Leachability of Compacted Aged and Fresh Coal Combustion Fly Ash under Hydraulic Flow Conditions

Abstract

Being that coal combustion byproducts (CCBs) such as fly ash are composed of trace and heavy metals that are known to pose great threat to human, ecology, and general environmental systems, addressing the long-term environmental concerns under field scenarios is paramount in any proposed management option. Leaching characteristics of trace metals under hydraulic flow conditions when subjected to isotropic confining stresses (35 kPa, 210 kPa and 420 kPa) are investigated. Leaching pattern of Zinc (ZN) and Copper (Cu) under this flow and stress conditions are similar. Concentrations of Cu and ZN are higher in leachates from fresh fly ash than aged fly ash. Cu and Zn are observed to be most leachable at 35 kPa and 420 kPa confining stresses. Leaching of Se is almost independent of the placement density and is higher in leachates from aged fly ash. While leaching of SE decreases with confining stress in the case of fresh fly ash, release of SE is approximately independent of confining stress in aged fly ash. Release of Cd is very minimal, dependent on the placement density, and not detectable in leachates from medium-dense aged fly ash.