Retention of Cs on zeolite, bentonite and their mixtures

The sorption behavior of cesium on zeolite and bentonite minerals and their mixtures was studied by means of a batch method and a tracer technique. All experiments were carried out in the presence of CsCl spiked with ¹³⁷Cs and NaCl as a supporting electrolyte in varying concentrations. The distribution coefficients (K _D) did not show significant differences at low Cs⁺ loadings while they decreased in the high loading region. Freundlich and D-R isotherms were applied to the adsorption data of zeolite and bentonite. Adsorption capacities and mean energies calculated from D-R isotherm parameters decreased by increasing ionic strength on both minerals. The identification of the specific uptake sites was attempted on the basis of the Freundlich isotherm. Experimentally observed distribution coefficients of Cs on two mineral mixtures were smaller than theoretically calculated values, except at the highest NaCl concentration.     

Electron irradiation studies on ammonium molybdophosphate

Ammonium molybdophosphate (AMP) was irradiated with electrons up to a dose of 1 MGy. X-ray diffraction patterns and FT-IR of irradiated and control AMP samples were recorded. Uptake of¹³⁷Cs from nitric acid in the range of 0.2 to 10 mol·dm^–3 was estimated by a batch equilibration technique. AMP undergoes perceptible changes in its physico-chemical characteristics on irradiation with electrons. Uptake of¹³⁷Cs from nitric acid by irradiated AMP was nearly the same as the control AMP in the nitric acid concentration range of 6 to 10 mol·dm^–3 and relatively higher in the range of 0.2 to 6 mol·dm^–3. The results are discussed in terms of available information on the physicochemical properties of 12-heteropoly acids and their salts.     

SuperLig 644 equilibrium sorption data for cesium from Hanford tank waste supernates

SuperLig 644 ion exchange resin is currently being evaluated for cesium (¹³⁷Cs) removal from radioactive Hanford tank wastes. To assess the performace of the resin in column configuration, a multiple batch contact method was used to determine the equilibrium distribution coefficients (K _d) and percent removal for ¹³⁷Cs from highly alkaline waste solutions obtained from the Hanford Site. The equilibrium loading data were interpreted in terms of Freundlich and Dublin-Radushkevics (D-R) isotherms. The equations fit the experimental data remarkably well considering the complexity of the Hanford tank waste compositions. The mean energy of adsorption and total resin capacity were calculated. The mean free energy for adsorption of cesium from Hanford tanks was ~9 kJ/mol. The total exchange capacity of the SuperLig 644 resin ranged from 0.72 to 3.46 mmole/g resin, depending on the Hanford tank composition. The K _d results reveal that SuperLig 644 resin in highly selective for cesium in the presence of relatively high concentrations of sodium and potassium salts.     

Adsorption of Mercury(II) on Amidoxime Chelating Resins with Magnetic Properties

Two amidoxime chelating resins were prepared. The preparation process was carried out through copolymerization of acrylonitrile with N,N′-methylene-bis-acrylamide (MBA) as a crosslinker in the presence and absence of magnetite (Fe₃O₄) particles. The resins obtained were subsequently treated with hydroxylamine to give the corresponding amidoxime chelating resins. The uptake behavior of the resins toward Hg(II) in aqueous solutions using batch and column techniques was studied. The oxide containing resin gave higher uptake capacities relative to oxide free resin confirming the advantage of embedded particles on the uptake capacity. Thermodynamic and kinetic parameters of the uptake process were calculated. Regeneration of the resins was carried out using 0.5 M KI and the desorption ratio was found to be more than 97%.     

Effect of temperature on SuperLig® 644 cesium removal from simulated Hanford tank waste supernate

Batch kinetic and column experiments have been carried out at 25, 35, and 45 °C to examine the effect of temperature on SuperLig® 644 cesium (Cs) removal from simulated Hanford tank waste supernate. The simulated solution mimicked the composition of the low-activity waste supernate from tank 241-AN-105 in the U.S. DOE Hanford site. Small quantities of toxic metals, such as Cd, Cr, Fe, and Pb were spiked into the simulant to evaluate the metal's competitiveness with Cs for sorption on SuperLig® 644 resin. The results indicated that the temperature affects the removal of Cs and metal ions, although the effect was not the same for all metal ions. The extent of Cs removal decreased with an increase in temperature. The Cs capacity at breakthrough point was 0.015, 0.013, and 0.011-mmole/g dry resin at 25, 35 and 45 °C, respectively. The column was effectively eluted to less than 1% (0.1 C/C ₀) of the feed concentration with approximately 10 BVs of 0.5M nitric acid. The resin showed limited affinity for toxic metal ions (Cr, Cd, Fe, and Pb) as compared to Cs. Based on the batch kinetic data, the Cs uptake of the resin was not hampered by the presence of the toxic metals in solution.     

Thermal study of irradiated polyacetylene films

Polyacetylene films irradiated by-rays up to 100 MRad were studied by means of TMA, DTG and DSC methods.It is shown that as the irradiation dose increases the concentration of topological branching knots into the polymer chains and theT _g values decrease, the total mass loss and the enthalpy of the thermal isomerization reaction also decrease.     

A comparative study on sorption and diffusion of Cs in crushed argillite and granite investigated in batch and through-diffusion experiment

The batch and through-diffusion experiments in this study were conducted and compared in order to investigate the sorption and diffusion of cesium (Cs) for two potential host rocks in Taiwan: argillite from Taitung and granite from Kinmen Island, with the purpose of establishing a reliable safety-performance assessment methodology for the final disposal of low level radioactive waste. The results of Cs mapping by scanning electron microscope equipping by energy dispersive spectrometer (SEM–EDS) showed that the distribution of Cs on argillite and granite were enriched in illite and biotite, respectively. In addition, it showed that higher sorption capacities were found for argillite than granite; due to the clay mineral content (illite) in the argillite. Experiments for diffusion of Cs is agreement to the values estimated for the diffusive results (D _a) of Cs in argillite were revealed to be lower than those of granite.

     

Treatment of low level radioactive liquid wastes using composite ion-exchange resins based on polyurethane foam

Composite ion-exchange resins were prepared by coating copper-ferrocyanide (CFC) and hydrous manganese oxide (HMO) powders on polyurethane (PU) foam. Polyvinyl acetate/Acetone was used as a binder. The foam was loaded with about five times its weight with CFC and HMO powders. The distribution coefficients of CFC-PU foam and HMO-PU foam for cesium and strontium respectively were estimated. Under similar conditions the HMO-PU foam showed higher capacity as well as better kinetics for removal of strontium than CFC-PU foam for Cs. The pilot plant scale studies were conducted using a mixed composite ion-exchange resin bed. About 1000 bed volumes could be passed before attaining a DF of 10 from an initial value of 60–80. The spent resin was digested in alkaline KMnO₄ and the digested liquid was fixed in cement matrix. The matrices were characterized with respect to compressive strength and leach resistance.     

Diffusion of cesium and selenium in crushed mudrock

In this study, the diffusion behavior of cesium and selenium with 10⁻⁴M concentration in mudrock was studied by trough-diffusion tests and summarized in order to provide confidence on long-term performance assessment of nuclear waste repositories. The diffusion process of Cs and Se reached equilibrium after 60 and 500 days, respectively. Besides, it also displays that the distribution coefficients (K _d ) of Se in through-diffusion tests is higher than that of Cs in agreement with that obtained from the batch method. The K _d value (15.14±1.99 mL/g) of Cs by diffusion techniques is equivalent to that of batch method (15.10±0.40 mL/g) because sorption of Cs was assumed to fast sorption step. However, the K _d value of Se (137.58±12.20 mL/g) derived from the diffusion technique is higher than that from batch tests (76.72±2.96) and showed an obvious variation with K _d of Cs. The difference of K _d between diffusion and batch methods resulted from the fact that 14 days were not long enough to reach equilibrium or stable state in the batch method.     

Radiation stability of macro-porous and gel-type cation exchangers

Macro-porous cation exchange resin Diaion CPK-08 and gel type cation exchange resin Dowex 50WX8 were irradiated with γ-rays from⁶⁰Co, while soaked in distilled water, 0.5M HNO₃ or 4M HNO₃, and the ion-exchange properties, such as strong- and weak-acid capacities, moisture content and wet resin volume, were examined in relation to absorbed dose. There was no appreciable difference between the radiation stabilities of the two cation exchangers. Increase of HNO₃ concentration reduced the loss of strong-acid capacity and increased the decross-linkage and the weak-acid capacity. Elution characteristics of¹³⁷Cs and⁹⁰Sr from columns packed with γ-irradiated resin were examined and the column distribution ratio of these radionuclides and the theoretical plate number were calculated. These values decreased with the increase of absorbed dose. Diaion CPK-08 was packed into a pressurized column and irradiated with γ-rays at a dose rate of 2·10⁶ R/hr, while water was passed through the column at a constant flow rate. The greatest change of the resin properties was observed at an upper stream position from the position of the highest radiation dose of 2·10⁶ R/hr.     

Resorcinol - formaldehyde adsorption of cesium from Hanford waste solutions

Batch equilibrium measurements were conducted at 25±2 °C with a granular resorcinol-formaldehyde (RF) resin to determine the distribution coefficients (K _d ) for cesium. In the tests, Hanford Site actual waste sample containing radioactive cesium (¹³⁷Cs) and a pretreated waste sample that was spiked with non-radioactive ¹³³Cs were used. Initial concentrations of non-radioactive cesium in the waste sample were varied to generate an equilibrium isotherm for cesium. Majority of the tests were conducted at 25±2 °C using a liquid to solid phase ratio of 100 ml/g and at a contact time of 72 hours. Two additional tests were conducted at a liquid to solid phase ratio of 10 and at contact time of 120 hours. The measured distribution coefficient (K _d ) for radioactive cesium (¹³⁷Cs) was 948 ml/g, the K _d for non-radioactive cesium (¹³³Cs) was 1039 ml/g. The K _d for nonradioactive cesium decreased from 1039 to 691 ml/g with increased initial cesium concentration from 8 to 64 g/ml. Very little change of the K _d was observed at initial cesium concentration above 64 g/ml. The maximum sorption capacity for cesium on granular RF resin was 1.17 mmole/g dry resin. This value was calculated from the fit of the equilibrium isotherm data to the Dubinin-Radushkevich equation. Previously, a total capacity of 2.84 mmole/g was calculated by Bibler and Wallace for air-dried RF resin.This work was conducted at the Savannah River Technology Center in Aiken, SC, which is operated for the U. S. Department of Energy (DOE) by Westinghouse Savannah River Company under Contract DE-AC09-96SR18500. The Hanford River Protection Project-Waste Treatment Plant (RPP-WTP) funded this work. The authors are very grateful to Karen Palmer, Betty Mealer, and Yvonne Simpkins for their assistance in the experimental work.     

Resorcinol - formaldehyde adsorption of cesium from Hanford waste solutions

Batch equilibrium measurements were conducted at 25±2 °C with a granular resorcinol-formaldehyde (RF) resin to determine the distribution coefficients (K _d ) for cesium. In the tests, Hanford Site actual waste sample containing radioactive cesium (¹³⁷Cs) and a pretreated waste sample that was spiked with non-radioactive ¹³³Cs were used. Initial concentrations of non-radioactive cesium in the waste sample were varied to generate an equilibrium isotherm for cesium. Majority of the tests were conducted at 25±2 °C using a liquid to solid phase ratio of 100 ml/g and at a contact time of 72 hours. Two additional tests were conducted at a liquid to solid phase ratio of 10 and at contact time of 120 hours. The measured distribution coefficient (K _d ) for radioactive cesium (¹³⁷Cs) was 948 ml/g, the K _d for non-radioactive cesium (¹³³Cs) was 1039 ml/g. The K _d for nonradioactive cesium decreased from 1039 to 691 ml/g with increased initial cesium concentration from 8 to 64 g/ml. Very little change of the K _d was observed at initial cesium concentration above 64 g/ml. The maximum sorption capacity for cesium on granular RF resin was 1.17 mmole/g dry resin. This value was calculated from the fit of the equilibrium isotherm data to the Dubinin-Radushkevich equation. Previously, a total capacity of 2.84 mmole/g was calculated by Bibler and Wallace for air-dried RF resin.This work was conducted at the Savannah River Technology Center in Aiken, SC, which is operated for the U. S. Department of Energy (DOE) by Westinghouse Savannah River Company under Contract DE-AC09-96SR18500. The Hanford River Protection Project-Waste Treatment Plant (RPP-WTP) funded this work. The authors are very grateful to Karen Palmer, Betty Mealer, and Yvonne Simpkins for their assistance in the experimental work.     

Lateral growth of microparacrystals in kevlar 49 fibers irradiated by Co60

Wide-angle x-ray diffraction experiments on Kevlar 49 fibers, irradiated with γ-rays from a Co⁶⁰ source, indicated that radiation-induced cross-linking in the form of H-bonding occurred within the microparacrystals (mPC) in the lateral direction b of the unit cell and had led to an increase in the mPC size in this direction. On the other hand, the mPC size I₂₀₀ along the axis and normal to the [200] netplanes did not change by radiation. In effect, the mPC size normal to the [110] netplanes increased from 4.23 nm to a maximum value of 6.04 nm at the 600 MRad dose level, after which it decreased. The mPC size in the direction of the fiber axis was 102 nm and did not change significantly by radiation (102–109 nm). Thus, essentially, the mPCs grew solely in the b direction. The paracrystalline distortion parameter (g) in the direction of the fiber axis was 2.8% and was not changed significantly by radiation (g = 2.9 ± 0.2%). The equatorial “crystallinity” maintained a value of 76% until a dose of 50 MRad and then became 73% at 100 MRad and 70% after this dose level The netplane distances were not affected by radiation.     

Study the radiation effects on 4-vinylpyridine-based porous resins in 99Tc adsorption

The 4-vinylpyridine-based porous resins (4VP–DVB and 4VP–DVBQ) were synthesized to adsorb ⁹⁹Tc from radioactive waste. The radiation stability of the synthesized resins were investigated in air, water, HCl, and HNO₃ mediums. The radiolytic degradation of resins was evaluated by the total organic carbon analysis. The weakly basic resin (4VP–DVB) and strongly basic resin (4VP–DVBQ) showed a remarkable resistance to radiation in HCl and HNO₃ solutions respectively. Moreover, adsorption behavior of irradiated 4VP–DVB and 4VP–DVBQ resins toward ⁹⁹Tc was studied by the batch experimental method.

     

Composite ion exchanger with ammonium molybdophosphate and its properties

An organic binding polymer based on polyacrylonitrile (PAN) was used for the preparation of the composite exchanger containing ammonium molybdophosphate (AMP) as the active component. Due to the improvement of granulometric properties of powdered AMP with a binding polymer, an exchanger suitable for the application in column operations was prepared. Study of the properties of the exchanger AMP-PAN proved that kinetics of cesium sorption, capacity of the exchanger for cesium and desorption of cesium are not influenced by the binding polymer. The composite exchanger AMP-PAN described is therefore suitable for the selective separation and concentration of cesium and purification of radioactive wastes from¹³⁷Cs.     

Biosorptive behavior of mango (<Emphasis Type="Italic">Mangifera indica</Emphasis>) and neem (<Emphasis Type="Italic">Azadirachta indica</Emphasis>) barks for <Superscript>134</Superscript>Cs from aqueous solutions: A radiotracer study

The role of dead biomasses viz., mango (Mangifera indica) and neem (Azadirachta indica) bark samples are assessed in the removal behavior of, one of important fission fragments, Cs(I) from aqueous solutions employing a radiotracer technique. The batch type studies were carried out to obtain various physico-chemical data. It is to be noted that the increase in sorptive concentration (from 1.0·10⁻⁸ to 1.0·10⁻² mol·dm⁻³), temperature (from 298 to 328 K) and pH (2.6 to 10.3) apparently favor the uptake of Cs(I) by these two bark samples. The concentration dependence data obeyed Freundlich adsorption isotherm and the uptake follows first order rate law. Thermodynamic data evaluation and desorption experiments reveal the adsorption to be irreversible and endothermic in nature proceeding through ion-exchange and surface complexation for both dead biomasses. Both bark samples showed a fairly good radiation stability in respect of adsorption uptake of Cs(I) when irradiated with a 300 mCi (Ra-Be) neutron source having an integral neutron flux of ∼3.85·10⁶ n·cm⁻²·s⁻¹ and associated with a nominal γ-dose of ∼1.72 Gy·h⁻¹.     

Investigation of cesium uptake from aqueous solutions using new titanium phosphates ion-exchangers

The uptake of cesium from aqueous solutions (pH 5) using titanium phosphates was investigated in the absence and presence of background electrolyte (0.1 M NaNO₃) using a batch technique. The determination of cesium was performed by gamma spectroscopy using ¹³⁷Cs as tracer. The obtained sorption isotherms could be satisfactorily reproduced by a Langmuir sorption equation. The maximum uptake capacity values (q _max) calculated fitting the experimental data by this equation were 167 and 118 mg/g for solutions of initial pH 5 in the absence and presence of background electrolyte. Kinetics data obtained at 293, 308 and 323 K could satisfactorily reproduced by the pseudo-second order equation. It was demonstrated that the new synthesized materials can remove considerable amounts of cesium from aqueous solutions and ion exchange is considered to be the principal mechanism for cesium removal. Toxicity characteristic leaching procedure and desorption tests provided data about the application of the sorbents in environmental remediation.     

Synthesis and characterization of ammonium molybdophosphate–silica nano-composite (AMP–SiO2) as a prospective sorbent for the separation of 137Cs from nuclear waste

The ammonium molybdophosphate–silica (AMP–SiO₂) nano-composites were prepared by sol–gel method. The material synthesized was nanocrystalline, with average crystallite size of primary particles in the range of 10–25 nm. Small angle X-ray scattering showed presence of mass fractal aggregates made of small particles with rough pore boundaries. To realize the scope of using AMP–SiO₂ nano-composites sorbent for removal of ¹³⁷Cs from nuclear waste solutions, its adsorption characteristics for cesium were evaluated. It was found that the AMP–SiO₂ nanocomposites were amenable for column operation, have high affinity for Cs, and possess very high adsorption capacity for Cs. From the perspective of separation of ¹³⁷Cs from acidic radioactive waste solution, AMP–SiO₂ nanocomposite holds significant promise.     

High resolution solid‐state 13C‐NMR study of as‐cured and irradiated epoxy resins

This article presents the effects of strong ionizing radiations on the physico‐chemical modifications of aliphatic or aromatic amine‐cured epoxy resins based on diglycidyl ether of bisphenol A (DGEBA). Such epoxy resins have a considerable number of applications in the nuclear industrial field and are known to be very stable under moderate irradiation conditions. Using extensively high resolution solid‐state ¹³C‐NMR spectroscopy we show that the aliphatic amine‐cured resin (DGEBA‐TETA) appears much more sensitive to gamma rays than the aromatic amine‐cured one (DGEBA‐DDM). On the one hand, qualitative analyses of the high resolution solid‐state ¹³C‐NMR spectra of both epoxy resins, irradiated under similar conditions (8.5 MGy), reveal almost no change in the aromatic amine‐cured resin whereas new resonances are observed for the aliphatic amine‐cured resin. These new peaks were interpreted as the formation of new functional groups such as amides, acids and/or esters and to alkene groups probably formed in the aliphatic amine skeleton. On the other hand, molecular dynamics of these polymers are investigated by measuring the relaxation times, T_CH, T_1ρH and T_1C , before and after irradiation. The study of relaxation data shows the formation, under irradiation, of a more rigid network, especially for the aliphatic amine‐cured system and confirms that aromatic amine‐cured resin [DGEBA‐4,4′‐diaminodiphenylmethane(DDM)] is much less affected by ionizing radiations than the aliphatic amine‐cured resin [DGEBA‐triethylenetetramine(TETA)]. Moreover, it has been shown that the molecular modifications generated by irradiation on the powder of the aliphatic‐amine‐cured resin appear to be homogeneously distributed inside the polymers as no phase separations can be deduced from the above analyses. Copyright © 2001 John Wiley & Sons, Ltd.