Clays and Clay Minerals, Vol. 54, No. 3, 363-374, 2006.
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Authors
Bourg, Ian C.
Sposito, Garrison
Bourg, Alain C.M.
Issue Date
2006
Type
Article
Language
en_US
Keywords
Periodicals , Geology , Bentonite , Diffusion , Geometric Factor , Interlayer , Montmorillonite , Nanopore , Smectite , Waste Containment
Alternative Title
Tracer Diffusion in Compacted, Water-saturated Bentonite
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.
Description
gsccm-54-3-07-bou.pdf 594KB PDF/A Document.
Citation
Clays and Clay Minerals, Vol. 54, No. 3, 363-374, 2006.
Publisher
The Clay Minerals Society
License
Copyright © 2006-2018.