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Tracer diffusion in compacted, water-saturated bentonite

Ian C. Bourg, Garrison Sposito and Alain C. M. Bourg
Tracer diffusion in compacted, water-saturated bentonite
Clays and Clay Minerals (June 2006) 54 (3): 363-374

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.


ISSN: 0009-8604
EISSN: 1552-8367
Serial Title: Clays and Clay Minerals
Serial Volume: 54
Serial Issue: 3
Title: Tracer diffusion in compacted, water-saturated bentonite
Affiliation: University of California at Berkeley, Department of Civil and Environmental Engineering, Berkeley, CA, United States
Pages: 363-374
Published: 200606
Text Language: English
Publisher: Clay Minerals Society, Clarkson, NY, United States
References: 65
Accession Number: 2006-062565
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Universite de Pau et des Pays de l'Adour, FRA, France
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Clay Minerals Society. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200635
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