Behavior of Minerals in Typical Shanxi Coking Coal during Pyrolysis

The transformation of inherent minerals during pyrolysis is the key for coke quality and metallurgy. Five different coals were selected to investigate the mineral transformation in coking coal from Shanxi province, and the influences of the coal matrix on mineral transformation were investigated. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopyenergy-dispersive spectrometry (SEM-EDS) were also used for exploring the mineral transformation. X-ray diffraction (XRD) and Rietveld-based TOPAS 4.2 software package were applied to quantify mineral matters at different temperatures. The results show that the mineral matter in the Shanxi coking coal includes a significant content of kaolinite (67.56-96.13%), tobelite (9.86-19.18%), calcite (1.56-12.75%), and quartz (0.78-4.93%). The catalytic minerals are rare in the Shanxi coking coals. Most minerals undergo complex reactions during pyrolysis, and the major mineral transformation is decomposition of kaolinite and tobelite and formation of mullite. The maximum decomposition rate temperatures of kaolinite and tobelite are 510 and 625 degrees C, and the formation of mullite occurs between 970 and 1010 degrees C. The amorphous phase is the dominant phase in the char above 700 degrees C. It is also found that the organic carbon matrix inhibits the mineral transformation, including dehydroxylation of kaolinite and deamination of tobelite, during pyrolysis.