Mineralogy of Weathered Flue Gas Desulfurization Sludges
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such as adsorption-desorption. Several experimental techniques have been used to directly characterize solid phases in FFC wastes. Among these, the methods used most frequently are X-ray diffraction (XRD), scanning electron microscopy (SEM), and infrared spectroscopy. Each of these methods has a different threshold limit of detection, and XRD can detect only crystalline phases. In addition, indirect methods, such as equilibrium solubility measurements, have also been used to assess the nature of solid phases in FFC wastes [3]. Many mineralogical characterization studies have focussed on fly ashes, while only a few have concerned identification of solid phases in FGD sludges. Therefore, the objective of this study was to identify crystalline solid phases in samples of weathered FGD sludge.
MATERIALS AND METHODS The FGD sludge samples were obtained from a disposal site in the midwestem United States. The sludge was derived from a Venturi scrubber that used CaCO3 as the absorber to remove sulfur from the combustion products of a subbituminous coal. Core samples were obtained from different parts of the sixteen year-old sludge pond. Elemental concentrations in air-dried samples were analyzed by X-ray fluorescence (XRF) or by inductively-coupled plasma (ICP) analysis. Inorganic carbon was coulometrically measured [4]. The X-ray diffraction analyses were performed on randomly oriented samples, and phase identification was made by using the Joint Committee on Powder Diffraction Standards (JCPDS)
Mat. Res. Soc. Symp. Proc. Vol. 136. '1989 Materials Research Society
Table I Total Concentrations (% by weight) of Selected Elements In Samples of Flue Gas Desulfurlzation Sludges* Element
Mean
Range
Al C(inorganic) Ca Fe K Mg Na P S Si
1.42 4.27 27.17 2.78 0.41 0.39 0.76 0.41 13.23 3.25
1.17-1.72 2.34-6.03 25.80-30.00 1.92-4.10 0.35-0.46 0.20-0.46 0.49-1.11
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