Leaching Behavior of Coal Fly Ash in Environmental Systems
Summary
Coal fly ash, the finely divided residue from coal combustion, is produced in vast quantities worldwide and commonly stored in ash ponds or used in construction applications. Its mineralogical composition—rich in aluminosilicate glass, quartz, mullite and variable amounts of unburnt carbon—governs the release of trace elements and major ions when water percolates through ash deposits or ash‐stabilised soils. Key environmental controls on leaching behaviour include pH, redox potential, liquid–solid ratio and the presence of competing ions. Under alkaline conditions typical of fresh fly ash, oxyanionic species such as arsenate and selenate exhibit high mobility, whereas many heavy metals become less soluble due to precipitation of hydroxides or incorporation into secondary mineral phases. As fly ash ages or interacts with acidifying waters, pH‐dependent shifts can enhance the release of certain contaminants. Column leaching tests, batch extractions and field monitoring have demonstrated that seasonal variations, groundwater chemistry and operational management all influence the potential for groundwater and soil contamination. Understanding these mechanisms is essential for risk assessment, regulatory compliance and the development of mitigation or beneficial‐use strategies.
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Leaching Behavior of Coal Fly Ash in Environmental Systems publication trend
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Technical terms
Leaching: The process by which soluble constituents are dissolved and transported from a solid matrix into percolating water.
Liquid–solid partitioning (LSP) curve: A plot showing the concentration of an element in leachate as a function of pH or liquid–solid ratio, used to assess mobility.
Toxicity Characteristic Leaching Procedure (TCLP): A standardised laboratory test simulating leaching under landfill conditions to determine if waste is hazardous.
Oxyanions: Negatively charged ions containing oxygen, such as arsenate (AsO43–) and selenate (SeO42–), which often control anion mobility.
Column leaching test: An experimental setup where water is percolated through a packed column of material to simulate field leaching behaviour over time.
References
- Assessment of the environmental impacts of utilizing coal ashes and OPC for soil stabilization applications: Leachate analysis in response to rainfall interaction. Case Studies in Construction Materials (2024).
- Leaching behavior of trace elements from fly ashes of five Chinese coal power plants. International Journal of Coal Geology (2020).
- A comprehensive review of toxicity of coal fly ash and its leachate in the ecosystem. Ecotoxicology and Environmental Safety (2024).
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