Solute Diffusion in Bentonite Pastes
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 142, Issue 8
Abstract
Sodium bentonite (Na-bentonite) is a high-swelling clay with low hydraulic conductivity () that is commonly used for hydraulic and chemical containment applications (e.g., engineered barriers, seals, and grouts) to limit advective (hydraulic) flow and chemical transport. In Na-bentonite pastes and other paste-like substances (e.g., high slump backfills, filter cakes, well seals, and slurried mine tailings) that exhibit low values of (), diffusion can be a significant chemical transport process such that measurement of diffusion properties of these materials may be necessary. Based on these considerations, diffusion of NaCl from Na-bentonite pastes with porosities ranging from 0.96 to 0.98 was evaluated by adapting standardized test methods for diffusive leaching of contaminants from stabilized/solidified waste to a dialysis procedure commonly used for clay purification. The apparent diffusion coefficients () measured with the proposed dialysis-leaching test method ranged from to for initial NaCl concentrations ranging from 1.0 to 0.1 M, respectively. Values of decreased as the exchangeable sodium percentage of the bentonite increased and as the average concentration of NaCl remaining in the bentonite decreased. The diffusion results were in agreement with expectations based on the literature and diffuse double layer theory. The dialysis-leaching test method may offer a simple, fast (), and inexpensive ( per setup) approach to measure diffusion in bentonite pastes and other paste-like substances.
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Acknowledgments
Financial support for this project was provided by the U.S. National Science Foundation (NSF), Arlington, Virginia under Grant No. CMMI-0926205. The opinions expressed in this paper are solely those of the authors and are not necessarily consistent with the policies or opinions of the NSF.
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Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 142 • Issue 8 • August 2016
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© 2016 American Society of Civil Engineers.
History
Received: Jul 1, 2015
Accepted: Jan 4, 2016
Published online: Apr 5, 2016
Published in print: Aug 1, 2016
Discussion open until: Sep 5, 2016
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