Hydraulic Performance of Sodium Carboxymethyl Cellulose-Amended Bentonite in Vertical Cutoff Walls for Containing Acid Mine Drainage

Sodium carboxymethyl cellulose (Na-CMC) was used to improve the chemical compatibility of natural sodium bentonite (NaB) used in vertical cutoff walls for containing acid mine drainage (AMD). Ab Na-CMC content from 2% to 15% was examined to determine the minimum Na-CMC content of sodium carboxymethyl cellulose-amended bentonite (CMCAB) needed to yield a low hydraulic conductivity (<10−9 m/s). Hydraulic conductivity (k), swell index, viscosity, XRD spectra, FT-IR spectra, and microstructures were measured for CMCAB to assess the hydraulic performance of CMCAB for containing AMD and to elucidate the mechanism of reduced k due to the addition of Na-CMC. The results show that the k of CMCAB decreased with the increase in Na-CMC content and stress. A 10% or higher content of Na-CMC is required to reduce the k of NaB down to 10−9 m/s. Na-CMC did not impact the interlayer structure of NaB but increased the viscosity of CMCAB. CMCAB with increased viscosity retained the Na-CMC within the pore spaces, narrowing the flow paths for AMD and yielding low k.