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Hexavalent Actinide Extraction Using N , N -Dialkyl Amides

2017; American Chemical Society; Volume: 56; Issue: 22 Linguagem: Inglês

10.1021/acs.iecr.7b01181

1520-5045

Kevin McCann, Bruce J. Mincher, Nicholas C. Schmitt, Jenifer C. Braley,

Nuclear materials and radiation effects

Recently, efforts toward closing the nuclear fuel cycle have considered oxidizing americium to a hexavalent, linear-dioxo cation for co-recovery with hexavalent U, Np, and Pu from molar nitric acid using solvating extraction ligands such as tributyl phosphate or diamyl amylphosphonate. This work assesses solvent extraction recovery of sodium bismuthate oxidized americium by N,N-di(2-ethylhexyl)butyramide (DEHBA), N,N-di(2-ethylhexyl)isobutyramide (DEHiBA), and N,N-dihexyloctanamide (DHOA). Extraction efficiency between the monoamides was found to increase in the order of DEHiBA < DHOA < DEHBA. For all monoamides, oxidized americium extraction was less than 50% from 4 M HNO3 and below. Extraction efficiency above 50% was obtained using concentrations of 5 M HNO3 or higher. The DEHBA extractant provided the highest distribution value of 5.4 at 7 M HNO3. Distribution values were found to be stable for up to 45 s aqueous/organic phase mixing times and indicated decreased reduction of hexavalent americium relative to separations completed with organophosphorus extractants. The simultaneous coextraction of U, Np, Pu, and Am was demonstrated using DEHiBA and was found to decrease with increasing atomic number (DU > DNp > DPu > DAm). Interestingly, a break in recovery was observed where lighter actinides, U and Np, were comparably recovered relative to the heavier actinides, Pu and Am, in this study. This observation seems to be related to differences in the extracted metal complex for light actinides compared to heavy actinides. The metal:extractant dependence suggests the presence of 1:1 and 1:2 complexes for U and Np, while data collected for Pu and Am suggests 1:2 for the presence of complexes.