Effect of Organic Matter on Index Swell Properties of a Conventional and Bentonite–Polymer GCL

Abstract

Like inorganic salts, organic matter is also a major component of leachate from municipal solid waste (MSW) landfills. This study uses humic substances (HS) to investigate the influence of organic matter on the swell index (SI) and liquid limit (LL), a conventional sodium bentonite (Na–B), and a dry mixture of Na–B and proprietary polymer (B–P), extracted from commercially available geosynthetic clay liners (GCLs). The SI and LL tests were performed using 5–200 mM NaCl and CaCl2 solutions prepared either with or without 100 mg/L HS. Adding 100 mg/L HS to the NaCl solutions resulted in an increase in SI of Na–B for \({\text{Na}}^{ + }\) concentration ≥20 mM. However, with the \({\text{Ca}}^{2 + }\) solutions adding HS caused a slight decrease in SI of Na–B at low \({\text{Ca}}^{2 + }\) concentrations (≤20 mM) but had no effects on the SI of Na–B at \({\text{Ca}}^{2 + }\) concentrations ≥50 mM. On the other hand, the SI of B–P with \({\text{Na}}^{ + }\) solutions containing HS was consistently lower than with the pure NaCl solutions. But like the Na-B, HS had no effect on the SI observed for B–P with the \({\text{Ca}}^{2 + }\) solutions. Within the range of \({\text{Na}}^{ + }\) and \({\text{Ca}}^{2 + }\) concentrations used in this study, the addition of 100 mg/L HS did had no significant influence on the LL of Na–B. At similar \({\text{Na}}^{ + }\) and \({\text{Ca}}^{2 + }\) concentrations, LL of B–P with solution containing HS was significantly higher than with the pure salt solution. Hydraulic conductivity testing of the GCLs is currently ongoing using test solutions of interest selected based on the results of the SI and LL tests.