Characterization of the low-temperature ash component of the herrin 6 coal seam (southwestern illinois) by thermal methods of analysis

Abstract

A low-temperature ash (LTA) specimen of the Herrin No. 6 Seam (Southwestern Illinois) was analyzed using the computerized thermal analysis techniques of differential thermal analysis (DTA), thermogravimetry (TG), and derivative thermogravimetry (DTG). The major features of the thermal curves were dominated by a large pyrite (FeS 2) and hydrated iron sulfate component, illite and illite-smectite mixed-layer clays, and a small calcite component. The presence of hydrated iron(II) sulfates was observed to catalyze the decomposition of pyrite in inert atmospheres. The presence of large amounts of iron oxides, generated from studies in dynamic air (oxidizing) atmospheres, was observed to interact or change the nature of the calcite decomposition relative to that normally obtained by DTA and DTG techniques. The use of multiple atmosphere techniques allowed the recognition of pyrite in DTA as both an endothermic event in flowing nitrogen and carbon dioxide and as a multi-step exothermic event in dynamic air atmosphere. Due to the fact that ferrous sulfate heptahydrate exhibits a different mechanism for the loss of the final water of hydration in inert atmospheres than in oxidizing atmospheres, recognition of ferrous sulfate monohydrate was possible by both DTA and DTG thermal curves. The amount of calcite present in the LTA specimen was quantified in dynamic carbon dioxide atmosphere by thermogravimetry. This value was compared to that found by X-ray diffractometry. Sulfur analysis and X-ray diffraction data were also obtained for this LTA specimen.