AsianScientist (Nov. 17, 2017) – Scientists in China and the US caution that coal ash from high-uranium deposits in China may be too radioactive for use. They reported their findings in the journal Environmental Science and Technology.
Manufacturers are increasingly using encapsulated coal ash from power plants as a low-cost binding agent in concrete, wallboard, bricks, roofing and other building materials. However, the source of coal ash and its attributes are rarely scrutinized.
In this study, scientists at Duke University’s Nicholas School of the Environment and the China University of Mining and Technology measured naturally occurring radioactivity in high-uranium coals from 57 sites in China. They also measured radiation levels in coal ash residues produced from this coal, and in soil collected from four sites. They found that coal ash from high-uranium deposits in China may be too radioactive for use.
“By comparing the ratio of uranium in the coal to the radioactivity of the coal ash, we identified a threshold at which uranium content in coal becomes too high to allow coal ash produced from it to be used safely in residential building construction,” said Ms. Nancy Lauer, a graduate student at Duke University who led the research.
This threshold—roughly ten parts per million of uranium—is applicable to high-uranium coal deposits worldwide, not just in China. Some of the coal ash samples analyzed in the new study contained radiation levels more than 43 times higher than the maximum safe limit established for residential building materials by the United Nations Scientific Committee on the Effects of Atomic Radiation.
“The magnitude of radiation we found in some of the Chinese coal ash far exceeds safe standards for radiation in building materials,” said Professor Dai Shifeng at the China University of Mining and Technology in China. “This calls into question the use of coal ash originating from uranium-rich coals for these purposes.”
“While most coals in China and the US have typically low uranium concentrations, in some areas in China we have identified coals with high uranium content,” said Profssor Avner Vengosh of Duke University. “Combustion of these coals leaves behind the uranium and radium and generates coal ash with very high levels of radiation.”
Now that the coal ash has been found to be unfit for use in construction, the challenge of their disposal becomes an issue as poor management of such waste could result in water or air contamination, added Vengosh.
The article can be found at: Lauer et al. (2017) Naturally Occurring Radioactive Materials in Uranium-rich Coals and Associated Coal Combustion Residues from China.
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Source: Duke University; Photo: Dai Shifeng.
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