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 full-size imageDownload as PowerPoint slide