TITLE:
Extraction Characteristics of Selenium as Affected by Coal Fly Ash Type, Water Extractant, and Extraction Time
AUTHORS:
Mark A. Cantrell, Kristofor R. Brye, David M. Miller, Esten Mason, Julian Fairey
KEYWORDS:
Arsenic, Chromium, Coal Fly Ash, Landfill, Selenium
JOURNAL NAME:
Journal of Environmental Protection,
Vol.5 No.12,
September
24,
2014
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 -1,
compared to extraction with deionized water (57.6 μg·L-1). Selenite SeO32- was greater (p ·L-1)
than in the weathered ash (0.70 mg·kg-1), while selenate SeO42- concentration was greater
(p ·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.