Hydraulic Performance of Untreated and Polymer-Treated Bentonite in Inorganic Landfill Leachates

Abstract

Short- and long-term exposure to inorganic solutions can cause significant degradation of the hydraulic properties of bentonite clay used in geosynthetic clay liners (GCLs). In particular, the increase in hydraulic conductivity due to cation exchange when Na-montmorillonite is subjected to leachates rich in Ca and Mg has caused problems in incinerator ash landfill liners located in wet environments, where large quantities of leachates are generated. Experimental results are presented to evaluate the immediate change in hydraulic conductivity of seven types of GCL clays upon permeation with leachate generated from three ash landfills. The composition of the ash, which is a by-product of the incineration of municipal solid waste (MSW), in turn influences the composition of the resulting leachate. Falling head permeability tests were performed on flexible-wall permeameter specimens, with back-pressure saturation. Chemical analysis shows that the three leachate products contain high, medium, and low concentration Ca and Mg cations. The clay component of GCL materials tested in this study consists of regular and polymer-treated bentonite. Polymer treatment is believed to render the clay non-reactive to many organic and inorganic chemicals. The results of this study indicate that: (1) polymer treatment is generally more beneficial if the clay is first saturated with water and not directly with the leachate; (2) high swell potential of the bentonite is more advantageous than polymer treatment, especially when low hydraulic conductivity is required in the short term and if the clay is pre-hydrated. Experiment setup and special specimen preparation procedures are also discussed.

Diffusion of Calcium Chloride in a Modified Bentonite: Impact on Osmotic Efficiency and Hydraulic Conductivity

“…Several types of contaminant-resistant bentonites have been developed with the aim of preserving low hydraulic conductivity in the presence of potentially aggressive permeants (Onikata et al, 1996;Lo et al, 1997;Ashmawy et al, 2002). This paper presents test results for MultiSwellable Bentonite (MSB), a chemically modified bentonite (Onikata et al, 1999).…”

Modified clays for barriers: a review

“…Such adsorption can be irreversible and entropy-driven. Cationic polymers are able to protect the clay from cation exchange because a cationic polymer chain contains thousands of cations that would need to be exchanged simultaneously [3,88]. However, the treatment with cationic polymers provides no decrease of the hydraulic conductivity of bentonites because the cationic polymer tends to aggregate clay particles, with a consequent compression of the diffuse double-layer thickness, which is not beneficial for the hydraulic performance of the clayey barrier.…”

State-of-the-art report: GCL shear strength and its measurement – ten-year update

“…Polymer-amended bentonites have been developed for cases where ion exchange results in much higher hydraulic conductivity for natural bentonite GCLs (Trauger and Darlington 2000;Ashmawy et al 2002;Di Emidio et al 2011;Benson et al 2014;Scalia et al 2014). Ion exchange has been shown to occur for GCLs in the laboratory and field, and is generally more problematic for conditions involving low confining stress, lack of prehydration with clean water, wet/dry cycling, and ambient solutions with high ionic strength, multivalent cations, or extremes in pH (Shackelford et al 2000;Kolstad et al 2004;Meer and Benson 2007;Benson and Meer 2009;Scalia and Benson 2011).…”