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Relative solubility of cations in Class F fly ash.
Ann G Kim1, George Kazonich, Michael Dahlberg
1National Energy Technology Laboratory, U.S. Department of Energy, 626 Cochrans Mill Road, P.O. Box 10940, Pittsburgh, Pennsylvania 15235-0940, USA. akim@netl.doe.gov
Environmental Science & Technology
|October 24, 2003
Summary
Coal fly ash contains cations that show limited leaching potential in natural fluids. This study quantifies cation release, finding most elements are insoluble or slightly soluble, indicating low environmental risk from acid rain or mine drainage.
Area of Science:
- Environmental Science
- Geochemistry
- Materials Science
Background:
- Coal utilization byproducts (CUB), like fly ash, can release cations when exposed to acidic fluids.
- Understanding cation mobility is crucial for assessing the environmental impact of fly ash disposal.
Purpose of the Study:
- To quantify the leaching of 19 cations from Class F fly ash using various acidic and basic leachants.
- To determine the relative solubility of cations in fly ash under different pH conditions.
Main Methods:
- A long-term column leaching study was performed on 32 Class F fly ash samples from pulverized coal combustion.
- Four leachants with pH ranging from 1.2 to 12 were used to simulate environmental fluid exposure.
- Relative solubility (M(L/T)) was calculated by comparing leached mass (M(L)) to total element concentration (M(T)).
Main Results:
- Most cations (Ba, Cd, Fe, Pb, Sb, Se) were found to be insoluble in pulverized coal fly ash.
- Elements like Al, Be, Ca, Co, Cr, Cu, K, Mg, Mn, Na, Ni, and Zn exhibited slight to moderate acid solubility.
- Only Ca and Na showed solubility in neutral water, while As and Ca were soluble in basic solutions.
Conclusions:
- The leaching of cations from Class F pulverized coal fly ash by naturally occurring fluids is generally very limited.
- This suggests a low potential for significant cation release into the environment from fly ash under typical conditions.