The ability of natural and modified montmorillonite clays from Belgorod oblast to sorb Cs, Sr, U, and Pu radionuclides was studied. The clays were modified by treatment with metal (Li + , Na + , K + , Mg 2+ , Ca 2+ , Fe 2+ , Zn 2+ ) chloride solutions or aqueous HCl. The natural and modified clays studied show high performance in sorption treatment of solutions to remove Cs radionuclides. The natural clay and the Na and Mg forms of clays show the best sorption characteristics with respect to Cs. The distribution coefficient K d of 137 Cs in sorption on the above samples from a 0.1 M NaNO 3 solution is (1.1-1.4) × 10 4 cm 3 g -1 , which is 4-5 times higher compared to natural clinoptilolite. The Sr, U, and Pu radionuclides are sorbed on the examined clay samples to a considerably lesser extent. The K d values in sorption of these radionuclides from tap water are lower by 2-3 orders of magnitude than in sorption of Cs. Addition of clay materials in the course of cementation of liquid radioactive wastes, including NPP bottom residues, allows the rate of radiocesium leaching from the hardened cement compounds to be decreased by a factor of 5-16. The most efficient sorption additive in cementation of NPP bottom residues is natural montmorillonite clay.

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