Том 60, № 6 (2018)

Experimental data on the kinetics of reactions of lanthanide and actinide ions with ОН radicals, e_aq^–, each other, and d element ions are analyzed. The reactions with ОН radicals are kinetically controlled, with the rate constants being independent of the redox potential of the ion. This is due to the fact that the ОН radical abstracts the H atom from Н₂О in the hydration shell, which is followed by the charge transfer. The An⁴⁺ ions are oxidized with the formation of the An⁵⁺ ions, followed by their hydrolysis. The hydrated electrons e_aq^– react with f element ions whose potential is less negative than–2.0 V, with the reaction being diffusion-controlled. The reactions of e_aq^– with An⁴⁺ and AnO₂²⁺ occur by the tunneling mechanism. The reactions of the ions with each other are kinetically controlled, with the rate constants depending on ΔЕ of the reaction. The correlation is broken in the case of formation of AnO₂⁺–An⁴⁺ cation–cation complexes or of reactions involving the structure rearrangement. The stability of heptavalent ions in an alkaline solution decreases with an increase in the oxidation potential and with a decrease in the ion charge.

The kinetics of the Np(VI) reduction with diformylhydrazine in a nitric acid solution was studied by spectrophotometry. The reaction rate increases with an increase in the reductant concentration and temperature and decreases with an increase in the HNO₃ concentration. The reaction order with respect to Np, diformylhydrazine, and HNO₃ is 1, 1.3, and–1.55, respectively. The activation energy of the reaction is 85 ± 10 kJ mol^–1.

The dynamics of gas evolution in thermal oxidation of solutions of 2,2'-bipyridine-6,6'-dicarboxylic acid di(N-ethyl-4-hexylanilide) (DYP-7), 2,6-pyridinedicarboxylic acid di(N-ethyl-4-fluoroanilide) [Et(pFPh)· DPA], and 2,2'-bipyridine-6,6'-dicarboxylic acid di(N-ethyl-4-ethylanilide) (DYP-9) in m-nitrobenzotrifluoride (F-3) diluent with 14 M HNO3 in open and closed vessels was studied. The effect of preliminary irradiation of the organic phase on the kinetics of thermolysis of the two-phase system was determined. Heating of the irradiated samples in a closed vessel (autoclave) leads to the pressure buildup, with the pressure reached increasing from 18 to 23 atm as the absorbed dose is increased from 0 to 1 MGy. The exothermic processes occurring in the systems caused a 4 to 10°С increase in the sample temperature. The thermal stability of all the irradiated diamide–F-3 diluent extraction systems studied is acceptable for practical use.

The extraction of REE(III), U(VI), and Th(IV) from nitric acid solutions with solutions of carbamoylmethylphosphine oxides (CMPOs) considerably increases in the presence of dinonylnaphthalenesulfonic acid. The stoichiometry of the extractable complexes was determined, and the influence of the aqueous phase composition, kind of organic diluent, and CMPO structure on the efficiency of the extraction of the metal ions was analyzed.

New nanostructured mesoporous materials of the composition TiO₂/ZrO₂/SiO₂ were prepared by the template sol–gel method using a siloxane–acrylate emulsion as a template. The morphology and structure of these materials and their ability to take up U(VI) were studied. The influence of various factors (ZrO₂ content, pH of solution) on the sorption properties was studied. The suggested materials allow efficient sorption of U(VI) from sulfate solutions with low U(VI) concentrations and can be used in final purification processes.

The possibility of labeling Cellex® with ¹²³I was examined. Labeling was performed by oxidative iodination in the presence of Chloramine-T and Iodogen. The optimum labeling conditions were found. The target product with the radiochemical purity higher than 95% was isolated from the reaction mixture by column gel chromatography. The label distribution between constituent proteins of different molecular masses was determined by gel electrophoresis.

Uranium-containing samples of magnesium potassium phosphate (MPP) compound were synthesized using a nitric acid uranium solution. Uranium is incorporated in the MPP compound in the form of potassium uranyl phosphate with the structure of metaankoleite natural mineral, K(UO₂)PO₄·3H₂O. The differential and integral uranium leach rates, determined in accordance with GOST (State Standard) R 52 126–2003 on the 28th day of contact of the compound with water, are 1.7 × 10^–6 and 2.7 × 10^–6 g cm^–2 day^–1, respectively, and the degree of leaching is 0.014%. High hydrolytic durability of the compound with respect to uranium leaching reduces the risk of release of uranium isotopes from radioactive waste into the environment.

Graphite samples from blocks and sleeves are characterized by extremely heterogeneous spatial distribution of radionuclides on the scale of tens and hundreds of micrometers. The graphite decontamination occurs in three steps: Up to 25% of ¹⁴C is removed in the course of low-temperature annealing or treatment of graphite with liquid reagents (total weight loss of graphite ≤10%); up to 70–80% of ¹⁴C is removed in the course of 20-h heat treatment under oxidizing conditions; and in the final step the degree of removal of ¹⁴C exceeds 90%, with a proportional decrease in the graphite weight. Oxidation of graphite in the first steps of thermochemical treatment mainly occurs along (micro)cracks and other defects, which favors the removal of relatively weakly bound ¹⁴C, e.g., from the pore space. The removal of ¹⁴C from the crystal lattice of graphite requires its breakdown, e.g., by high-temperature heat treatment.

Speciation of natural thorium isotopes (²²⁸Th, ²³⁰Th, ²³²Th) in water, bottom sediments, and soils in the region of the former plant for radium extraction from highly mineralized stratal waters was studied. The isotope ratio in water and bottom sediments corresponded to the natural mixture, whereas in contaminated podzolic and alluvial-soddy soils with the mean thorium content of 26.0 and 2.74 μg g^–1 the enrichment in ²³⁰Th was observed. At the hydrochemical background of 0.06 μg L^–1 for waters of the river and industrial sites, the Th concentration varied from 0.02 to 0.73 μg L^–1 and correlated with the content of the organic matter dissolved in water and of iron ions. Thorium was present both in the solution and in the suspended material. Its relative content in the suspended material (0.45–3.5 μm) reached 50%, which is lower than the background level for the river. In bottom sediments and soils, Th mainly occurred in the insoluble residue. Its fraction linearly increased with an increase in the total thorium content of the soils. The relative content of Th in fractions of Fe and Mn oxides and hydroxides, amorphous silicates, and especially organic matter was higher than in other mobile fractions. This trend was more pronounced for podzolic soil than for alluvial-soddy soil.