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What is Coal Ash?

Mary McMahon
Updated May 17, 2024
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Coal ash is a byproduct of coal combustion, created when coal is burned to generate energy. Coal-fired power plants are major producers of coal ash worldwide. In some regions, the components of this byproduct can be re-used in a variety of products, including concrete, while the remainder must be isolated and stored to prevent pollution. Failure to contain the ash properly can lead to catastrophic problems; a coal ash spill in Tennessee in 2008 generated over $1 billion United States Dollars (USD) in damage.

The components of the ash vary, depending on the original source of the coal. The major ingredient is minerals which could not be burned, including an assortment of radioactive isotopes. Bottom ash, found at the bottom of boilers, is a thick, coarse assortment of minerals. Fly ash is much finer, composed of fine particles which have bonded together. Boiler slag is another form of coal ash. In facilities where filters and scrubbing systems are in place, a product known as flue gas desulfurization (FGD) gypsum is also generated and needs to be handled with care.

When the ash is removed from a power generation facility, it is classically stored, often in a landfill. Some of the ash can be sold for other uses, with utilization rates varies, depending on the component. Fly ash, for example, can be very useful, and up to 75% of the fly ash from a power plant may be reused in concrete and other products.

Environmental studies have shown that coal ash can be quite dangerous. It is highly radioactive in some cases, with poor environmental controls which may not entirely prevent contamination. Unlike a nuclear facility, which is carefully monitored and must follow a series of laws to limit radiation exposure, a coal fired power plant can release radioactive material into the surrounding environment and handle its ash without safety measures comparable to those used to control nuclear waste. The ash also contains dioxins and other toxins which can be dangerous when released into the environment.

Coal ash disposal is a serious environmental concern in some regions of the world. The problem has been inadvertently complicated by environmental laws mandating more trapping of pollutants; the collection of pollutants in the stacks of power plants prevents them from being released into the environment, but generates more ash which must be properly disposed of. Some nations have initiated government programs to monitor coal fired power plants and develop recommendations for handling byproducts of combustion to keep the surrounding environment cleaner.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a WiseGeek researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By cougars — On Feb 22, 2011

@ Anon116666 & Comparables- I just wanted to share an interesting fact that I learned in one of my energy classes. The average coal power plant produces enough coal ash in a year to cover a football field under six stories of ash. Finding coal ash uses should be as much a priority as finding ways to sequester carbon and increase combustion efficiency.

By Comparables — On Feb 21, 2011

@ Anon116666- I would agree with you completely. Trying to figure what to do with the coal fly ash is one of the biggest considerations for coal burning plants, and it has been one of the biggest areas of contention between citizens and the utilities. The coal ash is filled with heavy metals, radioactive substances, and volatile toxins. When the ash is ejected into the air, it creates acid rain that contaminates local streams, killing countless birds and amphibians. Fly ash ponds leak into groundwater, and there is often a large radius around coal plants that suffers from elevated levels of cancer, lung problems, and other illnesses.

In my opinion, this is why there will never be such a thing as clean coal. The government doesn't classify fly ash as toxic waste, so there are very few considerations that need to be taken into account when it is stored. Clean Coal technology may scrub more pollutants from the atmosphere as well as sequester carbon, but it cannot make coal ash disappear.

By anon116666 — On Oct 07, 2010

Coal ash is toxic and people exposed to the ash have higher risks for cancer. Ash piles now pollute groundwater from leaking ash ponds in the US, including NC, WI, IL, TN, IN and MI. The ash when used in other products continues to create problems.

Ash piles at manufacturing plants leach into groundwater, especially when exposed to weather. Unless the ash is totally encapsulated, it creates health hazards. Who wants drywall made with toxic coal ash? It's used as a soil supplements for farming and chicken production.

The only time it isn't a hazard is when it's "encapsulated." It's used as a road filler and it's encapsulated until the road cracks and releases ash or when the road is ripped up and piles of discarded ash join garbage dumps. The ash then is lifted by the wind into neighboring communities.

Small seeds from fields in the Midwest turn up in NYC! Ash is not just a local problem. An ash pile in TN in 2008 flooded the town and killed several residents. These ponds, nearly 1,000 of the ponds, are located throughout the US!

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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