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Several chemical and physical cleaning methods for removing sulfur and ash-forming mineral matter from various kinds of bituminous coal were investigated. These methods involved grinding coal to a fine size to expose or liberate the mineral matter and either physical separation or chemical leaching of the resulting particles. By combining these methods, a multistep process was developed and demonstrated in smallscale laboratory experiments for the production of super clean coal with both a low-ash content and a low-sulfur content. In this process, the coal is first leached with a dilute sodium carbonate solution under oxygen pressure at 150°C to oxidize pyritic sulfur and some of the organic sulfur to produce water-soluble sulfur species. Next, the temperature of the alkaline suspension is raised above 250°C but under non-oxidizing conditions to convert clays and other minerals to acid-soluble materials. The solids are subsequently separated by filtration and then extracted with a dilute mineral acid. As a result of chis treatment, most of the mineral matter is removed from the coal and the sulfur content greatly reduced. In some cases, coal with a large ash content was precleaned by physical methods to remove part of the ash-forming mineral matter and thereby reduce the burden on chemical leaching. To better understand the behavior of mineral matter in this process, individual minerals including various clays, quartz, carbonates, and pyrite were reacted with hot alkaline solutions and the solid reaction products characterized by X-ray diffraction analysis. The solubility of the reaction products in dilute mineral acids was also investigated in

Coal desulfurization and demineralization by chemical/physical treatments