Fe. Huggins et al., Direct speciation of chromium in coal combustion by-products by X-ray absorption fine-structure spectroscopy, FUEL, 78(2), 1999, pp. 233-242
Chromium X-ray absorption fine-structure (XAFS) spectroscopy has been used
to determine the relative amounts of Cr(VI) and Cr(III) in coal combustion
by-products, principally fly-ash and bottom ash. The method, which is based
on the relative heights of the pre-edge peaks for the different Cr oxidati
on states in X-ray absorption near-edge structure (XANES) spectra, can be u
sed to speciate as little as 50 ppm of chromium in ash. The results indicat
e that the fraction of Cr(VI) oxidation state present in combustion ash sam
ples from most commercial combustion plants is typically below or close to
the detection limit (approximately 3-5% of the total chromium). There are e
xceptions, however, that have been found to reach as high as 20%. Such find
ings provide justification for a reappraisal of whether or not chromium sho
uld be considered a significant hazardous air pollutant in coal combustion.
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