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This study investigates the feasibility of using coal fly ash and fly ash-bentonite mixtures as a barrier material for mine waste. The hydraulic conductivity of the coal fly ash was measured to be in the order of 2 x 10-9 m/s when it was permeated with deionized water, and this value decreased significantly when the permeant was switched to acid mine drainage (AMD). Addition of bentonite to coal fly ash lowered the hydraulic conductivity during water permeation but no further significant change was observed upon switching the permeant to AMD. Chemical analyses on the effluent from the hydraulic conductivity tests indicated that heavy metals present in AMD were attenuated and were well below the leachate criteria set by the Ontario Government. X-ray diffraction and scanning electron microscopy analyses results of post permeation samples showed significant structural differences and formation of secondary minerals after AMD permeation. The results of this study suggest that the addition of 10% bentonite to coal fly ash reduced the hydraulic conductivity of the coal fly ash to less than 1 x 10 −9 m/s and improved the chemical compatibility for mine waste containment.

This study presents the results of physical, chemical, and mineralogical characterization of fresh and landfilled coal fly ash from Atikokan Thermal Generating Station, Ontario. The acid neutralization capacity, heavy metal sorption capacity, and possible environmental impact under different environmental conditions during utilization of the coal fly ash were also evaluated. The results show significant variations in morphology, mineralogy, and chemical composition between fresh and landfilled fly ashes attributed largely to weathering of the coal fly ash during landfilling. The formation of secondary minerals (predominantly calcite) in landfilled fly ash samples is confirmed by X-ray diffraction, thermal analysis, and Chittick tests. Chemical analysis of the generalized acid neutralization leaching test indicated that the heavy metals from both fresh and landfilled fly ash samples were below the leachate criteria set by the Ontario Government. Despite variations in acid neutralization capacity and physical and geochemical behaviors between fresh and landfilled coal fly ash materials, the overall results of this study suggest both materials have favorable engineering and environmental properties that make them suitable for various environmental applications.