Mineral Transformations During Ashing and Slagging of Selected Low-Rank Coals

摘要

The purpose of this study is to identify mineral transformations in low to high temperature ashes (125 exp 0 , 750 exp 0 , and 1000 exp 0 C) and slags (1300 exp 0 C) characteristic of lignites. The processes responsible for certain mineral transformation are also examined. Twelve low-rank coals were selected from the northern Great Plains and Gulf Coast. Nine North Dakota lignites, two Gulf Coast (Texas and Alabama) lignites, and one subbituminous coal from Montana were studied. The results of this study reflect the preliminary stage of investigation into the mineral phase transformations seen in low-rank coals. The original mineralogies of coals sampled do not vary a great deal. Quartz, kaolinite, pyrite, and bassanite are found in abundance in each LTA sample. Greater differences between samples are apparent at higher temperatures where complex alumino-silicates predominate. Perhaps this is a reflection of diffrences not so much in original mineral matter but in the total inorganic composition of the coal, specifically the presence of exchangeable alkali cations. The interactions of such organically-bound cations with crystalline inorganic phases in lignites account for differences in ashing and slagging behavior between coal samples. The processes responsible for most reactions identified are oxidation, dehydration, sulfur fixation, solid-state interactions, vaporization, and recrystallization. Isolating specific reactions occurring in a multi-component system is difficult at best. Understanding the thermodynamics of mineral transformations is a necessity and will be pursued in future study. In addition, future studies isolating mineral pairs to observe phase transformations at various temperatures will support or refute results presented here. 13 references, 2 tables. (ERA citation 09:024583)