Analytical Sciences

Abstract − Analytical Sciences, 24(10), 1251 (2008).

Extraction Behavior of Divalent Metal Cations in Ionic Liquid Chelate Extraction Systems Using 1-Alkyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imides and Thenoyltrifluoroacetone
Keiji KIDANI, Naoki HIRAYAMA, and Hisanori IMURA
Division of Material Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
The extraction behavior of several divalent metal cations (M2+) in ionic liquid chelate extraction systems was investigated using several 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids ([Rmim][Tf2N]) as extraction solvent and thenoyltrifluoroacetone (Htta) as extractant. The behavior was compared with that using less hydrophobic 1-alkyl-3-methylimidazolium hexafluorophosphates ([Rmim][PF6]). The extracted species in the [Rmim][Tf2N] systems were neutral M(tta)2 for M = Cu and anionic M(tta)3- for M = Mn, Co, Ni, Zn and Cd. Conversion of ionic liquid anion from PF6- to more hydrophobic Tf2N- resulted in changing the species extracted for Ni2+ from hydrated neutral complex to hydrophobic anionic one. Furthermore, the extractability for these metals was governed by the hydrophobicity of ionic liquid ions. Thus, in the ionic liquid chelate extraction system, selection of a suitable ionic liquid as extraction phase seems to be an important factor for enhancement of extraction selectivity.