Coal mineralogies by SEM automatic image analysis

Procedures for using SEM automatic image analysis (AIA) to obtain quantitative mineralogical descriptions of coals are updated from our earlier description (SEM/1978/I, pp. 561-568), as improvements have been made in many aspects of the method. Experiments designed to test the precision and accuracy of the method indicate that its precision is comparable to that of other techniques, but that it overestimates pyrite because the contrast of this mineral in the BSE image is much higher than that of all other common minerals. A multiplicative correction factor of about 0.75 for pyrite or indepedent measures of pyrite will ensure the most accurate results by the SEM-AIA method. As the SEM-AIA technique is applied directly to the coal, is more sensitive to minor constituents than other methods, and yields information on the distribution of particle-size parameters, it compares well with other techniques for quantitative coal mineralogies. Results obtained with this technique are summarized for two applications: mineralogical changes effected by washing and reconstructions of paleoenvironments for coal quality delineation. (18 refs.)