Analytical Sciences

Highly Efficient Extraction Separation of Lanthanides Using a Diglycolamic Acid Extractant

Kojiro SHIMOJO,*1 Noboru AOYAGI,*1 Takumi SAITO,*2 Hiroyuki OKAMURA,*1 Fukiko KUBOTA,*3 Masahiro GOTO,*3,*4 and Hirochika NAGANAWA*1

*1 Division of Chemistry for Nuclear Engineering, Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan
*2 Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
*3 Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan
*4 Center for Future Chemistry, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan

Liquid–liquid extraction of lanthanide ions (Ln³⁺) using N,N-dioctyldiglycolamic acid (DODGAA) was comprehensively investigated, together with fluorescence spectroscopic characterization of the resulting extracted complexes in the organic phase. DODGAA enables the quantitative partitioning of all Ln³⁺ ions from moderately acidic solutions, while showing selectivity for heavier lanthanides, and provides remarkably high extraction separation performance for Ln³⁺ compared with typical carboxylic acid extractants. Furthermore, the mutual separation abilities of DODGAA for light lanthanides are higher than those of organophosphorus extractants. Slope analysis, loading tests, and electrospray ionization mass spectrometry measurements demonstrated that the transfer of Ln³⁺ with DODGAA proceeded through a proton-exchange reaction, forming a 1:3 complex, Ln(DODGAA)₃. The stripping of Ln³⁺ from the extracting phase was successfully achieved under acidic conditions. Time-resolved laser-induced fluorescence spectroscopy revealed that the extracted Eu³⁺ ions were completely dehydrated by complexation with DODGAA.

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