Lauer, et al., (2017) report that most coals in China have uranium concentrations up to 3 ppm, yet several coal deposits are known to be enriched in uranium. Naturally occurring radioactive materials (NORM) in these U-rich coals and associated coal combustion residues (CCRs) have not been well characterized. The authors measured NORM (Th, U, 228Ra, 226Ra, and 210Pb) in coals from eight U-rich coal deposits in China and the associated CCRs from one of these deposits. We compared NORM in these U-rich coals and associated CCRs to CCRs collected from the Beijing area and natural loess sediments from northeastern China.
The authors found elevated U concentrations (up to 476 ppm) that correspond to low 232Th/238U and 228Ra/226Ra activity ratios (≪1) in the coal samples. 226Ra and 228Ra activities correlate with 238U and 232Th activities, respectively, and 226Ra activities correlate well with 210Pb activities across all coal samples. We used measured NORM activities and ash yields in coals to model the activities of CCRs from all U-rich coals analyzed in this study. The activities of measured and modeled CCRs derived from U-rich coals exceed the standards for radiation in building materials, particularly for CCRs originating from coals with U > 10 ppm. Since beneficial use of high-U Chinese CCRs in building materials is not a suitable option, careful consideration needs to be taken to limit potential air and water contamination upon disposal of U- and Ra-rich CCRs.
Overall, this study examined the occurrence and distribution of radionuclides from the U and Th decay series in U-rich coals and associated CCRs from several coal deposits in China, typical CCRs from Beijing area, and loess sediments in northeastern China. It was found that U is selectively enriched (up to 476 ppm) in the coals, resulting in low Th/U and 228Ra/226Ra activity ratios (≪ 1), relative to typical coals and CCRs with lower U contents (typically 1 to 3 ppm). The enrichment of nuclides in the CCRs originating from the U-rich coals is proportional to the U and ash yields of the coals. The radiation of modeled CCRs originating from most of the U-rich coals exceeds the upper limit of radiation hazard indices for building materials. Empirical data from the Chinese coals and associated CCRs indicate that the threshold for radiation levels above the acceptable threshold values for building materials corresponds to U content of ∼10 ppm in the source coals. We therefore suggest that CCRs originating from other coal resources with U concentrations >10 ppm could pose radiation risks if used for building materials in residential building.
Additionally, these CCRs could pose potential human health risks in areas located downwind from sites with fugitive CCR emissions. Future studies should examine the global occurrence of coals with U > 10 ppm and the management and disposal of CCRs originating from such U-rich coals.
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