Removal of platinum from water by precipitation or liquid–liquid extraction and separation from gold using ionic liquids

Abstract

Precipitation and liquid–liquid extraction of PtX₆²⁻ (X = Cl⁻, Br⁻, SCN⁻) in acidified aqueous solutions ranging from 0.1 M to 9 M HBr or 11 M of HCl have been studied using water-soluble or hydrophobic ionic liquids. Divalent hexachloroplatinate(IV) anions appear to be extracted much less efficiently than tetrachloroaurate(III) complexes. At a concentration of 11 M HCl, values of 15 and 800 for the distribution coefficients of PtCl₆²⁻ and PtBr₆²⁻ in [OMIM][NTf₂] have been obtained accordingly. The presence of a labile hydrogen on the imidazolium ring has been found to play a specific role in the extraction of platinum(IV) complexes in concentrated HCl or HBr. Pt(SCN)₆²⁻ appears to be very efficiently extracted at pH 1 using [OMIM][NTf₂], exhibiting a distribution coefficient of 6150. Finally, two methods for quantitative separation of gold and platinum in water using in each method two extraction steps have been proposed. The back extraction of platinum(IV) during the second separation process was also discussed.