CHLORINE IN FIVE ILLINOIS COALS AND THREE BRITISH COALS: AN X-RAY ABSORPTION NEAR-EDGE STRUCTURE (XANES) SPECTROSCOPY INVESTIGATION

摘要

The chlorine x-ray absorption near-edge structure (XANES) spectra of five Illinois coals and three British coals, and two series of char samples were examined. The char samples were prepared by stepwise heating one Illinois and one British coal in air at temperatures from 200 to 650℃. The chlorine XANES spectra for all the coals are similar and chloride anion was determined to be the predominant form of chlorine. The identity of the positive counter ions with which the chlorine anions are associated in the coals could not be unambiguously determined from XANES spectra. Nevertheless, the XANES spectra of the raw coal and its partially combusted char samples show significant changes in the form (and concentration) of chlorine with increasing char preparation temperature. The appearance of NaCl was observed in the chars from the British sample between 200 to 350℃ but was not observed in the chars from the Illinois sample. The appearance of sodium chloride in British chars and not Illinois chars may indicate an isolated incidence due to dehydration and to the high sodium content of these coals, but it could also imply that in the British coal sodium cations are paired with chloride anions and this sodium could be associated with the sodium sulfate mechanism of boiler corrosion.