Leaching Behavior of Fly-Ash Piles: The Phenomenon of Delayed Rise in Toxic Concentrations

Bo Shi
Arup K. Sengupta

DOI: 10.2190/22D2-HW73-J7JK-NL5C


Large fly-ash piles from coal-burning power plant utilities are generally viewed as innocuous solid wastes, because leachate generated by contact of rain water with fresh fly-ash particles is often very low in dissolved toxic concentrations. This view may be erroneous. With increased percolation of rain water, the concentrations of Cu, Zn, As, Cr, and other toxics in the run-off leachate may increase significantly, often over an order of magnitude. Fly-ash management practices must take this effect into consideration to avoid long-term groundwater contamination. The study reported here also shows that concentrations of dissolved non-toxic species-namely calcium, sodium, or potassium may be used as surrogate indicators to forewarn the impending rise in concentrations of various toxic species. Mass balance analysis on zinc shows that heavy metals distributed in various matrices of the fly-ash particles (glass, magnetic spinel and quartz) are quite accessible for complete dissolution in rain water.

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