Uranium Species in Peat and Rock Sediments Near Sludge Storage Facility

The study aims to investigate uranium species in the sediments of the natural-technogenic system within a sludge storage facility in Russia. The relevance of this work is underscored by the need to assess the geochemical mobility of radionuclides, a critical factor for predicting their migration and environmental impact. The objective of the research was to determine the uranium species in both peat and sedimentary rock samples of the sludge storage facility and the adjacent area. Laboratory analyses included XRD, XRF analysis using synchrotron radiation, and scanning electron microscopy to study the composition and properties of minerals. The uranium species were further identified using a modified Tessier sequential extraction method. The results revealed that uranium predominantly occurs in a stable silicate-bound form (up to 80%) in sedimentary rocks, indicating minimal geochemical mobility. In contrast, in peat deposits, uranium is primarily associated with manganese and iron oxides (30–60%) as well as organic matter (5–40%), with the most mobile forms constituting less than 5%. The decrease in uranium concentration with distance from the facility was attributed to sorption onto organic matter and co-precipitation with mineral compounds, manganese and iron oxides, which serve as effective natural sorbents. The findings highlight the critical role of organic matter and metal oxides in limiting uranium migration, thus identifying them as key components in the formation of natural barriers for radionuclides. These results are crucial for assessing environmental risks associated with radioactive waste management and for developing strategies to minimize the ecological impact of sludge storages.