Abstract
Chemical containment barriers comprising sodium bentonite (Na-bentonite) have been shown to exhibit semipermeable membrane behavior under saturated conditions. Since membrane behavior results in restricted migration of aqueous-phase chemicals (solutes), the existence of membrane behavior in bentonite-based barriers can significantly improve the containment function of the barriers. However, some bentonite-based barriers exist under unsaturated conditions, and the extent to which the degree of saturation, , of the barrier affects the existence and magnitude of membrane behavior has not been evaluated heretofore. Accordingly, the membrane efficiency coefficient, , of Na-bentonite was measured in the laboratory at constant in response to applied differences in potassium chloride (KCl) concentrations under closed-system conditions. The results indicated that, for a given , decreased as the source concentration of KCl () increased, which is consistent with previous studies based on . However, for a given , increased with decreasing , as expected on the basis that a reduction in corresponds to a reduction in the water-filled pore space accessible for solute migration. Overall, ranged from 0.31 at with KCl to 0.75 at for KCl. Although the range in that was evaluated was limited by the testing conditions, which resulted in test durations ranging from 232 to 335 days, the results of this study provide the first quantitative evidence illustrating the effect of on for Na-bentonite.
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Acknowledgments
Financial support for this study 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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Journal of Geotechnical and Geoenvironmental Engineering
Volume 144 • Issue 1 • January 2018
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©2017 American Society of Civil Engineers.
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Received: Mar 29, 2017
Accepted: Jun 14, 2017
Published online: Nov 2, 2017
Published in print: Jan 1, 2018
Discussion open until: Apr 2, 2018
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