Application of ionic liquids to extraction separation of rare earth metals with an effective diglycol amic acid extractant

グリコールアミド酸型抽出剤を用いたレアアースメタルの抽出分離へのイオン液体の応用

久保田 富生子*; 下堀 陽佑*; 馬場 雄三*; 小柳 裕介*; 下条 晃司郎   ; 神谷 典穂*; 後藤 雅宏*

Kubota, Fukiko*; Shimobori, Yosuke*; Baba, Yuzo*; Koyanagi, Yusuke*; Shimojo, Kojiro; Kamiya, Noriho*; Goto, Masahiro*

本研究ではレアアース金属のリサイクルのためにイオン液体を用いた抽出分離プロセスを構築した。レアアース金属の抽出分離効率の鍵を握る抽出剤としてグリコールアミド型抽出剤を使用した。その結果、遷移金属とレアアース金属の混合液からレアアース金属のみを選択的に抽出することに成功した。また、一般有機溶媒の代わりにイオン液体を抽出媒体として使用することで飛躍的に抽出能が向上した。また、酸性溶液を使用することで定量的な逆抽出も可能であった。

The application of ionic liquids as alternatives to conventional organic solvents in extraction processes 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 l-dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C min][TfN], = 4, 8, 12), was performed using a novel extractant, ,-dioctyldiglycol amic acid (DODGAA). Quantitative extraction of metal ions such as Y and Eu was selectively achieved in the presence of the base metal ion Zn, which was not extracted at all under the present experimental conditions. The extraction efficiency was enhanced for the shorter-alkyl-chain imidazolium ionic liquid [Cmim] [TfN] compared to that for a conventional organic solvent system. Extraction mechanism studies 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, or recovery, of the metal ions from the extracting phase was readily accomplished with an acid solution such as nitric acid.