Modeling cation diffusion in compacted water-saturated sodium bentonite at low ionic strength

Ian Charles Bourg, Garrison Sposito, Alain C M Bourg

Research output: Contribution to journalArticle

30 Scopus citations

Abstract

Sodium bentonites are used as barrier materials for the isolation of landfills and are under consideration for a similar use in the subsurface storage of high-level radioactive waste. The performance of these barriers is determined in large part by molecular diffusion in the bentonite pore space. We tested two current models of cation diffusion in bentonite against experimental data on the relative apparent diffusion coefficients of two representative cations, sodium and strontium. On the "macropore/nanopore" model, solute molecules are divided into two categories, with unequal pore-scale diffusion coefficients, based on location: in macropores or in interlayer nanopores. On the "surface diffusion" model, solute molecules are divided into categories based on chemical speciation: dissolved or adsorbed. The macropore/nanopore model agrees with all experimental data at partial montmorillonite dry densities ranging from 0.2 (a dilute bentonite gel) to 1.7 kg dm-3 (a highly compacted bentonite with most of its pore space located in interlayer nanopores), whereas the surface diffusion model fails at partial montmorillonite dry densities greater than about 1.3 kg dm-3.

Original languageEnglish (US)
Pages (from-to)8118-8122
Number of pages5
JournalEnvironmental Science and Technology
Volume41
Issue number23
DOIs
StatePublished - Dec 1 2007
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Environmental Chemistry

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