A. N. Kamenskaya

Chemistry of radioactive iodine in aqueous media: Basic and applied aspects

The results of studies on chemistry of radioactive iodine in aqueous media of various compositions, performed in the world in the past decade, are systematized and analyzed. Prospects for using the data obtained in various fields of nuclear power engineering are assessed.

Mechanism of UO2(NO3)2·6H2O Decomposition under the Action of Microwave Radiation: Part 2

Products of UO2(NO3)2·6H2O decomposition under the action of microwave radiation (MWR) were studied by thermal gravimetric analysis, X-ray phase analysis, IR spectroscopy, and electron microscopy. The results of physicochemical studies of these decomposition products were compared to the published data for various uranium compounds, including UO2(NO3)2·6H2O. Apart from gaseous products, the final products of decomposition of 2–10 g of UO2(NO3)2·6H2O under the action of MWR for 35 min (the maximal process temperature, 170–320°C, is attained in the first 2–5 min of irradiation) are uranyl hydroxonitrate UO2(OH)NO3 and uranium trioxide UO3 or their hydrates. The results obtained are consistent with the mechanism suggested in our previous paper and involving the reactions (1) UO2(NO3)2·6H2O → UO2(OH)NO3 + 5H2O + HNO3 and (2) UO2(OH)NO3 → UO3 + HNO3. The physicochemical study confirms the conclusions on the composition of products of UO2(NO3)2·6H2O decomposition under the action of MWR, made previously on the basis of chemical studies. The only precursor of UO3 in microwave treatment of UO2(NO3)2·6H2O is UO2(OH)NO3 (or its hydrates). This is the main difference between the courses of uranyl nitrate decomposition under the conditions of microwave and convection heating. In the latter case, uranyl nitrate and its hydrates also participate in the formation of UO3.

Physicochemical properties of uranium in lower oxidation states

Data on the properties of U in lower oxidation states, published between 1988 to 2005, are summarized. In this period, the interest in the chemistry of trivalent and bivalent uranium, especially in its coordination and organometallic chemistry, considerably increased. Possible applications of trivalent uranium are outlined.

Lower Oxidation States of f Elements: III. Properties of Low-Valence Lanthanide and Actinide Compounds in the Solid State and in Various Solvents

Properties of low-valence f-element compounds in the solid state and in protic, aprotic, and mixed solvents are discussed, including the solubility of low-valence f-element compounds, hydration of Ln2+ and An2+, and their complexation in aqueous and organic solutions with various anions (I−, Br−, Cl−, ClO4−, BF4−, BPh4− and polycyclic crown ethers.

Lower Oxidation States of f Elements: I. Preparation and Identification of Actinides and Lanthanides in Lower Oxidation States

Studies on the title subject, published mainly in the second half of the XX century and made both with macroamounts of lanthanides (Ln) and actinides (An) and with micro- and ultramicroamounts of radionuclides of these elements, are considered. Procedures for preparing f elements in lower oxidation states in solutions, melts, and solid matrices and methods for identifying these states (electrochemistry, spectrometry, high-temperature extraction, cocrystallization, etc.) are discussed.

Metal-Containing Zeolites as Sorbents for Localization of Radioiodine and CsI Aerosols from Vapor-Air and Aqueous Phases

New sorbents for efficient sorption of radioiodine and radiocesium from the vapor-gas phase and aqueous solutions were prepared by treatment of Cu+- and Ag+-substituted NaX and NaA zeolites with acetylene in aqueous solution. The distribution factor Kd of radioiodine and radiocesium between the modified sorbents and aqueous solutions is higher than 103-104 ml g-1. Decontamination factor of the vapor-gas phase with respect to radioiodine and 137CsI aerosols exceeds 102-103 and 103, respectively. The sorption properties of the modified sorbents in both aqueous solutions and the vapor-gas phase are better than those of the initial sorbents. However, localization of radioiodine from the vapor-gas phase with the Cu+-containing sorbents is less efficient than with the Ag+-containing zeolites. At the same time, in aqueous solutions the sorption capacity of the Cu+-containing sorbents for radioiodine is appreciably higher than that of the Ag+-containing sorbents. The sorption properties of the modified sorbents were studied as influenced by various factors. Paracomplexes of univalent copper and silver with C2H2, H2O, and anions present in the solution are probably formed during modification of the metal-containing zeolites. The dependence of Kd of radioiodine on the metal concentration in the sorbent, the free pore volume of the sorbent, and the anion nature was revealed.

Decomposition of uranyl nitrate in the silica gel matrix under the action of microwave radiation

Decomposition of aqueous solutions of uranyl nitrate in a matrix of granulated silica gel of KSKG grade under the action of microwave radiation (MWR) was studied. Microwave irradiation leads not only to formation of solid decomposition products UO3, UO2(OH)NO3, and their hydrates in pores of KSKG granules, but also to accumulation of gaseous NOx and H2O. The presence of NOx in KSKG pores leads to HNO3 formation in the course of washing of sorbent granules with water. This prevents hydrolysis of uranyl nitrate and formation of UO2(OH)2·H2O in KSKG pores. Washout of uranium with water and HClO4 solutions from the KSKG fraction containing products of decomposition of 2 and 10 g of the initial UO2(NO3)2·6H2O under the action of MWR (hereinafter denoted as KSKG-P-I) was studied. Upon ∼7-day contact of the solid and liquid phases at the total ratio S : L = 1 : 20, from 5 to 14% of U passes into the aqueous phase from KSKG-P-I samples obtained in experiments with 10 and 2 g of UO2(NO3)2·6H2O, respectively. In the course of repeated treatments of KSKG-P-I with water, pH of the wash water increased from 3 to 6, owing to removal of NOx from KSKG pores. Then an insoluble phase of uranyl hydroxide UO2(OH)2·H2O, which can also be presented as hydroxylated uranium trioxide UO3·2H2O, is gradually formed from the solution obtained by treatment of KSKG-P-I with water. On treatment of KSKG-P-I with HClO4 solutions (pH 1–2), virtually all uranium species formed by MWR treatment of aqueous uranyl nitrate solutions in KSKG matrix dissolve (at a contact time of the solid and liquid phases of ∼21 days, the amount of U that passed into HClO4 solutions is ∼90%). The amount of the U form that is not extracted with HClO4 solutions and remains in KSKG granules is ∼12% of its initial amount. X-ray phase analysis suggests that the uranium species remaining in KSKG are silicate compounds formed by sorbent saturation with a uranyl nitrate solution and subsequent MWR treatment.

Basic and applied aspects of the chemistry of radioactive iodine in a gas medium

The results of studies in the field of gas-phase chemistry of radioactive iodine, published in the past 15 years, are systematized and analyzed. The prospects for applying these data to various fields of nuclear power engineering are assessed. Particular attention is given to localization of nanodispersed aerosols of radioactive iodine and its poorly sorbable organic compounds. The topicality of further studies in the field of radioactive iodine chemistry, aimed to solve problems related to accidents at nuclear power plants and plants for reprocessing of spent nuclear fuel, is demonstrated.

Mixed condensed f-element clusters

Abstract Mixed condensed Gd 2 Cl 3 -type clusters for actinides (Pa, Np, Pu, Cm, Bk) and some lanthanides were studied and interesting results were obtained.

Behavior of 131I and 137Cs in the oil-water and oil-gas phase systems

The behavior of 131I and 137Cs in various chemical forms in the oil-water and oil-gas phase systems and the sorption of these radionuclides from radioactive transformer oil onto various inorganic and organic sorbents was studied. The degree of the 137Cs extraction depends neither on the time of contact of the oil with aqueous solutions nor on the 137CsI concentration in the solution. Under all the experimental conditions, the degree of extraction of 137Cs did not exceed 5%. The degree of 131I extraction from water by the oil depends on the chemical form of the radionuclide: 131I−, 31IO3−, or 131I2. The maximal extraction (∼70%) is observed for K131IO3, and the minimal (∼25%), for 131I2. Granulated nanocomposites containing particles of carbon or NaX zeolite and Fizkhimin sorbents based on coarsely porous silica gel and containing Ag and Ni in 1: 4 ratio allow efficient removal of 137Cs and 131I from spent transformer oil of GK grade.