Analysis of the association of minerals with coal using scanning electron microscope-based automated image analysis (SEM-AIA) is described and applied to physical coal cleaning. Results are expressed with regard to both density-based and surface-based cleaning processes. Samples of nominal 200-mesh Pittsburgh No. 8 coal used in column flotation experiments were analyzed by SEM-AIA to predict cleanability for both types of cleaning and for individual minerals. Results indicated good liberation of minerals based on particle mineral matter content and thus predicted good cleanability by density-based methods. Results also showed poor liberation of pyrite compared to other minerals when particles were categorized according to surface appearance, thus indicating poor cleanability. Predictions were generally borne out by actual separations although additional factors besides liberation appear to be hindering the cleanability of pyrite by column flotation.

Over 400 published papers, presentations at scientific meetings, and reports relating to the determination of sulfur and sulfur forms in coal-related materials have been accumulated, classified, and an evaluation made of their content.

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 -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 distribution 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.

Automated Image Analysis (AIA) in conjunction with Scanning Electron Microscopy (SEM) and energy-dispersive x-ray analysis (EDX) constitutes a very powerful tool for the in-situ characterization of mineral matter in coal. This AIA-SEM technique provides detailed information on size, shape, composition, and association of mineral phases with the coal matrix. In addition, the in-situ capability of the SEM and EDX techniques is augmented by computer control to provide quantitative information on the distribution of the mineral species present in coal. The AIA-SEM technique has been aplied to many samples of bituminous and sub-bituminous coals to characterize their mineral content. Some of the fundamental aspects of AIA as an analytical technique for coal are described. The description includes construction of suitable chemistry files for mineral phase definitions, the numbers of particles needed to develop reliable results and adequate reproducibility between samples, difficulties arising from a wide spead in the minimum and maximum particle sizes, comparison of AIA results with other characterization methods as x-ray diffraction and Fourier transform infrared (FTIR) analyses, the problems encountered in quantitation, such as the artificial enrichment of pyrite content due to instrumental factors. 8 refs., 6 tabs.

As the removal of sulfur from coal prior to combustion acquires more importance in order to meet evermore stringent antipollution regulations, research on the development of methods for the cleaning of coal continues to expand. Reviews are available which describe the various methods for desulfurizing coal (1, 2, 3). The sulfur content in coal is usually a few per cent, but it can range from less than 0.5 per cent to as much as 8 per cent or more. Much of the sulfur is inorganic in nature, occurring in discrete mineral phases; the inorganic sulfur is mostly pyrite with small amounts of sulfates such as gypsum. Part of the sulfur in coal is termed organic sulfur, being intimately bound to the organic coal matrix. The chemical nature of this organic sulfur is not well established. During the desulfurization of coal, some of the coarse inorganic sulfur components can be removed