Abstract
Selenium (Se) contamination can be a potential groundwater concern near un-lined coal ash landfills. Of all the Environmental Protection Agency’s priority and non-priority pollutants, Se has the narrowest concentration range considered beneficial and detrimental for aquatic and terrestrial organisms. The effects of ash type (i.e., fresh and weathered), water-extractant type (i.e., deionized water, rainwater, and groundwater), and extraction time (i.e., 2 and 6 hours) on Se, arsenic (As), and chromium (Cr) concentrations were investigated from Class C, subbituminous coal fly ash produced at the Flint Creek Power Plant (Benton County, AR). Water-extractable Se concentrations differed (p = 0.03) between ash types across water-extractants, but were unaffected (p > 0.05) by extraction times. Unexpectedly, fresh ash water-extractable Se concentrations were below minimum detection limits (i.e., 2.0 μg·L-1) for all treatments. In contrast, averaged over extraction times, the water-extractable Se concentration from weathered ash was greatest (p < 0.05) with groundwater and rainwater, which did not differ and averaged 60.0 μg·L-1, compared to extraction with deionized water (57.6 μg·L-1). Selenite SeO32- was greater (p < 0.001) in the fresh (3.85 mg·L-1) than in the weathered ash (0.70 mg·kg-1), while selenate SeO42- concentration was greater (p < 0.001) in the weathered (0.67 mg·kg-1) than in fresh ash (0.48 mg·kg-1). Results from this study indicate that environmental weathering of Class C, subbituminous fly ash promotes oxidation of selenite, to the less toxic, but highly mobile selenate. The formation of hydrated ettringite [Ca6Al2(SO4)3(OH)12·26H2O] and calcium selenite (CaSeO3) likely acted as a sink for weathered ash selenite. Implications of this research include a better understanding of the past, present, and future environmental and health risk potential associated with the release of watersoluble Se, As, and Cr to aid in the development of sustainable fly ash management strategies.
Highlights
In the United States (US), coal-fired plants provide approximately 45% of the total net electrical generation, with 847,930 metric tons of coal consumed per day [1]
Considering that relatively little is known about fly-ash-derived Se behavior in the environment, the objective of this study was to evaluate the effects of ash type, water-extractant type, and extraction time (i.e., 2 and 6 hours) on water-extractable Se, arsenic (As), and chromium (Cr) concentrations from a Class C, sub-bituminous fly ash
Fresh ash was collected from the outlet piping of the electrostatic precipitator (ESP) where the fresh ash had been exposed to temperatures of approximately 400 ̊C, while weathered ash was exposed to environmental weathering in the ash landfill
Summary
In the United States (US), coal-fired plants provide approximately 45% of the total net electrical generation, with 847,930 metric tons of coal consumed per day [1]. During the combustion of coal, inorganic constituents that are naturally enriched in the coal are further concentrated in the coal combustion residuals (CCRs): bottom ash and fly ash. Bottom ash is a coarse, heavy ash that is too dense to carry over in the gas stream after combustion [2] [3]. Bottom ash is collected at the bottom of the boiler. The particle size ranges from gravel to silt, with much of the bottom ash sized similar to that of natural sand [3]. Some beneficial re-use options of bottom ash include construction fill material, snow and ice control, concrete/cement products, mining applications, and as road and sub-surface material [3] [4]. The remaining unmarketable bottom ash is either land-filled or placed in impoundments or settling ponds for temporary storage
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
