Date of Graduation

5-2014

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Kristofor R. Brye

Committee Member

Julian L. Fairey

Second Committee Member

David M. Miller

Third Committee Member

Esten Mason

Keywords

Applied sciences, Health and environmental sciences, Arsenic, Chromium, Extraction, Fly ash, Leaching, Selenium

Abstract

Selenium (Se) contamination can be a potential groundwater concern near un-lined coal ash landfills. Out of all the Environmental Protection Agency (EPA) priority and non-priority pollutants, Se has the narrowest range between what is 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 located in Benton County, AR. Water-extractable Se concentrations differed (P = 0.03) between ash types across water-extractants, but were unaffected 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 weathered ash water-extractable Se concentration 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 (Se4+) was greater (P < 0.001) in the fresh (3.85 mg kg-1) than in the weathered ash (0.70 mg kg-1), while selenate (Se6+) 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 (Se4+), to the less toxic, but highly mobile selenate (Se6+). The formation of hydrated ettringite [Ca6Al2(SO4)3(OH)12 - 26H2O] and calcium selenite (CaSeO3) likely acted as a sink for weathered ash selenite (Se4+). Implications of this research include a better understanding of the past, present, and future environmental and health risk potential associated with the release of water-soluble Se, As, and Cr to aid in the development of sustainable fly ash management strategies.

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