Repository logo
 

Mechanisms of interaction between bentonite and anionic polymers in enhanced geosynthetic clay liners

Simple item page
dc.contributor.authorNorris, Anna, author
dc.contributor.authorScalia, Joseph, advisor
dc.contributor.authorShackelford, Charles, advisor
dc.contributor.authorBorch, Thomas, committee member
dc.contributor.authorBenson, Craig, committee member
dc.contributor.authorBailey, Travis, committee member
dc.date.accessioned2021-06-07T10:21:28Z
dc.date.available2022-06-02T10:21:28Z
dc.date.issued2021
dc.description.abstractPolymer enhanced bentonites (EBs) are a potential solution to the chemical incompatibility of natural bentonite in many containment applications. Relative to conventional (natural or un-enhanced) bentonites, EBs have shown improved (lower) hydraulic conductivity to high strength waste liquids, but the mechanisms underlying these improvements are not well understood. The EB geosynthetic clay liners (EB-GCLs) evaluated in this study were produced with linear anionic polymers poly(acrylic acid) (PA) and sodium carboxymethylcellulose (CMC), as well as a covalently crosslinked PA (PAx), using multiple mixing methods (dry-sprinkle, dry mix, and wet mix) and percent polymer enhancements (5-10% by mass). The results of hydraulic conductivity tests based on permeation with concentrated inorganic solutions, viz., 500 mM NaCl and 167 mM CaCl2, indicated that specific combinations of polymer type and mixing methods in the EB-GCLs produced a low hydraulic conductivity (≤ 5.0×10-11 m/s) for a given applied hydraulic gradient and permeant solution. The use of a lower hydraulic gradient (i.e., 30 vs. 300) also was shown to have the potential to yield a lower hydraulic conductivity of EB-GCLs, suggesting that EB-GCLs are sensitive to the applied hydraulic gradient in a way that conventional GCLs containing unamended sodium bentonite (NaB) are not. The reason for this difference is that there is less likelihood of any hydrogel existing within the EB-GCL being flushed from the EB-GCL at the lower hydraulic gradient. Batch adsorption tests were conducted with 16.7 and 167 mM CaCl2, 500 mM NaCl, 12.3 mM CaSO4 and 167 mM Na2SO4 solutions to compare the adsorption behavior with respect to cation and anion species and concentration. Poly (acrylic acid) adsorption onto NaB increased with increasing Ca2+ concentration (12.5 mM CaSO4 < 16.67 mM CaCl2 < 167 mM CaCl2), resulting in increasing solid (adsorbed) phase concentration of PA. Sodium bentonite tested with NaCl exhibited limited adsorption capacity for PA. Total carbon (TC) analysis was confirmed to be an accurate technique for measuring polymer loading of both as-prepared and hydrated/permeated EB-GCLs. A multiple lines of evidence approach was used to determine the mechanisms controlling the hydraulic conductivity of EB-GCLs. The results of the hydraulic conductivity testing were paired with measurements of polymer retention and qualitative measurements of hydrogel formation to understand the variables controlling polymer migration within and through the EB-GCL and the relationship between polymer retention and hydraulic conductivity. The results indicated that the low hydraulic conductivity of EB-GCLs (≤ 5.0×10-11 m/s) is controlled by a combination of pore blocking (mechanical entrapment) and adsorption of polymer hydrogel. The reduction in long-term hydraulic conductivity of EB-GCLs relative to unamended GCLs in aggressive inorganic solutions was determined to be the result of several factors, including (1) the formation of hydrogel, (2) the clogging of the largest (most conductive) pores by the hydrogel, (3) the balancing of seepage forces that are sufficient to mobilize the hydrogel into the pores but not sufficiently high to untangle and mobilize the hydrogel due to shear thinning or dislodging by inertial forces, and (4) the kinetics of hydrogel formation and adsorption of polymer to the surface of bentonite. This study illuminates the myriad of interconnected factors that can and must be optimized for EB-GCLs to provide effective long-term containment of aggressive inorganic wastes.
dc.format.mediumborn digital
dc.format.mediumdoctoral dissertations
dc.identifierNorris_colostate_0053A_16555.pdf
dc.identifier.urihttps://hdl.handle.net/10217/232623
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado State University. Libraries
dc.relation.ispartof2020-
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.subjectenhanced bentonite
dc.subjecthydraulic conductivity
dc.subjectwaste containment systems
dc.subjectgeosynthetic clay liner
dc.subjectanionic polymer
dc.subjectpolymer adsorption
dc.titleMechanisms of interaction between bentonite and anionic polymers in enhanced geosynthetic clay liners
dc.typeText
dcterms.embargo.expires2022-06-02
dcterms.embargo.terms2022-06-02
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.levelDoctoral
thesis.degree.nameDoctor of Philosophy (Ph.D.)

Files

Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
Norris_colostate_0053A_16555.pdf
Size:
10.35 MB
Format:
Adobe Portable Document Format
Download

Collections

2020-
Theses and Dissertations