@article {Bourg:2006-06-01T00:00:00:0009-8604:363,
author = "Bourg, Ian C. and Sposito, Garrison and Bourg, Alain C. M.",
title = "Tracer diffusion in compacted, water-saturated bentonite",
journal = "Clays and Clay Minerals",
volume = "54",
number = "3",
year = "2006-06-01T00:00:00",
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.",
pages = "363-374",
url = "http://www.ingentaconnect.com/content/cms/ccm/2006/00000054/00000003/art00007",
doi = "doi:10.1346/CCMN.2006.0540307",
keyword = "NANOPORE, INTERLAYER, MONTMORILLONITE, WASTE CONTAINMENT, DIFFUSION, GEOMETRIC FACTOR, SMECTITE, BENTONITE"
}