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 K _d 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 K _d of radioiodine on the metal concentration in the sorbent, the free pore volume of the sorbent, and the anion nature was revealed.     

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).     

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.     

The Effect of Hydrophobization of Ag-Containing Zeolites on Absorption of CH3131I from the Water Vapor-Air Phase

The effect of hydrophobization of Ag-containing nonmodified and acetylene-modified zeolites with poly(vinyl chloride) (PVC) on sorption characteristics of sorbents with respect to CH₃ ¹³¹I was studied. The PVC coating on the sorbent results in increased absorbtion of CH₃ ¹³¹I from a water vapor-air flow at a humidity of up to approximately 70 vol %; the decontamination factor of approximately 10⁵ is reached. The sorbent modified with PVC retains radioiodine at heating to 300°C and can be proposed for practical purposes.     

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.     

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.     

Cocrystallization of Radioiodine Compounds from the Gas Phase

The study of the behavior of ¹³⁷Cs¹³¹I in the presence of MCl (M = NH₄ ⁺, K⁺, Ag⁺, and Cu⁺) in the water vapor-gas phase showed that CsI aerosols are localized in the MCl matrix owing to both agglomeration cocrystallization [¹³⁷Cs¹³¹I-MCl systems (M = K⁺, Ag⁺, NH₄ ⁺)] and agglomeration capture [¹³⁷Cs¹³¹I-CuCl system]. The main advantage of the first process is formation of crystalline globules encapsulating radioiodine in their bulk, which prevents transformation of radioiodine into elemental iodine and methyl iodide.     

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.     

Sorption of CH3131I from Steam-Gas Phase on Modified Ag-Containing Zeolites

Sorption of CH₃ ¹³¹I from the steam-gas phase on Ag-containing zeolites modified with acetylene was studied. The radioiodine adsorption in a column depends on the silver concentration in the sorbent, humidity of the steam-gas flow, and the temperature. The modified sorbents AgX-m containing 30-57% silver efficiently localize CH3I at the humidity up to 80% and sorption temperature from 120 to 195°C. Under these conditions the decontamination factor of a gas flow with respect to CH₃ ¹³¹I at 7.5-cm height of the sorbent bed and a 0.2 s gas-sorbent contact time exceeds 99.99%. The sorption properties of the modified Ag-containing sorbents are better that those of the nonmodified sorbents and known Ag-substituted zeolites.     

Electrochemical polymerization of benzene in the presence of Ag+, Pb2+ and Cu+ ions

Poly(p-phenylene) (PPP) films were synthesized by using benzene and fluorosulphonic acid (FSO₃H) as a strong acid containing Ag⁺, Pb²⁺ and Cu⁺ ions in methylene chloride (CH₂Cl₂) solution. Addition of Ag⁺ or Pb²⁺ ions into the polymerization medium improved the PPP films formation, but Cu⁺ ion did not have an effect on polymerization. PPP films were characterized by cyclic voltammetry, IR and TGA. Dry conductivities were measured by using four probe technique. Received: 18 September 2000 / Reviewed and accepted: 20 September 2000     

Sorption of CH3 131I from a water vapor-air flow onto inorganic sorbents containing Ag and nonferrous metals (Cu,Ni, Zn)

Sorption of CH₃ ¹³¹I from a water vapor-air medium onto Fizkhimin inorganic sorbents containing Ag and nonferrous metals (Cu, Ni, Zn) was studied. Ag-free Fizkhimin inorganic sorbents exhibit poor ability to take up CH₃ ¹³¹I. No more than 51% of the initial 10-mg portion of CH₃ ¹³¹I is taken up by the sorbents heated to 350°C. The sorbents containing 1.4–2 wt % Ag and 5.6–8 wt % nonferrous metal (Cu, Ni, Zn) show high ability to take up CH₃ ¹³¹I (>99.8% uptake), with the performance of the Ni-containing sorbents remaining very high (>99.9%) with variation of various parameters of both the sorbents and the medium. The Cu- and Zn-containing analogs do not exhibit such properties.     

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 CH<Subscript>3</Subscript><Superscript>131</Superscript>I from water vapor-air medium on porous inorganic sorbents containing triethylenediamine and <Emphasis Type="Italic">d</Emphasis> element nitrates

Sorption of CH₃ ¹³¹I from a water vapor-air medium on porous inorganic sorbents based on silica gel of KSKG grade and containing triethylenediamine (CH₂-CH₂)₃N₂ and d element nitrates was studied. The sorbents prepared by impregnation with (CH₂-CH₂)₃N₂ and Zn, Ni, and Cu nitrates from aqueous solution recover CH₃ ¹³¹I from a water vapor-air flow poorly (degree of recovery <10%). Calcination of the sorbents at temperatures exceeding 250°C does not noticeably affect their sorption power. Heating of the complex Ag(NO₃)(OH)·(CH₂-CH₂)₃N₂H to 160°C causes its exothermic decomposition with a large heat release and formation of metallic silver. Thermal decomposition of the complex of Cu²⁺ with (CH₂-CH₂)₃N₂, synthesized from an aqueous solution at the molar ratio Cu(NO₃)₂: (CH₂-CH₂)₃N₂ = 1: 2, occurs similarly.     

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.     

Modified Cu+-Containing Zeolites as Sorbents for Localization of Radioiodine and Radiocesium Aerosols

New sorbents for efficient sorption of radioiodine and radiocesium from aqueous solutions and vapor-gas phase were prepared by treatment of Cu⁺-containing NaX and NaA zeolites with acetylene in aqueous solution. The modified zeolites sorb radioiodine and radiocesium from aqueous solution with the distribution coefficient more than 10⁴ and from a vapor-gas flow with the decontamination factor higher than 10² and 10³, respectively.     

Photoluminescence properties and photocatalytic reactivities of Cu/zeolite and Ag/zeolite catalysts prepared by the ion-exchange method

Transition metal ions (Cu⁺, Ag⁺) incorporated within the cavities of zeolites by an ion-exchange method exhibit unique photoluminescence under UV irradiation due to the inner shell type electronic transition (d⁹s¹ → d¹⁰). Detailed photoluminescence investigations revealed that the transition metal ions exist in highly dispersed state with linear 2 coordination sphere and interact with NO_x (NO and N₂O) in their photoexcited states. In fact, Cu⁺ and Ag⁺ ions within zeolites show an efficient and unique photocatalytic performance for the decomposition of NO into N₂ and O₂ at ambient temperature. Detailed studies of the interaction of NO_x with the excited states of these metal ions indicated that an electron transfer from the s orbital of the excited state of Cu⁺ or Ag⁺ ions into the π^* antibonding orbital of NO_x initiates the decomposition of NO_x into N₂ and O₂.     

Preparation and properties of modified spherically granulated chitosan for sorption of <Superscript>137</Superscript>Cs 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.     

Metal clusters and nanoparticles assembled in zeolites: an example of stable materials with controllable particle size

An ion-exchangeable zeolite (mordenite) is used to control the formation of nanoparticles and clusters within the solid matrix by the hydrogen reduction of metal ions (Ag⁺, Cu²⁺, and Ni²⁺). SiO₂/Al₂O₃ molar ratio in mordenite appears to be an efficient tool to manage the reducibility of the metal ions. Few-atomic silver clusters in line with the larger silver nanoparticles were observed with DRS for the reduced Ag⁺-exchanged mordenites. Cu²⁺-exchanged ones produce the copper nanoparticles with different optical appearance, and Ni²⁺-exchanged mordenites are reduced up to complicated species with no explicit assignment of metal particles under the conditions studied.     

Recovery of 137Cs, 90Sr, 90Y, and d-element ions from aqueous solutions with sorbents containing triethylenediamine

The possibility of using sorbents based on KSKG coarsely porous silica gel and containing triethylenediamine N(CH₂-CH₂)₃N (TEDA) for recovering ¹³⁷Cs, ⁹⁰Sr, ⁹⁰Y, and d-element ions (Cu²⁺, Ni²⁺) from aqueous solutions was examined. Both ⁹⁰Sr, ⁹⁰Y radionuclides and Cu²⁺, Ni²⁺ ions are sorbed on KSKG containing 0.01–6.72 wt % TEDA. However, on sorbents based on KSKG and containing complexes of Cu²⁺, Ni²⁺, and Zn²⁺ nitrates with TEDA, the ¹³⁷Cs, ⁹⁰Sr, and ⁹⁰Y radionuclides are not sorbed. The equilibrium in the systems with these sorbents is attained within 3 h. The sorption capacity for Cu²⁺ and Ni²⁺ strongly depends on the conditions of the sorbent synthesis. The capacity of the sorbents for Cu²⁺ varies from 63 to 320 mg of metal per gram of sorbent. For Ni²⁺, the sorption capacity is considerably lower (no more than 130 mg of Ni²⁺ per gram of sorbent). The distribution coefficients of ⁹⁰Sr and ⁹⁰Y are 300–700 ml g^?1 at the contact time of the solid and liquid phases of 96 h and V/m = 100 ml g^?1.     

Thermal decomposition of CH3 131I in a gas flow

Thermal decomposition of a volatile organic compound of radioactive iodine, methyl iodide CH₃ ¹³¹I, in a gas flow in the presence of various modifications of granulated materials based on KSKG silica gel impregnated with d elements was studied. Under comparable experimental conditions, 97–99% decomposition of CH₃ ¹³¹I is achieved at 770 ± 15°C without sorbents and at 540 ± 10 and 465 ± 20°C in the presence of straight KSKG silica gel and of the material based on it, impregnated with compounds of Ni or its mixture with Cu (8–10 wt %), respectively.