Transport of Cr(VI) through clay liners containing activated carbon or acid-activated bentonite

The potential of clays containing 3 or 6% granular activated carbon (GAC) or 3 or 6% acid-activated bentonite was assessed for use as a landfill liner-soil material. Permeability, batch adsorption and column tests were performed to evaluate the seepage properties, the Cr(VI) adsorption capacity and transport parameters of the soils. All soil specimens had a hydraulic conductivity of < 1 × 10−7 cm/s at a certain range of moulding water content. The Cr(VI) adsorption was much larger than adsorption by the raw clay. The improved clay prevented effectively the transport of Cr(VI). The diffusion coefficient of Cr(VI) for liner-soil materials was back-calculated by a one-dimensional nonlinear advection–dispersion–reaction numerical transport program. This coefficient for the clay or the improved clay was 2.2 × 10−10 to 8.3 × 10−10 m2/s. The improved clay may be used as a good barrier material to attenuate contamination of Cr(VI) in landfills.

Research Highlights
► To effectively prevent the transport of heavy metal ions, GAC and acid-activated bentonite are used as adsorptive amendments to trap Cr(VI) in liners. Permeability, batch adsorption and column tests were performed to evaluate the seepage properties, the Cr(VI) adsorption capacity and transport parameters of the soils. Cr(VI) adsorption on clay with activated bentonite or GAC was much higher than on the raw clay. The hydraulic conductivity of clay containing 3% or 6% GAC or 3% or 6% activated bentonite met the engineering requirement of 1 × 10−7 cm/s. The diffusion coefficient for the compacted clay or improved clays was within 2.2 × 10−10 to 8.3 × 10−10 m2/s. The improved clay landfill liners effectively prevented the Cr(VI) transport.