₁C₈Im][NTf₂] over the entire composition range. A drastic modification in the distribution coefficient of Pt(IV) was observed at ca x_AB = 0.8. A drop was also observed in the ionicity of the extracting phase (IL + BA) at a similar composition. The variation of the distribution coefficient is ascribed to changes in the interactions in the mixtures, which in turn could induce changes in the extraction mechanism.