Thermal transformation of coal pyrite with different structural types during heat treatment in air at 573–1473 K

Abstract

• The relationship between the transformations of coal pyrite and its geological characteristics has been established. • The geological formation stages of coal pyrite have been determined according to their structural types. • Behavior is different among syngenetic, diagenetic, and epigenetic coal pyrite during heat treatment. • Because of the difference of the assemblage of minerals, slagging is less likely to occur in samples containing syngenetic pyrite than those containing diagenetic or epigenetic pyrite in this study. Pyrite in coals is always attractive to many scholars because of its adverse impacts on the combustion systems, on the environment, and on human health. In this study, thermal behavior of coal pyrite of different structural types during a laboratory-scale heat treatment was studied. The formation stages (e.g. syngenetic, diagenetic, and epigenetic) of coal pyrite were deduced from its structural types. Behavior is different among samples containing syngenetic, diagenetic, and epigenetic pyrite during tube furnace combustion. Pyrite peaks disappear in samples containing syngenetic and diagenetic pyrite at 873–973 K, which is lower than that of the epigenetic pyrite samples (973 K). Hematite is the main combustion product of syngenetic pyrite samples. Pyrrhotite is an intermediate phase of epigenetic pyrite during combustion. Hematite and magnetite are the products of diagenetic and epigenetic pyrite samples. Slagging occurs or not depends on the kinds of minerals and their proportions in each sample, which are related to the pyrite in the original sample was syngenetic, diagenetic, or epigenetic. Slagging tends to occur in samples containing diagenetic or epigenetic pyrite in this study. Thus, determining what kind of pyrite (syngenetic, diagenetic, etc.) occurs in a coal sample, we can already make an informed estimate as to the slagging behavior of that specific coal.