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Membrane and diffusion behavior of a compacted sand-bentonite mixture for hydraulic and chemical containment applications

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dc.contributor.authorMeier, Amara Joy, author
dc.contributor.authorShackelford, Charles D., advisor
dc.contributor.authorBareither, Christopher A., committee member
dc.contributor.authorButters, Gregory L., committee member
dc.date.accessioned2016-07-13T14:50:11Z
dc.date.available2016-07-13T14:50:11Z
dc.date.issued2016
dc.description.abstractDue to the ability of sodium bentonite (Na-bentonite) to exhibit high swell, low hydraulic conductivity, k (≤ 10-10 m/s), and semipermeable membrane behavior when exposed to water and dilute chemical solutions, Na-bentonite is commonly used as a component for engineered barriers (e.g., geosynthetic clay liners (GCLs)), or as an engineered barrier (e.g., compacted Na-bentonite buffers) used to contain solid wastes and liquid contaminants. Compacted sand-bentonite (SB) mixtures typically comprising 5 to 20 % Na-bentonite (by dry weight) are commonly used as alternatives to compacted clay liners (CCLs) for containment of solid wastes and liquid contaminants when a suitable natural clay source is not readily or economically available. In addition, membrane behavior, or the ability of a porous material to selectively restrict the passage of dissolved chemical species (solutes), has been shown to exist in many of these bentonite-based barriers, including GCLs, bentonite amended natural clays used for CCLs, and soil-bentonite backfills for in situ vertical cutoff walls. However, compacted SB mixtures suitable for use as engineered hydraulic and chemical containment barriers previously have not been evaluated for membrane behavior. As a result of these considerations, the purpose of this study was to evaluate simultaneously the membrane and diffusion behavior of a SB mixture that would be suitable for use as an engineered barrier for hydraulic and chemical containment applications. Accordingly, membrane tests were conducted on duplicate specimens of a compacted SB mixture comprising 15 % bentonite that was shown to exhibit sufficiently low k (≤ 2.7 x 10-11 m/s) to be suitable for use as a hydraulic and chemical containment barrier. In addition, the simultaneous diffusion of the principal salt species evaluated in the study, viz., Cl- and K+, was evaluated for one of the specimens. The results indicated that both specimens exhibited virtually the same magnitude of membrane behavior, with measured values of the membrane efficiency coefficients, ω, ranging from 0.395±0.053 to 0.063±0.012 when exposed to KCl solutions with source concentrations, Cot, ranging from 5 mM KCl to 80 mM KCl, respectively. In addition, the diffusion of both Cl- and K+ was found to be restricted relative to the case in which the specimen would not exhibit membrane behavior (i.e., ω = 0). Despite the imposition of chemical conditions in the tests that were more complex than those imposed previously, the measured values of ω and the effective diffusion coefficients, D*, for Cl- were in good agreement with those reported in the literature for other bentonite-based engineered barriers when exposed to similar or the same types of salts and salt concentrations. Thus, this study provides the first results to illustrate that a compacted SB mixture that is suitable for use as a hydraulic and chemical containment barrier behaves as a semipermeable membrane that can restrict aqueous-phase diffusion of chemical species to an extent that the chemical containment function of the barrier is improved.
dc.format.mediumborn digital
dc.format.mediummasters theses
dc.identifierMeier_colostate_0053N_13416.pdf
dc.identifier.urihttp://hdl.handle.net/10217/173449
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado State University. Libraries
dc.relation.ispartof2000-2019
dc.rightsCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.
dc.subjectcompacted sand-bentonite liners
dc.subjectmembrane behavior
dc.subjectbentonite
dc.subjectwaste containment
dc.subjectdiffusion
dc.titleMembrane and diffusion behavior of a compacted sand-bentonite mixture for hydraulic and chemical containment applications
dc.typeText
dcterms.rights.dplaThis Item is protected by copyright and/or related rights (https://rightsstatements.org/vocab/InC/1.0/). You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
thesis.degree.disciplineCivil and Environmental Engineering
thesis.degree.grantorColorado State University
thesis.degree.levelMasters
thesis.degree.nameMaster of Science (M.S.)

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