ИСТИНА

Uranium, as the main component of radioactive waste, is of particular interest from the point of view of behavior in the environment as a result of emergency situations or improper handling of radioactive waste in the past. Its migration ability and bioavailability directly depend on its speciation under changing environmental conditions. The study of structures formed by uranium in natural systems is often complicated by the absence of long-range order, low U concentrations, and heterogeneity of samples. The study of such systems is possible using a highly sensitive and element-selective method of analyzing the local environment of the element of interest, X-ray absorption spectroscopy (XAS). Within this approach, the interpretation of the physicochemical forms of uranium in contaminated objects is carried out on the basis of comparison of parameters of U local surrounding (within 4-5 Å) with model laboratory systems prepared under strictly controlled conditions. In the course of the work, a number of model samples of uranium in intrinsic phases that are potentially formed under environmental conditions were studied – oxohydroxide, carbonate, phosphates of U(VI), uranates. The obtained spectral data on environmentally relevant U(VI) intrinsic phases were used to determine the speciation of uranium in a sample of radioactively contaminated soil of the sublimate enterprise "Angarsk Electrolysis Chemical Plant" (Angarsk, Russia). Based on the information about the sample obtained by the methods of SEM-EDX, X-ray diffraction, X- ray fluorescence and gamma spectroscopy, assumptions were made about the U compounds formed. Verification of the initial hypothesis by analyzing the local environment showed that the clay fraction of the soil contains mainly oxohydroxide phases and uranyl-calcium carbonates.