Extraction of iridium(iv) from aqueous solutions using hydrophilic/hydrophobic ionic liquids

Abstract

Anionic complexes of iridium(IV) were extracted from acidic solutions of HCl using ionic liquids (IL). The influence of the cationic structure of IL and of the aqueous phase pH on the distribution coefficients of IrCl₆²⁻ was investigated. Liquid–-liquid extraction and precipitation of iridium(IV) were studied. Iridium(IV) was precipitated from aqueous solutions using water-soluble ionic liquids by forming a water-insoluble salt composed of two cations from the ionic liquid. Pyridinium cations appear to be the most efficient at precipitating iridium(IV). Iridium(IV) was found to be efficiently extracted using simple hydrophobic ionic liquids, exhibiting D values ranging up to 71. Investigations on the extraction mechanism tend to show that iridium(IV) is exchanged with two [NTf₂]⁻ anions from the IL phase. Finally, elution of iridium(IV) from ionic liquids towards aqueous solutions was carried out from [BMIM][NTf₂], [OMIM][NTf₂] or [OdMIM][NTf₂] into solutions containing high amounts of hydrochloric acid or nitric acid.