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 function of various parameters, such as the initial 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.

Graphical AbstractPhosphorus functional ionic liquids (PFILs) have been successfully synthesized and used in Nd(III) extraction. The nature of the ionic liquid extractants determines the extraction behaviorFigure optionsDownload as PowerPoint slide