Coal fly ash is a by-product of coal combustion that has drawn renewed public scrutiny
due to the negative environmental impacts from accidental release of this waste material
from storage facilities. Historically, the leaching of toxic elements from coal fly ash into the
environment has always been a major environmental concern. Despite extensive efforts into
the characterization of coal fly ash, effective models for the fate and transport of toxic fly ash
constituents have remained lacking, making it difficult to perform accurate environmental
impact assessment for coal fly ash. To close this critical knowledge gap, the overall objective
of this study was to develop a predictive model for the leaching of toxic elements from fly
ash particles. First, physical properties of coal fly ash were characterized to evaluate their
contribution to elemental transport. Unburned carbon was shown to contribute to the sorption
of arsenic to fly ash, which slowed the release of arsenic from fly ash. In parallel, leaching
properties of various elements were determined to differentiate species of varying leaching
capacities, demonstrating that the majority of toxic elements were not mobile under
environmentally relevant conditions. Subsequently, a mechanistic model for the dissolution
of fly ash elements was developed and validated with batch kinetics studies. Furthermore,
elemental dissolution was integrated with hydrodynamic modeling to describe the leaching of
toxic elements from fly ash in dry disposal facilities, which was validated by column studies.
The mechanistic model developed and validated in this research represents the first such
model that successfully characterized the complex processes underlying the release and
transport of toxic elements in coal fly ash, providing a valuable tool to predict the
v
environment impact of coal fly ash and develop more effective management practices for
both the industry and regulators.