[en] The TALSPEAK Process, as developed by Weaver and Kappelmann at Oak Ridge National Laboratory in the 1960's, is a well established approach to accomplishing the difficult task of separating trivalent actinides from lanthanides. This separation is essential for fuel cycles that incorporate actinide transmutation, as several lanthanides compete strongly for neutrons needed for actinide transmutation. Under ideal conditions conventional TALSPEAK (0.5-1.0 M HDEHP, 0.05-0.1 M DTPA, 0.5-2.0 M lactate buffer operating at pH 3.5) achieves a very respectable lanthanide/actinide group separation factor of 100. Conventional TALSPEAK has not yet found application at production scale because the process exhibits, 1) a surprisingly steep (unexpected and undesirable) pH dependence, and 2) complex (and comparatively slow) phase transfer kinetics. The slow phase transfer kinetics is partially overcome by operating from lactate buffers of unusually high concentration, but recent studies indicate that high lactate concentrations amplify the pH dependence issues. As a result of this increased understanding, TALSPEAK research has evolved toward the consideration of alternative extractants (or extractant mixtures), actinide holdback reagents, and buffers. In this report, selected features of investigations into the Advanced TALSPEAK process (featuring a weaker phosphonic acid extractant matched to weaker complexants and less concentrated buffer solutions than Conventional TALSPEAK), new di-picolinate-based holdback reagents (as alternatives to DTPA), and a combined-process concept (TALSPEAK-MME - Mixed Monofunctional Extractants) are discussed. (authors)
Source
Societe Francaise d'Energie Nucleaire - SFEN, 103 rue Reaumur, 75002 Paris (France); 2455 p; ISBN 978-1-4951-6286-2; 
; 2015; p. 1677-1683; GLOBAL 2015: Nuclear fuel cycle for a low-carbon future; Paris (France); 21-24 Sep 2015; Available (USB stick) from: SFEN, 103 rue Reaumur, 75002 Paris (France); 27 refs.
; 2015; p. 1677-1683; GLOBAL 2015: Nuclear fuel cycle for a low-carbon future; Paris (France); 21-24 Sep 2015; Available (USB stick) from: SFEN, 103 rue Reaumur, 75002 Paris (France); 27 refs.
[en] Knowledge of the supramolecular structure of the organic phase containing amphiphilic ligand molecules is mandatory for full comprehension of ionic separation during solvent extraction. Existing structural models are based on simple geometric aggregates, but no consensus exists on the interaction potentials. Herein, we show that molecular dynamics crossed with scattering techniques offers key insight into the complex fluid involving weak interactions without any long range ordering. Two systems containing mono- or diamide extractants in heptane and contacted with an aqueous phase were selected as examples to demonstrate the advantages of coupling the two approaches for furthering fundamental studies on solvent extraction. (authors)
Journal
Angewandte Chemie (International Edition); ISSN 1433-7851; ; v. 53; p. 5346-5350
; v. 53; p. 5346-5350
[en] Fourier transformed infrared microreflectance spectroscopy is used to probe and compare the consequences of thermal quenching or ionic implantation on the structure of silica. A linear change in the main structural feature associated with Si-O-Si vibration with fictive temperature (Tf) is observed up to Tf=1400 deg. C. Ionic implantation is shown to shift the frequency of the main IR Si-O-Si vibration toward much lower wavenumbers, for all deposited energies, indicating that a comparison can be drawn between fictive temperature and irradiation effects. Extrapolating the linear changes in the IR structural bands obtained as a function of Tf for the implanted samples, we show that two structural (νTO) and (νB) contributions are not affected by ionic implantation, as they would be by a unique very high Tf. In the case of ionic implantation, we also evidence the development of some specific structural contributions indicating a depolymerization of silica network.
Journal
[en] The amounts of extracted water, nitric acid and uranyl nitrate by organic phases of 0.5 mol.L-1 N,N-di(ethylhexyl) isobutyramide (DEHiBA) in heptane have been measured experimentally. With the aim of investigating the influence of the solutes on the aggregation in these organic phases, Vapor Pressure Osmometry (VPO) and Small Angle X-rays Scattering (SAXS) measurements were carried out. The extraction of the different solutes promotes the aggregation in the order water ≤ nitric acid ≤ uranyl nitrate. Water extraction according to water activity seems to indicate the absence of chemical association between water and DEHiBA. The presence of nitric acid leads to the formation of small aggregates while uranyl extraction increases the organization of the organic solutions. This study is the first step to understand and quantify aggregation phenomenon in monoamide organic phases after solute extraction, which could explain the particular physical chemical behavior of such systems. (authors)
Journal
Procedia Chemistry; ISSN 1876-6196; ; v. 7; p. 27-32
; v. 7; p. 27-32
[en] This paper presents the methodology developed in order to thoroughly characterise a solvent extraction system containing high solute concentrations. The chemical system selected is N,N-(2-ethylhexyl)isobutyramide (DEHiBA) diluted in one alkane with increasing concentration of uranium(VI). Combining experiments with theoretical calculations allowed a deeper understanding of the extraction mechanism. A thermodynamic study was performed by the classical Van't Hoff method and also by direct calorimetry to provide the enthalpies of extraction and specific heats. Dedicated methods like vapour pressure osmometry and electro-spray ionisation mass spectrometry analysis provide information about the stoichiometry of the extracted species. Spectroscopic investigations with ultraviolet-visible and Fourier transform infrared probed the uranium coordination. Finally, a combination of molecular dynamics simulations, and small and wide-angle X-ray scattering experiments investigated the organisation in the organic phase beyond the molecular scale. It was shown that the high concentrations of uranium extracted have no influence on the stoichiometry of the complexes and the coordination of uranium in the inner sphere. The thermodynamic properties related to the extraction process and obtained with a fine consideration of the activity coefficients showed to be the same as those found with trace concentration. However, an unexpected organisation beyond the molecular scale was observed with an important role of nitrates as bridging ligands which could explain some physico-chemical properties. This approach could be applied to other chemical systems (other N,N-dialkyl-amides or other cations) to identify the origin of the different affinities between ligands and the difference of selectivity between cations. (authors)
Journal
Molecular Physics; ISSN 0026-8976; ; v. 112(nos9-10); p. 1362-1374
; v. 112(nos9-10); p. 1362-1374