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A closer look at coal ash

by on October 22, 2010

Story written by Rachel Hammer.

The U.S. Environmental Protection Agency (U.S. EPA) has proposed three options for regulation of coal combustion products (CCPs) including the fly ash, bottom ash, boiler slag and flue gas desulfurization (FGD) material produced by coal-fired power plants.

Of the three options proposed, coal-users like AEP contend that the appropriate classification is nonhazardous waste under Resource Conservation and Recovery Act (RCRA) Subtitle D prime. This classification provides the best approach for continued safe disposal and appropriate recycling of CCPs and provides federal oversight to fill in any gaps in existing state regulations, without causing unnecessary costs in an already struggling economy.

However, there are some who think that classification as hazardous waste under RCRA Subtitle C is the proper classification, claiming that CCPs contain toxic materials that threaten the environment and human health.

Just what is in coal ash?

“The chemical composition of coal ash varies somewhat, depending largely on the composition of the coal itself. Coal is primarily carbon and hydrogen. It also contains some mineral matter, and the percentage of this mineral matter varies by the coal type and source,” explained Joe Bittinger, lead engineer, Steam Generation Engineering.

After combustion, the mineral matter and unburned carbon remain as CCPs. “The combustion conditions and the operation of air emission control equipment also have some influence over the chemistry of the ash and FGD material produced,” Bittinger added.

Because ash content directly reflects the inorganic materials in the coal (quartz, feldspar, clays and metal oxides) the composition of coal ash is very similar to many of the rocks found in the Earth’s crust when the organic matter is removed. It often most closely resembles that of volcanic ash and shale.

The National Bureau of Standards has published data that shows that inorganic constituents in coal fly ash fall within the typical ranges of those found in soils across the U.S.

Coal ash does, in fact, often contain trace constituencies of heavy metals such as lead, zinc and arsenic, and some radioactive elements such as uranium. All soils contain these elements to some extent.

And, according to the U.S. Geological Survey, the concentrations of radioactive material in ash are within the range of concentrations found in other geologic materials such as granite and shale.

The FGD material produced at AEP plants that results from the process to remove sulfur dioxide from air emissions is either calcium sulfite or calcium sulfate – also known as synthetic gypsum.

U.S. EPA has studied coal ash several times in the past. In 1993 and in 2000, it published determinations that CCPs did not warrant regulation as hazardous waste. Currently, disposal of CCPs is regulated by individual states under nonhazardous provisions.

From → News From AEP

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