Ten samples of mineral-matter residue were obtained by the radio-frequency lowtemperature ashing of subbituminous and bituminous coals. The low-temperature ash samples were then heated progressively from 4OO'C to 1400ยฐC at 100ยฐC intervals. Mineral phases present at each temperature interval were determined by X-ray diffraction analyses. The minerals originally present in the coals (quartz, kaolinite, illite, pyrite, calcite, gypsum, dolomite, and sphalerite) were all altered to higher temperature phases. Several of these phases, including kaolinite, metakaolinite, mullite, anhydrite, and anorthite, were found only in limited temperature ranges. Therefore the temperature of formation of the ashes in which they occur may be determined. Mineralogical differences were observed between coal samples from the Rocky Mountain Province, the Illinois Basin, and the Appalachians; and as a result of these mineralogical differences, different high-temperature phases resulted as the samples were heated. However, regional generalizations cannot be made until a greater number of samples have been studied.
Minerals in coal have been studied in some detail, but very little work has been done on mineral phases formed from these minerals when coal is burned at high temperatures. The purpose of this paper is to explore the relations between coal minerals and ash formed in the temperature range from 4OO'C through 14OO'C.
Minerals in and associated with coal have been studied for many years. Good summaries of the older work on minerals in coal have been written by Selvig and Gibson' and by Watt2. Through low-temperature ashing3 (between 150 and 200'(J), a technique by which mineral matter from coal can be obtained in a relatively unaltered state, numerous quantitative studies of the chemistry and mineralogy of cod minerals have been conducted in recent years4-8.
In contrast, very few studies of the mineral phases of coal ash formed at elevated temperatures have been made, and in general these have been limited to European coals. Significant papers include those on coal ash by Sinaiskii et al', Vdovenko and Chursina", and O'Gorman and Walker", and those on slag by Koch12, Rost and Ney'j, and Kirsch and Pollmann14.