The Solvent Extraction And Coordination Of Platinum Group Metals With Ionic Liquids-based Imidazole Thione/Selone

The use of ionic liquids as either extractants or organic phases could notably reduce the emulsion and enhance the mass transfer. However, if the ionic liquid was used as extractants, the loss of ionic liquids is inevitable due to the ion exchange between the two phases. The adding of neutral extractants could not only avoid or reduce the ion exchange, but also maintain the advantages of ionic liquids. In this paper, we are dedicated to the building of neutral extractant/hydrophobic ionic liquids system, which was used in the solvent extraction and separation of platinum group metals.First, the sulfur-bearing extractant, 1,3-diethyl-imidazole-2-thione, in an ionic liquid organic phase was evaluated for palladium extraction. The extraction conditions were examined followed by mechanism studies. The aqueous Pd(II) was extracted through a neutral extraction mechanism, which can avoid or decrease the loss of ionic liquid used in traditional methods and highlight the green credentials of the ionic liquids. Investigations of the extracted complexes of palladium(II) with the EEImT ligand were conducted using single crystal X-ray diffraction and computational methods. The results showed that the Pd(II)-EEImT complexes with both 1:1 and 1:2 stoichiometry can be produced during extraction, rather than simply one structure. The cis geometry of the Pd(EEImT)2Cl2 complex was more favorable than the trans geometry. This was further explained by computer calculations, which suggested that the cis configuration with a larger dipole was energetically more stable than the trans configuration.Then we employed the selenium-bearing extractants 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{1H} 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.What is more, based on the ionic liquid system, newly synthesized 1-hexly-3-methylimidazole-2-selone was applied in the separation of Pd/Ru/Rh. The separation procedure was optimized according to the influences of acids, extractant concentration and activation.To summarize, the combination of thione or selone extractant and hydrophobic ionic liquids as organic phase not only elevates the stability and extractability, but also avoids the loss of ionic liquids and reduce the equipment requirements.