Understanding the speciation of technogenic uranium in natural systems is crucial for estimating U migration and bioavailability and for developing remediation strategies for contaminated territories. Reference EXAFS data of model laboratory-prepared uranium compounds (`standards') are necessary to analyze U-contaminated samples from nuclear legacy sites. To minimize errors associated with measurements on different synchrotrons, it is important not only to compare data obtained on environmentally contaminated samples with the literature but also with `standards' collected at the same beamline. Before recording the EXAFS spectra, all reference compounds were thoroughly characterized by Raman spectroscopy and powder X-ray diffraction. The U(VI) local molecular environments in the reference compounds, i.e. uranyl oxyhydroxides, phosphates, carbonates and uranates, were examined using XAFS. Based on the EXAFS fitting results obtained, including the nature of the bonding, interatomic distances and coordination numbers, parameters that are typical for a particular U compound were differentiated. Using data for `standards', U speciation in the sample of radioactively contaminated soil was determined to be a mixture of U oxyhydroxide and carbonate phases.

Highly efficient extraction system for Am( iii )/Cm( iii ) separation is developed based on DAPhenCN extractant.

A quantitative understanding of the molecular-scale mechanisms of radionuclide sorption on different clay minerals is crucial for the development and safe implementation of geological nuclear waste disposal technologies. We apply classical molecular dynamics (MD) computer simulations to study the adsorption of uranyl on the external basal surfaces of two typical clay models. In the illite model, negative charge is primarily localized in the tetrahedral sheets, while in the lower-charge smectite model, the isomorphic substitutions are introduced in the octahedral sheet. The comparison of atomic density distributions at the clay surfaces and adsorption-free energies profiles as a function of distance from these surfaces demonstrates that overall U behavior at the basal clay surface is quite similar for illite and smectite. Uranyl is sorbed as a mixture of outer-sphere aqua complexes [UO₂(H₂O)₅]²⁺ and hydrolyzed aqua complexes [UO₂(H₂O)_4–5OH]⁺ on both surfaces. The structural and compositional differences between the models do not greatly affect the uranyl’s nearest coordination environment and are mainly reflected in the specific localization and orientation of the uranyl ions at both surfaces and in the magnitude of the adsorption-free energies. The observed quantitative characteristics of uranyl interactions with illite and smectite surfaces will help to better understand U behavior during the sorption process on clay minerals for the entire range of mixed-layer illite–smectite structures. A comparison of two versions of the ClayFF force field in the simulations made it possible to more accurately and quantitatively evaluate some subtle features of the uranyl–clay interactions and to obtain a more precise composition of uranyl complex with the modified ClayFF force field (ClayFF-MOH).

Super-oxidized porous carbon produced starting from spruce cone biochar showed record high U( vi ) sorption of ∼7050 μmol g ⁻¹ .

Neptunium oxidation state and coordination were studied in organic solutions. In CH₃CN, Np^V–Np^VI mixed-valence state and cation–cation interactions are preserved. In solvent extraction systems, Np^V is extracted and then oxidized in organic media.