Polymer elution and hydraulic conductivity of polymer-bentonite geosynthetic clay liners to bauxite liquors

This study investigated the influences of polymer types (Super Absorbent Polymer, SAP and Polyanionic Cellulose, PAC), preparation methods (dry-mixed, dry-sprinkled, or wet-mixed), initial polymer loadings (1.0%, 2.5%, 5.0%, 10.0%, and 15.0%), and bauxite liquors (synthetic bauxite liquor, BLS and actual bauxite liquor, BLA) on the polymer elution and the hydraulic conductivity of polymer-bentonite geosynthetic clay liners (PB GCLs). Hydraulic conductivity, total organic carbon analysis, viscosity, scanning electron microscopy, Fourier transforms infrared spectroscopy, and X-ray diffraction tests were combined to investigate the mechanisms controlling the polymer elution and hydraulic conductivity of PB GCLs. The results demonstrated that PB GCLs with high initial polymer loading (10.0%, 15.0%) or prepared using the dry-sprinkled method had low hydraulic conductivities (< 1.0 × 10⁻¹⁰ m/s) and polymer eluting rates (< 10.0 mg/d). PAC-enhanced GCLs had a higher polymer eluting rate than SAP-enhanced GCLs due to the complete water solubility of linear polymer (PAC). When PB GCLs were permeated by BLS (higher ionic strength than BLA), polymer hydrogels had lower viscosity because of coiled or contracted conformation, resulting in a higher polymer eluting rate (> 50.0 mg/d) and hydraulic conductivity (> 1.0 × 10⁻¹¹ m/s).