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Guerinoni, E.*; 上田 祐生; 元川 竜平; Zemb, T.*; Pellet-Rostaing, S.*; Dourdain, S.*
Langmuir, 42(12), p.8313 - 8321, 2026/03
被引用回数：1 パーセンタイル：70.31(Chemistry, Multidisciplinary)Third phase formation in liquid-liquid extraction poses operational challenges by inducing organic phase separation, limiting extraction efficiency and process safety. Here, we employ combined ultra-small-angle X-ray (USAXS) and neutron scattering (USANS) to elucidate pre-transitional structures occurring during uranium extraction by tri-octylamine (TOA) in octane as diluent. SAXS highlights uranium-filled aggregates, while SANS captures all aggregates, regardless of uranium content. Extending the q-range from 0.004 to 3 
reveals two distinct populations: small spherical reverse micelle-like aggregates (radius 11 AA) and larger fluctuating domains exceeding 150 nm, consistent with Ornstein-Zernike critical fluctuations. Increasing TOA concentration amplifies these superstructures until divergence, the formation of a third phase. This study demonstrates that phase instability originates from the hierarchical condensation of water-filled aggregates around uranium-filled aggregates, rather than from simple micelle growth. Predicting such instability therefore requires accounting for the complete distribution of species, including water. The U-U distance in neighboring aggregate forming a supercluster is evidenced without ambiguity. Understanding such multiscale pre-transitional phenomena offers new routes to predict and mitigate phase separation in solvent extraction processes critical for nuclear fuel recycling.
Guerinoni, E.*; Zemb, T.*; 元川 竜平; 上田 祐生; 青柳 登; Pellet-Rostaing, S.*; Dourdain, S.*
Journal of Physical Chemistry B, 129(32), p.8210 - 8217, 2025/08
被引用回数：3 パーセンタイル：49.24(Biophysics)Liquid-liquid extraction of uranium involves an acidic aqueous phase in contact with an oil phase containing aliphatic amines and a linear alkane. Excess electrolyte in the oil phase leads to a third phase, hindering metal ion extraction and stripping. We determine the largest admissible extractant concentration (LOC) before macroscopic phase separation. Using small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS), we analyze the microstructure of the phases. In all aliphatic diluents, the third phase consists of weak water-in-oil (w/o) aggregates with interdigitated hydrocarbon chains. Even after centrifugation, SANS detects residual deuterated solvent molecules. A fraction of these w/o aggregates contains uranium(VI) cations (U-loaded aggregates), which exhibit stronger attractive interactions than unloaded aggregates. This leads to the segregation of U-loaded aggregates into large clusters, detected as a Porod-type decay in SAXSbut absent in SANS at a low q-values.
Guerinoni, E.*; Giusti, F.*; Dourdain, S.*; Dufr
che, J.-F.*; 元川 竜平; 上田 祐生; 青柳 登; Zemb, T.*; Pellet-Rostaing, S.*
Journal of Molecular Liquids, 403, p.124820_1 - 124820_11, 2024/06
被引用回数：8 パーセンタイル：73.74(Chemistry, Physical)In uranium production, liquid-liquid extraction using the AMEX (AMine EXtraction) process employs tertiary amines solubilized in an aliphatic diluent. Practical constraints as phase stability problems and co-extraction of competitive elements highlight the need for in-depth investigation and optimization. Modifying gradually the alkyl chain structure of tertiary amines, we investigate here the large variation in extraction performance in terms of Gibbs free energy of transfer using the ienaic decomposition taking into account long range interactions. We show hereby that structuration of the solvent phase can change uranium distribution by 2 orders of magnitude, which is incompatible with standard complexation theory of liquid-liquid extraction. We observe that co-extracted water is required to obtain extraction while extraction is quenched and no pair core can be formed when less than four as effective aggregation number. We conclude that the film term in the ienaic decomposition of the Gibbs energy of transfer, is the one that governs extraction performance. It shows that metal transfer is beyond complexation, and that organization of the solvent phase must be considered to quantitatively interpret the distribution coefficients.
元川 竜平; 上田 祐生; Micheau, C.; Bourgeois, D.*; Dourdain, S.*; Diat, O.*
no journal, ,
Neutron scattering is a useful complement to X-ray scattering each other in the study of material structures, mainly because the neutron cross-section varies randomly among elements, whereas the X-ray atomic scattering factor increases with atomic number. The large difference in the scattering cross-section between hydrogen and deuterium is crucial in the use of neutron scattering to analyze the microscopic structure of various materials, so that the difference enables us to observe only the structures formed by one specific component among scatterers composed of other multiple components. Recently, we have developed small-angle neutron scattering diffractometer (SANS-J), at JRR-3 of the Japan Atomic Energy Agency, Japan, and the various kinds of studies in chemical separation systems, such as biphasic solvent extraction, flotation process, and solids-liquid separation using adsorbent materials, which are well related to the nuclear process, have been conducted in the place. Here we will present our small-angle scattering diffractometer, SANS-J, which is a typical apparatus installed at the research reactor for neutron scattering, as well as some representative results obtained. We discuss the collaborative research with French institutions not limited to solvent extraction systems.
