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Fly ash—the residuum of coal burning—contains a considerable amount of fossilized particulate organic carbon (FOC ash ) that remains after high-temperature combustion. Fly ash leaks into natural environments and participates in the contemporary carbon cycle, but its reactivity and flux remained poorly understood. We characterized FOC ash in the Chang Jiang (Yangtze River) basin, China, and quantified the riverine FOC ash fluxes. Using Raman spectral analysis, ramped pyrolysis oxidation, and chemical oxidation, we found that FOC ash is highly recalcitrant and unreactive, whereas shale-derived FOC (FOC rock ) was much more labile and easily oxidized. By combining mass balance calculations and other estimates of fly ash input to rivers, we estimated that the flux of FOC ash carried by the Chang Jiang was 0.21 to 0.42 Mt C⋅y −1 in 2007 to 2008—an amount equivalent to 37 to 72% of the total riverine FOC export. We attributed such high flux to the combination of increasing coal combustion that enhances FOC ash production and the massive construction of dams in the basin that reduces the flux of FOC rock eroded from upstream mountainous areas. Using global ash data, a first-order estimate suggests that FOC ash makes up to 16% of the present-day global riverine FOC flux to the oceans. This reflects a substantial impact of anthropogenic activities on the fluxes and burial of fossil organic carbon that has been made less reactive than the rocks from which it was derived.
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Isotopic Signatures and Outputs of Lead from Coal Fly Ash Disposal in China, India, and the United States
Despite extensive research and technology to reduce the atmospheric emission of Pb from burning coal for power generation, minimal attention has been paid to Pb associated with coal ash disposal in the environment. This study investigates the isotopic signatures and output rates of Pb in fly ash disposal in China, India, and the United States. Pairwise comparison between feed coal and fly ash samples collected from coal-fired power plants from each country shows that the Pb isotope composition of fly ash largely resembles that of feed coal, and its isotopic distinction allows for tracing the release of Pb from coal fly ash into the environment. Between 2000 and 2020, approx. 236, 56, and 46 Gg Pb from fly ash have been disposed in China, India, and the U.S., respectively, posing a significant environmental burden. A Bayesian Pb isotope mixing model shows that during the past 40 to 70 years, coal fly ash has contributed significantly higher Pb (∼26%) than leaded gasoline (∼7%) to Pb accumulation in the sediments of five freshwater lakes in North Carolina, U.S.A. This implies that the release of disposed coal fly ash Pb at local and regional scales can outweigh that of other anthropogenic Pb sources.
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- Award ID(s):
- 1932087
- PAR ID:
- 10523513
- Publisher / Repository:
- ACS Publications
- Date Published:
- Journal Name:
- Environmental Science & Technology
- Volume:
- 57
- Issue:
- 33
- ISSN:
- 0013-936X
- Page Range / eLocation ID:
- 12259 to 12269
- Subject(s) / Keyword(s):
- lead (Pb) outputs coal combustion fly ash disposal isotopic compositions mixing model environmental impacts
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.est.3c03456
