HR: 1340h
AN: H23F-1499    [Abstracts]
TI: Diffusion of Water and Ions in Water-Saturated Bentonite
AU: * Bourg, I C
EM: ibourg@nature.berkeley.edu
AF: Civil and Environmental Engineering, University of California, Davis Hall # 1710, Berkeley, CA 94720-1710 United States
AU: * Bourg, I C
EM: ibourg@nature.berkeley.edu
AF: Environmental HydroGeochemistry (LHGE-JE2397), University of Pau, BP 1155, Pau Cedex, 64013 France
AU: * Bourg, I C
EM: ibourg@nature.berkeley.edu
AF: Geochemistry Department, Earth Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 United States
AU: Sposito, G
H23F-1499 AF: Civil and Environmental Engineering, University of California, Davis Hall # 1710, Berkeley, CA 94720-1710 United States
AU: Bourg, A C
H23F-1499 AF: Environmental HydroGeochemistry (LHGE-JE2397), University of Pau, BP 1155, Pau Cedex, 64013 France
AB: Bentonite (a strongly-swelling, smectite-rich clay) is commonly used in engineered barriers and geosynthetic liners for the isolation of landfills and contaminated sites. Bentonite barriers are under consideration in several countries as potential components of deep geological repositories for high-level radioactive waste. Because of the low hydraulic conductivity of water-saturated bentonite, molecular diffusive processes contribute significantly to the transport of solutes through such barriers. In the present study, we discuss the results of numerous studies of the diffusion of water and cations (Na⁺, Sr²⁺) in water-saturated bentonite carried out during the last decade. We note that the pore space of compacted, water-saturated Na-bentonite contains a significant fraction of nanopores, the nanometer-thin smectite interlayers. We develop a new conceptual model of the apparent diffusion coefficient (D_a) of water and ions in water-saturated bentonite that accounts for diffusion in two compartments: the interlayer nanopores and larger macropores. We show that our model can explain all available experimental data of the apparent diffusion coefficient of water and cations (Na⁺, Sr²⁺) with a single fitted parameter, a geometric factor G = 4.0 ± 1.6, for all bentonites studied (with montmorillonite contents between 35 and 100 %), in a broad range of partial montmorillonite dry density (0.2 to 1.7 kg dm^-3, the mass of montmorillonite per combined volume of montmorillonite and pore space).
DE: 1099 General or miscellaneous
DE: 1829 Groundwater hydrology
DE: 1847 Modeling
DE: 1899 General or miscellaneous
DE: 3022 Marine sediments: processes and transport
SC: Hydrology [H]
MN: Fall Meeting 2005