Compositional and structural changes during aerial oxidation of coal and their relations with technological properties

Coal oxidation produces remarkable compositional and structural modifications, which influence the technological properties in the industrial use of coal. Relationships between infrared data and plastic properties, volatile matter content, textural properties and combustion behaviour are discussed. Variations of mineral matter composition were studied by means of X-ray diffraction (XRD) and FTIR analyses of the low-temperature coal ashes. A decrease in siderite and an increase in calcite were observed, indicating that artificial oxidation follows a different pathway to weathering. The removal of hydrogenated groups is mainly responsible for the loss of plastic properties and also for modifications in the textural properties of coal. The formation of oxygenated groups (carbonyl, carboxyl and ether) in coal structure gives rise to an increase in volatile matter content. However, especially in the first stages of oxidation, this process competes with devolatilization. Oxygen functionality also plays an important role in combustion behaviour and a relationship between the carbonyl-to-hydrogen ratio and characteristic temperatures of the burning profiles of coal combustion was observed. (C) 1998 Elsevier Science B.V. All rights reserved.