Adsorption of cesium and strontium on natrified bentonites

The influence of chemical activation–natrification of bentonites on adsorption of Cs and Sr was studied with regards to utilization of bentonites for depositing high-level radioactive waste and spent nuclear fuel. Bentonite samples from three Slovak deposits in three different grain-size (15, 45 and 250 μm), natural and natrified forms (Na-bentonites); under various experimental conditions, such as contact time, adsorbent and adsorbate concentration have been studied. When comparing the Na-bentonites and their natural analogues, the highest adsorbed Cs and Sr amounts were reached on the natrified samples. After the Sr adsorption a drop in the pH equilibrium value was observed together with the increase of the initial Sr concentration. A disadvantage of the natrified bentonite forms is formation of colloid particles. After 2 h of phase mixing a gentle turbidity was observed as well as formation of a gel-like form. The above findings were confirmed by observing the particle distribution in dry and wet dispersion and centrifugation at two different speeds. Natrification as a technological process of bentonite quality improvement cannot be applied when constructing a long-term repository for high-level radioactive waste and spent nuclear fuel. The main problem of natrification is a technological process which leads to a significant pH increase. Alkaline environment in combination with the K presence and increased temperature in the vicinity of radio-active waste can lead to a rapid illitization of smectite and loss of the original adsorption qualities. Moreover, sodium additions are a significant point of uncertainty since it is not possible to state what amount of Na enters the interlayer space and what amount stays in the inter-partition space.     

Adsorption of cesium on minerals: A review

The adsorption behavior of cesium on pure minerals is reviewed. Although this field has been investigated intensively, the data are extremely variable in scope and interpretation with detailed information being available for only a few minerals. In current investigations in this field, the emphasis is on the nature of the adsorption sites and identification of these sites using spectroscopic techniques. In the first section of this review, the general mechanism of cesium adsorption is discussed and this is followed by consideration of the effect of parameters such as cesium concentration, the properties of the mineral and the characteristics of the solution phase, on cesium adsorption. Finally, interaction of cesium with some different minerals is described in some detail.     

Adsorption of dye from wastewater using chitosan-CTAB modified bentonites

Multifunctional magnetic-fluorescent nanohybrids were successfully fabricated by a facile layer-by-layer (LBL) self-assembly of in situ generated Eu, Gd co-doped LaF(3) nanocrystals (LaF(3):Eu:Gd) on the surface of multi-walled carbon nanotubes (MWNTs). Photoluminescence (PL) quenching occurred when LaF(3):Eu:Gd nanoparticles were directly coated on the surface of MWNTs. By growth of a SiO(2) shell spacer between MWNTs and LaF(3):Eu:Gd nanocrystals, we circumvented the PL quenching and achieved the magnetic-fluorescent MWNTs. Moreover, the nanohybrids showed powerful T(1) and T(2)-weighted magnetic resonance imaging (MRI) signal in water and could be used as MRI contrast agents. As a result, the nanohybrids can be expected to act as a promising multimodal MRI/optical imaging probe.     

Adsorption of benzoic acid and hydroquinone by organically modified bentonites

Two organobentonites (ODTMA-B, HDTMA-B) were synthesized using hexadecyltrimethyle ammonium bromide (HDTMAB) and octadecyltrimethyle ammonium bromide (ODTMAB). Synthesized organobentonites were characterized by X-ray diffraction particle size, and surface area analysis. Particle size analyses of the original bentonite and organobentonites showed that the organobentonites contained a greater number of coarse particles than present in the original bentonite. While the basal spacings of the organobentonites increased organic cation, the surface area decreased.

To evaluate the potential use of two modified bentonites in removing organic pollutants such as benzoic acid and hydroquinone from water, adsorption experiments were performed under conditions of varied pH (3, 6 and 11) and temperatures(298 and 313 K). Experimental results showed that the sorption capacities increase with decreasing pH value and increasing temperature. The adsorption equilibrium of benzoic acid and hydroquinone on organobentonites was described by the Langmuir and Dubinin–Radushkevich (D–R) models. It was concluded that the isotherm shapes were not affected by pH and temperature. Adsorption capacity of ODTMA-B for benzoic acid was higher compared to that of HDTMA-B at various pH and temperatures.     

Adsorption behaviour of microamounts of cesium on manganese dioxide

The adsorption of cesium on manganese dioxide from aqueous solutions has been studied in relation to pertinent variables such as shaking time, pH, composition of aqueous solutions, mass of adsorbent (10 mg–1 g) and concentration of adsorbate (10^–6–5·10^–3 M), using a radiotracer technique. The influence of various anions and cations on cesium adsorption was examined. The distribution coefficient of a variety of other elements was determined under similar conditions. The adsorption of cesium obeys a Freundlich-type isotherm over the entire concentration range investigated, whereas the Langmuir-type isotherm is followed only at moderate concentrations.     

Adsorption kinetics and equilibrium modeling of cesium on copper ferrocyanide

The copper ferrocyanide (CuFC) prepared in this study was characterized using X-ray diffraction and scanning election microscopy. The distribution of particle sizes of the CuFC suspension was determined. The adsorption kinetics data were evaluated for an intraparticle diffusion model, a pseudo-first order model and a pseudo-second order model at temperatures of 288, 298 and 308 K, respectively. It was found that the adsorption process of Cs⁺ on CuFC was best described by a pseudo-second order kinetic model, with a correlation coefficient (R ²) equal to 1.000, and the adsorption rate constant increased with increasing temperature. This result indicated that chemisorptions took place during the adsorption process. The adsorption equilibrium data fit well to the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. The mean adsorption energy (E) between 11 and 13 kJ/mol at different temperatures indicated that ion exchange was the main mechanism during the adsorption process. Thermodynamic parameters were also evaluated during the adsorption. The values of the standard Gibbs free energy change (ΔG ^o) and standard enthalpy change (ΔH ^o) suggested that the adsorption was a spontaneous and endothermic process. The distribution coefficient (K _d) was more than 2.94 × 10⁶ mL/g when the pH of solution was between 2.6 and 10.9, and the initial Cs⁺ concentration was 100 μg/L. The existence of K⁺ and Na⁺ did not affect the adsorption of Cs⁺ on CuFC when the concentration of K⁺ and Na⁺ in the solution was below 20 and 1,000 mg/L, respectively.     

Adsorption of benzoic acid from aqueous solution by three kinds of modified bentonites

Benzoic acid removal is important for the water treatment, and adsorption is an efficient treatment process. Three kinds of modified bentonites, hydroxy-aluminum pillared bentonite (Al(OH)-Bent), octadecyl trimethyl ammonium chloride modified bentonite (OTMAC-Bent), and both octadecyl trimethyl ammonium chloride and hydroxy-aluminum modified bentonite (Al(OH)-OTMAC-Bent) were prepared and characterized by XRD, FTIR, and BET analysis. Experiments were conducted on the adsorption of benzoic acid by the prepared modified bentonites at different temperatures in batch experiments. The results show benzoic acid adsorption capabilities of Na-Bent and Al(OH)-Bent are even low, but high for OTMAC-Bent and Al(OH)-OTMAC-Bent. Optimal conditions for the adsorption of benzoic acid on OTMAC-Bent and Al(OH)-OTMAC-Bent were as follows: pH of 3.5, 0.04 g/mL adsorbent, and contact time of 90 min. Increased adsorption with temperature indicates that the adsorptions of benzoic acid onto Al(OH)-OTMAC-Bent and OTMAC-Bent are spontaneous and endothermic. The adsorption data could be well interpreted by the Langmuir model and Temkin Equation. The adsorption efficiency was higher than 85%, suggesting that OTMAC-Bent and Al(OH)-OTMAC-Bent are excellent adsorbents for effective benzoic acid removal from water.     

Adsorption of cesium from spent nuclear fuel basin water

Summary Batch equilibrium and kinetic measurements were performed for Cs⁺ exchange in silicotitanate zeolite (Ionsiv^® TIE-96) at 30 and 60 °C. The Langmuir isotherm equation provided a good fit of the equilibrium data. The heats of exchange reaction between Cs⁺ in the aqueous solution and Na⁺ in the zeolite structure were derived from the equilibrium data. The results indicate that the exchange mechanism is different from that of physical adsorption on heterogeneous materials. The apparent diffusion coefficients and activation energy were derived from the kinetic data and the values obtained for inter-diffusion of Cs⁺ and Na⁺ cations in the zeolite structure were 1.33 ^. 10^-12 and 1.04 ^. 10^-12 cm^{2 .} s^-1 at 30 and 60 °C, respectively. The activation energy for Cs⁺ was 1.7 kcal/mol, suggesting that the Cs⁺ cation can access easily all the sites in the zeolite framework. Thus, the exchange of Cs⁺ with Na⁺ in the zeolite was not hindered by ion-sieve effects.     

Adsorption of cesium on mesoporous SBA-15 material containing embedded copper hexacyanoferrate

In this research, the copper hexacyanoferrate/SBA-15 composite was prepared by embedding method, which was further characterized using scanning electron microscope, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller, transmission electron microscopy and X-ray diffraction. The effects of different factors such as pH, temperature, contact time, initial cesium concentration on adsorption were studied. The pH significantly influenced the adsorption. The pseudo second-order kinetic model fitted the adsorption well, indicating chemisorption. The Langmuir isotherm proved that the adsorption happened on monolayer and the maximum adsorption capacity was determined as 0.123 mmol/g. The result showed that CHCF/SBA-15 could be directly used to adsorb cesium from aqueous solution.

     

Adsorption of cesium on,and desorption from,controlled porous glasses

Cesium contained in aqueous solutions of different composition was adsorbed in columns packed with controlled porous glasses (CPG) and then removed by means of 1M HCl. Recovery of cesium in the eluate was studied as a function of the solution composition and the kind of CPG.     

Adsorption behavior of cesium on montmorillonite-type clay in the presence of potassium ions

The adsorption behavior of Cs ions on a montmorillonite-type clay was investigated in the presence of potassium ions, using a radiotracer technique. The initial concentration of K⁺ added to the CsCl was between 10^-4 and 10^-1 mol/l. The addition of K⁺ to the CsCl solution at different concentrations (10^-6-10^-2 mol/l) reduced the amount of Cs⁺ adsorbed on clay. The maximum ratio of Cs⁺ exchanged, calculated from a linearized form of Langmuir plot was in agreement with the ion exchange isotherms of Cs-K ions. Sorption energy evaluated from the graph of corrected selectivity coefficients vs. equivalent fraction of Cs in the solid phase was compared to the energy values obtained from Dubinin-Radushkevich (D-R) isotherms. Freundlich isotherm parameters were used to characterize a site distribution function, which provides information about the affinity ratio of the adsorption sites of Cs⁺ and K⁺ ions. The ion exchange isotherm of Cs-K systems exhibited a Langmuir type curve for all K⁺ concentrations.     

Adsorption of cesium on a composite inorganic exchanger zirconium phosphate - ammonium molybdophosphate

The applicability of zirconium phosphate-ammonium molybdophosphate (ZrP-AMP) for the efficient removal of cesium from aqueous acidic solutions by adsorption has been investigated. The adsorption data analysis was carried out using the Freundlich, Dubinin-Raduskevich (D-R) and Langmuir isotherms for the uptake of Cs in the initial concentration range of 3.75^.10^-5-7.52^.10^-3 mol^.dm^-3 on the ZrP-AMP exchanger from nitric acid medium. The mean free energy (E) values for the adsorption of Cs were obtained from the D-R isotherm. Equilibrium adsorption values at different temperatures have been utilized to evaluate the change in enthalpy, entropy and free energy (ΔH°, ΔS°, ΔG°). The adsorption of cesium on the ZrP-AMP exchanger was found to be endothermic. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sorption of strontium on Slovak bentonites

Sorption of Sr on five Slovak bentonites of deposits has been studied with the use of batch technique. In the experiments there have been used natural, chemically modified and irradiated samples, in three different kinds of grain size. The pH influence on sorption of strontium on bentonites, pH change after sorption and influence of competitive ions have been studied. Distribution ratios have been determined for bentonite–strontium solution system as a function of contact time, pH and sorbate concentration. The data have been interpreted in term of Langmuir isotherm. The uptake of Sr has been rapid and the sorption of strontium has increased by increasing pH. The percentage sorption has decreased with increasing metal concentrations. The pH value after sorption for the natrificated forms of bentonite starts already in the alkaline area and moves to the higher values. For the natural bentonites the values occur in the neutral or in the acidic area. Sorption of Sr has been suppressed by presence of competitive cations as follows: Ba²⁺ > Ca²⁺ > Mg²⁺ > NH₄ ⁺ > K⁺ > Na⁺. By sorption on natrificated samples colloidal particles and pH value increase have been formed. The bentonite exposure as a result of interaction of γ-rays has led to expansion of the specific surface, increasing of the sorption capacity and to the change in the solubility of the clay materials.     

Adsorption characteristics of radiotoxic cesium and iodine from low-level liquid wastes

In order to remove the radiotoxic nuclides, Cs⁺ and I^–, from low-level liquid wastes, the adsorption characteristics have been studied using a mixed adsorbent of chabazite zeolite and activated carbon. The equilibrium data of each nuclide were well correlated with the DA equation in the wide range of equilibrium concentrations. The SEM-EDAX analysis provided precise understanding of the adsorption mechanism of each nuclide. A surface diffusion model was applied to estimate the intraparticle mass transfer and provided prediction results acceptable for practical implementation in the liquid waste treatment.     

Adsorption studies of cesium on potassium copper nickel hexacyanoferrate(II) from aqueous solutions

Adsorption of cesium from aqueous solutions on potassium copper nickel hexacyanoferrate(II) (KCNF) has been investigated in batch experiments and optimized as a function of concentration of acids, salts and adsorbate using a radiotracer technique. The results are presented in terms of distribution coefficient, K_d (ml·g^–1). The uptake of cesium obeys a Freundlich adsorption isotherm over the concentration range of 3.7 to 37 mmol·l^–1 with b values of 0.77, 0.68 and 0.56 at temperatures of 293, 313, 333 K, respectively. The Langmuir adsorption isotherm is followed in the concentration range of 15 to 75 mmol·l^–1 in the same temperature range. The values of limiting adsorption concentration (C_m) have been found to be 2.58, 2.44 and 2.32 mmol·g^–1. The heat of adsorption was calculated as 26.43 kJ·mol^–1. The influence of a number of anions and cations on cesium retention has also been studied. Column experiments have been performed and breakthrough have been obtained under different operating conditions. The low cesium capacity of 1.1 mmol·g^–1 has been obtained under dynamic conditions as compared to batch experiments. Desorption of cesium from the column has been achieved (45.4%) by nitric acid solution of 8M concentration at a flow rate of 0.5 ml·min^–1.     

Partially exchanged organophilic bentonites

Using a sodium bentonite (VCNa) as substrate differently exchanged organophilic clays were obtained by reaction with hexadecyltrimethylammonium (HDTMA) chloride, at increasing reacting ratios (R) from 20 to 120 meq/100 g of clay (VC20–VC120). The sodium bentonite was previously synthesized from a Verde Claro policationic bentonite (VC) from Bravo, Paraiba State, Brazil. From the thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses of these clays on calcined mass basis and from TG and DTG curves data of VCNa clay, a method was developed to estimate the mass fraction of the exchanged cation present in each organophilic clay (M _org), as a function of R. When all sodium cations of VCNa are exchanged by HDTMA, the obtained organophilic clay presents a maximum value for M _org. From this value and TG and DTG curves data of VC and VCNa clays, the cation exchange capacity of the original VC bentonite can be estimated.     

Adsorption of cesium using mesoporous silica gel evenly doped by Prussian blue nanoparticles

In this paper, a novel mesoporous silica gel evenly doped by Prussian blue nanoparticles (PBMSG) was successfully synthesized by using N,N-dimethylamide as template with a large Barrett-Emmett-Teller (BET) surface area of 505 m²/g and an average pore size of 2.9 nm. The static adsorption experiments showed that the equilibration time of PBMSG for Cs⁺ was about 30 min. The adsorption isotherm of PBMSG for Cs⁺ accorded with Langmuir model and the theoretical maximum adsorption capacity was 80.0 ± 2.9 mg/g. When the initial concentration of Cs⁺ was 1.00 mg/L, the adsorption partition coefficient K_d could reach 3.5 × 10⁴ mL/g After adsorption, Cs⁺ could be eluted by dilute hydrochloric acid (pH 2) with an efficiency of 89.8%, while no K⁺, Fe³⁺, Fe²⁺ was eluted. PBMSG exhibited good selectivity toward Cs⁺ and Rb⁺. In the presence of high concentration of K⁺, the selective adsorption of PBMSG could change the mass ratio of K⁺, Rb⁺ and Cs⁺ from 96.63:0.83:1.00–1.12:0.73:1.00. The separation of Cs⁺ and Rb⁺ from K⁺ with similar concentration (100 mg/g) was realized by column experiment. This indicated that PBMSG was suitable for rapid recovery of low concentration of rubidium and cesium from complex matrixes, such as wastewater and salt lake brine, etc.     

Partially exchanged organophilic bentonites

Phenol is a pollutant that has caused many problems even when present in low concentrations and still represents an environmental problem with difficult solution. This paper presents a study of phenol adsorption by organophilic clays, obtained from aVerde Claro bentonitic clay, from Bravo, Paraíba State, Brazil, at different partial cation exchange degrees with hexadecyltrimethylammonium (HDTMA) chloride, at increasing reacting ratios, from 20 to 120 mmol/100 g of clay, which were characterized in a previous paper. By using Freundlich isotherms obtained for each case, which presented the best correlation coefficients with experimental data, it can be seen that for equilibrium concentrations up to 0.53 mmol L⁻¹ of phenol, the adsorptive capacity decreases for organophilic bentonites obtained at cation exchange degrees higher than 80 mmol/100 g of clay. This indicates that in these cases, the higher is the exchange by organic cation, the higher is the difficulty for the phenol diffusion and sorption in the interlayer space of the organophilic clays. For higher equilibrium concentrations, the maximum adsorption occurs for the organophilic bentonite obtained at 100 mmol/100 g of bentonite exchange.