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.     

Sorption of CH3131I from the Gas Phase on Modified Metal-Substituted Zeolites Containing Copper and Silver Ions

Sorption of CH₃ ¹³¹I from vapor-gas flow with acetylene-modified Cu⁺- or Ag⁺-containing zeolites in argon atmosphere was studied. The decontamination factor of the gas flow from radioiodine with the sorbent containing 7% of Ag⁺ is considerably higher than that of the Cu⁺-containing zeolite and reaches more than 10⁴ at the bed height of 6.5 cm and contact time of 3.4 s. The sorbent capacity is more than 9 mg of CH₃I per 1 g of the sorbent. In treatment of the sorbent with water after absorption of CH₃I, ¹³¹I is not noticeably desorbed to aqueous phase.     

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.     

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.     

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.     

Determination of the Parameters of Selective <Superscript>137</Superscript>Cs Sorption onto Natural and Ferrocyanide-Modified Glauconite and Clinoptilolite

The effect exerted by surface modification of natural aluminosilicates, glauconite and clinoptilolite, with ferrocyanides on the parameters of selective ¹³⁷Cs sorption was studied. The modification leads to an increase in the specific sorption and in the radiocesium interception potential in the presence of potassium, RIP(K). RIP(K) of the modified sorbents NPF-Gl and NPF-Cl was 6.1 × 10⁵ and 5.0 × 10⁶ mmol kg^–1, and the specific sorption capacity, 138 ± 14 and 136 ± 12 mg g^–1, respectively. The regular trends in variation of the ¹³⁷Cs distribution coefficients in sorption onto the natural and modified sorbents at K⁺ and Са²⁺ concentrations ranging from 10^–4 to 2.0 M were found. The modified sorbents exhibit high specificity to ¹³⁷Cs in a wide range of Ca and K concentrations in the solutions.     

Preparation, Properties, and Application of Modified Mikoton Sorbents

To improve the performance of chitin-containing Mikoton-Ch sorbent, it was modified with K2Cu[Fe(CN)6] or Fe2O3. The sorbents modified with a mixture of these agents were also prepared. The modifying agents are strongly fixed on the Mikoton surface. The techniques for preparing the modified Mikoton are described. The sorption of Cs, Sr, Pu, and Am on modified Mikoton sorbents was studied in relation to the modifier content. Mikoton modified with K2Cu[Fe(CN)6] efficiently sorbs ¹³⁷Cs with the distribution factor K _d of up to 10⁴ ml/g but exhibits low sorption power for Sr, Pu, and Am. Mikoton modified with Fe3O4 is a ferromagnetic material. This sorbent exhibits increased sorption power for Pu and Am (K _d = 10⁴-10⁵ ml/g) but poorly sorbs ¹³⁷Cs. The feasibility of practical application of different kinds of modified Mikoton sorbents is demonstrated.     

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.     

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.     

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.     

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.     

Sorption of Cs,Sr, U,and Pu radionuclides on natural and modified clays

The ability of natural and modified montmorillonite clays from Belgorod oblast to sorb Cs, Sr, U, and Pu radionuclides was studied. The clays were modified by treatment with metal (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Fe²⁺, Zn²⁺) chloride solutions or aqueous HCl. The natural and modified clays studied show high performance in sorption treatment of solutions to remove Cs radionuclides. The natural clay and the Na and Mg forms of clays show the best sorption characteristics with respect to Cs. The distribution coefficient K _d of ¹³⁷Cs in sorption on the above samples from a 0.1 M NaNO₃ solution is (1.1–1.4) × 10⁴ cm³ g⁻¹, which is 4–5 times higher compared to natural clinoptilolite. The Sr, U, and Pu radionuclides are sorbed on the examined clay samples to a considerably lesser extent. The K _d values in sorption of these radionuclides from tap water are lower by 2–3 orders of magnitude than in sorption of Cs. Addition of clay materials in the course of cementation of liquid radioactive wastes, including NPP bottom residues, allows the rate of radiocesium leaching from the hardened cement compounds to be decreased by a factor of 5–16. The most efficient sorption additive in cementation of NPP bottom residues is natural montmorillonite clay.     

Recovery of <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr from wastewater by sorption on finely dispersed minerals under static conditions

The natural minerals clinoptilolite and tripoli were used for sorption treatment of liquid radioactive waste (LRW) to remove ¹³⁷Cs and ⁹⁰Sr. The efficiency of sorption recovery of these radionuclides with finely dispersed mineral sorbents under static conditions was studied in relation to the sorption time, pH, size of mineral granules, sorbent amount, salt content and chemical composition of solutions, and number of successive sorption steps. The distribution coefficient of radionuclides between the sorbent and aqueous phase and the sorption capacity of sorbents for radionuclides were determined. It was found that treatment of real salt-containing LRW from the Leipunskii Institute of Energy Physics, State Scientific Center of the Russian Federation, with the natural sorbents decreased their activity by 2–3 orders of magnitude owing to recovery of ¹³⁷Cs and ⁹⁰Sr.     

Nanostructured Magnetic Sorbents for Selective Recovery of Uranium(VI) from Aqueous Solutions

Direct sol-gel, novel template, and additional high-temperature reduction procedures for preparing iron oxides and their composites, showing promise for selective sorption of dissolved U(VI) from aqueous media of various acidities, are described. The sorption activity of the materials was studied, the kinetic curves of the sorption were obtained, and the efficiency of the selective recovery of U(VI) from aqueous solutions with different pH values using the new sorbents was compared. The probable mechanism of the U(VI) sorption onto the sorbents studied was suggested on the basis of SEM, XPS, emf, and BET data. The quantitative sorption of U(VI) is determined to a greater extent by the composition of the sorbent solid phase, rather then by the specific surface area of the sorbents, which ranges from 0.1 to 47.3 m² g^?1 depending on the synthesis procedure. The crystalline Fe⁰ phase in the sorbents prepared using additional high-temperature reduction plays the key role in the U(VI) sorption by the reducing deposition mechanism. The saturation magnetization for this type of sorbents can reach 133–140 emu g^?1, which is an additional advantage allowing magnetic separation of the spent sorbents from the treated solutions.

     

Removal of Radiocesium from Aqueous Media with Zinc–Aluminum Layered Double Hydroxide Intercalated with Copper(II) Hexacyanoferrate

Sorption of radiocesium from aqueous media with zinc–aluminum layered double hydroxide intercalated with copper(II) hexacyanoferrate (Zn/Al-CuFeCN) was studied. The highest ¹³⁷Cs distribution coefficients (790–850 cm³ g^–1) on this sorbent are reached at initial pH in the range 5.0–9.0 (pH after sorption 6.8–7.3). The limiting value of the Cs⁺ adsorption onto Zn/Al-CuFeCN, calculated from the Langmuir equation, is 64.1 mg g^–1. At a concentration of up to 100 mg dm^–3, Na⁺ ions do not noticeably affect the Cs⁺ sorption onto Zn/Al-CuFeCN, whereas the K⁺ and Ca²⁺ ions slightly (by 5–10%) decrease the degree of the Cs⁺ removal. The sorbent shows high selectivity (99.8%) in decontamination of natural water.     

Dynamics of sorption of cesium radionuclides on selective ferrocyanide sorbents. Distribution of the 137Cs activity in the stationary phase

A method was suggested for studying the dynamic sorption properties of ferrocyanide sorbents toward Cs radionuclides by analyzing the radiocesium distribution in the solid phase of the sorbent. The dynamic sorption characteristics are determined by measuring the activity of successive sorbent layers after passing definite volumes of the solution. The method is efficient in analysis of the stability of various sorbents in liquid media. The sorption characteristics of the following ferrocyanide sorbents were examined: Termoksid-35 (nickel-potassium ferrocyanide on zirconium hydroxide), FNS-2 (nickel-potassium ferrocyanide on silica), and FS-2 (copper-potassium ferrocyanide on silica). In alkaline solutions, Termoksid-35 is the most stable. The effect of oxalic acid on the activity distribution in a ferrocyanide sorbent bed was studied. In alkaline solutions containing oxalic acid, copper ferrocyanide (FS-2) is the least stable. At the same time, at low pH values and in the absence of oxalic acid, it is preferable to use sorbents based on copper ferrocyanides.     

Sorption Recovery of 137Cs and 90Sr with Carbonate-Containing Natural Mineral Tripolite

The sorption characteristics of a carbonate-containing mineral (tripolite) were studied on model aqueous solutions and real wastewaters in a wide range of pH in the presence of isotopic and nonisotopic carriers and organic impurities. The sorption of ¹³⁷Cs and ⁹⁰Sr is adequately described by a power function. Analysis of ¹³⁷Cs sorption isotherms suggests that radiocesium is adsorbed by the ion-exchange mechanism, during which Cs⁺ ions from the solution exchange mainly with bivalent ions of the sorbent, whereas in ⁹⁰Sr sorption trivalent ions of the sorbent also participate in the process. The saturation capacities of tripolite with respect to cesium and strontium were evaluated to be 0.3 and 1.0 mg-equiv g^{- 1}, respectively.     

Sorption of Radioactive Iodine on Polymeric Sorbents from Aqueous Solutions and Gas Phase

Sorption of various species of radioactive iodine from aqueous and gas phases on polymeric sorbents Styrosorb and Polysorb-1 was studied. These sorbents do not take up ionic species of radioactive iodine (¹³¹I^- and ¹³¹IO₃ ^-) from aqueous solutions. At the same time, both sorbents take up ¹³¹I₂ from aqueous solutions at 25°C. At V/m = 500 ml g^{- 1}, the distribution factors K _d are 1350 and 590 ml g^{- 1} with Styrosorb and Polysorb-1, respectively. These sorbents efficiently recover ¹³¹I₂ from an air flow at 25°C and flow velocity of 0.33 cm s^{- 1}. The sorption capacity of Styrosorb is approximately four times higher than that of Polysorb-1 and amounts to 97.0 mg of I₂ per gram of sorbent. These data are consistent with the specific surface areas of the sorbents.     

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 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.