Metal leachability from coal combustion residuals under different pHs and liquid/solid ratios

- Comprehensive characterization of metal concentrations in coal combustion residues.
- First study to test the new USEPA LEAF Method 1313 and 1316 in fly ash..
- Ni, Zn and Pb were the highest with Pb being close to Florida industrial Soil Cleanup Target level.
- All metals except Cd showed amphoteric behaviors with increasing solution pH.
- All metal leaching excluding Ba and Pb decreased with increasing liquid:solid ratios.

Coal combustion residuals (CCRs) contain variable amounts of trace metals, which can negatively impact the environment. We analyzed metal concentrations and leachability of CCRs from seven coal-fired power plants from Florida. The purpose of this study was to characterize and assess metal leachability in representative CCRs samples from coal-fired power plants, including As, Ba, Cd, Cr, Pb, and Se. The specific objectives were to: (1) measure metal leachability under different pH conditions and liquid-to-solid ratios using USEPA Leaching Environmental Assessment Framework (LEAF) Methods 1313 and 1316, and (2) compare their leachability with those obtained by the Synthetic Precipitation Leaching Procedure (SPLP). All metals excluding Cd showed amphoteric behavior, presenting higher concentrations at low and high pH using LEAF Method 1313. The highest Cd leaching was observed at pH 2-4 and decreased at pH > 7. SPLP results were highly variable when compared to the LEAF data. All metals except Ba exceeded the Florida Groundwater Cleanup Target Levels at all pH levels, however, metal leaching was low at typical soil pH of 4-9. Metal concentrations in fly ash decreased in most cases with increasing LS ratio. Therefore, due to potential leaching of some metals, evaluation is needed before beneficial use of CCRs.

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