The state of iron in coal gangue minerals is an important factor in determining the potential for value-added utilization of this solid waste; this is especially true for the coal gangue coming from the Pingshuo open-pit mine in China. The objective of the present study was to characterize the petrologi-cal, mineralogical, and chemical states of Fe in the coal gangue from the Carboniferous Taiyuan Formation. Methods used included polarizing microscopy, X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), X-ray fluorescence, micro-Fourier-transform infrared (micro-FTIR) spectroscopy, and Mossbauer spectroscopy. The coal gangues are mudstones, silty mud-stones, and pelitic siltstones, which are composed primarily of kaolinite, quartz, feldspar, pyrite, illite, and magnesite. In coal gangue, the Fe was found to occur in ferruginous minerals, in crystal-lattice substitutions, or in a colloidal state. The ferruginous minerals in the coal gangue are pyrite and marcasite, and the pyrite morphologies are framboidal, euhe-dral octahedral crystals, subhedral granular crystals, and irregular crystals. The results of SEM-EDS and micro-FTIR confirmed that the lattice substitution of Fe in the coal gangue minerals occurred mainly in kaolinite, resulting in two types of kaolinite: iron-containing and iron-free kaolinite. The former may be transformed from volcanic biotite and the latter from volcanic feldspar. The Mossbauer spectra of kaolinite showed intense doublets with isomer shift and quad-rupole splitting values consistent with tetrahedrally coordinated Fe~(3+) and ocahedrally coordinated Fe~(2+), suggesting the presence of two types of substitution sites: (1) Fe~(2+) replacing Al~(3+) in the octahedral sheet; and (2) Fe~(3+) replacing Si~(4+) in the tetrahedral sheet. This study has important theoretical significance for the high-value utilization of coal gangue.
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