The thermal processes during progressive calcination of sulfur-rich calcareous oil shales were analyzed using FT-IR spectroscopy and applying curve-fitting technique. The spectroscopic analysis is advantageous in the analysis of amorphous and short-range ordered thermal phases lacking of XRD peaks. The raw calcareous oil shales are composed of organic matter, kaolinite, smectite, calcite, and apatite (francolite). The principal thermal phases are metakaolinite, meta-smectite, free lime, anhydrite, gehlenite, and ellestadite. The thermal reactions observed with increase temperatures includes decomposition of organic matter followed by release of sulfur gas; dehydroxylation of kaolinite; and smectite at 500–600 °C; and thermal transformation to metakaolinite and meta-smectite; decarbonation of microcrystalline calcite to free lime at 600 °C; reaction of the sulfur gas with the free lime; formation of anhydrite at 600 °C; reaction of apatite and formation of ellestadite at 800 °C; reaction of the metakaolinite; the meta-smectite with the free lime; formation of gehlenite at 900 °C. Owingto the sulfatization process, a great part of the sulfur content of the raw oil shales is retained in the calcined ashes and the release of sulfur gas to the atmosphere decreases. Thus, the combustion of calcareous oil shales for energy source has less pollution effect than that of the clayey oil shales. FT-IR spectroscopy and spectral analysis seems to be useful methods for phase analysis of oil shales in combustion industry.
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