Sorption of cesium and strontium radionuclides onto crystalline alkali metal titanosilicates

Sorption of tracer amounts of ¹³⁷Cs and ⁹⁰Sr radionuclides from model solutions of various compositions onto synthetic titanosilicates, framework ivanyukite and layered SL3, both synthesized at the Center for Nanomaterials Science, Kola Scientific Center, Russian Academy of Sciences, was studied. Synthetic ivanyukite and titanosilicate SL3 well compete with Termoxid-25 ferrocyanide sorbent in the ability to take up cesium from neutral NaNO₃ solutions and from a simulated solution of bottom residue from a nuclear power plant with RBMK reactors. The maximal sorption of ¹³⁷Cs onto ivanyukite is observed at pH 6–7. The dependence of the ¹³⁷Cs distribution coefficient (K _d) on ivanyukite on the concentration of sodium and potassium ions in the solution was studied. Potassium ions affect the cesium sorption more strongly than sodium ions do. In the ability to take up ⁹⁰Sr, synthetic ivanyukite well competes with synthetic zeolite of type A and with the sorbent based on modified manganese dioxide. The dependences of K _d of ⁹⁰Sr on the concentrations of the Na⁺ and Ca²⁺ ions in the solution were determined. Calcium ions affect the strontium sorption more strongly than sodium ions do. Ivanyukite and SL3 show promise as sorbents for removing cesium and strontium radionuclides from multicomponent salt solutions.     

Sorption of cesium on finely dispersed composite ferrocyanide sorbents

Sorption of microamounts of cesium on finely dispersed composite ferrocyanide sorbents was studied. The sorbents were prepared by precipitation of nickel potassium ferrocyanide in the presence of various mineral supports (chalk, wollastonite, bentonite, clinoptilolite, diatomite, biosilica). The distribution coefficient (K _d) of ¹³⁷Cs on composite ferrocyanide sorbents is considerably higher than on nickel potassium ferrocyanide without support. The K _d values on the composite sorbents increase by a factor of 25–110 when separating the solid phase with a paper filter and by a factor of 4.3–8.2 when using a microfiltration membrane. Considerable increase in K _d of ¹³⁷Cs on composite sorbents is attributed to the formation of a nickel potassium ferrocyanide phase firmly fixed on the support surface and resistant to peptization. Composite ferrocyanide sorbents were tested for the ¹³⁷Cs recovery from a simulated NPP bottom residue in the pH range 8.5–12.0. On the composite sorbents, K _d of ¹³⁷Cs is 2.5–3.0 times higher than on the nickel ferrocyanide precipitate throughout the examined pH range. The composite sorbent based on biosilica and nickel potassium ferrocyanide was tested for treatment of real liquid radioactive waste with a total salt content of 22.0 g dm⁻³ to remove ¹³⁷Cs. The decontamination factor as high as 5190 was attained owing to simultaneous use of the finely dispersed composite ferrocyanide sorbent and an ultrafiltration ceramic membrane.     

Optimal design and performance evaluation of a metal fiber filter for capturing radioactive aerosols

ABSTRACT

Conventional high-efficiency particulate air (HEPA) filters made of glass fiber media are prone to recycling problem and restrictions in extreme environmental condition such as high flow rate, high temperature, and fire. Therefore, metal fiber filters with minimal maintenance can replace conventional HEPA filters. The objective of the study is to evaluate the theoretical and experimental characteristics of a SUS316L metal fiber filter made from the fiber diameter of 8 µm. Theoretical modeling for predicting the collection efficiency of the radioactive aerosol is performed on the metal fiber as a function of particle size, filter thickness, and flow rate. Comparison between the experimental and theoretical results demonstrates that they are in good agreement. Consequently, the model is later utilized for performance optimization of the metal fiber filter. Also the metal filter for collecting the radioactive aerosol is optimized at the particle collection efficiency of 99.97% in most penetrating particle size (MPPS) of region 0.3 µm which complies with the standards established for conventional glass fiber HEPA filters.     

Sorption of radioactive substances in chromatographic columns

An analytical expression is derived for the steady-state concentration distribution of a radioactive substance in the gaseous phase along a column for a linear adsorption isotherm. Mass transport in the gas at the surface of the sorbent grains and diffusion inside the grains are taken into account. The temperature dependence is examined.     

Sorption of cesium on ferrocyanide sorbents from highly saline solutions

Sorption of microamounts of Cs from highly saline solutions (bottom residues from nuclear power plants) on various types of ferrocyanide sorbents was studied. The dependences of the distribution coefficient (K _d) of ¹³⁷Cs on pH of solution were determined under static conditions. They strongly depend on the type of the sorbent used. FS-2 sorbent prepared by joint precipitation of silicic acid and copper ferrocyanide exhibits the best sorption characteristics toward Cs. On this sorbent, K _d of ¹³⁷Cs in a model solution with pH < 11 is (5–6) × 10⁵ cm³ g^?1. In alkaline solutions at pH > 11, the Cs sorption drastically decreases because of dissolution of the ferrocyanide component of the sorbent. Data on Cs sorption under dynamic conditions on various types of ferrocyanide sorbents from the bottom residue with pH 8–11 are presented. The volume of the solution passed up to 1% ¹³⁷Cs breakthrough was determined. FS-2 sorbent exhibits the best dynamic characteristics. Its use allows decontamination of 1000–4500 column volumes of the bottom residue depending on pH.     

Sorption behavior of cesium on various soils under different pH levels

In the present study we investigated the sorption behavior of Cs in four different soils (sandyloam, loam, clayloam and clay) by using batch experiment. Cs sorption characteristics of the studied soils were examined at 4 mgL(-1) Cs concentration, at various pH levels, at room temperature and with 0.01 M CaCl(2) as a background electrolyte. Among different soils the decrease of k(d) (distribution coefficient) of cesium, at all pH levels, followed the sequence sandyloam > loam > clayloam > clay, indicating that the particle size fractions and especially the clay content plays predominant role on sorption of Cs. The effect of pH on cesium sorption displays a similar pattern for all soils, depending on soil type. At acid pH levels less cesium was sorbed, due to a greater competition with other cations for available sorption sites. The maximum sorption of Cs was observed at pH 8, where the negative charge density on the surface of the absorbents was the highest. For all soils was observed significantly lower Cs sorption at pH 10.     

Decomposition of radioactive methyl iodide in an electric discharge field

The possibility of using electric discharge for removing radioactive iodine in the form of volatile organic compounds from air-gas streams was examined. In an electric discharge field, at the methyl iodide concentration in the range from 0.9 to 19 mg l^?1, relative humidity within 48–90%, and linear flow velocity of 0.5–3.5 cm s^?1, the decontamination factor characterizing the methyl iodide decomposition is ≥1.4 × 10⁵.     

Sorption of metal ions on lignite and the derived humic substances

The study presents results of sorption of metal ions (Pb2+, Zn2+, Cu2+, and Cd2+) onto lignite mined in South Moravia, Czech Republic, and solid humic substances (humin and humic acid) derived from it. The efficiency of these sorbents has been studied as a function of contact time, solution pH, and metal concentration. The sorption efficiencies were higher for humin and lower for humic acid samples than for the original lignite. With its high sorption capacities of several mmol/g, particularly for Pb2+ and Cd2+, the South Moravian lignite can provide a cheap source material for preparation of sorbents utilizable in removal of toxic metals from wastewaters.     

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 K _d of Sr by a factor of more than 40. After 96-h contact of the solid and liquid phases, K _d 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, K _d 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 K _dz of Sr drastically decrease (virtually to zero) and those of Y change insignificantly.     

Imaging the edge of a 4He prewetting film on a cesium metal surface

The edge of a metastable ⁴ He prewetting film on a cesium metal surface is investigated using polarization interference microscopy. This technique images the local gradient of the coverage through its optical thickness. The cesium metal is a film evaporated on a polished copper substrate. A liquid helium film is deposited on the surface through raising and lowering the bulk liquid surface. Its edge is clearly observed for temperatures below 1.6 K. The apparent optical thicknesses of the films, larger than what is expected for a normal saturated film, remain to be explained.     

Coprecipitation of microamounts of cesium with precipitates of transition metal ferrocyanides in alkaline solutions

Experiments on coprecipitation of microamounts of Cs with precipitates of copper, nickel, and cobalt ferrocyanides in alkaline solutions showed that the dependences of the distribution coefficients (K _d) of ¹³⁷Cs on pH of the liquid phase have a pronounced maximum at pH 10.0 ± 0.2 (K _d ≈ 8 × 10⁵), 10.5 ± 0.2 (K _d ≈ 2 × 10⁶), and 10.6 ± 0.3 (K _d ≈ 5 × 10⁵), respectively. This phenomenon is associated with the formation of mixed precipitates of transition metal ferrocyanides and hydroxides, surpassing in the sorption characteristics the phases of the corresponding ferrocyanides. The mechanism of coprecipitation of microamounts of cesium with precipitates of transition metal ferrocyanides in alkaline solutions and the conditions of maximum recovery of cesium from solutions of various compositions were determined.     

Examination of corrosion cracks in metal of a high-pressure steam line

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 5, pp. 83–87, September–October 1992.     

Determination of the solubility and size distribution of radioactive aerosols in the uranium processing plant at NRCN

Inhalation is the main route of internal exposure to radioactive aerosols in the nuclear industry. To assess the radiation dose from the intake of these aerosols, it is necessary to know their physical (aerodynamic diameter distribution) and chemical (dissolution rate in extracellular lung fluid) characteristics. Air samples were taken from the uranium processing plant at the Nuclear Research Center, Negev. Measurements of aerodynamic diameter distribution using a cascade impactor indicated an average activity median aerodynamic diameter value close to 5 microm, in accordance with the recent recommended values of International Commission on Radiological Protection (ICRP) model. Solubility profiles of these aerosols were determined by performing in vitro solubility tests over 100 d in a simultant solution of the extracellular fluid. The tests indicated that the uranium aerosols should be assigned to an absorption between Types M and S (as defined by the ICRP Publication 66 model).     

Probing the early-stage/rapid processes in hydrolysis and condensation of metal alkoxides

Understanding and control of the early-stage sol-gel reaction processes involving metal alkoxides are important to many advanced materials development and applications. In this work, Fourier transform infrared spectroscopy (FTIR) and small angle X-ray scattering (SAXS) were coupled with a specially designed, rapid flow-through mixing cell for monitoring such processes. The rapid, early-stage hydrolysis and condensation of zirconium n-butoxide in ethanol were chosen as the basis for a model system. FTIR was used to study soluble-species reaction kinetics, while the SAXS technique monitored in situ the solid-phase particle formation/growth (i.e., the nucleation and aggregation kinetics of polymeric clusters/particles). Monitoring the reactions and cluster/particle growth within a millisecond time regime was achieved. In addition, key parameters such as reaction time, concentration of base (i.e., quarternary tetramethyl ammonium hydroxide), temperature, water concentration, and alkoxide concentration were fully investigated in a continuous flow-through reactor.     

稠油油藏蒸汽驱阶段汽窜的研究

本文分析了稠油油藏蒸汽驱汽窜情况及其成因，研究了一些防汽窜的措施，提出了在蒸汽驱阶段利用循环转注方式生产有望延缓汽窜的发生并提高蒸汽总体波及体积和最终采收率。     

Sorption of U(VI) with soil from the region of location of the Novi Khan radioactive waste repository in Bulgaria

Sorption of U(VI) with soil from the region of location of the radioactive waste repository was studied. The radionuclide ²³⁷U produced by the photonuclear reaction ²³⁸U(γ, n)²³⁷U on an electron accelerator, MT-25 microtron (FLNR, JINR), was used as tracer. The U(VI) speciation in solution at various U concentrations was calculated in the range pH 1–7 using the Speciation program.     

Temperature distribution and heat-transfer coefficient during condensation of steam on a rectangular fin

The distribution of temperature with height and length of a rectangular fin in the condensation of vapor has been found theoretically. The effectiveness of fins under different conditions is demonstrated.