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.     

Distribution of strontium in milk component

The distribution of strontium between the milk components, i.e., serum, casein micelles, whey and hydroxyapatite was determined. The sorption on hydroxyapatite was investigated using batch method and radiotracer technique. The aqueous phase comprised of either milk or whey. The sorption of strontium on hydroxyapatite depended on the method of its preparation and on the composition of the aqueous phase. The sorption of strontium was increased with an increase of pH. The presence of citrate species resulted in decrease of the sorption of strontium on hydroxyapatite. The sorption of ⁸⁵Sr on hydroxyapatite decreased with the increasing concentration of Ca²⁺ ions. Addition of Ca²⁺ ions to milk resulted in milk pH decrease. The decrease in pH value after calcium addition to milk is related to exchanges between added calcium and micellar H⁺. The average value of strontium sorption on casein micelles in milk with presence of hydroxyapatite was (47.3 ± 5.6) %. The average value of sorption of ⁸⁵Sr on casein micelles in milk without the addition of hydroxyapatite was (68.9 ± 2.2) %.     

Sorption of the long-lived radionuclides cesium-134, strontium-85 and cobalt-60 on bentonite

The sorption of long-lived radionuclides of cesium, strontium and cobalt (¹³⁴Cs, ⁸⁵Sr and ⁶⁰Co) on bentonite under various experimental conditions, such as contact time, pH, sorbent and sorbate concentrations have been studied. The uptake of Cs and Sr was rapid and equilibrium was reached almost instantaneously in both the cases, while Co sorption was time dependent. The sorption of these nuclides increased by increasing pH. The uptake of Cs, Sr and Co increased with increasing the amount of the bentonite clay. The percentage sorption for Cs, Sr and Co decreased with increasing metal concentrations. The desorption studies with 0.01M CaCl₂ and ground water at low-metal loadings on bentonite showed that about 95% of Cs, 85-90% of Sr and 97% of Co were irreversibly sorbed. These results could be helpful for nuclear waste management, for waste water effluents containing low concentrations of cesium, strontium and cobalt.     

Quality assessment of hydrosphere in the vicinity of Czech nuclear power plants by radioanalytical methods

Summary The paper deals with the impact of nuclear plants and radioactive waste disposal on surface and ground water quality in their vicinity using various radiometric and radioanalytical methods. The impact of nuclear power plant Temelin on activation concentrations and fission products in hydrosphere, including tritium, was detected. The annual average tritium concentrations in Vltava River correspond to the previously calculated estimates for average and minimal quaranteed flow rates. The concentrations histories of ⁹⁰Sr and ¹³⁷Cs in surface water show a decreasing trend. This trend was not influenced by the nuclear power plant pilot operation. In the case of tritium, a concentration increase trend has been already observed since the startup of pilot operation. An attempt has made interpreting the sorption and diffusion data for radionuclides of cesium, strontium and tritium and technetium as representatives of multivalent elements. Sorption and diffusion data of ¹³⁷Cs and ⁹⁰Sr in contact with natural sorbent bentonite lead to the conclusion that both diffusion and batch sorption experiments can be simulated by an exchange model. Sorption of technetium on various bentonites plus additives materials is described. Retention of technetium on these solid phases is driven by sorption of reduced form of technetium Tc(IV).     

Adsorption of cesium on domestic bentonites

Bentonite is a natural clay and one of the most promising candidates for use as a buffer material in the geological disposal systems for spent nuclear fuel and high-level nuclear waste. It is intended to isolate metal canisters with highly radioactive waste products from the surrounding rocks because of its ability to retard the movement of radionuclides by adsorption. Slovak Republic avails of many significant deposits of bentonites. Adsorption of Cs on five Slovak bentonites of deposits (Jelšovy potok, Kopernica, Lieskovec, Lastovce and Dolná Ves) has been studied with the use of batch technique. In the case of Dolná Ves deposit, the mixed-layer illite–smectite has been identified as the main clay component. Natural and irradiated samples, in two different kinds of grain size: 45 and 250 μm have been used in the experiments. The adsorptions of Cs on bentonite under various experimental conditions, such as contact time, adsorbent and adsorbate concentrations have been studied. The Cation Exchange Capacity values for particular deposits drop in the following order: Jelšovy potok > Kopernica > Lieskovec > Lastovce > Dolná Ves. Bentonites irradiated samples with 390 kGy have shown higher specific surface and higher values of the adsorption capacity. Distribution coefficients have been determined for bentonite-cesium solution system as a function of contact time and adsorbate and adsorbent concentration. The data have been interpreted in terms of Langmuir isotherm. The uptake of Cs has been rapid and the adsorption of cesium has increased with increasing metal concentrations. The adsorption percentage has decreased with increasing of metal concentrations. Adsorption of Cs has been suppressed by presence of Ca²⁺ more than Na⁺ cation. Sorption experiments carried out show that the most suitable materials intended for use as barriers surrounding a canister of spent nuclear fuel are bentonites of the Jelšovy potok and Kopernica deposits.     

Sorption of cobalt on bentonite

Sorption of Co on bentonite has been studied by using a batch technique. Distribution coefficients (K _d ) were determined for the bentonite-cobalt solution system as a function of contact time, pH, sorbent and sorbate concentration and temperature. Sorption data have been interpreted in terms of Freundlich, Langmuir and Dubinin-Radushkevich equations. Thermodynamic parameters for the sorption system have been determined at three different temperatures. The positive value of the heat of sorption, H ⁰=22.08 kJ/mol at 298 K shows that the sorption of cobalt on bentonite is endothermic, where as the negative value of the free energy of sorption, G ⁰=–10.75 kJ/mol at 298 K shows the spontaneity of the process. G ⁰ becomes more negative with an increase in temperature which shows that the sorption process is more favourable at higher temperatures. The mean free energyE7.7 kJ/mol for sorption of cobalt on bentonite shows that ion-exchange is the predominant mode of sorption in the concentration range of the metal studied i.e. 0.01 to 0.3 mol/dm³. The presence of some complementary cations depress the sorption of cobalt on bentonite in the order of K⁺>Ca²⁺>Mg²⁺>Na⁺. Some organic complexing agents and natural ligands also affect the sorption of cobalt. The desorption studies with ground water at low cobalt loadings on bentonite show that about 97% metal is irreversibly sorbed.     

Sorption and diffusion processes with134Cs and85Sr in natural sorbents

Sorption and diffusion processes with¹³⁴Cs and⁸⁵Sr in natural bentonites have been investigated. The distribution coefficients (K _d ) have been determined by a batch method. Various factors affecting theK _d value as water-to-bentonite ratio, concentration of the competitive cations in the aqueous phase or bentonite-to-sand ratio in the mixed sorbents have been evaluated. A comparison of the sorption and diffusion data has been made.     

Effect of gamma-irradiation on adsorption properties of Slovak bentonites

One of the basic prerequisites for the use of bentonite as engineering barrier in deep geological repositories for radioactive waste and spent nuclear fuel is their stability against ionizing radiation stemming from radionuclides present in radioactive waste and spent nuclear fuel. The aim of this study was to compare the changes in the adsorption properties of selected Slovak bentonites in relation to uranium fission products (¹³⁷Cs and ⁹⁰Sr), prior to and after irradiation of bentonites with a ⁶⁰Co γ-source and specifying the changes in the structure of Slovak bentonites induced by γ-radiation. The changes in irradiated natural forms of Slovak bentonites and the changes in their natrified analogues and fractions with different grain sizes were studied from five Slovak deposits: Jelšovy potok, Kopernica, Lastovce, Lieskovec and Dolná Ves. The EPR spectra of bentonites from deposits Jelšovy potok and Lieskovec with absorbed doses of 10⁴ and 10⁵ Gy γ-rays showed no changes in the structure of the studied Slovak bentonites. The changes, which in terms of structure destabilization can be considered insignificant, occurred only in bentonites with absorbed doses of γ-radiation as much as 1 MGy. The absorbed dose of 1 MGy γ-radiation did not have an effect on the adsorption of cesium on every studied bentonite. Changes that can also be regarded as insignificant occurred only during strontium adsorption, especially on Fe–bentonite from deposit Lieskovec and Ca–Mg–bentonite from deposit Jelšovy potok, when an increase in the adsorption capacity occurred. Attention should be paid in further research of this topic which would require carrying out experiments on bentonite samples with absorbed doses higher by several orders of magnitude.     

Sorption of Th(IV) from aqueous solution to GMZ bentonite: effect of pH, ionic strength, fulvic acid and electrolyte ions

Bentonite has been studied extensively because of its strong sorption and complexation ability. In this study, GMZ bentonite (China) was studied as a potential sorbent for the removal of Th(IV) from aqueous solutions. The results indicate that the sorption of Th(IV) is strongly dependent on pH and ionic strength at pH <5, and is independent of ionic strength at pH >5. Outer-sphere surface complexation or ion exchange in inter-layer sites of the montmorillonite fraction of the GMZ bentonite may be the main sorption mechanism of Th(IV) onto GMZ bentonite at low pH values, whereas the sorption of Th(IV) at pH >5 is mainly dominated by inner-sphere surface complexation or surface precipitation. The presence of soil fulvic acid has a positive influence on the sorption of Th(IV) on GMZ bentonite at pH <5. The competition between Th(IV) with aqueous or surface adsorbed cation ions (e.g., herein Li⁺, Na⁺ and K⁺) and surface functional groups of GMZ bentonite is important for Th(IV) sorption on GMZ bentonite. The results of high sorption of Th(IV) suggest that the GMZ bentonite is a suitable backfill material in nuclear waste management.     

Characterization of MX-80 bentonite and its sorption of radionickel in the presence of humic and fulvic acids

MX-80 bentonite is considered as one of the best backfill materials for high-level radioactive nuclear waste. Herein, the bentonite is characterized by using XRD and FTIR techniques. Sorption of radionickel to MX-80 bentonite in the presence/absence of humic acid (HA) or fulvic acid (FA) as a function of pH is investigated. The results indicate that the presence of HA or FA decreases the sorption of Ni²⁺ obviously. The different experimental processes do not affect the sorption of nickel to FA/HA bound bentonite. The sorption of Ni²⁺ on FA/HA-bound bentonite decreases with the increasing FA/HA content in the systems. The mechanism of nickel sorption is also discussed in detail.     

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.     

Sorption of cesium from water solutions on potassium nickel hexacyanoferrate-modified <Emphasis Type="Italic">Agaricus bisporus</Emphasis> mushroom biomass

In order to gain biosorbent that would have the ability to bind cesium ions from water solution effectively, potassium nickel hexacyanoferrate(II) (KNiFC) was incorporated into the mushroom biomass of Agaricus bisporus. Cesium sorption by KNIFC-modified A. bisporus biosorbent was observed in batch system, using radiotracer technique using ¹³⁷Cs radioisotope. Kinetic study showed that the cesium sorption was quite rapid and sorption equilibrium was attained within 1 h. Sorption kinetics of cesium was well described by pseudo-second order kinetics. Sorption equilibrium was the best described by Freundlich isotherm and the distribution coefficient was at interval 7,662–159 cm³ g⁻¹. Cesium sorption depended on initial pH of solution. Cesium sorption was very low at pH₀ 1.0–3.0. At initial pH 11.0, maximum sorption of cesium was found. Negative effect of monovalent (K⁺, Na⁺, NH₄ ⁺) and divalent (Ca²⁺, Mg²⁺) cations on cesium sorption was observed. Desorption experiments showed that 0.1 M potassium chloride is the most suitable desorption agent but the complete desorption of cesium ions from KNiFC-modifed biosorbent was not achieved.     

Sorption/desorption study of strontium on Ain Oussera soils around the Es-Salam reactor facility

Four types of undisturbed soils around the Es-Salam reactor (Algeria) were used to evaluate the sorption behavior of strontium. The batch study was carried out under different experimental conditions. The kinetics were well fited by pseudosecond order model. Soils’s activation energies were 12.37, 14.76, 15.5 and 16.17 kJ mol⁻¹, corresponding to ion-exchange-type sorption. Sorption was exothermic (ΔH° < 0), spontaneous (ΔG° < 0) and favorable at low temperature. Competing cations, particularly Ca²⁺ reduce the Sr adsorption. Desorption reaction showed a higher value of Sr in the easily extractible phase indicating a relative availability of the element.

     

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.     

Study of sorption processes of strontium on the synthetic hydroxyapatite

The sorption of strontium on synthetic hydroxyapatite was investigated using batch method and radiotracer technique. The hydroxyapatite samples were prepared by a wet precipitation process followed by calcination of calcium phosphate that precipitated from aqueous solution. Also, commercial hydroxyapatites were used. The sorption of strontium on hydroxyapatite depended on the method of preparation and it was pH independent ranging from 4 to 9 as a result of buffering properties of hydroxyapatite. The distribution coefficient K _d was significantly decreased with increasing concentration of Sr²⁺ and Ca²⁺ ions in solution with concentration above 1 × 10⁻³ mol dm⁻³. The percentage strontium sorption for commercial and by wet method prepared hydroxyapatite was in the range of 83–96%, while calcined hydroxyapatite was ranging from 10 to 30%. The experimental data for sorption of strontium have been interpreted in the term of Langmuir isotherm. The sorption of Sr²⁺ ions was performed by ion-exchange with Ca²⁺ cations on the crystal surface of hydroxyapatite. Although calcined hydroxyapatite is successfully used as biomaterial for hard tissues repair, it is not used for the treatment of liquid wastes.     

Surface structure of CTMA modified bentonite and their sorptive characteristics towards organic compounds

This work was to examine the correlation between surface structure and sorptive characteristics of cetyltrimethylammonium cations (CTMA⁺) modified bentonite, which will provide novel information for exploring the sorptive mechanisms of organoclays. Various amounts of CTMA⁺ (0.21–1.98 mmol/g) were intercalated into bentonite to prepare a series of organobentonites with different structures. N₂ adsorption–desorption isotherms were plotted for the organobentonites to obtain the surface structure information, and sorption capacities of these organobentonites toward phenol, aniline, nitrobenzene and naphthalene were examined. It was shown that surface areas, pore volumes and surface fractal dimension of the organobentonites decreased with increasing CTMA⁺ loading amount. Sorption capacities of the organobentonites towards the four organic compounds have no evident correlation with their surface structures, and K_oc values of the organic compounds were shown to first increase until the maximum and then decrease as CTMA⁺ loading amount further increased. Combining with the surface structure and sorption capacities of the organobentonites, we proposed that the solute molecules were penetrated into the CTMA⁺ aggregates, and partition rather than adsorption mechanism dominated the sorption processes. The CTMA⁺ aggregates formed optimal partition phases in the intermediate surfactant loading range.     

The effects of pH and ionic strength on fulvic acid uptake by chitosan hydrogel beads

The objective of this work is to investigate the effects of pH and ionic strength on the adsorption capacity for fulvic acid (FA) by chitosan hydrogel beads. The results indicated that the sorption amount increased with decreasing pH and increasing ionic strength concentration. The sorption isotherms were well described by using non-linear Langmuir, Freundlich and Redliche–Peterson equation. The adsorption kinetics of FA onto chitosan hydrogel beads could be described by pseudo-second-order rate model. The extent of FA removal in the presence of other ions decreases in the order Ca²⁺ > Mg²⁺ > Na⁺ ≈ K⁺ and Cl⁻ > NO₃⁻ > CO₃²⁻. FTIR along with XPS analyses revealed the amine groups on the beads were involved in the sorption of FA and the organic complex between the protonated amino groups and FA was formed after FA uptake. Sorption mechanisms including electrostatic interaction and surface complexation were found to be involved in the complex sorption of FA on the chitosan hydrogel beads.     

Sorption and desorption of radiostrontium on powdered bentonite: Effect of pH and fulvic acid

The effect of pH and fulvic acid on the sorption of Sr on bentonite was investigated by using batch experiments. The sorption and desorption isotherms of Sr on bentonite were determined at room temperature, at pH 6.0±0.2 and in presence of 0.1M NaCl. It was found that the sorption of Sr is independent at pH<8, and then increases slightly with increasing pH. Fulvic acid increases the sorption of Sr significantly on bentonite at low pH, but decreases the sorption of Sr at pH>8. The sorption of Sr on bentonite can be described by a reversible sorption process and the sorption mechanism consists mainly of ion exchange. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation of TiO<Subscript>2</Subscript> nanoparticles by sonochemical method,isotherm, thermodynamic and kinetic studies on the sorption of strontium

The objective of this study is to evaluate the use of titanium dioxide nanoparticles which were prepared by novel sonochemical method as an ion exchange material for the removal of Sr from aqueous solution. The pH effect on the Sr²⁺ sorption was investigated. The data obtained have been correlated with Freundlich, Temkin and Dubinin–Radushkevich (D–R) isotherm models. Thermodynamic parameters fort he sorption system have been determined at four temperatures. Simple kinetic models have been applied to the rate and isotherm sorption data and the relevant kinetic parameters were determined from the graphical presentation of these models at 298°K. Results explained that the pseudo second-order sorption mechanism is predominant and the overall rate constant of sorption process appears to be controlled by chemical sorption process. The value of sorption energy E = 13 kJ/mol at 298°K and the value of Gibbs free energy ∆G° = 3,222 kJ/mol at 298°K prove that the sorption of strontium on titanium dioxide nanoparticles is an endothermic and non-spontaneous process.     

Sorption characteristics of137Cs onto clay minerals: Effect of mineral structure and ionic strength

The sorption behavior of¹³⁷Cs onto kaolinite, bentonite, illite, and zeolite was studied at different ionic strengths of Na⁺, K⁺, Ca²⁺. A significant effect of ionic strengths on the sorption has been observed. Clay minerals with 21 structure (bentonite, illite) showed much higher sorption than that of 11 structure (kaolinite). Zeolite showed high selectivity for¹³⁷Cs sorption. Sorption behavior of¹³⁷Cs on clay minerals can be explained by their surface charge characteristics originated from mineral structure.