ИСТИНА

As a result of past activities in nuclear industry, a lot of radioactive waste and objects called “nuclear legacy sites” were created. Operation with such objects requires a vast scientific basis from nano- to macroscale. A special attention should be paid to Uranium, as the most strongly involved element in the nuclear sector. Complexity of contaminated nuclear legacy sites and low concentration of U in samples limit a set of instrumental techniques available for identification of U speciation. One of the available methods is identification of U phases by analyzing U local surrounding, determined from the analysis of the Extended X-ray Absorption Fine Structure (EXAFS) Spectra. To accurately identify U speciation in nuclear legacy sites, a huge base of model compounds is required. Aim of our work was to create the base of model systems and identify U speciation in radioactively contaminated soil from Sublimate Enterprise of FSUE “AECC””. Model systems were used to (i) determine characteristic EXAFS parameters, which could be used to identify U phases in different surroundings; (ii) to study patterns of U behaviour under various conditions and in presence of several sorbents. Model systems include: U(VI) intrinsic phases; binary systems of U sorbed on a set of clay minerals and organic sorbents under various pH and [U] conditions; ternary systems of U sorbed on Fe3+-organic nanoaggregates; multicomponent systems of U sorbed on soil of different composition. Finally, relying on interpretation of EXAFS parameters, and model systems, U speciation was determined in two fractions of radioactively contaminated soil from Sublimate Enterprise of FSUE “AECC”: fraction with particle size less than 100 µm and coal fragments from “light” fraction. Investigation of model systems show that EXAFS parameters of U sorbed on clay minerals of smectite group and organic sorbents are slightly sensitive to pH and U concentration in studied ranges. In ternary systems with Fe3+-organic matter nanoaggregates U is predominantly associated with organic matter. In systems with soil (in the presence of Fe oxides, organic matter and clay minerals) U is mainly associated with clay minerals, Fe oxides and organic matter play minor role. In radioactively contaminated soil with particle size <100 µm U is present as uranyl intrinsic phases: oxyhydroxides and carbonates. In coal fragments from “light” fraction U forms uranyl complexes with natural organic matter. Acknowledgement: Authors acknowledge Prof. Dr. K. Kvashnina and PhD E. Bazarkina for their help in XAS data collection at Rossendorf Beamline of ESRF. This work was supported by the Russian Science Foundation, grant 19-73-20051 and Interdisciplinary Scientific and Educational School of Moscow University «Future Planet and Global Environmental Change».