Application of Ionic Liquids to Extraction Separation of Rare Earth Metals with an Effective Diglycol amic Acid Extractant

概要

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The application of ionic liquids as an alternative to conventional organic solvents in solvent extraction has been actively investigated. A crucial step towards the practical use of ionic liquids is the development of extractants that work effectively within these new media. In the present study, the extraction separation of rare earth metals into ionic liquids, 1-butyl, 1-octyl and 1-dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Cnmim][Tf2N] n = 4, 8,12) was performed using a novel extractant, N, N-dioctyldiglycol amic acid (DODGAA). Quantitative extraction of the metal ions such as Y3+ and Eu3+ was achieved whereas the base metal ion Zn2+ was not extracted at all under the present experimental conditions. The extraction efficiency was enhanced in the shorter-alkyl chain imidazolium ionic liquid [C4mim][Tf2N] compared to that in a conventional organic solvent system. The extraction mechanism has been studied and it was elucidated that the metal extraction proceeds via proton exchange reactions between DODGAA and the metal ions in the ionic liquid (the same mechanism as in the conventional organic solvent). The stripping reaction of the metal ions from the extracting phase was readily completed with an acid solution such as nitric acid.