Long-Term Column Testing of Zeolite-Amended Backfills. II: Solute Transport Properties
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 143, Issue 9
Abstract
Eight, long-term column tests (1.05–3.75 year) involving soil-bentonite (SB) backfills with 5 or 10% (by dry weight) of one of three types of zeolite amendment (clinoptilolite, chabazite-UB, chabazite-LB) and permeated with either 35 mM KCl or 20 mM solutions were conducted to determine the effects of type and amount of zeolite amendment on the hydrodynamic dispersion coefficient, , and the retardation factor, , of , , and . The superimposed effluent breakthrough curves for were virtually coincidental indicating excellent reproducibility of all eight column specimens, and solute transport generally was dominated by diffusion relative to mechanical dispersion owing to low imposed seepage velocities (). Also, of tended to be greater for the zeolite-amended backfills relative to the unamended backfill, which was attributed to the replacement of the coarse-grained sand with fine-grained zeolite amendments, leading to more tortuous pathways. The of was essentially unity () for seven of the eight column tests, suggesting the absence of any effective porosity. Retardation of and correlated reasonably well with the measured cation exchange capacity of the backfills, as expected on the basis that cation exchange was the dominant attenuation (sorption) mechanism. Overall, as little as 5% zeolite amendment was effective in enhancing the sorption capacity () of the SB backfill by a factor ranging from 2.4 to 3.2 for and 1.4 to 2.2 for , whereas the backfill with 10% chabazite-UB amendment was 4.7 times more effective than the unamended backfill in sorbing . Thus, the column test results support the hypothesis that SB backfills for vertical cutoff walls that are amended with zeolite can significantly increase the sorption capacity for metals, thereby enhancing the containment function of the cutoff walls.
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Acknowledgments
Financial support for this work was provided by the National Science Foundation (NSF) through Grant No. 0624104. The opinions and recommendations provided in this paper are solely those of the authors and are not necessarily consistent with the policies of NSF.
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©2017 American Society of Civil Engineers.
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Received: Aug 30, 2016
Accepted: Feb 23, 2017
Published online: May 29, 2017
Published in print: Sep 1, 2017
Discussion open until: Oct 29, 2017
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