Tracer diffusion in compacted, water-saturated bentonite
Bourg, Ian C. (ANDRA)
Sposito, Garrison (Lawrence Berkeley National Laboratory. Geochemistry Department)
Bourg, Alain C. M. (Université de Pau et des Pays de l'Adour. Department of Environmental HydroGeochemistry (LHGE-JE2397))

Date:	2006
Abstract:	Compacted Na-bentonite clay barriers, widely used in the isolation of solid-waste landfills and other contaminated sites, have been proposed for a similar use in the disposal of high-level radioactive waste. Molecular diffusion through the pore space in these barriers plays a key role in their performance, thus motivating recent measurements of the apparent diffusion coefficient tensor of water tracers in compacted, water-saturated Na-bentonites. In the present study, we introduce a conceptual model in which the pore space of water-saturated bentonite is divided into 'macropore' and 'interlayer nanopore' compartments. With this model we determine quantitatively the relative contributions of pore-network geometry (expressed as a geometric factor) and of the diffusive behavior of water molecules near montmorillonite basal surfaces (expressed as a constrictivity factor) to the apparent diffusion coefficient tensor. Our model predicts, in agreement with experiment, that the mean principal value of the apparent diffusion coefficient tensor follows a single relationship when plotted against the partial montmorillonite dry density (mass of montmorillonite per combined volume of montmorillonite and pore space). Using a single fitted parameter, the mean principal geometric factor, our model successfully describes this relationship for a broad range of bentonite-water systems, from dilute gel to highly-compacted bentonite with 80% of its pore water in interlayer nanopores.
Rights:	Aquest material està protegit per drets d'autor i/o drets afins. Podeu utilitzar aquest material en funció del que permet la legislació de drets d'autor i drets afins d'aplicació al vostre cas. Per a d'altres usos heu d'obtenir permís del(s) titular(s) de drets.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Subject:	Bentonite ; Diffusion ; Geometric Factor ; Interlayer ; Montmorillonite ; Nanopore ; Smectite ; Waste Containment
Published in:	Clays and Clay Minerals, Vol. 54, Núm. 3 (2006) , p. 363-374, ISSN 1552-8367

DOI: 10.1346/CCMN.2006.0540307

12 p, 462.6 KB  UAB restricted access

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