What is Fly Ash?
Description: Fly ash consists of silt-sized particles which are generally spherical, typically ranging in size between 10 and 100 micron. Fly ash can be tan to dark gray, depending on its chemical and mineral composition. Lighter colors generally indicate a high lime content, while brown color indicates iron. Dark gray to black hues reflect a higher unburned carbon content. Fly ash color is usually very consistent for each power plant and coal source.
Chemistry: Fly ash consists primarily of oxides of silicon, aluminum iron and calcium. Magnesium, potassium, sodium, titanium, and sulfur are also present to a lesser degree. Trace elements are also present alongside the remaining coal ash, including arsenic, selenium, mercury, and naturally occurring radioactive elements.
Disposal: The U.S. electric utility industry generates about 100 million metric tons of coal combustion waste annually. Just over half of this amount is fly ash. While some coal combustion waste is recycled, 70 million tons are disposed of in impoundments and landfills each year. Fly ash is the most frequently recycled type of coal combustion byproduct, commonly used in place of portland cement in concrete.
Status: Regulated by the U.S. Environmental Protection Agency under Subtitle D of Resource Conservation and
Recovery Act (RCRA).