Efficient separation of americium by a mixed solvent of two extractants, a diamideamine and a nitrilotriacetamide

Suzuki, Hideya*; Ban, Yasutoshi

Analytical Sciences, 39(8), p.1341 - 1348, 2023/08

https://doi.org/10.1007/s44211-023-00344-2

The Japan Atomic Energy Agency (JAEA) has proposed the Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation (SELECT) process by solvent extraction as a new separation technology to recover minor actinides (MA) from high-level liquid waste (HLLW) produced by spent fuel reprocessing. The MA separation in the SELECT process comprises the batch recovery of MA and rare earths (RE) from HLLW, MA/RE separation, and Am/Cm separation. Three highly practical extractants are used in the MA separation. Furthermore, this flow configuration facilitates the preparation of nitric acid concentrations in the aqueous phase. However, the separation factor between Cm and Nd in the MA/RE separation is small ( = 2.5), requiring many extraction stages for continuous extraction in a mixer-settler. Therefore, this study investigated the separation of only Am from an aqueous nitric acid solution containing MA (Am and Cm) and RE using an organic phase mixed with two extractants alkyl diamideamine with 2-ethylhexyl alkyl chains (ADAAM(EH)) and hexa-n-octylnitrilotriacetamide (HONTA) used in the SELECT process. Under high-concentration nitric acid conditions, Am and La, Ce, Pr, Nd (light lanthanides) were extracted in the ADAAM(EH) + HONTA mixed solvent, whereas Cm, medium, and heavy lanthanides, and Y were partitioned in the aqueous phase. Subsequently, only light lanthanides could be back extracted from the ADAAM(EH) + HONTA mixture solvent containing Am and light lanthanides in low nitric acid concentrations. Furthermore, Am could be easily stripped with 0.2 M or 5 M nitric acid. This method does not require the mutual separation of Cm and Nd, which have low separation factors. Am can be efficiently separated by one extraction and two back-extractions, reducing the number of steps in the SELECT process.

Design of MA(III)/Ln(III) separation process of extraction chromatography technology

Akuzawa, Tadashi*; Kim, S.-Y.*; Kubota, Masahiko*; Wu, H.*; Watanabe, So; Sano, Yuichi; Takeuchi, Masayuki; Arai, Tsuyoshi*

Journal of Radioanalytical and Nuclear Chemistry, 331(12), p.5851 - 5858, 2022/12

https://doi.org/10.1007/s10967-022-08658-7

Study on the mechanism of radiolytic degradation of an extractant for minor actinides separation

Toigawa, Tomohiro; Kumagai, Yuta; Yamashita, Shinichi*; Ban, Yasutoshi; Matsumura, Tatsuro

UTNL-R-0502 (Internet), 2 Pages, 2022/04

This report summarizes the results obtained in FY2020 at the Electron Linac Facility of the University of Tokyo. The radiolysis process of -hexaoctyl nitrilotriacetamide (HONTA), which is expected to be used as an extractant in a separation process for minor actinides, diluted in dodecane was investigated by pulse radiolysis experiments. The radical cation and the triplet-excited state of HONTA were observed in the nanosecond time region. The transition from the radical cation to the triplet excited state was slowed down by adding electron scavengers, and further, the reactivity of the triplet excited state was also suppressed.

Radiation-induced effects on the extraction properties of hexa--octylnitrilo-triacetamide (HONTA) complexes of americium and europium

Toigawa, Tomohiro; Peterman, D. R.*; Meeker, D. S.*; Grimes, T. S.*; Zalupski, P. R.*; Mezyk, S. P.*; Cook, A. R.*; Yamashita, Shinichi*; Kumagai, Yuta; Matsumura, Tatsuro; et al.

Physical Chemistry Chemical Physics, 23(2), p.1343 - 1351, 2021/01

https://doi.org/10.1039/D0CP05720G

The candidate An(III)/Ln(III) separation ligand hexa--octylnitrilo-triacetamide (HONTA) was irradiated under envisioned SELECT (Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation) process conditions using a solvent test loop in conjunction with cobalt-60 gamma irradiation. We demonstrate that HONTA undergoes exponential decay with increasing gamma dose to produce a range of degradation products which have been identified and quantified by HPLC-ESI-MS/MS techniques. The combination of HONTA destruction and degradation product ingrowth, particularly dioctylamine, negatively impacts the extraction and back-extraction of both americium and europium ions. The loss of HONTA was attributed to its reaction with the solvent (-dodecane) radical cation of (HONTA + R) = (7.61 0.82) 10 M s obtained by pulse radiolysis techniques. However, when this ligand is bound to either americium or europium ions, the observed -dodecane radical cation kinetics increase by over an order of magnitude. This large reactivity increase to additional reaction pathways occurring upon metal-ion binding. Lastly nanosecond time-resolved measurements showed that both direct and indirect HONTA radiolysis yielded the short-lived (100 ns) HONTA radical cation as well as a longer-lived (s) HONTA triplet excited state. These HONTA species are important precursors to the suite of HONTA degradation products observed.

Selective Sc recovery from rare earths in nitric acid medium by extraction chromatography

Watanabe, So; Suzuki, Hideya; Goto, Ichiro*; Kofuji, Hirohide; Matsumura, Tatsuro

Nihon Ion Kokan Gakkai-Shi, 29(3), p.71 - 75, 2018/09

https://doi.org/10.5182/jaie.29.71

Study of radiolysis of HONTA extractant for MA/Ln separation

Toigawa, Tomohiro; Suzuki, Hideya; Ban, Yasutoshi; Ishii, Sho; Matsumura, Tatsuro

no journal, , 

Degradation of extractants and generation of radiolytic products are considered as problem for feasibility of the minor actinides separation process. In this study, degradation amount of hexaoctyl-nitrilotriacetamide (HONTA), which is a candidate extaractant for MA/Ln separation, and its products yields were obtained by using -rays emitted from Co-60. Our results showed the cleavage sites in HONTA radiolysis and suggest that the mechanism for HONTA radiolysis is differ depending on the absorbed dose.

radiolysis of an extractant for minor actinides, Hexaoctyl-nitrilotriacetamide (HONTA), in dodecane diluent

Toigawa, Tomohiro; Suzuki, Hideya; Ban, Yasutoshi; Ishii, Sho*; Matsumura, Tatsuro

no journal, , 

Radiolytic stability of an extractant, N,N,N',N',N'',N''-hexaoctyl-nitrilotriacetamide (HONTA), for separation between minor actinides and rare-earth elements were investigated by using -ray emitting from cobalt-60. Degradation amount of HONTA and its products yields were obtained by gas chromatographic analysis. Our results showed the cleavage sites in HONTA radiolysis and suggested that the radiolysis of HONTA was ruled by different mechanism depending on the absorbed dose.

Current status of R&D on reprocessing and minor actinide separation process with CHON ligands in JAEA

Matsumura, Tatsuro; Ban, Yasutoshi; Suzuki, Hideya; Tsubata, Yasuhiro; Hotoku, Shinobu; Tsutsui, Nao; Suzuki, Asuka; Toigawa, Tomohiro; Kurosawa, Tatsuya*; Shibata, Mitsunobu*; et al.

no journal, , 

PUREX process was established for industrial scale reprocessing plant. TRUEX and the 4 group separation were developed for partitioning of minor actinides from HLW, and demonstrated using genuine HLW. Although the extractants for the processes have excellent performance, the molecules contain phosphorus which could be cause for the secondary waste from the solvent extraction processes. To minimize the radioactive waste, we have conducted research and development of the new reprocessing and MA separation processes using innovative extractants in accord with CHON principle. The extractants for reprocessing process are monoamides as alternative extractants for TBP. For An(III)+RE recovery process, we developed TDdDGA. HONTA and ADAAM were developed for An(III)/RE separation process and Am/Cm separation process respectively. The separation performances of the flowsheets were evaluated by continuous extraction tests using simulated and genuine spent fuel and high level liquid waste.

Influence of -radiolysis of MA separation agent of HONTA on extraction performance

Toigawa, Tomohiro; Suzuki, Hideya; Ban, Yasutoshi; Ishii, Sho*; Matsumura, Tatsuro

no journal, , 

To evaluate the radiolytic stability of a novel tetradentate extractant of N, N, N', N', N", N"-hexaoctyl-nitrilotriacetamide (HONTA), batch extractions of lanthanide (Ln) elements were performed by using -irradiated HONTA extraction solvents. The distribution ratios decreased exponentially with increasing the absorbed dose, and no difference between Ln could be observed. These indicate that the degradation products of HONTA did not act as Ln extractants, and the decay of Ln extraction were caused by degradation of HONTA.

Research and development of the "SELECT process" for actinide separation, 2; Investigation of new extractants for MA/RE separation

Suzuki, Hideya; Tsubata, Yasuhiro; Kurosawa, Tatsuya*; Kawasaki, Tomohiro*; Shibata, Mitsunobu*; Matsumura, Tatsuro

no journal, , 

The Japan Atomic Energy Agency is engaged in research and development of the "SELECT process" which is a separation technology for recovering actinides from spent fuel. A highly practical reagent, called HONTA, was developed. In the present study, HONTA was tested for the mutual separation of MA and RE.