Although renewable energy sources have gained traction, the global economy still heavily relies on fossil fuels. Of these fossil fuels, coal use has declined in some developed countries, but millions of tons of coal byproducts are still generated from the combustion process. Coal fly ash (CFA) is a byproduct of this combustion process. More than 50% of CFA generated in the U.S. was repurposed in other applications, while the remaining CFA was disposed of in either dry land fills or ash ponds. CFA is a heterogenous material made up of varying minerals, carbon, major elements (&gt;1000 ppm), and trace elements (&lt; 100 ppm). Arsenic and selenium are toxic trace elements found in CFA; their toxicity depends on their physical and chemical states. More than 16 CFA samples have been collected with representative coal sources and combustion conditions. Our study aims to systematically analyze As and Se speciation in CFA samples from various power plants across the U.S. with representative coal source, boiler type, and removal of gases and trace metals during the combustion process. Samples were characterized for elemental composition, mineralogy, morphology, as well as As/Se concentration, and speciation. Thus far, samples have been collected and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and synchrotron micro-X-ray fluorescence microscopy (µ-XRF) coupled with micro-X-ray absorption spectroscopy (µ-XAS). XRD results revealed a majority of samples contain quartz, lime, hematite, magnetite, and portlandite. SEM images revealed irregular and spherical morphology. Synchrotron X-ray absorption near edge spectroscopy (XANES) revealed As(V) as the major oxidation state for most samples, while 4 samples contained &gt;10% As(III). The dominant oxidation states for Se were Se(0), Se(IV), and Se(VI). Micro-X-ray fluorescence (μ-XRF) coupled with μ-XANES revealed an association of arsenic with calcium, and co-localization of iron and calcium with Se. Particle sizes ranged from 5x5 μm to 40x40 μm.

Comprehensive investigation of As and Se in coal fly ash

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