Study on transport of Cr(VI) through the landfill liner composed of two-layer soils

A new landfill liner system composed of two-layer soils was proposed. The upper soil layer composed of 90% raw clay plus 10% lime contributes significant to bearing capacity of liners, and the lower soil layer containing 3 or 6% granular activated carbon (GAC) or 3 or 6% acid-activated bentonite contributes to adsorption capacity of liners. The results from unconfined compressive strength tests showed that the method of adding lime into liner soil material was effective measure to improve compressive strength of liners. The batch test results indicated that GAC and acid-activated bentonite were two potential materials for use as adsorptive amendments for trapping heavy metal ions in liners. To investigate the transport of Cr(VI) through the new liner system, laboratory column tests were performed. The column tests results indicated that the lower soil layer containing adsorptive amendments prevented effectively the transport of Cr(VI). The diffusion coefficients of Cr(VI) for liner soil materials were back-calculated by a one-dimensional numerical transport program. The diffusion coefficient of Cr(VI) was 4.64 × 10−8 m2/s on average for the upper soil layer. The diffusion coefficient of the lower soil layer was 5.4 × 10−10 m2/s to 7.0 × 10−10 m2/s. The differences of diffusion coefficients may be due to different grain size distributions and moulding density between these soils.

Research Highlights
► A new landfill liner system composed of two-layer soils was proposed.
► The upper soil layer improved effectively compressive strength of liners.
► The lower soil layer prevented effectively Cr(VI) transport.
► The diffusion coefficient of the upper soil layer was 4.64×10–8 m2/s.
► The diffusion coefficient of the lower soil layer was 5.4×10–10~7.0×10–10 m2/s.