Hydraulic conductivity of polymer-enhanced bentonite geosynthetic clay liners to coal gangue leachate

This study investigated the influences of polymer types, polymer loadings, and preparation methods on the hydraulic conductivity of polymer-enhanced bentonite geosynthetic clay liners (EB GCLs) to coal gangue leachate (CL). Sodium carboxymethylcellulose (CMC) and xanthan gum (XG) were selected to modify the sodium-bentonite GCLs (Na-B GCLs), with a range of polymer contents from 5% to 15%. The EB GCLs were prepared by wet-mixed, dry-mixed, and drysprinkled methods. Detection of effluent in the hydraulic conductivity test by inductively coupled plasma mass spectrometry (ICP) and analysis of EB GCLs' morphologies by scanning electron microscopy (SEM) were conducted to explore the mechanisms controlling the hydraulic conductivity of EB GCLs. The hydraulic conductivity decreased with increasing swelling of the bentonite when the EB GCL had a low polymer loading (5%). However, no significant correlation was observed between the swell index and the hydraulic conductivity when the EB GCL had a high polymer loading (10% and 15%). Moreover, the polymer type and preparation method had little effect on the hydraulic conductivity of the EB GCLs when polymer loading increased to 15%. The ICP results indicated a decrease in ionic strength and an increase in RMD of the CL by cation scavenging, leading to an increase in the possibility of osmotic swelling. Additionally, SEM images showed that the clogging of pore spaces by the polymer was the main reason for the decreased hydraulic conductivity of EB GCLs.