Adsorption of strontium and caesium onto an Na-illite and Na-illite/Na-smectite mixtures: Implementation and application of a multi-site ion-exchange model (original) (raw)
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Applied Geochemistry
Multi-site ion exchange modelling permits describing the different adsorption behaviour of cations onto clay minerals. Considering several adsorption sites in the clay minerals' structure allows accurately representing the overall variations of adsorption behaviours. For a wider applicability in soils and sediments, it appears necessary to build a coherent thermodynamic adsorption database for radionuclides. 90 Sr and 134,137 Cs are major radionuclides to be considered in the case of nuclear accidents, but thermodynamic data on their adsorption on purified smectites are scarce. Therefore, a detailed study to determine Sr 2+ and Cs + adsorption parameter on smectite seems necessary. To provide this kind of information, this study is proposing multi-site ion exchange modelling of the adsorption of Sr 2+ and Cs + onto a pure Na-MX80 montmorillonite. The intrinsic parameters-site concentration and corrected selectivity coefficient for the Na + /H + exchange-were first fitted using an already available Na saturation curve of a purified smectite. The adsorption of Sr 2+ and Cs + on a purified Na-MX80 bentonite was explored, including a kinetic study for Sr, as a function of pH and equilibrium concentration. The isotherms were modelled to determine the corrected selectivity coefficients for the 2Na + /Sr 2+ and Na + /Cs + exchange reactions. This study provides a part of a wider databasis that is currently under construction, which can be used to predict the adsorption of Sr and Cs in soils and sediments.
Langmuir : the ACS journal of surfaces and colloids, 2016
Strontium is an important contaminant radionuclide at many former nuclear sites. This paper investigates the effect of changing pH and ionic strength on the sorption of Sr to a range of common soil minerals. Specifically it focuses on the sorption of Sr onto illite, chlorite, goethite, and a mixed sediment. The interplay between ionic strength and pH was determined by varying the background ionic strength of the system using both NaCl (for a constant pH) and NaOH (to also vary pH). Under conditions of moderate pH, Sr sorption decreased with increasing ionic strength, due to competition between the Na and Sr atoms for the outer-sphere complexes. However, where increasing ionic strength was accompanied by increasing pH, Sr sorption remained high. This suggested that Sr was sorbed to the minerals without competition from background Na ions. Extended X-ray absorption fine structure (EXAFS) spectra confirmed that at highly alkaline pH (>12.5) Sr was forming inner-sphere complexes on t...
Applied Clay Science, 2018
Surface complexation models (SCMs) have been developed in the last decades to describe metal ion sorption to clay minerals and especially to montmorillonite. In principle, these models can provide relevant information about sorption of radionuclides to be used in performance assessment (PA) of radioactive waste disposal systems. However, these SCMs have been developed in parallel with the acquisition of distinct adsorption datasets, which are not always consistent with each other. The objective of this study was to compare new experimental adsorption results with literature data to understand these discrepancies and to propose a SCM approach that could be amenable to determine sorption related retention parameters necessary for PA calculations. This study focused on lead (Pb) adsorption on montmorillonite, illite and in a natural clay (Callovo Oxfordian) as case studies of a strongly sorbing radionuclide that undergoes a range of retention processes depending on the chemical conditions. The experiments showed that many experimental artifacts lead to misinterpretations of the processes underlying the measured retention values. These include Pb precipitation in the presence of carbonate in solution. The determination of SCM parameters to provide sorption related information for PA of clay minerals should rely on preliminary building of an adequate adsorption database, where adequate means that all experimental conditions are met to quantify surface complexation only. *Revised manuscript with no changes marked Click here to view linked References
Molecular Models of Cesium and Rubidium Adsorption on Weathered Micaceous Minerals
Journal of Physical Chemistry A, 2015
Understanding the adsorption mechanisms of metal cations onto soils and sediments is of critical importance in the protection of the environment, especially for the case of radioactive materials including the fission product 137 Cs. Mechanism-based adsorption models for the longterm interaction of chemical and radionuclide species with clay minerals are needed to improve the accuracy of groundwater reaction and flow models, and related simulations for performance assessment of waste sites and repositories. Towards this goal, molecular simulation using geometry optimization and molecular dynamics methods have been used to investigate the adsorption behavior of Cs + and Rb + cations at frayed edge wedges (a proxy for frayed edge sites, FES) and in the interlayer region formed as a result of the transformation of muscovite to Alhydroxy interlayered vermiculite (HIV) during weathering and pedogenesis. Frayed edge wedges, formed both on individual smectite and illite phases and on the mica-HIV intergrade, have previously been recognized as significant sinks for the strong adsorption of Cs + and Rb +. Atomic density profiles, interlayer adsorption site maps, radial distribution functions, and
Thermodynamic Modeling of the Adsorption of Radionuclides on Selected Minerals. I: Cations
Industrial & Engineering Chemistry Research, 2001
A general model that couples the diffuse-layer theory of surface complexation with an aqueous activity coefficient model based on the B-dot equation has been developed to study the adsorption of ions at the solid-water interface. The model takes into account the effect of changing aqueous speciation on the formation of surface complexes. It has been applied to determine the binding constants for the sorption of selected radionuclide cations, namely, Am(III), Pu(IV), Pu(V), and Np(V), on a number of (hydr)oxide minerals. The results show that the model accurately represents adsorption data in all examined cases. The binding constants of radionuclide cations were found to increase with their hydrolysis constants, and a linear correlation was developed to reproduce this behavior. The approach presented in this work can be generalized to study the ionic adsorption effects in other waste-abatement processes at solid-water interfaces and in water streams where ion separation is required.
2010
The retention of strontium from solutions (concentration range 2 to 30 mg/l) by soils developed under arid conditions of Iran was investigated using a batch technique. Sr sorption characteristics a clayey and a silty clay loam soil were examined at room temperature and with 0.01M CaCl 2 as a background electrolyte. Sorption processes are found to show a Freundlich8type behavior. Results indicated the clay content and ionic strength play predominant role on sorption of Sr. At soil with high soluble cations (saline8sodic soil) less strontium was adsorbed at lower concentrations of strontium due to greater competition with other cations especially with soluble Ca and Mg. Electrical conductivity and ratio of soluble Ca and Mg to total soluble cations is important especially in soils with high EC and SAR.
Modeling of Organic and Inorganic Cation Sorption by Illite
Clays and Clay Minerals, 1999
Sorption of several organic and inorganic cations on illite (Clay Minerals Society Source Clay Imt-2) was determined experimentally and results compared to model calculations. The cations studied were crystal violet (CV+), benzyltrimethylammonium (BTMA ยง benzyltriethylammonium (BTEA+), Ca 2+, Mg 2+, K +, Na +, Cs +, and Li +. The adsorption-model calculations involved a solution of the electrostatic Gouy-Chapman equations. The model considered specific adsorption and sorption/exclusion in the double-layer region in a closed system. Model calculations considered the simultaneous presence of four to six cations in the system. The adsorption of CV included formation of neutral and charged complexes. The adsorption attained 0.37 mol kg i or 150% of the cation exchange capacity (CEC) of illite in aqueous suspension. The adsorption of BTMA and BTEA did not exceed the CEC and was reduced with an increase in ionic strength. The sorption of CV below the CEC was rather insensitive to the ionic strength because of the large binding coefficients and was only slightly reduced in NaC1, CsC1, or Na2SO4 solutions. When added in amounts exceeding the CEC in high ionic strength, 0.667 M NaNO 3, NaC1, or CsC1 solutions, the adsorbed quantities of CV increased to three times the CEC. At high sulphate concentrations (0.333 M Na2SO4), the adsorption was below the CEC. Model calculations yielded satisfactory simulations for the adsorption, particularly for cations added in amounts approaching or exceeding the CEC. The binding coefficients for formation of neutral complexes followed the sequence: CV > Ca > BTMA > BTEA > Cs > Mg > K > Na > Li. Model calculations also suggested that sites were present which bound exchangeable cations, particularly K +, Na +, and Mg 2+, very tightly.
Sorption Characteristics of 137Cs and 90Sr into Rembang and Sumedang Soils
Indonesian Journal of Chemistry, 2016
In order to understand the sorption behavior of 137Cs and 90Sr into soil sample from Rembang and Subang, it is important to estimate the effect of contact time, ionic strength and concentration of metal ion in the solution. For this reason, the interaction of 137Cs and 90Sr with soil sample has been examined. The study performed at trace concentration (~10-8 M) of CsCl and SrCl2, and batch method was used. NaCl has been selected as a representative of the ionic strength with 0.1; 0.5 and 1.0 M concentrations. Concentration of 10-8~10-4 M CsCl and SrCl2 were used for study the effect of Cs and Sr concentrations in solution. Apparent distribution coefficient was used to predict the sorption behavior. The sorption equilibrium of 137Cs and 90Sr into soil was attained after 5 days contacted with Kd value around 3300-4200 mL/g, where Kd was defined as the ratio of number of radionuclide activity absorbed in solid phase per-unit mass to the number of radionuclide activity remains is soluti...
1997
This project is designed to determine how organic chelating ligands can influence the partitioning of ionic solutes (heavy metals and radioactive isotopes) between the solution phase and metal-oxide surfaces. Equilibrium states and kinetics of partitioning in these ternary systems will control contaminant transport and bioavailability of the ligands and contaminant metals in groundwater. As a result, this work represents a significant contribution toward efforts to develop predictive modeling for the transport and transformation of groundwater contaminants. Uranium(VI), strontium(II) and lead(II) have been chosen as representative of high priority pollutants at DOE and non-DOE sites. Strontium in particular has received relatively little detailed attention in the literature. Mineral surfaces chosen for this project include goethite, gibbsite, and kaolinite. The organic chelators-EDTA, NTA, and citric acid-are components of both DOE and industrial wastes. In addition, citric acid is found naturally as a product of metabolic processes in soils and groundwater.
The effect of some operating variables on the adsorption of lead and cadmium ions on kaolinite clay
Journal of Hazardous Materials, 2006
Modification of kaolinite clay mineral with orthophosphate (p-modified sample) enhanced adsorption of Pb and Cd ions from aqueous solutions of the metal ions. Increasing pH of solutions of metal ions, increasing adsorbent dose and increasing concentration of metal ion, increased the adsorption of metal ions. Adsorption of both metal ions simultaneously on both unmodified and p-modified samples indicates that adsorption of one metal ion is suppressed to some degree by the other.