COMPOSITIONAL AND STRUCTURAL-CHANGES DURING AERIAL OXIDATION OF COAL AND THEIR RELATIONS WITH TECHNOLOGICAL PROPERTIES

Coal oxidation produces remarkable compositional and structural modifi cations, which influence the technological properties in the industria l use of coal. Relationships between infrared data and plastic propert ies, volatile matter content, textural properties and combustion behav iour are discussed. Variations of mineral matter composition were stud ied by means of X-ray diffraction (XRD) and FTIR analyses of the low-t emperature coal ashes. A decrease in siderite and an increase in calci te were observed, indicating that artificial oxidation follows a diffe rent pathway to weathering. The removal of hydrogenated groups is main ly responsible for the loss of plastic properties and also for modific ations 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 fi rst stages of oxidation, this process competes with devolatilization. Oxygen functionality also plays an important role in combustion behavi our and a relationship between the carbonyl-to-hydrogen ratio and char acteristic temperatures of the burning profiles of coal combustion was observed. (C) 1998 Elsevier Science B.V. All rights reserved.