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The use of ceramics as matrices for immobilization of radionuclides for the purpose of their safe long-term disposal or useful application is studied with an emphasis placed on phase stability, structural integrity, hydrolytic stability, etc. This work implements a combined approach based on the sol–gel citrate synthesis of nanosized La2Ti2O7 powder and its subsequent spark plasma sintering to produce dense ceramics. The phase composition and structure of the nanosized La2Ti2O7 powder and the ceramic samples obtained in the temperature range of 900–1300°C were studied by powder X-ray diffraction and SEM. It was shown that the conditions of synthesis of the powder ensure the formation of nanosized crystalline La2Ti2O7 grains, consolidation of which under spark plasma heating is accompanied by a change in the phase composition of La2Ti2O7 from a single-phase monoclinic structure to orthorhombic structure with a LaTiO3 impurity at temperatures above 1200°C. It was found that a change in the ceramic structure is accompanied by the formation of non-porous and defect-free monolithic samples. This type of change was shown to lead to an increase in the relative density (81.3–95.7%) and compressive strength (78–566 MPa) of the ceramics. However, the hydrolytic stability decreases, as indicated by increasing La3+ leaching rate from 10–7 to 10–5 g/(cm2 day). The obtained results are useful for the systematic study of materials suitable for immobilization of radioactive waste in ceramics. [ABSTRACT FROM AUTHOR]

Composite sorbents based on Fe3O4 and Zn-Al-LDH with different weight ratios of magnetic and sorbing phases were obtained by the precipitation method. The optimal weight ratio of Zn/Fe was 16, which resulted in a 62% increase in hydromechanical strength. The maximum sorption exchange capacity towards U(VI) was 268.65 ± 22.22 mg/g. The efficiency of U(VI) adsorption was not affected by the presence of Cl−, SO42−, NO3− and Na+, Ca2+. The distribution coefficient in a groundwater model solution was Kd(U(VI) = 0.5–3 × 105 mL/g. The materials possess high exchange capacity and selectivity, which makes them suitable sorbents for U(VI) removal. [ABSTRACT FROM AUTHOR]

The water pollution with Cs+ and Sr2+ radionuclides in the nuclear fuel cycle is a pressing environmental problem. The selective adsorption of radionuclides onto inorganic sorbents of zeolite structure, exhibiting the ion-sieve effect, is a promising procedure for the treatment of the liquid radioactive waste formed. Titanosilicate of the CST structural type, corresponding to the formula Na1.64H0.36Ti2O3SiO4(H2O)1.84, was prepared by hydrothermal synthesis performed at 190°С and a pressure of 1.3 MPa for 24 h. This sorbent allows efficient removal of the Cs+ and Sr2+ cations from liquid media. The sorption exchange capacity qeq is 1.58 mg-equiv/g for Cs+ and 2.56 mg-equiv/g for Sr2+. Preliminary oxidation of Ti3+ to Ti4+ with H2O2 increases the sorption capacity for Cs+ and Sr2+. The phase composition, elemental composition, specific surface area, and pore size of the materials synthesized were determined. The titanosilicates obtained can be used as sorbents for liquid radioactive waste treatment. [ABSTRACT FROM AUTHOR]