Article pubs.acs.org/est
Arsenic Speciation in Bituminous Coal Fly Ash and Transformations in Response to Redox Conditions Amrika Deonarine,*,†,¶ Allan Kolker,† Andrea L. Foster,‡ Michael W. Doughten,† James T. Holland,† and Jeremy D. Bailoo†,§ †
US Geological Survey, 12201 Sunrise Valley Drive, Reston, Virginia 20192, United States US Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, United States
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S Supporting Information *
ABSTRACT: The risk of the mobilization of coal ash into the environment has highlighted the need for the assessment of the environmental behavior of coal ash, particularly with respect to toxic trace elements such as arsenic (As). Here, we examined As speciation in coal fly ash samples and transformations in response to aquatic redox conditions. X-ray absorption spectroscopy indicated that 92−97% of total As occurred as As(V), with the remainder present as As(III). Major As-bearing hosts in unamended ashes were glass, iron (oxyhydr)oxides, and calcium arsenate. Oxic leaching resulted in immediate As mobilization to the aqueous phase, reprecipitation of As-iron ferrihydrite, and As adsorption to mineral surfaces. Under anoxic conditions, the (reductive) dissolution of As-bearing phases such as iron ferrihydrite resulted in increased dissolved As compared to oxic conditions and reprecipitation of iron arsenate. Overall, As in coal ash is not environmentally stable and can participate in local biogeochemical cycles.
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In this study, we focused on Class F fly ash which was derived from the combustion of bituminous coal8 and contained higher iron (Fe) oxide content than calcium (Ca) and magnesium (Mg) oxides.9 Previous research has determined that As concentrations in Class F fly ash typically range from 1 to 1000 ppm and that the As(V) oxidation state is prevalent, with a small fraction (
