S. N. Kalmykov

Interaction of neptunyl with goethite (α-FeOOH), maghemite (γ-Fe2O3), and hematite (α-Fe2O3) in water as probed by X-ray photoelectron spectroscopy

The sorption behavior is studied and the physicochemical neptunium species existing on the surface of goethite (α-FeOOH), maghemite (γ-Fe2O3), and hematite (α-Fe2O3) are determined. Solvent extraction and X-ray photoelectron spectroscopy (XPS) are used to determine the neptunium surface species. The ion and elemental composition of the surface of the minerals and surface neptunyl NpO2+ complexes is determined using these data. Compounds containing neptunium(IV) or neptunium(VI) ions do not appear; rather, neptunyl (Np(V)O2+ group is complexed with surface hydroxide groups of α-FeOOH, γ-Fe2O3, and α-Fe2O3. Presumably, the oxygen atoms of iron oxides and water and/or carbonate (CO32-) or nitrate (NO3-) group lie in the equatorial plane of the neptunyl (NpO2+) group.

Extraction chromatographic behavior of actinium and REE on DGA, Ln and TRU resins in nitric acid solutions

The extraction-chromatographic behavior of actinium, rare earth elements and other radionuclides formed upon the irradiation of thorium by medium energy protons was studied. The k′ values for Ac(III), Ce(III) and La(III) in nitric acid solutions using Ln Resin, DGA Resin and TRU Resin (Triskem Int.) were determined. The optimal conditions for separation of Ac(III) and rare earth elements (REE(III)) were defined. The obtained results can be used to develop the multipurpose analytical procedure for actinium separation either for the needs of nuclear medicine or for radiochemical analysis of environmental samples.

Speciation of radionuclides in colloidal matter of underground waters taken from observation wells in the zone of impact of Lake Karachai

Associations of radionuclides with colloidal particles of various sizes, isolated from underground waters of the Lake Karachai contamination area, were studied. Analysis by photon correlation spectroscopy showed that the total content of colloidal matter in deeper horizons is higher by an order of magnitude than in near-surface horizons. The mean particle radius also increases with the depth. The major fraction of Pu, Am, and Cm is associated with colloids (40–90%). U and Np are associated with colloidal particles to a lesser extent (2–20%), which determines their higher migration mobility in underground waters. The amount of actinides associated with coarse colloidal particles of size from 450 to 200 nm is insignificant. A considerable fraction of actinides is in the deep-lying water (depth ≥40 m) is associated with colloidal particles of size from 200 to 50 nm. No more than 30% of Pu and Am in water of these horizons is associated with finer colloids (from 10 kDa to 50 nm). With approaching the surface, the amount of actinides in the fraction of nanometer-sized particles (50 nm-10 kDa) increases (to 50%).

Sorption of protactinium(V) on extraction chromatographic resins from nitric and hydrochloric solutions

Retention of Pa(V) on the extraction chromatographic resins (DGA, TRU, TEVA, UTEVA and octanol resin) produced by Triskem International Company has been studied. The capacity factor k′ values of Pa(V) were determined in static experiments (batch technique) for a wide concentration range of nitric and hydrochloric acid solutions. The obtained data are useful to devise chromatographic separation of Pa(V) from other actinides.

Effect of corrosion products on the Pu partitioning in rocks of reservoir horizon upon interaction with acidic solutions under hydrothermal conditions

Plutonium sorption on various types of sands of reservoir horizon depends on the presence of corrosion products in solutions simulating highly saline acidic (pH 2.4) liquid radioactive waste (LRW) under hydrothermal conditions (T = 150°C, 50 h). The effect of corrosion products (Fe, Cr) present in LRW consists not only in considerably increased Pu sorption, but also in increased fraction of its strongly fixed fraction. α-Track radiography revealed essentially heterogeneous distribution of Pu between mineral phases of sands of reservoir horizon after interaction with simulated LRW and predominant association of Pu with separate phases containing Fe and Cr (data of X-ray microanalysis based on scanning electron microscopy, SEM-EDX). Examination by Raman spectroscopy and X-ray diffraction analysis showed that the phases responsible for the predominant sorption of Pu are phases of Cr-containing hematite.

Interaction of Sr(II) and Np(V) with potassium ferrate(VI) reduction products in aqueous solution

The interaction of Sr(II) and Np(V) with potassium ferrate(VI) reduction products in aqueous solution at pH 4–8 was studied by liquid scintillation spectrometry. The ferrihydrite precipitate formed by reduction of ferrate ions quantitatively sorbs Sr(II) and Np(V) from 0.1 M NaClO4. The precipitate particle size determined by scanning electron microscopy is in the nanometer range. The degree of recovery of the radionuclides from simulated liquid radioactive wastes containing such complexing agents as acetate, citrate, and nitrate ions is 70 ± 5 and 84 ± 2%, respectively.

Humic Acids as Barriers in Actinide Migration in the Environment

Humic acids (HAs) and fulvic acids (FAs) are the main components of natural waters that can influence the migration ability of cations. They form stable complex compounds with actinide elements that can change their solubility. In addition, HAs could be responsible for migration of colloidal species. The role of HAs in formation of geochemical barriers in actinide migration in the geosphere is discussed on the basis of results of laboratory experiments and speciation of plutonium and neptunium in field samples collected from the regions contaminated by human-made radionuclides.

Interaction of plutonium with iron- and chromium-containing precipitates under the conditions of reservoir bed for liquid radioactive waste

The behavior of Pu under the conditions of liquid radioactive waste (LRW) disposal in a reservoir bed was studied. The pH dependence of the Pu sorption is the same in the cases when the radionuclide is introduced together with the simulated LRW solution or after the precipitate formation. The composition and morphology of Fe,Cr-containing precipitates formed under the conditions simulating the radioactive waste disposal were determined. The solid phase was characterized by X-ray diffraction analysis and by transmission and scanning electron microscopy. The phase composition of the precipitates was determined in relation to the presence of acetate ions, Fe concentration in the solution, and storage time and temperature. The main phases formed are ferrihydrite, goethite, hematite, and grimaldiite.

Extraction of radionuclides from natural waters using alginates

Fourteen samples of wastes from algal plants were tested for possible analytical and/or technological use for90Sr and137Cs extraction from natural waters. Sorption experiments were carried out in static and dynanic conditions. It was noted that the examined sorbents posses high affinity for Sr2+. The sorption capacity reached the value of 4.72·10−3 mole/g. Simple and express analytical procedures for90Sr determination were developed and tested in the Dnieper estuary region.

Behavior of U(VI) under the Conditions of a Reservoir Bed for Liquid Radioactive Waste

The behavior of U(VI) under the conditions of liquid radioactive waste (LRW) disposal in a reservoir bed was studied. Model experiments were performed to determine the radionuclide binding mechanism and the role of hydrolysis products of LRW cations and of sands from the reservoir bed. The U(VI) binding with the reservoir bed rocks depends on pH of the solution. The U(VI) binding with the solid phase under the conditions of LRW reservoir bed is determined by sorption reactions with components of the surrounding rocks. The kinetic of uranium leaching occurring with a decrease in pH of the solution was studied.