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.     

Removal of volatile 137Cs and 131I compounds from an air flow

The removal of volatile ¹³⁷Cs and ¹³¹I compounds from an air flow on various filtering elements was studied. ¹³¹I₂ and ¹³⁷CsOH are sorbed on basalt wool, but the degree of their recovery is low: ～86 and 90–93%, respectively, at the basalt wool bed height of 15–18 cm. The use of a cascade of bubblers in combination with a column packed with basalt wool allows virtually complete (>99.9%) removal of ¹³¹I and ¹³⁷Cs in the form of ¹³¹I₂, ¹³⁷Cs¹³¹I, and ¹³⁷CsOH from an air flow.     

Cocrystallization of microamounts of <Superscript>137</Superscript>Cs, <Superscript>90</Superscript>Sr,and <Superscript>90</Superscript>Y from aqueous solutions with the solid phase of mixed potassium neodymium ferrocyanide

Cocrystallization of microamounts of ¹³⁷Cs, ⁹⁰Sr, and ⁹⁰Y with the solid phase of mixed potassium neodymium ferrocyanide was studied in relation to the K₄[Fe(CN)₆]: Nd(NO₃)₃ ratio in aqueous solution. At the K₄[Fe(CN)₆]: Nd(NO₃)₃ ratio higher than 2, all the radionuclides studied virtually quantitatively (to 96–99%) cocrystallize with the KNd[Fe(CN)₆]·4H₂O solid matrix. The cocrystallization coefficients D calculated by the Henderson-Krechek equation exceed 10³. Leaching of ¹³⁷Cs and ¹⁵²Eu from the K(¹³⁷Cs)Nd(¹⁵²Eu)· [Fe(CN)₆]·4H₂O solid matrix with water and with aqueous solutions of HNO₃ (0.1 and 1.0 M) and KOH (4.0 M) was studied.     

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.     

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.     

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 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 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.     

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.     

Radiation resistance of a composite ferrocyanide-silica gel sorbent

The radiolytic behavior of FNS composite ferrocyanide sorbent based on potassium nickel ferrocyanide and silica gel was studied. γ-Irradiation of the sorbent results in formation of hydrogen due to radiolytic decomposition of water in the solid phase. The hydrogen yield (molecules/100 eV) is 0.02 for the dry sorbent and 0.07 for the wet sorbent. The amount of hydrogen formed in the course of storage of the sorbent saturated with ¹³⁷Cs was calculated. On irradiation of the dry sorbent in the potassium form to a dose of 4 MGy, the ¹³⁷Cs distribution coefficient K _d decreases by a factor of 2.5. However, K _d of ¹³⁷Cs on irradiated sorbents remains sufficiently high (>10⁴), i.e., the FNS ferrocyanide sorbent shows high functional resistance to radiation. γ-Irradiation of dry and wet samples of the ferrocyanide sorbent to a dose of 4 MGy does not lead to oxidation of Fe(II) to Fe(III) in [Fe(CN)₆] groups. Thus, FNS ferrocyanide sorbent is a radiation-resistant material suitable for recovery of cesium radionuclides from liquid radioactive wastes and the subsequent long-term and safe storage.     

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.     

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.     

Decontamination of 137Cs-contaminated sandy soils by a combination of separation of finely dispersed fraction by sedimentation in water with reagent treatment

Possibilities of reagent decontamination of sandy soils contaminated with ¹³⁷Cs are considered. Treatment with a 2 M H₂SO₄ solution for 7 h at 80°C and liquid-to-solid ratio (L : S) of 2 : 1 results not only in complete recovery of the finely dispersed fraction but also in additional leaching of ¹³⁷Cs from particles of sandy size, with the decontamination factor reaching ∼60–70. The reagent treatment is the most efficient at L : S from 3 : 1 to 4 : 1 after preliminary separation of finely dispersed particles by sedimentation in water.     

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.     

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.     

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.     

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.     

Influence of the potassium and ammonium ion concentrations on the selective sorption of 137Cs by illite and clinoptilolite

It is suggested to describe the dependence of K _d ^?1 of ¹³⁷Cs on the potassium ion concentration for clinoptilolite and illite with a quasi-Langmuir equation in which the maximal radiocesium interception potential relative to potassium, RIP(K)_max, is used instead of the maximal sorption capacity of the sorbent. For describing the dependence of the selective sorption of ¹³⁷Cs on the concentration of ammonium ions, an approximation equation consisting of two normalized quasi-Langmuir equations is suggested, with one equation describing the ¹³⁷Cs sorption on low-affinity sorption centers for concentrations exceeding 3 mM and the other equation describing the sorption on high-affinity centers for ammonium concentrations of up to 3 mM.     

Coprecipitation of 137Cs and 85,90Sr radionuclides from aqueous solutions with the solid phases of CsBPh4 and [M(18-crown-6)]BPh4 (M = Na+, Cs+)

The possibility of joint recovery of cesium and strontium radionuclides from their aqueous solutions with the solid phase of CsBPh₄ or [M(18-crown-6)]BPh₄ (M = Na⁺, Cs⁺) was examined. Depending on the solid phase composition, the degree of coprecipitation of ^85,90Sr and ¹³⁷Cs varies from 40 to 95%. The degree of coprecipitation of ^85,90Sr and ¹³⁷Cs from solutions with the solid phase of the complex compounds is 1.5–3 times higher than with the CsBPh₄ phase. The kind of the anion (NO₃⁻ or Cl⁻) affects the coprecipitation of^85,90Sr and ¹³⁷Cs with the solid phase of the complex compounds [M(18-crown-6)]BPh₄.     

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.