UTILIZING COAL FLY-ASH AS A LANDFILL BARRIER MATERIAL

The chemical barrier properties of a composite of coal fly ash, lime d ust and bentonite were studied as a potential barrier material for a l andfill. 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 materia l was found to have a hydraulic conductivity of 4.3 +/- 1.6x10(-8) m/s with water. More importantly, the composite material had chemical bar rier properties for metal ions in the leachate liquid. Results show th at the principal retarding mechanism for the heavy metal ions was prec ipitation. In accelerated tests, for the metal ions studied, the retar dation order was Pb > Zn > Fe. The migrating front of the heavy metals (Fe, Zn and Pb) under landfill conditions is estimated to be less tha n 0.10m in 15 years assuming a constant pH of 6. The coal fly ash barr ier appears to be an effective chemical barrier for MSW landfill leach ate. (C) 1997 Elsevier Science Ltd.