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Abstract  

Back-extraction of tri- and tetravalent actinides from diisodecylphosphoric acid (DIDPA) is studied using hydrazine carbonate as back-extractant. In experiments using 0.5M DIDPA–0.1M TBP n-dodecane solution, Am(III), Eu(III), Pu(IV) and Np(IV) are back-extracted, and the distribution ratios are decreased with an increase of hydrazine carbonate concentration. The back-extraction equilibria are confirmed by slope analysis in consideration of neutralization between DIDPA and hydrazine carbonate, which occurs quantitatively during back-extraction. In particular, oxidation of Np(IV) to Np(V) during back-extraction is observed by measuring absorption spectra. The hydrazinium ion acts as an oxidation reagent in the back-extraction of Np(IV). Separation factors of those metals are compared with the results of HDEHP. Hydrazine carbonate back-extracts Np(IV) more selectively from DIDPA than from HDEHP.

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Abstract  

The interactions of dissolved or colloidal actinides with tuffaceous rock are being studied at Los Alamos National Laboratory in support of the Nevada Nuclear Waste Storage Investigations project. We have used small columns of crushed tuff to obtain information on the sorption of neptunium, plutonium and americium during short (<1 day) time spans. Data from these experiments supplement information obtained from longer term batch-type experiments and provide insight concerning sorption kinetics, speciation, and colloid migration. We find that Np(V), Pu(VI) and Pu(V) show limited sorption on crushed tuff. Pu(IV) polymer and Am(III) are largely retained by the tuff, with a small fraction of the imput material moving through the column as colloids.

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Abstract  

The position of Pu/III/ within lanthanides in respect to G0, H0 and S0 of complex formation with nitrate and thiocyanate ligands was determined by the extraction method. It was found that in respect to G0, Pu/III/ is a light pseudolanthanide for nitrate ligands and a heavy pseudolanthanide for thiocyanate ligands. A comparison of the positions of Pu/III/ and Am/III/ in respect to G0, H0 and S0 shows that the radius of plutonium is greater than that of americium in the An/NO3/ 5 2– complex and smaller in the An/NCS/3/TBP/n complex. The increase in the radii between plutonium and americium in the thiocyanate complex points out to a contribution from 5f orbitals to bonding.

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Abstract  

Previously it was found that in the extraction separation on lanthanides and americium from acidic nitrate solutions of nuclear fission products, benzyldimethyldodecylammonium nitrate gives high values of separation coefficients. The change in the extraction capacity of this agent and its solutions in benzene in the extraction of Eu(III) and Am(III) was investigated as a function of the adsorbed dose of ionizing radiation. The slight reduction in the extraction of both metals is caused mainly by the radiolysis products of nitric acid in the organic phase that enter into secondary reactions with both the solvent and the extractant. Comparison of the radiation stability of benzyldimethyldodecylammonium nitrate systems with tertiary amines show that the changes in distribution coefficients in the range of investigated absorbed doses are significantly lower in the former case. The investigated system may be characterized as radiation stable up to about 100 kGy even in the presence of nitric acid.

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Abstract  

Extraction of Tm(III), from thiocyanate media, by different sulfoxides (R2SO) has revealed that the extractable complex is Tm(SCN)3·4 R2SO. When mixtures of DPSO and HTTA are used for the extraction of Tm(III) from thiocyanate or perchlorate media, synergistic enhancement of the extraction of Tm(III) results. The complexes responsible for the enhanced extraction are Tm(TTA)3·DPSO and Tm(TTA)3·2 DPSO when perchlorate media were employed for the extraction and Tm(SCN)(TTA)2·2 DPSO and Tm(SCN)2(TTA)·3 DPSO, in addition to the above two when a thiocyanate medium was employed for the extraction. Values of equilibrium constants for some equilibria encountered in the extraction of Am(III) and Tm(III) by mixtures of DPSO and HTTA are given.

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Abstract  

The extraction of Am(III), Pu(IV) and U(VI) as representatives of tri-, tetra- and hexavalent actinides by dibutyl-N,N-diethylcarbamoylmethylenephosphonate (DBDECMP) from nitric acid solution has ben studied with an objective of understanding the extraction mechanism. The dependence of the distribution ratios of the actinide ions was studied as a function of the concentration of H+, DBDECMP and NO 3 . The extraction data revealed that all the three actinide ions are extracted as their neutral nitrate complexes solvated by DBDECMP which behaves as neutral extractant only. The absorption spectra of DBDECMP and TBP extracts of these actinide ions were recorded. From the close similarity of these spectra it is inferred that DBDECMP acts as a monodentate extractant in the present system.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Toshiyuki Fujii, Genki Okude, Akihiro Uehara, Shun Sekimoto, Hirokazu Hayashi, Mitsuo Akabori, Kazuo Minato, and Hajimu Yamana

Abstract  

Distribution behavior of Ce(III), Am(III), and Cm(III) between tri-n-butyl phosphate solution and molten calcium nitrate hydrate Ca(NO3)2·RH2O or molten calcium chloride hydrate CaCl2·RH2O was studied radiochemically. In Ca(NO3)2·RH2O systems, maximum separation factors of Ce and Cm to Am were observed to be 12 (Ce/Am) and 1.7 (Cm/Am). The distribution ratios of these elements increased with the decrease of water activity in the hydrates, and the extractabilities at the water deficient region was less sensitive compared to those at the water abundant region. This trend was similar to the coordination circumstance change observed in electronic absorption spectra of Nd(III) in the hydrates.

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Abstract  

To simplify TRPO process, a novel ligand, N,N’-dimethyl-3-oxa-glutaramic acid (DMOGA), was synthesized and used for stripping of An(III, IV) from 30% TRPO-kerosene. The distribution ratios for transuranium elements, including Np(IV), Pu(IV), Am(III), and some fission products, including Eu(III), Fe and Zr between 30% TRPO-kerosene and various HNO3-DMOGA solutions were measured. An(III, IV) and Ln(III) extracted to TRPO from simulated high level liquid waste could be recovered with an efficiency of 99.9% above in one stream with a 3-stage crosscurrent strip experiment with 0.2M DMOGA in HNO3 solution. Using this new agent, the back extraction of TRU elements from loaded TRPO phase becomes more simple and practical. Therefore, the original TRPO process could be simplified.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: T. Tanaka, M. Mukai, T. Maeda, J. Matsumoto, H. Ogawa, Zhentang Li, Xudong Wang, Zhiwen Fan, Liangtian Guo, and Cunli Liu

Abstract  

Migration experiments with 237Np(V) and 241Am(III) have been performed using a column system, packed with loess, taken from Shanxi, China. The adsorption mechanism of 237Np and 241Am on the loess was examined by a chemical extraction method. Most of 237Np was adsorbed on the influent edge of the column, and the adsorbtion was mainly controlled by surface complexation. However, the migration of 237Np in loess media could be roughly evaluated by the distribution coefficient. In the case of 241Am, particulate, the 241Am species was formed in the influent solution and moved in the column. The 241Am adsorbed on loess was controlled by irreversible reactions. The migration behavior of particulate 241Am in loess media could be expressed by the filtration theory.

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Abstract  

Adsorption experiments were performed to measure distribution coefficients of237Np(V),238Pu(IV) and241Am(III) for sedimentary sequential chemical extraction of the adsorbed radionuclides was carried out with water, CaCl2, KCl, NH2OH−HCl, K-oxalate and H2O2 solutions, to elucidate their dominant sorption mechanisms. The distribution coefficient of237Np was two orders of magnitude smaller than that of238Pu and241Am. Most of237Np adsorbed was extracted with CaCl2 solution and its sorption was controlled by a reversible ion exchange reaction. The adsorbed238Pu was mainly extracted with NH2OH−HCl+K-oxalate solution and its sorption was possibly controlled by irreversible reactions.

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