One of my early computer consulting jobs was to create an automated system to display the daily location of rail cars carrying pozzolan or fly ash from the burning of coal in Midwestern coal fired power plants. This material was being shipped to the West Coast to be used in the production of cement. Manufacturers are using increasing amounts of this fly ash as an inexpensive binding agent in concrete, wallboard, bricks, roofing and other building materials.
A recent study of fly ash samples from different coal fired power plants at different locations in China found that some of these samples released forty-three times as much radiation as considered safe under standards created for residential building materials by the United Nations Scientific Committee on the Effects of Atomic Radiation. Minerals containing uranium are varied and ubiquitous. The highly radioactive fly ash came from areas where the amount of uranium in the coal deposits was unusually high.
The study was published in the journal Environmental Science and Technology. It was part of a collaboration between CUMT, Duke and Duke Kunshan University. This joint research is dedicated to investigating the environmental impacts of coal and coal ash in China. The research team tested samples from fifty-seven sites in China where there is a lot of uranium in the coal deposits.
Avner Vengosh is a professor of geochemistry and water quality at Duke University's Nicholas School of the Environment. He was on the team the conducted the study on Chinese fly ash. He said, “While most coals in China and the U.S. have typically low uranium concentrations, in some areas in China we have identified coals with high uranium content. Combustion of these coals leaves behind the uranium and radium and generates coal ash with very high levels of radiation.”
Shifeng Dai is a professor of geochemistry at the state key laboratory of coal resources and safe mining at China University of Mining and Technology (CUMT) in Beijing and Xuzhou, China. He was also on the team the conducted the study on Chinese fly ash. He said, "The magnitude of radiation we found in some of the Chinese coal ash far exceeds safe standards for radiation in building materials/ This calls into question the use of coal ash originating from uranium-rich coals for these purposes.”
Nancy Lauer is a Ph.D. student at Duke's Nicholas School who led the research for the new study. She said, “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.”
Ten parts per million of uranium in coal deposits is a threshold limit for commercial use of fly ash that applies to all coal deposits in the world, not just Chinese coal deposits. Lauer said that fly ash from coal deposits with higher levels of uranium "… should not be considered when deciding whether to allow coal ash to be recycled into building materials.”
Vengosh said, “Since our findings demonstrate that using ash from this high-uranium coal is not suitable in building materials, the challenge becomes, how do we dispose of it in ways that limit any potential water or air contamination. This question requires careful consideration.”