Characterization of fly ash from Kentucky power plants

Fly ashes from 21 Kentucky power plants were grouped according to the sulfur content of the feed coal. The highest-carbon fly ashes tended to be from the lowest-sulfur feed coals, partly because many of those plants were smaller and older than the higher-sulfur units. Iron oxide content increased at the expense of aluminium and silicon oxides in the higher-sulfur feed ashes. An increase in calcium and magnesium oxides towards the higher-sulfur feed ashes was due to the greater abundance of carbonate minerals in the higher-sulfur Illinois Basin coals. The highest arsenic values were among electrostatic precipitator ashes from medium-sulfur sources. The arsenic and lead contents of low- and medium-sulfur central Appalachian coals could be higher than those of high-sulfur Illinois Basin coals. Where direct comparison of fly ash and bottom ash was possible, the bottom ash was enriched in Fe₂O₃ relative to the fly ash and most minor elements were depleted in the bottom ash relative to the fly ash. TCLP testing of selected fly ashes indicated that all of the leachates would pass the established RCRA limits. Some of the higher As and Cr levels were from fly ashes in the highest-sulfur category. For As, though, there is no significant correlation between fly ash As and leachate As.