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Abstract  

The sorption of caesium and strontium from its aqueous solutions by ten clinoptilolite-and mordenite-containing sedimentary materials from Slovakia, Bulgaria, Ukraine and Greece was investigated by batch-type procedure and radiotracer techniques. The concentration of the solutions, that were performed in and without the presence of competing cations (0.005 mol·dm−3 KCl) varied between 1·10−4 and 5·10−2 mol·dm−3. The uptake and distribution coefficient (K d) values determined for the materials of the different origin, were correlated with their mineralogical composition and gross cation exchange capacity (CEC). The identification of the specific uptake sites was attempted on the basis of the sorption isotherms and the content of exchangeable cations. The experimental results provide information on the suitability of the individual materials for the treatment of radioactive wastes and their application as backfills in potential nuclear waste repositories.

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Abstract  

The present investigation entails the biosorption studies of radiotoxic Strontium (90Sr), from aqueous medium employing dry cow dung powder (DCP) as an indigenous, inexpensive and, eco-friendly material without any pre or post treatments. The Batch experiments were conducted employing 90Sr(II) as a tracer and the effect of various process parameters such as optimum pH, temperature, amount of resin, time of equilibration, agitation speed and concentration of metal ions have been studied. The kinetic studies were carried out employing various models but the best fitting model was Lagergren pseudo-second order model with high correlation coefficient R 2 value of 0.999 and cation exchange capacity of DCP was found to be 9.00 mg/g. The thermodynamic parameters for biosorption were evaluated as ΔG° = −5.560 kJ/mol, ΔH° = −6.396 kJ/mol and ΔS° = 22.889 J/mol K, which indicated spontaneous and exothermic process with high affinity of Sr(II) for DCP.

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Abstract  

The intercalation compounds Ti(C3H7NH2)(HPO4)2·H2O (18.4 Å) (-TiP/n-Pr) and Ti(C4H9NH2)(HPO4)2·H2O (20.5 Å) (-TiP/n-Bu) have been prepared using -titanium phosphate, Ti(HPO4)2·2H2O (11.6 Å), as precursor. The retention of UO 2 2+ , in aqueous solutions by -TiP is very low being only a superficial adsorption phenomenon. When the intercalated materials are used, the retention is quantitative until 95% of the cation exchange capacity in the -TiP/n-Pr case (c.e.c.=6.30 mequiv./g), and over 80% for the -TiP/n-Bu compound (c.e.c.=6.04 mequiv./g).

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Abstract  

The preparation and characterization of a Mexican organo clinoptilolite-heulandite mineral as well as the evaluation of its sorption properties for cadmium and cobalt are presented. The mineral was modified with different concentrations of hexadecyltrimethyl-ammonium bromide (HDTMA), the resulting materials were characterized by electron microscopy, IR spectroscopy, BET surface analysis, X-ray diffraction and their cation exchange capacities were determined. The cobalt and cadmium uptake was carried out in different concentrations. Neutron activation was used to measure the sorption of cobalt and cadmium. Organo zeolitic mineral samples were obtained with different surface characteristics compared with the original material and it was found that the retention of cobalt and cadmium by the organo zeolite diminishes due to the presence of HDTMA.

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Abstract  

Plant uptake of radiocesium (137Cs) was investigated in consideration of the relationships with naturally existing 133Cs and potassium (K). We first determined plant-unavailable fraction of 137Cs in soil by batch sorption and sequential extraction methods with a radiotracer. Then, using the data obtained from the batch sorption and extraction methods, we clarified the relationships of plant-available and plant-unavailable fractions between 137Cs, 133Cs, and K in soil. Additionally, 137Cs concentrations in crop were estimated using 137Cs in soil and several factors, i.e. fixation ratio of 137Cs in soil, cation exchange capacity, and K concentration in crop. The results implied that the fixation ratio of 137Cs in soil was a very important key to understanding 137Cs plant uptake.

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Summary  

Composite adsorbents were prepared and tested for their ability to remove UO2 2+ in aqueous solution. Synthetic zeolite (zeolite-X) and natural zeolite (clinoptilolite) as an active component were mixed with polyacrylonitrile (PAN) solution as a binder to form the PAN-zeolite-X (composite-X) and PAN-clinoptilolite (composite-C) composite adsorbents. Optimum preparation conditions for the composites were determined. Effects of various parameters on the preparation of the composites were investigated. Each of the prepared composite adsorbents was treated with UO2(NO3)2 . 6H2O and Th(NO3)4 . 4H2O in aqueous solution to determine their sorption capacities. It was found that both composites have about four times higher thorium than uranium uptake capacity. XRD-diffraction patterns were obtained for zeolite-X, composite-X, clinoptilolite and composite-C. Surface area and cation exchange capacities (CEC) were also determined for both composites.

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Abstract  

The uptake of technetium on bentonite materials has been studied from the point of view of the characterization of long-term radioactive elements behavior in nuclear waste repository. It is generally known that bentonite materials show an excellent cation-exchange capacity and on the other hand a poor uptake of anions. The aim of our research has been to find out the conditions suitable for technetium sorption on selected bentonite under oxidizing conditions. The influence of the addition of different materials (e.g., activated carbon, graphite, Fe2+, Fe) with bentonite, the effect of solid:aqueous phase ratio and a pH value on the percentage of technetium uptake and on the K d values were tested.

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Abstract  

A sodium smectite (NaS) with a cation exchange capacity (CEC) of 1.08 mol kg−1 was intercalated with methyltributylammonium cation (MTBA+) with proportions equivalent to 0.2, 0.4, 0.6, 0.8 and 1.0 times the CEC. The contents of adsorbed water and intercalated MTBA+ in the prepared organosmectites (OSs) were determined by using the differential thermal analysis (DTA) and thermogravimetry (TG) curves. The adsorbed water of 8% in the NaS decreases greatly in OSs with the increase of the MTBA+ content and reduces to 2.0% for the 1.0 CEC sample. This explains the gradual change of the NaS from hydrophilic to hydrophobic character. Thermal degradation of the intercalated MTBA+ in OSs occurs approximately between 250–450°C. The oxidation of the formed charcoal to CO2 occurs between 450–850°C. The intercalated MTBA+ content for each OS is obtained from both the TG and carbon analysis. The results do not agree exactly, but both the results tend to increase by increasing initial content of the MTBA+ in solution.

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Abstract

Extreme changes of environmental conditions can alter the soil properties and influence the migration ability and bioavailability of pollutants. Elucidation of the effects of the extreme weather conditions, such as sharp temperature change, drought and floods, on the fractionation of radionuclides in different soil types is especially important for adequate risk assessment after radioactive contamination. The effects of short-term and prolonged freezing and soil drought on the geochemical fractionation of americium in two soil types (Fluvisol and Cambisol, classified according to the World Reference Base for Soil Resources/FAO) from Bulgaria were studied. The changes of the physico-chemical forms of 241Am after storage under different conditions were determined by the sequential extraction procedure and gamma-spectrometric measurements. The impact of the sharp temperature decrease and drought on the association of the radionuclide with the various soil phases was considered in terms of the soil characteristics. The results showed that the risk of increased mobility and bioavailability of americium in the loamy-sand soil with acidic pH and very low cation exchange capacity (CEC) exists under the examined extreme environmental conditions. The soil with sand-loam texture tended to immobilize americium after freeze and drought storage.

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Coleman, N, T., Weed, S. B. & McCracken, R. J., 1959. Cation exchange capacity and exchangable cations in Peidmont soils of North Carolina. Soil Sci. Soc. Amer. Proc. 23 . 146--149. Cation exchange capacity and exchangable

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