Utilizing coal fly ash as a landfill barrier material

The chemical barrier properties of a composite of coal fly ash, lime dust and bentonite were studied as a potential barrier material for a landfill. An experimental study was performed to measure the hydraulic and chemical barrier properties of the material using both water and a synthetic municipal solid waste (MSW) leachate. The composite material was found to have a hydraulic conductivity of 4.3 ± 1.6 × 10−8 m/s with water. More importantly, the composite material had chemical barrier properties for metal ions in the leachate liquid. Results show that the principal retarding mechanism for the heavy metal ions was precipitation. In accelerated tests, for the metal ions studied, the retardation order was Pb > Zn > Fe. The migrating front of the heavy metals (Fe, Zn and Pb) under landfill conditions is estimated to be less than 0.10 m in 15 years assuming a constant pH of 6. The coal fly ash barrier appears to be an effective chemical barrier for MSW landfill leachate.