Recovery of iodine and cesium radionuclides localized on granulated sorbent Fizkhimin from air-vapor phase

A procedure for recovery of ¹³¹I and ¹³⁷Cs radionuclides from Fizkhimin sorbent containing ¹³⁷Cs¹³¹I and ¹³⁷CsOH radioaerosols and also of Ag¹³¹I formed in the sorbent matrix during chemisorption of gaseous ¹³¹I₂ and CH₃ ¹³¹I was developed. Sequential treatment of the sorbent with 6.0 M HNO₃ and then 10.0 M N₂H₄·nH₂O allows practically complete (more than 99%) removal of ¹³⁷Cs and noticeable decrease of the ¹³¹I content in the sorbent matrix (in some cases, by a factor of more than 10).     

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^?, ³¹IO ₃ ^? , 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.     

Behavior of radioaerosols formed by evaporation of 137Cs131I and 137CsOH from the metal surface in an electrostatic field

The behavior of radioaerosols formed by condensation of supersaturated ¹³⁷Cs¹³¹I and/or ¹³⁷CsOH vapor in an electrostatic field was studied. Supersaturated ¹³⁷Cs¹³¹I and/or ¹³⁷CsOH vapor was generated by evaporation of salt crystals from a metal surface heated to high temperatures owing to ohmic resistance. By applying additional potential to the aerosol generator, it is possible to control the behavior of ¹³⁷Cs¹³¹I, ¹³⁷CsOH, or ¹³⁷Cs¹³¹I + ¹³⁷CsOH aerosols in an electrostatic field.     

Sorption of cesium iodide radioactive aerosols on metal felt during oxidative hydrolysis in steam gas-system

The behavior of ¹³⁷Cs ¹³¹I radioactive aerosols at sorption in a column packed with Bekipor WB metal felt from argon, air, and steam-gas flow was studied to assess the possibility of formation of CsI CsOH and CsI₃ in the course of CsI oxidative hydrolysis. The layer distribution of radionuclides in the column was analyzed as influenced by temperature (405–560 K), carrier gas humidity (up to 60 vol %), flow velocity (2–6 cm s¹), and amount of cesium iodide sorbed on the felt (0.7–65.0 mg). It was found that the oxidative hydrolysis under certain conditions yields CsI CsOH and CsI₃ aerosols. Although under the experimental conditions studied the sorption of radionuclides on the metal felt is nearly quantitative (97–99%), escape of the radionuclides from the column upon prolonged passing of steam-gas mixtures cannot be excluded.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 449–453.Original Russian Text Copyright © 2004 by Kulyukhin, Mikheev, Kamenskaya, Rumer, Konovalova, Novichenko.     

Removal of volatile radioactive iodine compounds from water vapor–air medium

Sorption of CH₃ ¹³¹I and ¹³¹I₂ from water vapor–air medium onto SiO₂–C (2 wt %) composite material and a mixture of SKT-3I with SiO₂–Cu⁰ (10 wt %) was studied. SKT-3I shows high performance in sorption of ¹³¹I₂ and CH₃ ¹³¹I. The degree of localization of ¹³¹I₂ and CH₃ ¹³¹I exceeds 99.99% at ~60°С and gas phase–sorbent contact time τ of ~0.45 s. The degree of sorption of ¹³¹I₂ and CH₃ ¹³¹I onto the SiO₂–C (2 wt %) composite material under similar conditions does not exceed ~87 and ~8%, respectively. Experiments on ¹³¹I₂ and CH₃ ¹³¹I sorption onto mechanical mixtures of SiO₂–Cu⁰ and SKT-3I in the weight ratio varied from 1: 4 to 1: 1 showed that the degree of the ¹³¹I₂ and CH₃ ¹³¹I sorption at ~60°С and τ ~0.45 s exceeded 99.95 and 99.0%, respectively. The scheme of layer-by-layer arrangement of SiO₂–Cu⁰ and SKT-3I in the column was examined. It shows promise for use in AUI-1500VM filters in ventilation systems of nuclear power plants.     

Effect of UV radiation on the behavior of CsI radioaerosols in the gas phase

¹³⁷Cs¹³¹I radioactive aerosols formed upon evaporating CsI from a Pt support to an Ar atmosphere or air under UV irradiation or without it are studied. Without UV radiation, the degree of localization of the aerosols in a bubbler filled with aqueous Na₂S₂O₃ varies from 30% in argon to 60% in air. In sublimation of ¹³⁷Cs¹³¹I from the Pt heater, a considerable amount of nanoparticles is formed, which are not absorbed by the aqueous solution in the bubbler and are even capable of penetrating through a combined filter fabricated from a Petryanov filter and a “White Ribbon” paper filter. In the Ar atmosphere, the conversion of CsI is minimal, being initiated by traces of oxygen and moisture, as demonstrated by data on the Cs/I ratio in various fractions. In both Ar and air, UV radiation increases the localization of the radionuclides in the bubblers, simultaneously decreasing practically by half the amount of ¹³⁷Cs penetrating across the combined filter. Evidently, this is due to the fact that photoactivation promotes coarsening of nanoparticles through self-agglomeration or interaction with some coarser aggregates. A conclusion is made that UV radiation affects essentially the kinetics of aggregation of the aerosols in the gas phase, but not the rate of the chemical reactions occurring in the gas phase with participation of the aerosols.     

Removal of 131I and 137Cs from aqueous and aqueous-organic solutions with porous polyvinyl formal

The removal of ¹³¹I and ¹³⁷Cs from aqueous and aqueous-organic solutions with porous polyvinyl formal (PPVF) was studied. The degree of radionuclide removal from water with a PPVF sample is determined by the amount of water absorbed by the polymer and is not influenced by the concentration of salts in solution. Porous polyvinyl formal allows recovering ¹³⁷Cs from aqueous-organic solutions with 70 to 99% efficiency.     

Recovery of <Superscript>131</Superscript>I and <Superscript>137</Superscript>Cs from a solution simulating NPP trap waters

Sorption of ¹³¹I and ¹³⁷Cs from a solution simulating NPP trap waters on various inorganic and organic sorbents was studied. The highest degree of ¹³¹I recovery (>99%) can be attained with Fizkhimin granulated sorbents based on coarsely porous silica gel containing Ag and Ni in 1: 4 ratio, with K _d for ¹³¹I exceeding 10⁵ ml g⁻¹ at V/m = 10³ ml g⁻¹ and contract time of the solid and liquid phases of 120 min. Elevation of the solution temperature to 40°C does not affect the degree of ¹³¹I and ¹³⁷Cs recovery. The degree of ¹³⁷Cs recovery in all the experiments did not exceed 35%. The degree of ¹³¹I recovery by coprecipitation with AgCl and Ag₄[Fe(CN)₆] was about ∼96% and only 65%, respectively.     

Oxidative hydrolysis of CsI radioaerosols localized on TRUMEM metallic membrane filter

Oxidative hydrolysis of ¹³⁷Cs¹³¹I aerosols localized on TRUMEM metallic membrane filter under the action of air-water vapor medium was studied. It was shown that, at a temperature of air flow of 403–423 K, water vapor content from ～3–4 to 90 vol%, and flow velocity from ～2 to ～9 cm s^?1 the ¹³⁷Cs¹³¹I aerosols localized on TRUMEM metallic membrane filter undergo oxidative hydrolysis. In sublimation of 0.3 to 0.8 mg of CsI, the degree of conversion of CsI radioaerosols into oxidative hydrolysis products varies from 0 to approximately 17%.     

Sorbents for treatment of water vapor-air flows to remove volatile organic compounds of radioactive iodine

Sorption of CH₃ ¹³¹I from water vapor-air medium on Fizkhimin and Siloksid inorganic sorbents and on SKT-3I activated carbon was studied. The sorption power of Fizkhimin, Siloksid, and SKT-3I sorbents toward CH₃ ¹³¹I was examined (1) after their 20-h contract with water, followed by removal of the liquid phase and drying at 110°C; (2) after 4-h treatment with steam (95–98°C), followed by drying at 25°C; (3) after keeping for 9 months in 100% humid air at ambient temperature of 10 to 45°C; and (4) after treatment with a water vapor-air flow (95–98°C, 60–80 vol % water vapor) for 2 h. In most cases, Fizkhimin sorbent and SKT-3I activated carbon preserve high sorption efficiency toward CH₃ ¹³¹I from water vapor-air flow.     

Localization of cesium radioaerosols on granulated materials from the water vapor-air medium

The paper deals with localization of ¹³⁷Cs¹³¹I radioaerosols and products of their oxidative hydrolysis from the water vapor-air medium with various filtering elements: granulated sorbents based on silica gel and their combination with a helical filtering element (HFE) and TRUMEM metallic membrane filter (pore size ～2.0 μm). The degree of localization of ¹³⁷Cs¹³¹I aerosols was studied in relation to the air flow temperature, water vapor content, linear flow velocity in the sorption column, and amount of ¹³⁷Cs¹³¹I aerosols delivered to the filtration system. Localization of ¹³⁷Cs₂MoO₄ radioaerosols on the granulated sorbents was also studied.     

Sorption of 131I2 and CH3 131I from gas-water vapor medium with porous inorganic sorbents containing d elements

Sorption of ¹³¹I₂ and CH₃ ¹³¹I from gas-water vapor medium on porous inorganic sorbents based on silica gel of the MSKG type, containing d elements, was studied. Sorbents containing Zn, Ni, Cu, and Co ammoniates show a low degree of recovery of ¹³¹I₂ and CH₃ ¹³¹I from the gas-water vapor flow (less than 30%); their calcination at a temperature above 250°C does not noticeably affect the sorption power of the sorbent. The sorbents containing Zn, Ni, and Cu nitrates, both unmodified and modified, show a low degree of recovery of CH₃ ¹³¹I from the gas-water vapor medium (less than 1%). At the same time, whereas for unmodified sorbents the degree of recovery of ¹³¹I₂ from the gas-water vapor phase does not exceed 70%, their modified analogs have higher degree of absorption of ¹³¹I₂ (more than 99%), comparable with the similar data for Ag-containing sorbents based on silica gel of the MSKG type.     

Localization of CsI Radioaerosols from the gas phase using various filtration elements

The behavior of ¹³⁷Cs¹³¹I radioaerosols, yielded by CsI evaporation from a Pt healer into argon or air, during their localization with aqueous solutions and various filtration materials [filters based on Petryanov fabric (from here on, Petryanov filter), “while band” paper filter, and TRUMEM metallic membrane filter] was studied. The degree of localization of ¹³⁷Cs¹³¹I radioaerosols was examined in relation to the amount of sublimed ¹³⁷Cs¹³¹I, the number of bubblers in the system, the size of the nozzle in the bubbling system, and the gas stream flow rate. The efficiency of localization of ¹³⁷Cs¹³¹I radioaerosols with a 10-layer stack of Petryanov filters from the gas stream with and without bubbling system was estimated. It was found that, at the stream velocity of 2–3 cm s^?1, a 10-layer stack of Petryanov filters with the total thickness of 3 cm takes up ca. 97% of total ¹³⁷Cs¹³¹I sublimed from the Pt heater. It was shown that the bubbling system does not affect the efficiency of localization of ¹³⁷Cs¹³¹I radioaerosols by Petryanov filters but only favors decrease of the aerosol load on these filters. Electron-microscopic examination of the particle-size distribution of the CsI aerosols penetrating through aqueous solutions was carried out, and various filtration materials (Petryanov filter and “white band” paper filter) were tested.     

Influence of calcium ion concentration on the selective sorption of 137Cs with illite

The ¹³⁷Cs sorption and desorption equilibrium between illite and a solution containing 0.5 mM K⁺ and 1 to 100 mM Ca²⁺, determined using a kinetic method with direct measurement of the radioactivity in the sorbent solid phase, was attained within 20–25 days. The kinetic curves of the ¹³⁷Cs sorption onto/desorption from illite, normalized on the maximal sorbed radioactivity, almost coincided at different Ca²⁺ concentrations. An increase in the ¹³⁷Cs distribution coefficient (K _d) with a decrease in the Ca²⁺ concentration did not exceed 60% and was due exclusively to the influence of the solution ionic strength. With an increase in the Ca²⁺ concentration from 1 to 100 mM, the fraction of ¹³⁷Cs extracted with 1 M CH₃COONH₄ (α_Ex) decreased from 24.1 to 14.8%.     

Sorption-diffusion model of 137Cs uptake by a water body bottom in estimations of water contamination

For a sample including 22 lakes, the ¹³⁷Cs concentrations in water were determined by the sorption-diffusion model. The ¹³⁷Cs levels in waters of lakes of the Kola Peninsula and Karelian Isthmus are satisfactorily described by the suggested model at the distribution coefficient K _d of 4000 L kg^?1 and diffusion coefficient D of 1.0 × 10^?7 cm² s^?1 for 2–4-year exposure. For mid-latitude lakes, the ranges of K _d and D of ¹³⁷Cs were 6000–1200 L kg^?1 and 1.0 × 10^?7–0.2 × 10^?7 cm² s^?1, respectively. The ¹³⁷Cs concentration in water is determined by the major contribution of silts, which are characterized by high K _d of ¹³⁷Cs and by large thickness of sediments on the bottom of lake hollows, to the watter-bottom sorption system. After 2-year exposure of “Chernobyl” ¹³⁷Cs in lakes, its inventory in water relative to the amount that fell out in 1986 did not exceed 14% for deep lakes and 2–3.6% for shallow lakes.     

Gas-Phase UV Photolysis of CH<Subscript>3</Subscript><Superscript>131</Superscript>I

Gas-phase UV photolysis of ¹³¹I-labeled CH₃I was studied. CH₃ ¹³¹I (228 mg) is completely photolyzed within 5 min under the static conditions at room temperature in an argon atmosphere. The final radioiodine compound formed under these conditions is ¹³¹I₂. The chemical composition of the final products of CH₃I photolysis in air is more complex. Agglomeration corcystallization of the CH₃I photolysis products with NH₄Cl in the gas phase was studied. The results of this study suggest that the main final product of CH₃I photolysis in air is a fine I_xO_y aerosol. In the presence of NH₄Cl, formation of NH₄ ¹³¹I aerosols is possible.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 269–273.Original Russian Text Copyright © 2005 by Kulyukhin, Kulemin, Rumer, Konovalova.     

Sorption of CH3 131I from the water vapor-air medium onto nanocomposite materials

Sorption of CH₃ ¹³¹I from the water vapor-air medium onto inorganic nanocomposite materials containing 1, 2, 4, and 8 wt % Ag in various chemical forms was studied. Despite high ability of the synthesized nanocomposite materials containing 1, 2, and 4 wt % Ag in various chemical forms to take up ¹³¹I₂ (>99%), they cannot be used for localizing CH₃ ¹³¹I from the gas flow. The material containing 8 wt % Ag, namely, the SiO₂-8% Ag nanocomposite prepared by treatment of the precursor with a 0.01 M hydroxylamine solution, is the most suitable for this purpose.     

Sorption of 131I2 and CH3 131I from Water Vapor-Air Phase on Polysorb-1

Sorption of ¹³¹I₂ and CH₃ ¹³¹I from water vapor-air phase on Polysorb-1 polymeric sorbent was studied. The efficiency of radioiodine sorption depends on the humidity and flow rate of the vapor-air stream, column temperature, and the amount of volatile radioiodine compounds. Polysorb-1 effectively removes molecular iodine at the relative humidity of up to 100% and the sorption temperature from 20 to 125°C. Under these conditions, more than 99.9% of ¹³¹I₂ is removed from a gas flow at the height of the sorbent bed of 22.0 cm and time of gas-sorbent contact of 3.4 s. Polysorb-1 does not sorb methyl iodide from a water vapor-gas flow.     

Localization of CH<Subscript>3</Subscript><Superscript>131</Superscript>I from Water vapor–Air flow on granulated sorbents containing nanoparticles of Ag and Ni compounds

Sorption of CH₃ ¹³¹I from the water vapor–air medium onto Fizkhimin inorganic sorbents containing nanoparticles of Ag and Ni compounds was studied. The developed solvents containing 2 wt % Ag and 4–10 wt % Ni exhibit high performance in CH₃ ¹³¹I sorption (>99.9% uptake). The sorption efficiency remains very high (>99.9%) as characteristics of the sorbents and the medium are varied.     

Sorption of <Superscript>137</Superscript>Cs from seawater onto resorcinol–formaldehyde resin

Sorption of ¹³⁷Cs from seawater onto a selective cation exchanger based on resorcinol–formaldehyde resin was studied. The maximal distribution coefficient of ¹³⁷Cs at the ratio S: L = 1: 1000 is (4.1–4.5) × 10³ cm³ g^–1. The sorption-selective characteristics of the resin are negatively affected by alkaline earth meal ions. In the dynamic regime, the operation life of the resorcinol–formaldehyde resin exceeds 700 bed volumes with more than 95% efficiency of cesium sorption. More than 95% of ¹³⁷Cs is eluted with a 1–3 M HNO₃ solution. The eluate volume does not exceed 10 bed volumes.