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Separation of Am, Cm and Ln by combination of two novel-diamide compounds at $$n$$-dodecane and HNO$$_{3}$$ system

2つの新規なジアミド化合物を用いるAm, Cm, Lnの溶媒抽出分離

佐々木 祐二; 北辻 章浩; 津幡 靖宏; 須郷 由美; 白数 訓子; 森田 泰治

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

高レベル廃液の効率的な処分を目指して、Am, Cmのようなマイナーアクチノイドの分離を検討した。Am, Cmは化学的性質が似通っており、相互分離は大変難しい。われわれは2つの分離剤を組合せた新しい相互分離法を検討した。DGA(ジグリコールアミド)やDOODA(ジオキサオクタンジアミド)のようなジアミド化合物はその合成が比較的簡単であり、疎水性,水溶性の化合物を容易に得ることができる。それぞれの化合物を溶媒抽出の水相,有機相に溶解して、2つの分離性能を組合せる相乗効果で相互分離を試みた。講演では、DGA, DOODAとランタノイド、Am, Cmとの錯形成定数や相互分離比について述べる。

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$$_{3}$$ 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$$_{3}$$, respectively, and the condition of 0.1 M TDdDGA in n-dodecane and 0.5 MDOODA(C2) in 3 M HNO$$_{3}$$ gives the separation factors of La/Gd: 1128 and Am/Cm:3.26.

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