Fly ash is hazardous waste

From Wikipedia, the free encyclopedia

Fly ash (one of several coal combustion products, or CCPs) is the finely divided mineral residue resulting from the combustion of coal in electric generating plants. Fly ash consists of inorganic, incombustible matter present in the coal that has been fused during combustion into a glassy, amorphous structure.


Fly ash like soil contains trace concentrations of the following heavy metals: nickel, vanadium, arsenic, beryllium, cadmium, barium, chromium, copper, molybdenum, zinc, lead, selenium and radium. Though these elements are found in extremely low concentrations, their mere presence has prompted some to sound the alarm.

The Environmental Protection Agency (EPA) confirms that coal fly ash need not be regulated as a hazardous waste (see Federal Register Vol. 65, No. 99, Monday, May 22, 2000, page 32214). The EPA's headquarters building in Washington, D.C. is constructed with concrete containing fly ash.

Studies by the United States Geological Survey and others conclude fly ash compares with common soils or rocks and should not be the source of alarm. More information is available in the USGS fact sheet (FS-163-97) “Radioactive Elements in Coal and Fly Ash: Abundance, Forms and Environmental Significance”.

In the past, fly ash produced from coal combustion was simply taken up by flue gases and dispersed into the atmosphere. This created environmental and health concerns. These days, most power plants are required by law to reduce their fly ash emissions to less than 1 percent of ash produced. The remainder is collected using electrostatic precipitators or filter bags in a baghouse.

This collected ash either is sold for use in the cement/construction industry or disposed of in ash ponds or landfills. Recently, more fly ash is used beneficially, though more than 65% of fly ash produced from coal power stations is still disposed of. This amounts to approximately 7 million tonnes (Mt) disposed of annually in Australia, 40 Mt in the United States and hundreds of megatonnes in India and China. As a result, the disposal of fly ash is a growing concern for many countries worldwide. In India alone, fly ash landfills cover an area of 40,000 acres (160 km²).

It is probable that the recent invention of the fly ash brick will alleviate the problem of landfill disposal greatly.


  1. ^ U.S. Federal Highway Administration. Fly Ash.
  2. ^ Scott, Allan N; Thomas, Michael D A (Jan/Feb 2007). "Evaluation of Fly Ash From Co-Combustion of Coal and Petroleum Coke for Use in Concrete". ACI Materials Journal 104 (1): 62-70. Retrieved on 2007-02-23.
  3. ^ Popular Science Magazine, INVENTION AWARDS : A Green Brick, May 2007
  4. ^ National Science Foundation, Press Release 07-058, "Follow the 'Green' Brick Road?", May 22, 2007
  5. ^ [1] N-Viro International
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