Composite low-carbon biopolymer-amended bentonite in geosynthetic clay liners for containing acid mine drainage leachate

Acid mine drainage (AMD) leachate is a global pollutant issue that impacts groundwater environment quality. This study investigated the feasibility of a composite biopolymer-amended bentonite as a geosynthetic clay liner core material to contain AMD leachate. The real AMD leachate with a pH of 3.1, sourced from an acidic pyrite tailings site, was employed as a specific test leachate used in this study. The composite biopolymer was composed of welan gum (WG) and xanthan gum (XG) at different dry weight-based ratios. Modified fluid loss (MFL) tests were conducted to evaluate hydraulic conductivity ( k ) of bentonites to optimize WG:XG ratio. Rheological properties of biopolymer solutions were measured, serving as indicative parameters of biopolymer elution. The results indicated biopolymer-amended bentonites with the WG:XG ratio of 8:2 possessed lowest k (1.5 ×10 -11 m/s to 7.2×10 -11 m/s), lower than unamended bentonite (1.2×10 -10 m/s to 8.6×10 -10 m/s) in the AMD leachate condition. In addition, biopolymer solutions with WG:XG ratio of 8:2 exhibited highest viscosity. Thermogravimetric analysis, ultraviolet-visible spectroscopy, and Fourier transform infrared spectroscopy were conducted on the composite biopolymer, revealing that WG and XG interacted via physical cross-linking. Additionally, scanning electron microscopy and atomic force microscopy images indicated that a physical cross-linking and dense network structure conformation was developed in the composite biopolymer hydrogel at the WG:XG ratio of 8:2. The results demonstrate that the composite biopolymer is a promising low-carbon amendment material for enhancing containment performance of bentonite used in geosynthetic clay liners to contain AMD leachate. • The real AMD leachate was employed to biopolymer-amended bentonites performance. • The interaction between welan gum and xanthan gum is physical cross-linking. • The composite biopolymer conformation is presented in AFM for the first time.