Sorption characteristics of Am(III), Sr(II) and Cs(I) on bentonite and granite

The ability of the back-fill and the host rock materials to take up radioisotopes like ²⁴¹Am, ^85,89Sr and ¹³⁷Cs has been examined as a function of contact time, pH, amount of sorbent, sorbate concentration, and the presence of complementary cations. A batch technique using actual borehole water from the granite formation has been utilized. In general, the uptake of nuclides by bentonite is much higher than that with granite. The sorption order of nuclides on bentonite is Am>Cs>Sr. The presence of complementary cations, Na⁺, K⁺, Ca²⁺ and Mg²⁺ depresses the sorption of Cs and Sr on bentonite. The sorption data have been interpreted in terms of Freundlich and Langmuir isotherm equations. Utilizing the Langmuir isotherm equation, the monolayer capacity, V _m ,and the binding constant, K, have been evaluated. The change in free energy for the sorption of nuclides on bentonite has also been calculated.     

Adsorption of Cs(I), Sr(II) and Co(II) on Al2O3

The sorption of Cs(I), Sr(II) and Co(II) from aqueous solutions on alumina under various experimental conditions has been studied by batch techniques. Freundlich, Langmuir and Dubnin-Raduskevich equations have been used to interpret the sorption data. The values of various thermodynamic parameters have been determined. The sorption of Cs(I) and Sr(II) on alumina is exothermic in nature while that of Co(II) is an endothermic process. The H ^o values for Cs(I), Sr(II) and Co(II) were–23.29 KJ/mol at 298K,–35.3 KJ/mol at 293 K and 13.49 KJ/mol at 293 K, respectively. Negative values of G ^o show the spontaneity of the sorption processes; G ^o values of Cs(I) and Sr(II) becomes less negative at higher temperatures while the G ^o values of Co(II) become more negative with increasing temperature. At higher temperatures, less amounts of Cs(I) and Sr(II) and greater amounts of Co(II) are sorbed on alumina. The values of the mean free energies of sorption,E, for Sr(II) and Co(II) at various temperatures were within the range of 7–10 KJ/mol which show that these metals are sorbed on alumina predominantly by an ion-exchange process.     

Sorption and diffusion of 90Sr2+in compacted bentonite investigated by a capillary method

Summary The effects of bentonite density and fulvic acid on the sorption and diffusion of ⁹⁰Sr²⁺in compacted bentonite were investigated by using a capillary method. The experiments were carried out at pH 7.0±0.1 in the presence of 0.01M NaClO₄. The results suggest that the sorption and diffusion of ⁹⁰Sr²⁺in compacted bentonite decreases with increasing the density of compacted bentonite. The presence of FA enhances the sorption of Sr²⁺, but reduces the diffusion of Sr²⁺in compacted bentonite. The porosity of the compacted bentonite plays an important role in the sorption and diffusion behavior of ⁹⁰Sr²⁺. Using the calculated effective diffusion coefficients the long-term relative concentration distribution of strontium was evaluated in compacted bentonite.     

Sorption of Cs(I) on Magnetite in the Presence of Silicates

The sorption of H(4)SiO(4) on magnetite has been qualified and quantified using three different surface complexation models, CCM, DLM, and NEM. The three tested models can account for the sorption of silicates using the same stoichiometry, one neutral species binding on a neutral surface, and the same constant, error aside. Experiments have also been performed to demonstrate that the sorption of dissolved silicates has a nonnegligible effect on the behavior of the surface of magnetite. Then, the sorption of cesium is insignificant on the neat surface of magnetite and is increased up to 10-20% when silicates are present in solution. A theoretical model, where the rule of electrostatics is pointed out, has been developed to account for the experimental observations. This model allows the reproduction of the sorption of cesium in the presence of dissolved silicates for the following four cases: -concentration of silicates under solubility limit -concentration of silicates over solubility limit -binary mixtures of silica and magnetite -natural magnetite with silica as impurity. The reaction given in the model to account for the experimental observations proposes that silicates may act as a "bridge" between the surface of magnetite and cesium. Copyright 2000 Academic Press.     

Retention behaviour of Cs(I), Sr(II), Tc(VII) and Np(V) on smectite-rich clay

The smectite-rich natural clay is being considered as a backfill and buffer material for Indian repository programme. In the present study, batch sorption measurements have been performed at trace concentrations for one of the minor actinide elements [Np(V)] and for the long lived fission products, Cs(I), Sr(II), and Tc(VII) on purified and conditioned smectite-rich clay at varying conditions of pH and ionic strength. In case of Cs(I) and Sr(II) the sorption was found to increase with pH. At any pH the sorption was found to decrease with increasing ionic strength of the suspension maintained with NaCl. Further, at any pH the sorption of Sr(II) is less than the corresponding value for Cs(I). This is indicative of effect of size selectivity on the sorption by the clay. Tc(VII), on the other hand, is poorly retained by the clay, which can be explained in terms of the negative charge on the TcO₄ ^? ion, which has negligible interaction with the predominantly negatively charged clay surface. In the case of Np(V), the sorption was found to increase albeit, slowly compared to Cs(I) and Sr(II) with pH, and it with no effect of ionic strength on the sorption at all pH values. This suggests that Np(V) primarily interacts with the surface sites via inner sphere complexation mechanism.     

Modelling of the Sorption of Sr(II) on Hydrous Zirconium Oxide

The amphoteric acid-base behavior of hydrous zirconium oxide (HZO) was investigated by titrating HZO with 0.05M HNO₃ and NaOH at constant ionic strength. The sorption of strontium from 0.05M NaNO₃ solution was measured as a function of pH. Abrupt increase in sorption was observed at the equilibrium pH of 9. The experimental titration and strontium sorption data on HZO were evaluated using the constant capacitance model (CCM) and diffuse double layer model (DLM). Various model parameters of Surface Complexation Models (SCM) were estimated, numerically, by non-linear regression. Modeling the sorption and speciation of Sr²⁺ on HZO indicated that the hydrolysis of Sr²⁺ to lower charged SrOH⁺ is the pre-requisite for the abrupt sorption behavior at pH 9.     

Sorption of Sr(II) onto nanocomposites of graphene oxide-polymeric matrix

The simple method for preparation of nanocomposites of graphene oxide or carboxylated graphene oxide on polystyrene matrix and graphene oxide on PA66 matrix were developed and structures of nanocomposites were characterized by X-ray diffraction, infrared spectroscopy, Raman spectroscopy, high-resolution scanning electron microscopy, transmission electron microscopy and scanning transmission electron microscopy. The nanocomposites were investigated for radiostrontium removal from aqueous solutions. The Sr(II) sorption was dependent on pH and ionic strength at pH < 7. The Sr(II) equilibrium data were fitted by Freundlich and Langmuir models. The nanocomposites prepared were evaluated as suitable for the radiostrontium removal from contaminated wastewater.     

Modification of the structure of natural bentonite and study on the sorption of Cs+

Natural bentonite clay was treated in order to remove impurities to increase the cation exchange capacity of the montmorillonite and to obtain a more effective radioactive cesium sorption. It was found that the treatment of the clay determines the amount of sorbed cesium. On the other hand it was shown that montmorillonites may retain cesium through several mechanisms which provide strongly retained cations occupying cationic sites into the clay structure or sorbed cesium which may be lost by purification treatments.     

Mitigation of radionuclide deposition in contaminated water: effects of pH on coprecipitation of Cs(I) and Sr(II) with Fe(III) in aqueous solutions

Journal of Radioanalytical and Nuclear Chemistry - In the present study, the amounts of caesium and strontium were quantified in the precipitates formed in solutions of sodium hydroxide and...     

Distribution studies of metal ions on arsenophosphates of Sn(IV) and Cr(III) and on amine Sn(II) hexacyanoferrates (II) using radio tracers: Separation of Sr2+−Cs+, Hg2+−Ag+ and Hg2+−Zn2+

Summary Distribution studies of some metal ions have been made on Sn(IV) and Cr(III) arsenophosphates and on some samples of Sn(II) amine hexacyanoferrates(II), using radiotracers. The K_d values of Cs⁺ and Rb⁺ have been followed at varying HNO₃ concentrations also. As a result 3 useful binary separations have been achieved on Sn(IV) and Cr(III) arsenophosphates, such as Sr²⁺–Cs⁺, Hg²⁺–Ag⁺ and Hg²⁺–Zn²⁺.     

Sorption of Th(IV) on MX-80 bentonite: effect of pH and modeling

MX-80 bentonite was characterized by XRD and FTIR in detail. The sorption of Th(IV) on MX-80 bentonite was studied as a function of pH and ionic strength in the presence and absence of humic acid/fulvic acid. The results indicate that the sorption of Th(IV) on MX-80 bentonite increases from 0 to 95% at pH range of 0–4, and then maintains high level with increasing pH values. The sorption of Th(IV) on bentonite decreases with increasing ionic strength. The diffusion layer model (DLM) is applied to simulate the sorption of Th(IV) with the aid of FITEQL 3.1 mode. The species of Th(IV) adsorbed on bare MX-80 bentonite are consisted of “strong” species o \textYOHTh^{4 +} \equiv {\text{YOHTh}}^{4 + } at low pH and “weak” species o \textXOTh(OH)₃ \equiv {\text{XOTh(OH)}}_{3} at pH > 4. On HA bound MX-80 bentonite, the species of Th(IV) adsorbed on HA-bentonite hybrids are mainly consisted of o \textYOThL₃ \equiv {\text{YOThL}}_{3} and o \textXOThL₁ \equiv {\text{XOThL}}_{1} at pH < 4, and o \textXOTh(OH)₃ \equiv {\text{XOTh(OH)}}_{3} at pH > 4. Similar species of Th(IV) adsorbed on FA bound MX-80 bentonite are observed as on FA bound MX-80 bentonite. The sorption isotherm is simulated by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models, respectively. The sorption mechanism of Th(IV) on MX-80 bentonite is discussed in detail.     

Microhydration of Cs+ ion: a density functional theory study on Cs+-(H2O)n clusters (n=1-10)

Structure, energy enthalpy, and IR frequency of hydrated cesium ion clusters, Cs+-(H2O)n (n=1-10), are reported based on all electron calculations. Calculations have been carried out with a hybrid density functional, namely, Becke's three-parameter nonlocal hybrid exchange-correlation functional B3LYP applying cc-PVDZ correlated basis function for H and O atoms and a split valence 3-21G basis function for Cs atom. Geometry optimizations for all the cesium ion-water clusters have been carried out with several possible initial guess structures following Newton-Raphson procedure leading to many conformers close in energy. The calculated values of binding enthalpy obtained from present density functional based all electron calculations are in good agreement with the available measured data. Binding enthalpy profile of the hydrated clusters shows a saturation behavior indicating geometrical shell closing in hydrated structure. Significant shifts of O-H stretching bands with respect to free water molecule in IR spectra of hydrated clusters are observed in all the hydrated clusters.     

Sorption of Copper(II) and Silver(I) by Four Bacterial Exopolysaccharides

Metal remediation was studied by the sorption of analytical grade copper Cu(II) and silver Ag(I) by four exopolysaccharides (EPS) produced by marine bacteria. Colorimetric analysis showed that these EPS were composed of neutral sugars, uronic acids (>20 %), acetate, and sulfate (29 %). Metal sorption experiments were conducted in batch process. Results showed that the maximum sorption capacities calculated according to Langmuir model were 400 mg g^?1 EPS (6.29 mmol g^?1) and 333 mg g^?1 EPS (3.09 mmol g^?1) for Cu(II) and Ag(I), respectively. Optimum pH values of Ag(I) sorption were determined as 5.7. Experiment results also demonstrated the influence of initial silver concentration and EPS concentrations. Microanalyzing coupled with scanning electron microscopy demonstrated the presence of metal and morphological changes of the EPS by the sorption of metallic cations. The Fourier transform infrared spectroscopy analysis indicated possible functional groups (e.g., carboxyl, hydroxyl, and sulfate) of EPS involved in the metal sorption processes. These results showed that EPS from marine bacteria are very promising for copper and silver remediation. Further development in dynamic and continuous process at the industrial scale will be established next.     

Sorption of Co(II), Ni(II), Ag(I) and Au(III) on pyrazolone-containing inorganic sorbents

The sorption capacity of 3-methyl-1-phenyl-pyrazolone-5 (HMPP)- modified inorganic sorbents has been investigated. The new sorbents are suitable for simultaneous concentration of the 3d elements being investigated over a wide pH range. Choosing appropriate pH values for the corresponding elements, it is possible to achieve their separate extraction.     

Additivity of the distribution ratio of Cs and Se on bentonite/quartz sand mixture in seawater

Summary To provide comprehensive information for assessing the safety of geological disposal of radioactive waste, the additivity of sorption properties during different reaction times for various bentonite/quartz sand mixtures was investigated. Se and Cs were the nuclides of interest. Synthetic seawater (SW) was employed as the liquid phase tosimulate the possible groundwater conditions while the disposal site is an island area. Batch sorption experiments were conducted to measure the distribution ratio, R_d. Regardless of whether Cs and Se were used, the additivityat the reaction time of 7 and 14 days was better than that of 28 and 56 days.Interactions between bentonite and quartz sand might occur in synthesized seawater in reactions beyond 14 days. Under the experimental conditions,the additivity equation could be corrected by the composition ratio and reaction time. Long-term prediction of the R_dby short term batch sorption experiments would be helpful while assessing buffer materials mixed by bentonite and quartz sand.     

Optimization of Nb-substitution and Cs+/Sr+2 ion exchange in crystalline silicotitanates (CST)

Crystalline silicotitanate inorganic ion exchanger, with a sitinakite structure is a candidate material for remediation of aqueous nuclear waste streams. Niobium substituted crystalline silicotitanates (Nb-CST) with varying concentrations of Nb (2, 4, 8, 12 and 24 mmol) and with constant concentrations of Ti-12 mmol, Si-16 mmol, Na-165 mmol were prepared hydrothermally and the products were characterized using techniques viz., XRD, SEM/EDS, DTA/TGA, surface area respectively. Batch experiments were carried out to study the kinetics of uptake of Cs¹³⁷ and Sr⁹⁰, to estimate the decontamination factor (DF) values and distribution coefficients (K _d) for the above synthesized Nb-CST samples from actual radioactive waste solutions. The DF values for uptake of Cs and Sr by Nb-CST for the optimized Nb-concentration of 4 mmol after 24 h of equilibration was 355 and 136 respectively. The K _d values for uptake of Cs and Sr for Nb-CST (Nb-4 mmol) after 24 h of equilibration was found to be 35,490 and 13,500 ml/g respectively. The ion exchange capacity of Nb-CST (Nb-4 mmol) towards Sr ⁹⁰ and Cs¹³⁷ was estimated to be 11.8 and 3.2 meq/g respectively.