RADIONUCLIDE LEVELS AND ISOTOPIC RATIOS IN COAL COMBUSTION PRODUCTS IN THE UNITED STATES

Coal combustion results in the concentration of naturally occurring radioactive elements in coal combustion products (CCP), which poses major human health and environmental concerns upon emission of fly ash into the air from smoke stacks and dry ponds. Here we characterize the radioactivity level and isotopic fingerprints of radionuclides from the U- and Th-decay series (²²⁸Ra/²²⁶Ra, ²¹⁰Pb/²²⁶Ra) in coal and CCPs from three major coal basins in the US: Illinois, Appalachian, and Powder River basins.

Using a Canberra High Resolution Broad Energy Germanium Detector, the activities of ²²⁶Ra, ²²⁸Ra, and ²¹⁰Pb were measured in CCPs (n=68) and coal samples (n=13) collected from coal burning power plants (n=15) in which the feed coal source is known. The data show that CCPs from Illinois Basin has the highest total radioactivity (591 ± 118 Bq/kg) with the lowest ²²⁸Ra/²²⁶Ra ratio (0.30 ± 0.09), followed by CCPs from the Appalachian basin (0.63 ± 0.09 Bq/kg; 0.63 ± 0.09), and Powder River Basin (242 ± 41 Bq/kg; 0.83 ± 0.03). The total radioactivity in CCPs from all three basins appeared to be influenced by the fractionation of ²¹⁰Pb during combustion, resulting in the enrichment of ²¹⁰Pb in very fine fly ash particles. Finer grained fly ash collected from later rows (i.e., lower temperature) in the electrostatic precipitator (ESP) had ²¹⁰Pb activities significantly higher than ²¹⁰Pb activities in fly ash collected from earlier rows (higher temperature). In contrast, ²²⁶Ra showed a small enrichment, while ²²⁸Ra showed no enrichment. The ability to differentiate the ²²⁸Ra/²²⁶Ra in CCPs from different coal sources and other potential contamination sources highlights the great potential of the use of ²²⁸Ra/²²⁶Ra ratios as a tool for delineating the distribution and impact of CCPs in the environment.