Complex formation of light and heavy lanthanides with DGA and DOODA, and its application to mutual separation in DGA-DOODA extraction system

We studied the stepwise formation constants (β) of water-soluble diglycolamide (DGA) and dioxaoctanediamide (DOODA) for the mutual separation of Ln in a solvent extraction system. TODGA (N,N,N',N'-tetraoctyl-diglycolamide) and DOODA(C8) (N,N,N',N'-tetraoctyl-dioxaoctanediamide) exhibit opposite behaviors in extracting both light and heavy Ln through Ln-patterns. Metal complexes of two- and three-folding with water-soluble DOODA and DGA, respectively, were found, and each β value was calculated using distribution ratios. Taking β, their distribution ratio, D, and separation factor, SF, values into consideration, the suitable separation conditions (aqueous phase: 30 mM DOODA(C2) in 1 M HNO₃; organic phase: 0.1 M TODGA in n-dodecane) of multistage extraction (10 × 10 extraction using aqueous and organic phases, including one sample solution) were determined. In this study, La, Pr, and Nd were mainly present in the aqueous phase, whereas Sm-Dy existed in the organic phase. Although these two groups can be easily separated into two phases, the resolution, Rs, values provide for little mutual separation between La-Nd and Sm-Dy under the present conditions. (author)