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Modeling diffusion and adsorption in compacted bentonite: a critical review.
Ian C Bourg1, Alain C M Bourg, Garrison Sposito
1Environmental Hydrogeochemistry Group, LCABIE, UMR 5034, University of Pau-CNRS, Hélioparc Pau Pyrénées, 64053 Pau, Cedex 9, France. ibourg@yahoo.com
Journal of Contaminant Hydrology
|February 25, 2003
Summary
Current models for clay diffusion use many fitting parameters, hindering predictive modeling for applications like waste containment. A new model accounting for adsorbed phase volume offers improved accuracy for clay diffusion analysis.
Area of Science:
- Geochemistry
- Environmental Science
- Materials Science
Background:
- Current diffusion models for compacted clays rely on simple diffusion with adsorption coefficients.
- Existing models often require adjustable parameters like surface diffusion coefficients and effective porosity to match experimental data.
- These models, derived from hydrogeology, may not be fully applicable to compacted clays, particularly regarding the volume of the adsorbed phase.
Purpose of the Study:
- To address limitations in current diffusion models for compacted clays.
- To propose a modified diffusion/adsorption model that incorporates the volume of the adsorbed phase.
- To improve the predictive capabilities of models for applications such as nuclear waste confinement.
Main Methods:
- Development of a modified diffusion/adsorption model.
- Theoretical analysis of diffusive transport considering the adsorbed phase volume.
- Comparison with existing models and their assumptions.
Main Results:
- The proposed model suggests that diffusion in highly compacted clay primarily occurs within the interlayers (adsorbed phase).
- Accounting for the adsorbed phase volume offers a more physically realistic representation of transport.
- This approach reduces reliance on multiple empirical fitting parameters.
Conclusions:
- A modified diffusion/adsorption model that includes the adsorbed phase volume is proposed.
- This model provides a more accurate description of diffusive transport in compacted clays.
- Further research into surface reactivity and interlayer species mobility is needed for quantitative flux prediction.