Hydraulic Conductivity of Bentonite-Polymer Geosynthetic Clay Liners to Coal Combustion Product Leachates

Abstract

Experiments were conducted to evaluate the compatibility of bentonite-polymer (B-P) GCLs to Coal Combustion Product (CCP) leachates. The B-P GCLs were manufactured by dry-mixing polymer and sodium bentonite (NaB). Six synthetic leachates were selected based on database of coal ash leachates. Hydration characteristics (i.e., free swell index) and hydraulic conductivity of B-P GCLs were investigated using deionized water and synthetic leachates. The hydraulic conductivity of B-P GCL with low polymer loading (1.2%) is strongly affected by the ionic strength of leachates and controlled by swelling of bentonite. However, the hydraulic conductivity of B-P GCL with high polymer loading (≥5.1%) is controlled primarily by hydrogel blockage in the pore space. Polymer hydrogel forms reticular structure and bonds free water when hydrated with DI water. However, under 20 mM CaCl2, the reticular structure of polymer hydrogel is inhibited by self-entanglement due to divalent cations and high ionic strength.