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XAFS SPECTROSCOPY ANALYSIS OF SELECTED HAP ELEMENTS IN FINE PM DERIVED FROM COAL COMBUSTION
Citation:
Shoji, T., F. E. Huggins, G. P. Huffman, W P. Linak*, AND C A. Miller*. XAFS SPECTROSCOPY ANALYSIS OF SELECTED HAP ELEMENTS IN FINE PM DERIVED FROM COAL COMBUSTION. ENERGY AND FUELS 16(2):325-329, (2002).
Description:
X-ray absorption fine structure (XAFS) spectroscopy has been used to investigate the valence states and molecular structures of sulfur (S), chromium (Cr), arsenic (As), and zinc (Zn) in fine particulate matter (PM) separated from coal flyash produced in a realistic combustion system. A cyclone separator was used to separate the PM into fractions <2.5 micrometers in mean diameter (PM2.5) and > 2.5 micrometers in diameter (PM2.5+). Sulfate was the dominant form of S present. However, thiophene was present in many samples, and sulfite was significant in two of the PM2.5+ samples. For Cr and As, the valence states were of primary concern. Analysis of the x-ray absorption near-edge structure (XANES) regions of the spectra revealed that the toxic Cr6+ valence state accounted for approximately 10 to 30 % of the Cr in PM derived from the flyash of several low-rank coals from the Western United States. However, only Cr3+ was observed in a number of PM samples from Eastern U.S. bituminous coal flyash. For As, only As5+ (arsenate) was detected in all of the samples examined. However, structural differences were observed between the arsenate observed in Western and Eastern coal flyash PM. Zn exhibited a rich chemistry, with significant variations in phase distributions between the dominant phases observed for Eastern coal flyash PM (principally ZnFe2O4) and Western coal flyash PM (mixed phases). These phase differences undoubtedly reflect the differences in the suite of inorganic constituents contained in the parent coals.