Chemical Composition, Speciation, and Elemental Associations in Coal Fly Ash Samples Related to the Kingston Ash Spill

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• 作者：Nelson Rivera ; Navdeep Kaur ; Dean Hesterberg ; Colin R. Ward ; Robert E. Austin ; Owen W. Duckworth
• 刊名：Energy & Fuels
• 出版年：2015
• 出版时间：February 19, 2015
• 年：2015
• 卷：29
• 期：2
• 页码：954-967
• 全文大小：558K
• ISSN：1520-5029

文摘

Environmental impacts of potentially toxic trace elements from coal fly ash are controlled in part by the mineralogy of the ash matrix and the chemical speciation of the trace elements. Our objective was to characterize the chemical and mineralogical composition of fly ash samples that are pertinent to the 2008 release of coal ash from a containment area at the Tennessee Valley Authority (TVA) Kingston fossil plant, which left 4 to 500 t of trace elements in adjoining river systems. Three fly ash samples were analyzed for elemental composition by digestion or neutron activation analysis, mineralogy and macroelement speciation by conventional and synchrotron-based X-ray diffraction (XRD and SXRD) and X-ray absorption spectroscopy (XAS), and for spatial associations of elements by electron probe microanalysis (EPMA). Ash samples were mainly composed of Si (20鈥?7% w/w), Al (10鈥?4% w/w), Fe (4鈥?% w/w), and Ca (4鈥?% w/w). Concentrations of selected trace elements ranged from 8 to 1480 mg kg^鈥?, with the following general trend: Sr > Mn 鈮?Zn 鈮?Cu 鈮?Cr > As 鈮?Pb > Se 鈮?U. XRD and EPMA analyses indicated that fly ash matrices were heterogeneous mixtures of minerals and aluminosilicate glass containing Fe, Ca, Ti, Mg, Na, and K. XAS fitting analyses suggested that Fe was mostly in a poorly ordered, polymerized hydroxyl-Fe(III) phase, with minor proportions of magnetite, and hematite or maghemite. Consistent with XRD data, fits to Ca XAS data included standards of glass, anhydrite, lime, and calcite; and fits to S XAS data included anhydrite and reduced organic S forms. Electron microprobe analysis showed frequent correlations among Ca, Si, and Al (and with Sr), consistent with the glass and mineral phases identified. Ash composition and mineralogy help to define a geochemical basis for projecting the long-term fate of trace elements in residual ash left in sediments following cleanup operations at the TVA-Kingston site.