Coal Macerals Chemistry and Its Implications for Selectivity in Coal Floatability

Abstract

Macerals are the smallest components of coal recognizable on the microscopic scale and, even when optically homogeneous, they may have variable elemental and molecular chemistry not only across different coal ranks but also in iso-rank coals. These variations in maceral chemistry may have significant impact on the behavior of the coal during processing and may also complicate predictions of this behavior. Flotation is one of the processes that is impacted by intermaceral variations. Flotation is used as a main process to upgrade the fines of higher rank coals. It depends on the surface properties of coal particles, hence their chemical composition. Most of the minerals associated with coal, with the exception of a few (elemental sulfur or some pyrites), are hydrophilic and can easily be separated if liberated from coal by flotation. The organic matter (macerals) possesses different degrees of hydrophobicity, and its response to flotation can vary depending on the surface properties that result from chemical composition of macerals and their associations with each other and minerals. This article addresses research progress in the area of chemistry of macerals and their hydrophobicity with a special reference to achieving selectivity in coal flotation.