Characterization of mineral matter in sub-bituminous coals by AIA (automated image analysis)-SEM (scanning electron microscopy)

Automated image analysis (AIA) was used with scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy to characterize the mineral matter in two western sub-bituminous coals from the Adaville No. 11 seam (Kemmerer, WY) and the Dietz No. 1 and 2 seams (Decker, MT). The samples were ground to {minus} 200 mesh and cleaned by float-sink separation at 1.40 and 1.38 sp. gr., respectively. The particles were characterized before and after cleaning for mineral phase and size distributions by classifying them into 6 sizes and 16 mineral categories. Quartz was the dominant mineral in both coals, with the Adaville sample containing primarily quartz and an iron-rich mineral. Traces of apatite were also detected in the Adaville samples. The Dietz coal contained primarily quartz and kaolinite. Preliminary results are also presented for the association of the mineral particles with the coal matrix. These analyses were performed by automatically classifying the composite mineral - coal features into 10 types of particles of increasing specific gravity. The results closely estimated the total mineral matter content, as calculated from the ASTM ash content, and the specific gravity distributions were consistent with data obtained from the cleaning step.