Sorption behaviour of neptunium in marine and fresh water bottom sediments in Far East area of Russia (Lake Khanka and Amur Bay).

The concentration and sorption behavior of 237Np on the bottom sediments of water bodies in the Far East region of Russia (Lake Khanka and Peter the Great Bay) were studied for the first time. The 237Np concentrations vary from 1.06 × 10-6 to 4.43 × 10-5 mBq g-1 in the bottom sediments of Lake Khanka and from 1.05 × 10-4 to 2.52 × 10-3 mBq g-1 for Amur Bay. The experiment on the adsorption of Np on marine and lake sediment showed that it is sorbed through complexation with silicates (albite, leucite). The Np sorption isotherm on marine sediments is described by the Langmuir equation; the distribution coefficients (Kd) of Np vary from 57 to 588 mL g-1. For lake sediments, the isotherm is described by the Henry equation; the Kd value reaches 935 mL g-1.

Effect of the type of N-substituent in the benzo-18-azacrown-6 compound on copper(II) chelation: complexation, radiolabeling, stability in vitro, and biodistribution in vivo.

In this work, we synthesized two new benzo-18-azacrown-6 ethers bearing picolinate and pyridine pendant arms and studied the copper complexes of these ligands, as well as those of an acetate analog. All considered ligands were capable of forming mono- and dinuclear complexes due to their large size and large number of donor sites. Among all forms of complexes, the coordination of cations inside the macrocycle has only been shown for the mononuclear form of the acetate complex, while out-cage coordination has been observed for other forms. Electrochemical studies have shown the instability of the mononuclear form of the complex with the pyridine ligand to the reduction in the range of redox potentials of bioreductants. The stabilities of labeled acetate complexes with "in-cage" coordination of the cation and picolinate with "out-cage" coordination were compared in an excess of serum and superoxide dismutase; while the former turned out to be unstable to transchelation, the latter was stable throughout the experiment. Additional studies in biologically relevant media were performed for the picolinate complex and demonstrated its stability in vitro. The biodistribution of this complex in mice after 6 hours post-injection demonstrates a slow excretion from the body; however, the accumulation is noticeably lower than that of free copper cations.

Photonuclear production of medical radioisotopes 161Tb and 155Tb.

The production possibility of 161Tb and 155Tb by irradiating of natural dysprosium with gamma rays obtained by decelerating an electron beam with an energy of 55 MeV has been demonstrated experimentally. The yield of 161Tb was 14.4 × 103 Bq × µA-1 × h-1 × cm2 × gDy2O3-1. Simultaneously, upon irradiation, 155Dy is formed with the yield of 25 × 103 Bq × µA-1 × h-1 × cm2 × gDy2O3-1, which leads to the formation of 1.6 × 103 Bq × µA-1 × h-1 × cm2 × gDy2O3-1 of 155Tb. It has been shown that the isolation of terbium radioisotopes from tens of mg of dysprosium target can be achieved by extraction chromatography, and final separation yield was 39%. The impurity of 160Tb is 7.3% of the 161Tb activity at EOB.

Structural Insight into Complexation Ability and Coordination of Uranyl Nitrate by 1,10-Phenanthroline-2,9-diamides.

Reprocessing of spent nuclear fuel (SNF) is an important task in a frame of ecology and rational use of natural resources. Uranium, as the main component of SNF (>95%), can be recovered for further use as fresh nuclear fuel. To minimize an amount of solid radioactive waste generated during SNF reprocessing, new extractants are under investigation. Diamides of 1,10-phenanthroline-2,9-dicarboxylic acid are perspective tetradentate N-donor ligands that form strong complexes with f-elements, which are soluble in polar organic solvents. As an example of three ligands of this class, we conducted a comparative study and showed how the substituent in the amide functional group affects the extraction ability toward uranyl nitrate from nitric acid media. We have performed a careful study (NMR, FT-IR, XRD, RMC-EXAFS) of the structures of synthesized complexes of new ligands with uranyl nitrate and used quantum mechanical calculations to explain the discovered regularities through.

Artificial radionuclides association with bottom sediment components from Mayak Production Association industrial reservoirs.

About ten years have passed since the last published report in Russian on the speciation and distribution features of radionuclides in the bottom sediment of Production Association (PA) "Mayak" (further mentioned as Mayak) artificial reservoirs. Herein, the desorption parameters of 137Cs, 90Sr, 241Am, and 238,239+240Pu and their association with bottom sediment components were investigated in two Mayak reservoirs (R-17 (decommissioned) and R-4 (still in use) with big differences in size, activity and water regime). It was established that 137Cs and 90Sr desorption from the R-17 bottom sediment reach constant values after 24 h, and the desorption degree is not dependant on pH but on ionic strength. Sequential extraction indicated that the main accumulation mechanism of 137Cs is incorporation into the clay minerals. The maximum plutonium content was detected in the residual fraction of the R-17 bottom sediment, which could be associated with the effects of precipitation aging. In R-4, plutonium is equally distributed between residual and bound to organic matter fractions. The 241Am is associated with carbonates in the R-17 bottom sediment and with organic matter in the R-4 bottom sediment and to lesser extent with iron-manganese oxides. The radionuclides are becoming less environmentally available with time since deposition.

The plutonium isotopes and strontium-90 determination in hot particles by characteristic X-rays.

This paper reports the developed non-destructive methods for the plutonium isotopes and strontium-90 content determination in hot particles and other samples. The proposed methods are based on the measurement of the characteristic X-rays accompanying the decay of these radionuclides. For hot particles of NPP accident origin, the proposed method's error limits are 10-15% for hot particles (samples) with activity above 100 Bq and 15-20% for hot particles (samples) with activity less than 100 Bq. For explosive particles, the determination accuracy is 10-15% for activity more than 5 Bq and 20-30% for 0.1-5 Bq activity. The accuracy of the proposed method for determining 90Sr in samples with its specific content of more than 104 Bq/sample is 5%, with ~102 Bq/sample its content is 15-20%. The cost of one sample measurement and the processing time of these methods are significantly reduced compared to traditional studies. The proposed methods are reasonably simple measurement methods and can be carried out even in the field condition. They open up new possibilities for the quick search and study of hot particles and environmental samples.

A first phosphine oxide-based extractant with high Am/Cm selectivity.

A new phosphine oxide ligand demonstrates high selectivity for the Am-Cm pair with SF = 2.9-3.5 and the Am-Eu pair with SF = 7.3-8.5 in a range of 0.1-3 M nitric acid. Thermodynamic measurements show that the entropy factor is responsible for selectivity observed in the extraction experiment. The most prevalent complexes of all three metal ions were (Ph2PyPO)2M(NO3)3. According to their DFT modelling, the M-N distances for the Cm ion were larger than those for Am, so the last ion enters deeper into the pseudo-cavity of the ligand, which causes the observed selectivity.

A novel highly selective ligand for separation of actinides and lanthanides in the nuclear fuel cycle. Experimental verification of the theoretical prediction.

We have predicted earlier by DFT simulation that tridentate O,N,O-donor cyclic dilactams (B) belonging to the family of pyridine-2,6-dicarboxamides are much more selective and efficient extractants for the separation of lanthanides and actinides than open-structure pyridine-2,6-dicarboxamides due to the higher degree of "ligand preorganization". In the present work, three new ligands of type (B) were synthesized. Extraction experiments showed that, in line with the data from DFT simulation, these ligands have 5-6-fold higher selectivity for the separation of an Am3+/Eu3+ pair and provide distribution coefficients D which are by three orders of magnitude higher than those for the related parent ligands with an open structure. Determination of the solvate numbers (SNs) for Eu3+ and Am3+ cations by slope analysis has shown that the stoichiometry of complexes, in the form of which these ions pass from the aqueous into the organic phase, depends to a considerable extent on the polarity of the organic solvent. Strongly polar solvents (ε > 20) extract these cations mainly in the form of 1 : 1 complexes LM(NO3)3 having according to the DFT simulation the largest dipole moments (µ = 18.6-19.7 D). The solvents of low polarity (ε ≤ 10) extract these cations mainly in the form of less polar 2 : 1 complexes L2M(NO3)3 (µ ≈ 1.6 D). For solvents of intermediate polarity fractional values of solvate numbers were obtained which indicates the coexistence of complexes LM(NO3)3 and L2M(NO3)3 in the organic phase.

N,N'-Dialkyl-N,N'-diaryl-1,10-phenanthroline-2,9-dicarboxamides as donor ligands for separation of rare earth elements with a high and unusual selectivity. DFT computational and experimental studies.

N,N'-Dialkyl-N,N'-diaryl-1,10-phenanthroline-2,9-dicarboxamides (IV) were predicted (DFT simulation) and then were proved experimentally to be efficient donor ligands with high and unusual selectivity for the extraction separation of lanthanides. Distribution coefficients D of lanthanide cations in two-phase aqueous solution-polar organic solvent decrease with increasing Ln(3+) atomic number. The selectivity factors SFLn1/Ln2 for adjacent lanthanide ions were found to be about 3.

Influences of different environmental parameters on the sorption of trivalent metal ions on bentonite: batch sorption, fluorescence, EXAFS and EPR studies.

The presence of long-lived radionuclides in natural aquatic systems is of great environmental concern in view of their possible migration into biospheres of mankind. Trivalent actinides such as (241/243)Am can contribute a great deal to radioactivity for several thousand years. This migration is significantly influenced by various factors such as pH, complexing ions present in aquatic environments, and the sorption of species involving radionuclides by sediments around water bodies. Clay minerals such as bentonite are known to be highly efficient in radionuclide retention and hence are suitable candidates for backfill materials. This study presents experimental results on the interaction of Eu(iii) and Gd(iii) (chemical analogs of Am(iii) and Cm(iii)) with bentonite clay under varying experimental conditions of contact time, pH, and the presence of complexing anions such as humic acid (HA) and citric acid (cit). The sorption of HA on bentonite decreased with increasing the pH from 2 to 8, which was attributed to electrostatic interactions between HA and the bentonite surfaces. The sorption of Eu(iii) on bentonite colloids showed marginal variation with pH (>95%). However, a decrease in Eu(iii) sorption was observed in the presence of HA beyond pH 5 due to the increased aqueous complexation of Eu(iii) with deprotonated HA in the aqueous phase. The complexation of Eu(iii) with citrate ions was studied using Time Resolved Laser induced Fluorescence Spectroscopy (TRLFS) to explain the sorption data. Extended X-ray absorption fine structure (EXAFS) and electron paramagnetic resonance (EPR) investigations were carried out to understand the local chemical environment surrounding Eu(iii) and Gd(iii) (EPR probe) sorbed on bentonite under different experimental conditions. Surface complexation modelling shows the predominant formation of ≡XOEu(+2) (silanol) up to pH < 7, and beyond which ≡YOEu(OH)(+) (aluminol) is responsible for the quantitative sorption of Eu(iii) onto bentonite in the studied pH range.

[Distribution and activity of microorganisms in the deep repository for liquid radioactive waste at the Siberian Chemical Combine].

The physicochemical conditions, composition of microbial communities, and the rates of anaerobic processes in the deep sandy horizons used as a repository for liquid radioactive wastes (LRW) at the Siberian Chemical Combine (Seversk, Tomsk oblast), were studied. Formation waters from the observation wells drilled into the production horizons of the radioactive waste disposal site were found to be inhabited by microorganisms of different physiological groups, including aerobic organotrophs, anaerobic fermentative, denitrifying, sulfate-reducing, and methanogenic bacteria. The density of microbial population, as determined by cultural methods, was low and usually did not exceed 10(4) cells/ml. Enrichment cultures of microorganisms producing gases (hydrogen, methane, carbon dioxide, and hydrogen sulfide) and capable of participation in the precipitation of metal sulfides were obtained from the waters of production horizons. The contemporary processes of sulfate reduction and methanogenesis were assayed; the rates of these terminal processes of organic matter destruction were found to be low. The denitrifying bacteria from the underground repository were capable of reducing the nitrates contained in the wastes, provided sources of energy and biogenic elements were available. Biosorption of radionuclides by the biomass of aerobic bacteria isolated from groundwater was demonstrated. The results obtained give us insight into the functional structure of the microbial community inhabiting the waters of repository production horizons. This study indicates that the numbers and activity of microbial cells are low both inside and outside the zone of radioactive waste dispersion, in spite of the long period of waste discharge.