Extraction of lanthanide ions with an organophosphorous extractant into ionic liquids

Kubota, Fukiko*; Koyanagi, Yusuke*; Nakashima, Kazunori*; Shimojo, Kojiro   ; Kamiya, Noriho*; Goto, Masahiro*

Extraction of lanthanide ions was carried out with the organophosphorous extractant PC-88A dissolved in an imidazolium-based ionic liquid. PC-88A was soluble in ionic liquids having long-chain alkyl substituents such as octyl and dodecyl groups, [Cmim] and [Cmim][TFSI], although short-chain imidazolium ionic liquids could not solubilize the extractant. The extraction equilibrium observed in the ionic liquid system was similar to that in the n-dodecane system, and the extraction behavior could be explained by the same proton exchange mechanism as for the conventional organic solvent system, although the extraction efficiency was not improved. An ionic liquid having shorter alkyl chain [Cmim] showed a higher extraction ability than [Cmim][TFSI]. Stripping of the metal ions from the ionic liquids was also examined. Quantitative stripping of the metal ions was achieved by nitric acid in the [Cmim][TFSI] system.