S. A. Kulyukhin

Sorption of cesium, strontium, and yttrium radionuclides from the aqueous phase on layered double hydroxides

Sorption of 137Cs, 85,90Sr, and 90Y from aqueous solutions on the solid phase of layered double hydroxides (LDHs) and layered double oxides (LDOs) of various compositions was studied. On the solid phase of Mg-Al and Cu-Al LDHs and Mg-Al LDO, the Sr and Cs radionuclides are very weakly sorbed from aqueous solutions containing 10−5 M of the corresponding element (Cs+ or Sr2+). Introduction of EDTA ions into Mg-Al LDH increases the distribution coefficients Kd of Sr by a factor of more than 40. After 96-h contact of the solid and liquid phases, Kd of radioactive Sr in sorption from aqueous solution on Mg-Al LDH and Mg-Al LDH-EDTA is 2.4 and 100 ml g−1, respectively. The Sr and Y radionuclides are efficiently sorbed from aqueous solutions containing 10−5 M Sr2+ and Y3+ on the Mg-Nd LDH solid phase. After 5-min contact of the solid and liquid phases, Kd of Sr exceeds 105 ml g−1. For Y, the distribution coefficients equal to 700–800 ml g−1 are attained after 30-min contact of the solid and liquid phases. Aging of the Mg-Nd LDH precipitate does not affect its sorption properties toward Sr and Y radionuclides. With an increase in the Sr(NO3)2 concentration in the solution from 10−5 to 10−1 M, the distribution coefficients Kdz of Sr drastically decrease (virtually to zero) and those of Y change insignificantly.

Sorption of U(VI) from aqueous solutions on layered double hydroxides of Mg, Al, and Nd

Sorption of 60Co from aqueous solutions of various compositions on layered double hydroxides (LDHs) of Mg, Al, and Nd in carbonate and hydroxide forms and on layered double oxides (LDOs) of Mg and Al was studied. 60Co is poorly sorbed from aqueous nitrate solutions onto LDH-Mg-Al-OH. The 60Co distribution coefficient Kd does not exceed 50 ml g−1 at a phase contact time of 15 min and V/m = 50 ml g−1. At the same time, 60Co is efficiently sorbed from 10−3–10−5 M aqueous Co(NO3)2 solutions onto LDH-Mg-Al and LDH-Mg-Nd with CO32− in the interlayer space. At a phase contact time of 15 min and V/m = 50 ml g−1, Kd exceeds 2 × 104 ml g−1 for LDH-Mg-Nd and does not exceed 5 × 103 ml g−1 for LDH-Mg-Al. The 60Co desorption from LDH-Mg-Nd-CO3 into 0.05–0.2 M solutions of Na2CO3, NaNO3, (NH4)2C2O4, and Na2H2EDTA and into distilled water was studied. Na2H2EDTA is the most efficient desorbing agent. After 15-min contact of LDHMg(60Co)-Nd-CO3 with 0.1 and 0.05 M Na2H2EDTA solutions, the degree of desorption of 60Co is ∼100 and ∼99%, respectively.

Sorption of radioiodine from aqueous solutions on layered double magnesium aluminum hydroxides at 300 K

Sorption of 131I− and 131IO3− from aqueous solutions at 300 K on solid layered double magnesium aluminum hydroxides (Mg-Al-LDH) in the carbonate (Mg-Al-LDH-CO3) and nitrate (Mg-Al-LDH-NO3) forms was studied. The distribution coefficients of 131I− and 131IO3− between solid Mg-Al-LDH-CO3 and an aqueous solution after contact of these phases for 60 min are 38 and 34 ml g−1, respectively. The distribution coefficients of 131I− and 131IO3− between solid Mg-Al-LDH-NO3 and an aqueous solution, measured under the similar conditions, are about 5 ml g−1. After contact of the solid and liquid phases for 14 h, the distribution coefficients of 131I− and 131IO3− between an aqueous phase and solid layered double magnesium aluminum oxides (Mg-Al-LDO) prepared by thermolysis of Mg-Al-LDH are 7999 and 7068 ml g−1, respectively.

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.

Preparation and properties of modified spherically granulated chitosan for sorption of 137Cs from solutions

A composite sorbent based on spherically granulated chitosan modified with a mixed ferrocyanide K2Cu3[Fe(CN6)]2 (SGC-FC) was prepared. The sorbent is highly effective toward 137Cs. The physicochemical parameters of 137Cs+ sorption by this sorbent were determined: total and equilibrium static exchange capacity, dynamic exchange capacity, sorption equilibrium constants, etc. The influence of the chemical composition of the solution on the 137Cs+ sorption by SGC-FC was examined in detail. Based on the calculated value of the dimensionless Biot number Bi, a conclusion was made that the kinetics of 137Cs+ sorption on SGC-FC is mainly determined by external diffusion of 137Cs+ ions to reaction centers of the sorbent. The possibility of using the sorbent in monitoring of sea areas was considered.

Morphological Memory of Dispersed Solid Phases

A formalism of the morphological memory of disperse systems was formulated. Using CsI as an example, it was established that a dispersed solid phase formed by vapor condensation stores information on the nucleation, growth, and aggregation of its particles for a long time. Therefore, the determination of distribution functions of properties and the texture of particles at the end of the condensation allows us to qualitatively describe the genesis of the phase. Basic equations and conditions relating properties of crystals of the dispersed phase, which are necessary for the extraction of information on the genesis from data on final distribution functions of crystal states, were considered.

Gas-phase conversion of the U, Sr, Mo, and Zr oxides into water-soluble compounds in the NO x –H2O (vapor)–air atmosphere

The gas-phase conversion of U3O8, MoO3, SrO, and their mechanical mixtures, and also of ZrO2 into water-soluble compounds in the NOx–H2O (vapor)–air atmosphere was studied. In the course of gas-phase conversion, U3O8 and SrO transform into water-soluble compounds (nitrates, hydroxonitrates), whereas MoO3 and ZrO2 undergo no changes. The principal possibility of separating U from Mo and Zr by gas-phase conversion of the oxides in the NOx–H2O (vapor)–air atmosphere was demonstrated.

Sorption of 137Cs from aqueous solutions onto layered double hydroxides containing the Fe(CN)64− ion in the interlayer space

Sorption of 137Cs from aqueous solution onto layered double hydroxides (LDHs) of the composition LDH-M2+-M3+-Fe(CN)6 (M2+ = Mg, Cu, Ni, Zn; M3+ = Al, Fe) was studied. The LDH-Mg-M3+-Fe(CN)6 solid phases (M3+ = Al, Fe) take up 137Cs from 10−5 M aqueous CsNO3 solutions extremely weakly, whereas the LDH-M2+-M3+-Fe(CN)6 solid phases (M2+ = Cu, Ni, Zn; M3+ = Al, Fe) efficiently take up 137Cs. After 15-min contact of the solid and liquid phases, the apparent distribution coefficient Kd* of 137Cs ranges from ≈3 × 102 to ≈104 mL g−1 for M2+ = Cu, from ≈4 × 103 to ≈2 × 104 mL g−1 for M2+ = Ni, and from ≈5 × 103 to ≈3 × 104 mL g−1 for M2+ = Zn at V/m = 50 mL g−1. As the NaOH concentration in the solution is increased, the sorption performance of the examined LDHs, except LDH-Ni-Al-Fe(CN)6, drastically decreases, which is due to the formation of LDH-M2+-M3+-OH (M2+ = Ni, Zn; M3+ = Al, Fe) having low ability to take up 137Cs.

Absorption of molecular radioiodine from the water vapor-air flow

Sorption of 131I2 from the water vapor-air medium on inorganic nanocomposite materials was studied. All the nanocomposite materials synthesized, containing 1, 2, 4, and 8 wt % Ag in various chemical forms, remove 131I2 from the water vapor-air flow with more than 99% efficiency.