Understanding Sorption Behavior and Properties of Radionuclides in the Environment (original) (raw)
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Sorption of radionuclides onto minerals: Experiments and modelling
E3S Web of Conferences, 2019
Sorption of various radionuclides such as Cs(I), Eu(III)/Am(III), Np(V), U(VI) and others onto iron oxide (goethite, hematite) and clay minerals (montmorillonite, kaolinite) was studied at wide experimental range (pH ionic strength, total radionuclides concentrations). In all case athermodynamic model for describing sorption onto studied minerals was built and successfully applied for all experiments. The required constants were calculated or verified from published data. For modelling sorption in mineral assemblages Component Additivity (CA) approach was successfully applied.
Radiochimica Acta, 2006
For the safe final disposal and/or long-term storage of radioactive wastes, deep or near-surface underground repositories are being considered world-wide. A central safety feature is the prevention, or sufficient retardation, of radionuclide (RN) migration to the biosphere. To this end, radionuclide sorption is one of the most important processes. Decreasing the uncertainty in radionuclide sorption may contribute significantly to reducing the overall uncertainty of a performance assessment (PA). For PA, sorption is typically characterised by distribution coefficients (K d values). The conditional nature of K d requires different estimates of this parameter for each set of geochemical conditions of potential relevance in a RN´s migration pathway. As it is not feasible to measure sorption for every set of conditions, the derivation of K d for PA must rely on data derived from representative model systems. As a result, uncertainty in K d is largely caused by the need to derive values f...
Journal of Contaminant Hydrology, 1993
Sorption of radionuclides on fracture surfaces is strongly dependent upon the chemical properties of both the surface and the groundwater. Normally, it is assumed that some kind of mean properties may be used in simulations. Since the mineral distribution in real rock is strongly heterogeneous, the sorption is switched on and off while the groundwater propagates through a fracture system. The CRACKER program, which models the rock as a random distribution of minerals, has been used to study effects of heterogeneity. In the model simulations, retardation due to homogeneous sorption has been compared with that caused by heterogeneous sorption. Contaminated groundwater step inputs have been followed through fractures in one-and two-dimensional simulations. The model results indicate that the heterogeneous distribution of rock minerals may influence the migration of radionuclides in a fracture system. In the model considered, mineralgroundwater reactions cause local pH and pE to deviate from the mean values. Thus sorption is also influenced. Further, "chemical channelling" may result in a rapid propagation of radionuclides in fractures.
Guidelines for thermodynamic sorption modelling in the context of radioactive waste disposal
Environmental Modelling & Software, 2013
Thermodynamic sorption models (TSMs) offer the potential to improve the incorporation of sorption in environmental modelling of contaminant migration. One specific application is safety cases for radioactive waste repositories, in which radionuclide sorption on mineral surfaces is usually described using distribution coefficients (K d values). TSMs can be utilised to provide a scientific basis for the range of K d values included in the repository safety case, and for assessing the response of K d to changes in chemical conditions. The development of a TSM involves a series of decisions on model features such as numbers and types of surface sites, sorption reactions and electrostatic correction factors. There has been a lack of consensus on the best ways to develop such models, and on the methods of determination of associated parameter values. The present paper therefore presents recommendations on a number of aspects of model development, which are applicable both to radioactive waste disposal and broader environmental applications.
Radionuclide sorption–desorption pattern in soils from Spain
Applied Radiation and Isotopes, 2008
The pattern of radiostrontium and radiocesium sorption-desorption was examined in 30 Spanish soils by the quantification of the distribution coefficients (K d ) with batch tests, the evaluation of sorption reversibility with a single extraction, the estimation of sorption dynamics by the application of drying-wetting cycles, and the calculation of K adjusted d values as an input for risk assessment models. The data obtained overlapped with those found in soils from other climatic areas, suggesting identical interaction mechanisms and allowing the extrapolation of parameterisations and prediction models among different scenarios. r
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.
Radiochimica Acta, 2005
Summary. A series of batch sorption and column experiments was conducted to investigate sorption and transport behavior of 99 Tc, 129 I, 79 Se, and 90 Sr on and through borehole sediments collected from the proposed low-level radioactive waste disposal facility at the Hanford Site (200 East Area). Batch sorption experiments were conducted on Hanford sediment using uncontaminated Hanford groundwater and simulated glass leachates spiked with individual radionuclides. Strongest sorption occurred for 90 Sr, while 79 Se sorption was intermediate, and 129 I and 99 Tc showed the least sorption affinities on Hanford sediment among these radionuclides studied. The results of column experiments that measured transport behavior of these radionuclides through Hanford sediment were similar to the mobility that can be calculated from the batch sorption results, that is high mobility for 99 Tc and 129 I compared to the intermediate and strong retardation for 79 Se and 90 Sr, respectively. These contaminant sorption data on sediments from below the proposed disposal facility, especially the tests using simulated glass leachate, corroborate values obtained for sediments collected in the past from near by locations and for generic solutions such as regional groundwater. These new data should provide more technical defensibility for past performance assessment predictions that did not use site-specific sediments and leachates. Further, the new data will be incorporated into future performance assessment activities that will update and improve past predictions.
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.
Radiochemistry, 2017
Sorption and desorption characteristics of natural materials (apatite, vermiculite, haydite, wood sawdust, perlite, zeolite produced by Tseolit-Treid, shungite) were studied, and the possibility of using them in filtration barriers in upper aquifers contaminated with cesium, strontium, uranium, and technetium was discussed. Changes in the sorption properties of the materials under the action of natural groundwater microflora were evaluated. Under the conditions of the barrier operation, microbiological action does not significantly affect the sorption characteristics of the materials studied.