Volatile complexes of fluorinated β-diketonates of neodymium(III) (hexafluoroacetylacetonates with glyme and diglyme and decafluoroacetylacetonate with glyme) were studied for applicability in lowbackground Nd-containing organic liquid scintillators. The complexes were prepared in one step and purified by vacuum sublimation. The composition of complexes was determined by 1 H, 19 F, and 13 C NMR and IR spectroscopy and confirmed by elemental and functional analysis. It was shown that these adducts are suitable for the design of Nd-containing organic liquid scintillators with neodymium concentration of ~1–2 g/L.

Formulation of the forming paste for preparing unsupported granulated triuranium octoxide U3O8 was developed. The mixture contains U3O8 and (NH4)2U2O7 in a weight ratio from 1: 1 to 1: 1.5, and also water in an amount of 25–40 wt % relative to the sum of the dry components. Calcination of crude granules at 800–1100°С results in formation of strong ceramic granules with 57–45% open porosity, consisting of U3O8. Granulated U3O8 efficiently catalyzes the conversion of ammonium nitrate to nitrogen in an NH4NO3–H2O vapor–gas mixture with the addition of ammonium carbonate. The absence of support makes the catalyst composition more definite and simplifies its regeneration.

It was demonstrated with an example of floodplain soil of the Yenisei River (Atamanovskii Isl.) that, in long-time percolation of the liquid phase through the soil, partial oxidation of the bioreduced iron with atmospheric oxygen strongly (by several times) increases the leaching of radiostrontium as compared to that under anaerobic conditions. The experiments were carried out on a laboratory setup allowing long-term controlled steady-state percolation of the liquid phase through a soil bed and collection of mobile soluble and colloid radiostrontium species at the outlet. Species coarser than 500 Å were retained on a specially designed combined bilayer membrane operating in the contact ultrafiltration mode without applying external pressure. It was found that 92% of radiostrontium is leached from the soil with fine species (<500 Å). As under anaerobic conditions, in the case of aerobic activation, the leaching of radiostrontium correlates with the iron loss. The results obtained are consistent with the concept that, in waterlogged soils, mobilization of radionuclides proceeds by the mechanism of concerted biogenic solubilization of the soil gel films and radionuclides associated with organomineral complexes.

Gleyzation-mediated leaching of radiostrontium from floodplain soils of the Krasnoyarsk Mining and Chemical Combine (MCC) activity zone [Atamanovskii Island (front part), Oseredysh Island (front part), and Berezovyi Island (rear part)] is studied with model systems. Leaching of radiostrontium from waterlogged soils is analyzed in terms of the model of anaerobic biosolubilization of gel films. The leaching of radiostrontium is found to correlate with that of iron, confirming the cosolubilization model. Addition of glucose (0.5%) as a stimulant for growth of iron-reducing microorganisms increases the dynamic coefficient of radiostrontium leaching, particularly in soils with lower organic matter content. The model experiments showed that the radiostrontium leaching rate from floodplain soil is higher by 2–3 orders of magnitude than that of radio-cesium, suggesting the possibility of escape of radiostrontium from the floodplain of the Yenisei River with the intrasoil runoff. This conclusion is supported by the experimental data on the 90 Sr/ 137 Cs ratio in the floodplain of the Yenisei River downstream of MCC (0.01–0.1).

Leaching of radiostrontium from soil under gleyzation is studied with a laboratory setup allowing controlled long-term percolation of the liquid phase through a soil sample and collection of mobile soluble and colloid species at the outlet. Introduction of a nutrient substrate for the growth of microorganisms promoting gleyzation enhances the leaching of radiostrontium from waterlogged soil. The results suggest joint solubilization of the macrocomponents of the clay-humus complex of the soil and associated radiostrontium under gleyzation. Data on the dynamic leaching and distribution coefficients show that, in the stagnant water regime, remobilization of strontium is less intensive than in the percolation mode. The gleyzation-mediated leaching of radiostrontium is suppressed after 2–2.5 months, which can be attributed to the inhibiting effect of Fe(II) accumulated in the system.

Joint leaching of iron and other macro- and microelements including radionuclides from radioactively contaminated floodplain soil of the Yenisei River is studied on miniecosystems. In developing anaerobic conditions, the redox potential E-h decreased to +140 mV, causing partial reduction of iron and solubilisation of iron hydrous oxide and organomineral films of the soil. Leaching of stable elements and radionuclides with water proceeds parallel to that of iron. To accelerate reductive mobilization of iron, 0.4% aqueous ascorbic acid was used instead of water as the leaching liquid phase. In this case, E-h approached -60 mV, and the leaching of stable and radioactive elements considerably increased, the effect being most pronounced for plutonium. (C) 2004 Academie des sciences. Published by Elsevier SAS. All rights reserved.

A model study is made of joint leaching of iron and other macro- and microelements, among them radionuclides, from radioactively contaminated floodplain (aquic moisture regime). In developing anaerobic conditions, the redox potential Eh decreased to +140 mV, causing partial reduction of iron and solubilization of iron hydrous oxide and iron-containing organomineral films of the soil. Leaching of stable elements and radionuclides with water proceeds parallel to that of iron. To accelerate reductive mobilization of iron, 0.4% aqueous ascorbic acid was used instead of water as the liquid phase in the model system. In this case, Eh approached -60 mV, and the leaching of stable and radioactive elements considerably increased, the effect being most pronounced for plutonium.

It is demonstrated in model experiments that in the presence of Ca ions (typomorphous cations of water of the Yenisei River) fulvic acids of floodplain soils and associated radionuclides (Am, Eu) form poorly soluble mixed Ca, Fe, Al(Am, Eu) fulvates. As a result, under the flooding conditions the migration of Am and Eu in the form of solubilized organomineral complexes is practically totally suppressed. With decreasing pH in the model system from 8 to 6 the mobility of the radionuclides noticeably increases.

For 35 years Krasnoyarsk Mining-Chemical Combine (MCC) manufactures weapon plutonium in single-pass production reactors cooled with water of the Yenisey River. Water discharge from these reactors is the major source of radioactive contamination of the Yenisey River. We have demonstrated that after putting the reactors out of operation (in late 1992) the contamination level of the Yenisey River with short-lived radionuclides considerably decreased, and now the radioactive contamination is caused essentially by Cs-137, Eu-152, Pu-239,240, Sr-90, and Am-241, whose concentration in the aqueous phase is lower than in bottom sediments and, particularly, flood-land deposits by several orders of magnitude (except for Sr-90). The flood-land deposits are classified with the most contaminated environmental objects in the territories under the impact of MCC: their radioactivity is comparable with that of low-level waste. Taking into account the considerable depth and area of the flood-land deposits, this allows their classification as a great technogenic radiation anomaly. Comparison of the maximal Cs-137 and Pu-239,240 levels in flood-land soils and bottom sediments of the Yenisey River with those in bottom sediments of the Pripyat' River and the Kiev reservoir shows that these values are close each to other. A direct correlation is found between the spatial distribution of Cs-137 on the one hand and Pu-239,240, Eu-152, and Am-241 on the other hand in the aqueous phase and bottom sediments, which is not the case for Sr-90. Data on the distribution coefficients of the indicated radionuclides between the deposits and aqueous phase (obtained with actual and model systems) and also on the radionuclide distribution throughout geochemical mobility forms suggest that the essential part of Cs, Pu, Eu, and Am migrates with fine-disperse suspended material, the transport and distribution of which is controlled by the hydrological regime of the Yenisey River. By contrast, strontium migrates as soluble species weakly sorbed by the solid phase, causing the observed low content of Sr-90 in flood-land deposits and bottom sediments of the Yenisey River. The indicated migration behavior of radionuclides is characteristic of the Yenisey Gulf and the adjacent part of the Kara Sea also. We made similar conclusions when studying the migration behavior of Cs-137, Pu-239,240, and Sr-90 in the Kiev reservoir (1987). The formation of radioactive flood-land deposits is provided by rapid deposition of suspended material in stagnant zones during periodical flood. Humus compounds contribute significantly to accumulation of radionuclides in the flood-land deposits and bottom sediments, which is supported by the observed correlation between the radionuclide (Pu, Am, Eu) and total organic carbon distributions in them. Radiochemical analysis of separate fractions showed that about 20% of Pu and Am are associated with the organic fraction: Pu is nearly equally distributed between humic and fulvic acid fractions, whereas Am is preferentially associated with the fulvic acid fraction (the most mobile fraction of humus matter). It was demonstrated in model experiments that the calcium-hydrocarbonate type of water of the Yenisey River causes suppression of formation of mobile fulvate complexes of hydrolyzable radionuclides and, therefore, their transfer into the aqueous phase. In combination with the observed very high distribution coefficients of the radionuclides and low content of their mobile geochemical forms in flood-land deposits of the Yenisey River this suggest that they cannot contribute somewhat significantly to the secondary radioactive contamination of the river water by all mechanisms except migration by mechanical transfer. (author)

The distribution of macrocomponents (aluminum and fulvic acid) and microcomponents (Am-241 and Eu-152) between aluminum fulvate gel and equilibrium aqueous solution at pH 1-9 is studied. The solubility of aluminum fulvate as well as the fraction of radionuclides passed into the liquid phase show minima at pH 3-4. As pH increases or decreases relative to the minimum, vigorous solubilization of the gel phase occurs, and at pH 9 aluminum fulvate as well as the radionuclides practically totally pass into the solution. The molecular structure and solubilization mechanism of aluminum fulvate are studied by IR spectroscopy.

The method was developed allowing quantitative extraction of fulvic acids from soil samples in the form close to native. Formation of gel-like and soluble forms of iron(III) fulvates in the systems containing equivalent amounts of iron(III) and fulvic acid was studied within pH range 1–9. The molecular structure of fulvates and the mechanism of transformation of gel to soluble forms was analyzed by IR spectroscopy. Distribution of microamounts of europium between gel-like iron fulvates and their solutions was studied. The correlation between phase distribution of europium and solubilization of iron(III) fulvates was analyzed.

The method was developed allowing quantitative extraction of fulvic acids from soil samples in the form close to native. Formation of gel-like and soluble forms of iron(III) fulvates in the systems containing equivalent amounts of iron(III) and fulvic acid was studied within pH range 1-9. The molecular structure of fulvates and the mechanism of transformation of gel to soluble forms was analyzed by IR spectroscopy. Distribution of microamounts of europium between gel-like iron fulvates and their solutions was studied. The correlation between phase distribution of europium and solubilization of iron(III) fulvates was analyzed.

The mechanism of solubilization of poorly soluble gel phases of polyvalent metal fulvates is studied by examples of europium(III) and uranyl fulvates in HCl and EDTA solutions, using spectroscopic and physicochemical methods. Europium fulvate undergoes solubilization by a two-stage mechanism. In the first stage, the solubilizing agent displaces Eu(III) from the gel phase, with no degradation of the polymer matrix. In HCl solutions, the gel phase absorbs a considerable excess of HCl relative to the amount required for purely ion-exchange mechanism. In the second stage, after about 60% of the initial metal passes into solution, the gel phase loses its aggregative stability, and simultaneous solubilization of the fulvate component starts. Uranyl forms less stable coordination polymers, and their solubilization proceeds by the second mechanism only.

The europium fulvate complex is synthesized and characterized by spectroscopic and chemical methods. By an example of this complex, it is demonstrated that metal complexes of humic substances are solubilized in the presence of complexing anions such as OAc-, C2O42-, and EDTA(2-). The solubilization is studied by the optical and radioactive tracer methods. The solubilization of europium fulvate increases parallel to the complexing power of anions. In the solid fulvate europium is bonded stronger than in the ethylenediaminetetraacetate complex. The solubilization is considered as a potential source for decomposition of the ''absorbing soil complex,'' resulting in mobile forms of a metal and a humic component in soils and soil waters.

Lanthanides di-(2-ethylhexyl)phosphates (LnA(3)) crystallize as needle-like samples exhibiting an axial texture with an identity period along texture of 5.3 Angstrom. A hexagonal elementary cell of EuA(3) has the following parameters: a = 18.6 Angstrom, c = 10.4 Angstrom, z = 2. As is evident from IR and luminescence (EuA(3)) spectra, LnA(3) molecules form rigid-chain coordination polymer structure with neighbouring coordination octahedra linked by alkylphosphate bridges. LnA(3) is very poorly soluble in alkanes as well as in donor solvents. However, we developed the series systems in which the solubility of LnA(3) increases dramatically as a result of the formation of oligomers or mixed-ligand complexes. Coordination chemical processes occurring in these systems have been studied using thermodynamic and spectroscopic methods. The structural formulae and strength of the complexes formed are discussed. On the decomposition of mixed-ligand complexes, considerable separation in the Am-lanthanides and Eu-lanthanides series occurs.

Dissolution of solid rare earth (RE) di-(2-ethylhexyl)phosphates (LnA3)n in octane on addition of di-(2-ethylhexyl)phosphoric acid (HA) is demonstrated to occur through formation of an acidic mixed-ligand complex LnA2(AHA). Such a complex is formed in the organic phase after extraction of Ln3+ by HA solutions in octane with a deficit of HA that leads to precipitation of LnA3. The formation constant of LnA2(AHA) decreases with increasing lanthanide atomic number Investigation of the octane solutions Of LnA2(AHA) by spectroscopic methods (IR, luminescence) demonstrated that the complex is polymeric with neighboring Ln3+ ions bound to two alkylphosphate bridges and an AHA- chelated to the RE ion. According to the luminescence spectra, the chelate causes great distortion of the LnO6 coordination sphere. With a large excess of HA, the homoleptic complex Ln(AHA)3 with three chelating anions and prismatic Ln3+ coordination is formed.