Enhancing extraction ability by rational design of phosphoryl functionalized ionic liquids and mechanistic investigation on neodymium(III) extraction

Four ionic liquids （ILs）： 3-（diethoxyphosphoryl）propyl triphenylphosphinium hexafluorophosphate [Ph3PC3P（OEt）2][PF6] （IL-1）, 3-（ethoxyphenylphosphoryl）propyl triphenylphosphinium hexafluorophosphate [Ph3PC3PPh（OEt）][PF6] （IL-2）, 3-（diphenylphosphoryl）propyl triphenylphosphinium hexafluorophosphate [Ph3PC3P（Ph）2][PF6] （IL-3）, and 3-（diethoxyphosphoryl）propyl triphenylphosphinium bis（trifluoromethanesulfonyl）imide [Ph3PC3P（OEt）2][NTf2] （IL-4） were synthesized and characterized by IR and 31p, 1H, 13C NMR spectroscopy. The liquid-liquid extraction of neodymium（Ⅲ） by these phosphorus functionalized ionic liquids （PFILs） diluted with common room temperature ionic liquid 1-hexyl-3-methylimidazolium bis（trifluoromethylsulfonyl）imide [C6mim][NTf2] was studied. The extraction percentage of Nd（Ⅲ） was measured as a fimction of various parameters, such as the ini- tial pH of aqueous phase, equilibrium time, temperature, and concentration of PFIL extractant. The influence of the nature of diluents and salting-out reagents on extraction was also investigated. The results indicated that the extraction process was exothermical and the extraction percentage of Nd（Ⅲ） by IL-1 was the highest among the PFILs investigated. A possible metal complexation mechanism was proposed for the present PFIL/IL extraction system. And the loaded Nd（Ⅲ） ions by PFIL could be stripped completely from the ionic liquid phase by 1 mol/L nitric acid.