Removal of palladium(II) from aqueous chloride solutions with cyphos phosphonium ionic liquids as metal ion carriers for liquid-liquid extraction and transport across polymer inclusion membranes

This paper presents an application of three phosphonium ionic liquids for removal of Pd(II) ions from aqueous chloride solutions with liquid-liquid extraction and transport across polymer inclusion membranes (PIM). Trihexyl(tetradecyl)phosphonium chloride and bromide (Cyphos IL 101 and 102) and bis-(2,4,4-trimethylpentyl)phosphinate (Cyphos IL 104) were investigated as carriers of Pd(II) from aqueous chloride media. Extraction of Pd(II) with Cyphos IL 102 has not been previously described in the literature. Cyphos IL 102 used for the first time as metal ion carrier, efficiently extracts palladium(II) ions both with liquid-liquid extraction and PIM. NaCl concentration does not affect Pd(II) extraction with Cyphos IL 102, while increasing HCl content in the feed aqueous phase causes decrease in extraction efficiency. Stripping of Pd(II) with 0.5 M NH4OH is efficient (84 to 90%) and the organic phase after stripping could be reused for extraction. For PIM transport the highest values of the normalized initial flux are obtained for CTA membrane containing Cyphos IL 101 and a receiving phase: mixture 0.1 thiourea + 0.5 M HCl. It is indicated that initial flux does not determine the final result of the transport through the membranes because from the separation point of view, the most important is a complete transport of the solute to the receiving phase, described by the Pd(II) recovery factor.