Document Type

Article

Abstract

When coal fly ash is initially mixed with water, the initial pH of resulting extract or leachate may be strongly acidic (pH 4) or alkaline (pH12). With time, however, this pH range tends to narrow because of geochemical buffering reactions. Because pH is the major variable that controls the leaching of many potential groundwater contaminants, understanding the long-term pH behavior of fly ash leachate is crucial to evaluating the environmental impacts of fly ash management. Using laboratory extract data, kinetic-geochemical models were created to gain a better understanding of the potential buffering that influences the long-term pH of ash leachate. The initially low pH of acidic fly ashes may be short-lived because the acidity is neutralized by the dissolution of calcium and magnesium oxides, is ultimately buffered by carbon dioxide yielding a pH of 7 to 8. Alkaline fly ash leachate (pH . 10) tends to absorb carbon dioxide, and the resulting pH of the liquid phase will decrease with time to a pH between 8 and 9. Kinetic modeling suggests that the chemical composition of short-term laboratory extracts of coal fly ash will not be representative of long-term leachate after equilibrating with the atmosphere.

First Page

63

Last Page

66

DOI

10.4177/CCGP-D-11-00013.1

Volume

3

Publication Date

1-1-2011

Download

Share

COinS