Diglycolamic acid-type extractant for rare-earth elements

Shimojo, Kojiro   ; Sugita, Tsuyoshi   ; Okamura, Hiroyuki   ; Naganawa, Hirochika  

We report on solvent extraction of rare-earth (RE) cations using N,N-dioctyldiglycolamic acid (DODGAA) as a novel extractant. This extractant enables the quantitative partitioning of all rare-earth metal ions (RE) from moderately acidic solutions, while showing selectivity for heavier lanthanides, and provides remarkably high extraction separation performance for RE compared with commercial extractants. Slope analysis demonstrated that RE transfer with DODGAA proceeded through a proton-exchange reaction, forming a 1:3 complex. Structural characterization by X-ray diffraction revealed that three ligand molecules coordinated to the La3+ in a tridentate fashion and the La primary coordination sphere consisted of three oxygen atoms from the amide group, three oxygen atoms from the ether group, and three oxygen atoms from the carboxy group.