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

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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 ... continued below

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Bourg, Ian C.; Sposito, Garrison & Bourg, Alain C.M. August 28, 2007.

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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{sup -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 1.2 kg dm{sup -3}.

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  • Journal Name: Environmental Science and Technology; Journal Volume: 41; Journal Issue: 23; Related Information: Journal Publication Date: 10/05/2007

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  • Report No.: LBNL--63446
  • Grant Number: DE-AC02-05CH11231
  • DOI: 10.1021/es0717212 | External Link
  • Office of Scientific & Technical Information Report Number: 929677
  • Archival Resource Key: ark:/67531/metadc896440

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  • August 28, 2007

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  • Sept. 27, 2016, 1:39 a.m.

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  • Oct. 31, 2016, 3:54 p.m.

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Bourg, Ian C.; Sposito, Garrison & Bourg, Alain C.M. Modeling cation diffusion in compacted water-saturatedNa-bentonite at low ionic strength, article, August 28, 2007; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc896440/: accessed October 20, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.