Extraction Behavior of Rare-earth Elements Using a Mono-alkylated Diglycolamic Acid Extractant

Abstract

Liquid-liquid extraction of rare-earth (RE) cations has been investigated using N-dodecyldiglycolamic acid (C 12 DGAA) with a secondary amide group, and compared with that using N,N-dioctyldiglycolamic acid (DODGAA) with a tertiary amide group. C 12 DGAA enables quantitative transfer of all RE cations from moderately acidic solution, while being selective toward the heavier RE cations, and performs better than typical carboxylic-acid-type extractants. However, C 12 DGAA provides low extraction performance and separation ability for RE cations compared with DODGAA because of the weaker basicity of the amide oxygen. Slope analysis demonstrated that RE 3+ transfer with C 12 DGAA proceeded through a proton-exchange reaction, forming a 1:3 complex, RE(C 12 DGAA) 3 . Structural characterization by X-ray diffraction revealed that three N-butyldiglycolamic acid (C 4 DGAA) molecules coordinated to the La 3+ central ion in a tridentate fashion and the La 3+ 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.

A Comprehensive Extraction Study Using a Mono-alkylated Diglycolamic Acid Extractant: Comparison Between a Secondary Amide Group and a Tertiary Amide Group

“…C 12 DGAA and DODGAA were synthesized according to published procedures [15,16,18,22]. The analogous extractant N-octyldiglycolamic acid (C 8 DGAA, Figure 1) was synthesized as follows: diglycolic -62 -anhydride (6.5 g, 53.2 mmol) was dispersed in dry CH 2 Cl 2 (40 mL).…”

“…For rare-earth (RE) metal ions (group-3 elements), C 12 DGAA enabled quantitative transfer of light RE(III) at pH eq ≥ 3.5 and middle and heavy RE(III) at pH eq ≥ 2.8 [22]. Although C 12 DGAA performs better than typical carboxylic acid-type extractants, the metal transfer with C 12 DGAA occurred in higher pH ranges than that with DODGAA.…”

“…In contrast, the extraction performance of DGAA-type extractants was much higher for RE(III) cations compared with the other metal ions tested in this study, thus the extractants are useful for the separation of RE(III) cations from foreign metal ions. In addition, slope analysis and structural characterization by X-ray diffraction revealed that three C 12 DGAA molecules coordinated to the RE(III) cation in a tridentate fashion through three oxygen atoms from the amide group, three oxygen atoms from the ether group, and three oxygen atoms from the carboxy group, forming a 1:3 complex, RE(C 12 DGAA) 3 [22]. for Mn(II), Fe(III), Co(II), and Ni(II) was observed.…”

“…In a previous study, we synthesized N-dodecyldiglycolamic acid (C 12 DGAA, Figure 1) with a secondary amide group (R-NH-C=O) as an analogous extractant to DODGAA with a tertiary amide group (R-NR-C=O), and compared the extraction performance for rare-earth elements with both extractants [22].…”

Alkylation and pre-organisation of diglycolamide ligands on flexible platforms for nuclear waste treatment

“…great influence on the extraction performance and separation ability for RE cations: these values were more than ten times lower than those of DODGAA. 189 In little selectivity against RE metal ions. 193,194 The same substitution performed on DGAs made the ligands unable to extract Am (III) and Eu(III), unless a third amide group was also introduced, as in NTA-amide ligands.…”