Authors: Bourg, Ian C.; Sposito, Garrison; Bourg, Alain C.M.

Source: Clays and Clay Minerals, Volume 54, Number 3, June 2006 , pp. 363-374(12)

Publisher: The Clay Minerals Society

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.

Keywords: BENTONITE; DIFFUSION; GEOMETRIC FACTOR; INTERLAYER; MONTMORILLONITE; NANOPORE; SMECTITE; WASTE CONTAINMENT

Document Type: Research article

DOI: http://dx.doi.org/10.1346/CCMN.2006.0540307

Publication date: 2006-06-01

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• The JOURNAL publishes articles of interest to the international community of clay scientists, including but not limited to areas in mineralogy, crystallography, geology, geochemistry, sedimentology, soil science, agronomy, physical chemistry, colloid chemistry, ceramics, petroleum engineering, foundry engineering, and soil mechanics. Clays and Clay Minerals exists to disseminate to its worldwide readership the most recent developments in all of these aspects of clay materials. Manuscripts are welcome from all countries.

  Clays and Clay Minerals is the official publication of The Clay Minerals Society.

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