Volume 61, Nº 5 (2019)

Np(V) acetate in glacial acetic acid and aqueous acetic acid solutions is resistant to disproportiona-tion and occurs in equilibrium with the NpO₂(Ac)·H₂O precipitate. Within the time of dehydration with excess acetic anhydride, Np(V) disproportionates. The inverse reproportionation process occurs after adding excess water to anhydrous acetic acid containing acetic anhydride, Np(IV), and Np(VI). Addition of HClO₄ causes rapid disproportionation of Np(V) in anhydrous acetic acid and in concentrated acetic acid solutions. The spectra of suspensions containing Np(V) and potassium acetate in concentrated acetic acid contain absorption bands with maxima at 990 and 1020 nm, assigned to NpO₂(Ac)₃^2- anions and K₂NpO₂(Ac)₃ particles, respectively.

The generation properties of Nd³⁺ in optical pumping of lasers on inorganic liquids based on phosphorus oxychloride and sulfuryl chloride, activated with Nd³⁺ and UO₂²⁺, were studied. In pumping with visible light with λ ≥ 500 nm, uranyl does not affect the generation properties of Nd³⁺ in laser liquids. Extension of the pumping range to 400 nm leads to deterioration of the laser properties of the liquids and to the formation of U(IV). The uranyl photoreduction in the POCl₃–SnCl₄–UO₂²⁺–Nd³⁺ system is irreversible. In the SO₂Cl₂–GaCl₃–UO₂²⁺–Nd³⁺ system, reverse oxidation of U(IV) occurs after ceasing the photoirradiation, and in ≈200 h the generation properties of the laser liquid are restored.

A model was suggested for calculating the enthalpy of adsorption or deposition temperature in thermochromatography of ultramicroamounts of substances from the thermodynamic data. In this model, the entropy of adsorption on an inert surface is assumed to be the same as in the adsorption of adsorbate molecules on the surface of a macroamount of the same substance, and the enthalpy of adsorption, calculated with this assumption, shows good and universal correlation with the enthalpy of desublimation of a macroamount of the same substance. The process accompanied by chemical reactions on the surface is also described within the framework of this approach. The experimental data on thermochromatography of Zr, Hf, W, Re, Tl, Pb, Bi (carrier-free), and other analogs of transactinide elements under various conditions are in good agreement with the calculation results. Thus, the suggested model is applicable to interpretation and prediction of the thermochromatographic data.

Innovated two-stage technique was developed for the uranium purification starting from Egyptian crude yellowcake. Preliminary purification using urea-tetrahydrofuran system allowed removal of large amounts of undesirable gangues. The second purification stage using acetate aqueous liquor/Alamine 308 solvent extraction system allowed removal of the remaining gangues from the semirefined cake. The maximum loading capacity of the organic solvent was 42 g_U L^-1 after five contacts between the two phases under the optimized conditions: 10% solvent concentration in kerosene, 5 min shaking time, aqueous feed pH 0.25, and 1 : 1 organic to aqueous ratio. Uranium stripping was done using ammonium carbonate solution. The final purified uranium peroxide cake (66.2% U) of nuclear purity, meeting the ASTM C788-03 standard, was obtained from the stripping solution after hydrogen peroxide precipitation.

The hydrodynamic properties of three promising extraction mixtures, 0.05 M solutions of 2,2′-bi-pyridine-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 trifluoromethyl phenyl sulfone (FS-13), were studied. The density, viscosity, surface tension, and settling rates in the steps of nitric acid extraction, stripping, and regeneration with sodium carbonate solutions were determined for these systems before and after the action of ionizing radiation. The concentrations of the extrac-tants in the irradiated samples were determined, and the radiation-chemical yields of their decomposition were calculated. The density and surface tension increase upon irradiation to a dose of 100 kGy but decrease upon further irradiation.

The uranium removal from radioactive liquid waste using expanded perlite (EP) was studied. The influence of the contact time, solution pH, initial uranium concentration, sorption temperature, and mass/ volume ratio on the uranium sorption was examined. The theoretical capacity of EP adsorbent is about 95 mg g⁻¹. About 90% of the loaded U(VI) can be eluted with 1 M HNO₃.

Chelating sorbents containing norsulfazole and sulfadimezine fragments were prepared by modification of maleic anhydride-styrene copolymer with amines. The conditions of the Th(IV) sorption onto these sorbents were studied. The maximal sorption was observed at pH 5. The effect of various acids on the Th(IV) desorption from the sorbents was examined. The developed procedure was applied to the Th(IV) determination in water via preconcentration.

A numerical kinetic model of leaching of aluminophosphate glass, an analog of a glass matrix for radioactive waste, in the batch mode in the presence of bentonite, taking into account the sorption processes, was constructed on the basis of the experimental data. The model describes the glass dissolution kinetics within the framework of the concept of approach to the equilibrium, taking into account shielding of the surface with glass corrosion products. The sorption is described within the framework of the ion exchange model. Modeling was performed using PhreeqC code.

The degree of radionuclide leaching from soil in the region of the Atomic Lake (Kazakhstan) was determined. The ³H and ⁹⁰Sr concentrations in aqueous extracts increase with increasing time of interaction of the soil with the leaching solution. A decrease in the ^239+240Pu transfer into the solution with time may be due to the formation of colloids in the course of leaching, followed by their deposition or sorption onto soil components. Despite relatively high initial content of γ-emitting radionuclides (¹³⁷Cs, ²⁴¹Am, ^152,154Eu, ⁶⁰Co) on the level from n × 10² to n × 10⁴ Bq kg⁻¹ in the soil, in leaching experiments the content of these radionuclides in aqueous extracts was below the detection limit of the procedure used (<1 Bq L⁻¹). The influence exerted on the leaching by the grain-size distribution of soil, pH of the medium, degree of mineralization, and chemical composition of water was determined. The tests performed suggest that the transfer of artificial radionuclides from the soil into water by leaching is one of the main mechanisms of radioactive contamination of the Atomic Lake water.

The indoor and outdoor radon and thoron and γ-exposure rates were measured in different types of houses in selected locations along coastal regions of Trivandrum and Kollam districts, Kerala, which are reported as high-background-radiation areas (HBRAs). The dose to lungs due to indoor radon, the annual effective dose due to radon and thoron, and the γ-dose rates were estimated. The average concentrations of radon and thoron are well within the action level recommended by ICRP. The average effective doses are also within the safe limit (3-10 mSv year⁻¹). The average value of excess lifetime cancer risk (ELCR) is 6.8 × 10⁻³, being higher than the world-average value of 0.29 × 10⁻³.