Том 60, № 3 (2018)

Mixed-cation salts of the composition NaM₂[PuO₄(OH)₂]·4H₂O, where M = Rb (I) and Cs (III), and NaRb₅[PuO₄(OH)₂]₂·6H₂O (II) were synthesized and structurally characterized. The central Pu atom in [PuO₄(OH)₂]^3– anions has oxygen surrounding in the form of a tetragonal bipyramid with oxygen atoms of hydroxide ions in apical positions. The hydrated Na⁺ cations have oxygen surrounding in the form of a distorted octahedron. In the structure of I, there are two independent Rb⁺ cations with 10- and 12-vertex coordination polyhedra (CPs), and in the structure of II, three independent Rb⁺ cations with the 12-, 11-, and 13-vertex CPs. In the structure of III, the Cs⁺ cation has a 12-vertex CP. Frameworks of large Rb⁺ or Cs⁺ cations can be distinguished in the structure. The CPs of the Pu and Na atoms (I, III) sharing a common edge or the isolated CPs of the Pu and Na atoms (II) are incorporated in these frameworks. Hydrogen bonds influence the crystal packing and the geometric characteristics of the [PuO₄(OH)₂]^3– anions.

The extraction of microamounts of U(VI), Th(IV), and REE(III) from HNO₃ solutions in the form of complexes with 2,6-bis(diphenylphosphorylmethyl)pyridine N-oxide (I) was studied in relation to the kind of organic diluent and to the HNO₃ concentration in the equilibrium aqueous phase. The stoichiometry of the extractable complexes was determined. With respect to the ability to extract Th(IV) and REE(III), compound I considerably surpasses tetraphenylmethylenediphosphine dioxide and tetraalkyl-substituted analogs of I.

kinetic model of the mass transfer of a microcomponent in the simplest competitive system from the sorbed state (A) into a solution (B) and then into a sorbent (C) in accordance with the scheme A ⇄ B ⇄ C was formulated within the framework of competitive sorption statics. The kinetic equations were solved numerically. The influence exerted by the weight of competing sorbents А and С and by the degree of reversibility of linear reactions on the nonequilibrium decontamination factor K_dec(t) was determined. The time in which the equilibrium decontamination factor is attained for the model of chemical sorption kinetics was estimated from the experimental data on the rate constants of direct and reverse heterogeneous reactions and on the distribution coefficients of Cs(I) in the SiO₂ (A)–CsCl solution (B)–Prussian Blue (C) system.

Samples of cerium(IV) tungstate (CeW) inorganic ion exchanger were synthesized using different Ce(IV) salts: (NH₄)₂Ce(NO₃)₆·2H₂O, (NH₄)₄Ce(SO₄)₄·2H₂O, and Ce(SO₄)₂·4H₂O. The samples were characterized using FT-IR and X-ray diffraction. The adsorption behavior of ^152+154Eu(III) and ⁶⁰Co(II) on CeW was studied under batch and dynamic conditions. Factors influencing the adsorption kinetics were examined. Loading and elution behavior of both ions was studied using different eluents. Complete separation of Eu(III) and Co(II) (^152+154Eu and ⁶⁰Co tracers) was achieved using small columns packed with CeW.

Thermal degradation of VP-1AP anion-exchange resin in the nitrate form was studied by DSC–TG. The degradation occurs in steps and is accompanied by exothermic effects in the temperature ranges 170–190, 200–280, 280–390, and 400–550°С. The first two exothermic peaks are associated with thermal degradation of the sorbent, and all the other peaks, with oxidation of the matrix with atmospheric oxygen. The kinetic parameters of separate steps were determined. A mathematical model of degradation of VP-1AP anion-exchange resin in the nitrate form was developed. It can be applied to evaluation of the safety in handling this form of the sorbent. Principal possibility of constructing a kinetic model of degradation of ion-exchange materials on the basis of the results of DSC–TG experiments performed with milligram amounts of samples, applicable to simulation of enlarged installations, was demonstrated. An experimental cell suitable for ion-exchange materials was developed for validation of the degradation kinetic models constructed on the basis of the DSC data. The thermal explosion of VP-1AP in the nitrate form in the experimental cell is observed at a thermostat temperature of 245°С, but is not observed up to 230°С. The calculated critical temperature of thermal explosion of VP-1AP anion-exchange resin in the nitrate form under the experimental conditions is in the interval 237–242°С.

A procedure was developed for complex analysis of γ-emitting nuclides and ⁹⁰Sr in natural and wastewaters with two methods of preparation of counting samples for ⁹⁰Sr activity measurement: coprecipitation of ⁹⁰Sr with strontium sulfate and coprecipitation of ⁹⁰Y with yttrium hydroxide. Strontium-90 is concentrated on KU-2-8chs strongly acidic sulfonic cation-exchange resin in the Н+ form after removing γ-emitting radionuclides on complex selective sorbents, which are simultaneously counting samples for measuring the activity of γ-emitting nuclides. The main steps of the sorption procedure for the complex analysis are described, and the choice of the method for preparing a counting sample based on ⁹⁰Y for current radioecological monitoring is substantiated.

Timonacic acid (TCA) was labeled with ^99mTc in the presence of three different reducing agents: NaBH₄, Na₂S₂O₄, and SnCl₂·2H₂O. The optimum conditions were as follows: with Na₂S₂O₄, pH 8, 7 mg of Na₂S₂O₄, room temperature, 2 mg of TCA, 30 min (radiochemical yield 98 ± 0.3%, complex was stable for 24 h); with NaBH₄, pH 8, 10 mg of NaBH₄, room temperature, 2 mg of TCA, 30 min (radiochemical yield 95 ± 0.3%, complex was stable for 6 h). The biodistribution of the complex in mice was studied. The liver uptake depends on the reducing agent used, reaching in 30 min 33.5 ± 0.3, 18.4 ± 0.18, and 22.3 ± 0.3% ID/g for the complexes prepared using Na₂S₂O₄, NaBH₄, and SnCl₂·2H₂O, respectively.

A new type of a promising glassy-crystalline host material was prepared by ultradisperse synthesis in model experiments. The starting product is the nitric acid fraction of fission products (Cs, Sr, Ba), obtained radiochemically from irradiated nuclear fuel of a WWER-1000 reactor (1000-MW_el water-cooled water-moderated energy reactor). Equivalent amounts of La(NO₃)₃, H₃PO₄, and Fe₂O₃ are added, and water is removed on heating. After complete removal of moisture, the residue is calcined at 600°С. The phosphated calcinate is dispersed in acetone to obtain slurry and, after removing acetone, converted to the glassy form at 950°С by self-igniting high-temperature synthesis. The whole process of preparing the composite is performed in one container crucible, which is then sealed. The major constituent of the host material is iron (pyro)phosphate glass (~55%); the finely grained crystalline phase, according to X-ray diffraction data, consists mainly of monazite of the composition La₂(Sr,Ba)₃(PO₄)₄. The monazite content is about 40%. Monazite forms with the glass via covalent bonding a composite exhibiting high corrosion resistance. The steady-state rate of Cs leaching form the monazite glass is 0.1 μg cm^–2 day^–1 (90°С, 100 days).