Separation of Am, Cm and Ln by combination of two novel-diamide compounds at -dodecane and HNO system

Sasaki, Yuji  ; Kitatsuji, Yoshihiro  ; Tsubata, Yasuhiro   ; Sugo, Yumi; Shirasu, Noriko  ; Morita, Yasuji  

Mutual separation of Am, Cm and lanthanides (Ln) is important to develop the partitioning process of high-level radioactive waste, although this method is difficult to establish due to their very similar chemical behavior, same oxidation state (III) and similar ionic radii. Relative high separation values for these metals can be seen when the multidentate ligands, e.g., diethylene-triamine-N,N,N',N'',N''-pentaacetic acid (DTPA), and softN-donor extractants are employed. We examine to use the combination of two-multidentate ligands having N atoms in their structures in behalf of the high separation of Am, Cm and Ln. Various diamide-type ligands can be synthesized from the initial materials of carboxylic acid and amine, and the aimed materials can be tailored to have high solubility in either HNO orn-dodecane, in case short or long alkyl chains are attached in amidic Natoms. Taking the simultaneous use of these materials into consideration, hydrophilic and lipophilic diamide compounds with different complexing ability for trivalent Ln and actinide (An) are used into both of the aqueous and the organic phases in order to enlarge their separation factors. This technique is applicable in the salt-free system and diamide can be gasificated by combustion, which reduces the secondary-radioactive waste. Two diamide compounds, DGA (diglycolamide) and DOODA (dioxaoctanediamide) as the representative multidentate ligands, have the different features for Ln-complexation, namely DGA has higher D values for middle-Ln than those of light-Ln, and DOODA shows the opposite trend to DGA. TDdDGA (N,N,N',N'-tetradodecyl-diglycolamide) and DOODA(C2) (N,N,N',N'-tetraethyl-dioxaoctanediamide) have high solubility in n-dodecane and HNO, respectively, and the condition of 0.1 M TDdDGA in n-dodecane and 0.5 MDOODA(C2) in 3 M HNO gives the separation factors of La/Gd: 1128 and Am/Cm:3.26.