Chemical Decomposition of Iron in Spanish Coal Pyrolysis Identified by Mossbauer Spectroscopy at Different Temperatures

Three chars from lignite (Se) sub bituminous (AA6), bituminous (BCA) Spanish coals produced at 673 K, 773K and 873K were analyzed by Mossbauer spectroscopy at room temperature, and 80K, except BCA char produced at 873K, its analysis was extended down to 10K. Least square fit analysis for the spectra of Se chars showed that, jarosite/Fe3+ was hydrolysed into rozenite/Fe2+ at 873K. Pyrite was reduced to troilite (FeS) at 773 K. Both of jarosite and very broad doublet were observed at T=673 K. The hyperfine parameters of this phase gave close values to microcrystalline iron in either Fe (II) or Fe (III) states. On the other hand, the spectral analysis of AA6 chars ascertained that rozenite was hydrolysed to goethite (FeOOH) in the range of 773K-873K, whereas pyrite was reduced to pyrrohotite (Fe1-xS). However, no chemical changes were observed for jarosite in all AA6-chars. Likewise, siderite was changed into magnetite in the BCA chars produced at 673 K and 773 K. Spectrum performed at 10K for char produced at 873 K proved the presence of ferrihydrite (H=489.2 kOe), troilite (H=355.3 kOe) and a broad paramagnetic doublet belong to an organic iron. These phases and still remaining siderite inferred also that such transformations are incomplete.