Taiyuan Ligong Daxue xuebao (Nov 2023)
Hydraulic Performance of Polymer-Modified Bentonite in Containment Barriers under Aggressive Conditions
Abstract
Purposes Polymer-modified bentonite (PMB) has very low hydraulic conductivity to aggressive solutions that are highly saline, highly acidic, or highly alkaline, and thus is more capable of achieving improved contaminant control efficacy than conventional bentonite. Methods This paper investigates the performance of PMB-enhanced low-permeability materials in the containment barriers such as geosynthetic clay liner (GCL), vertical cutoff wall, and cover system. According to the application requirements of various containment barriers, the PMB-enhanced low-permeability materials were prepared and the permeability tests were conducted to study their hydraulic conductivity to highly acidic, alkaline, or saline solutions. Moreover, the interlayer structure, pore structure, and micro-morphological characteristics of the PMB were evaluated by using microscopic techniques, such as XRD, FTIR, and SEM. Findings The results showed that the conventional bentonite without polymer was highly permeable to aggressive solutions (e.g., the hydraulic conductivity to 3.4% NaCl solution was as high as 2.76×10-7 m/s). In contrast, the PMB exhibited a much superior performance in aggressive environment, with the hydraulic conductivity to 3.4% NaCl solution being <10-11 m/s for polymer loading≥10%, which is 4 orders of magnitude lower than that of the conventional bentonite. Microscopic analyses of the soil samples indicated that monomers were polymerized in bentonite slurry as expected. The formed polymer increased interlayer spacing of montmorillonite to increase the expansibility in aggressive environment, and filled the pores between the bentonite particles to form a dense structure that has narrow and tortuous flow pathways and, as a result, the permeability of the modified bentonite was maintained low in aggressive environment.
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