Selone behavior towards palladium(II) extraction with hydrophobic ionic liquids and mechanism studies

A selenium-bearing extractant was evaluated for palladium extraction for the first time. The 1-butyl-3-methyl-imidazole-2-selone was synthesized, and dissolved in hydrophobic ionic liquids to extract palladium from aqueous solutions. Based on the studies of the influencing factors, the first elaboration of the selone extraction mechanism is offered. One of the Pd-selone complexes was analyzed with single crystal X-ray diffraction to explain the elevation of extractability relative to thiones from the molecular level. A novel combination of UV-vis spectroscopy, HPLC and Se-77{H-1} NMR was first used to characterize the extraction system and to determine the complexing number. It was confirmed that various kinds of complexes had been extracted to the organic phase at different selone concentrations, thus the apparent complexing number was proposed to describe the extraction system. Both the extractability and the selectivity of the selone for Pd(II) extraction over other metal ions were evaluated to be high.