The compositional and structural changes to selected bituminous coals during natural weathering (outcropping) and low-temperature laboratory oxidation were determined. The volatile matter contents of the oxidized coals were higher than those of the corresponding fresh coals. Lower carbon and hydrogen contents, higher oxygen contents and therefore lower heating values were characteristic of the crop and laboratory-oxidized coals. The sulphur contents of the crop coals were significantly lower than those of the laboratory-oxidized and fresh coals, due primarily to the oxidation of pyrite in the crop coals. Changes in the organic structure of the coals upon natural weathering and laboratory oxidation, as shown by diffuse reflectance and 13C n.m.r. spectroscopy, were similar in nature but different in magnitude. One structural difference between the laboratory-oxidized and naturally weathered coals was the formation of ester groups in the former, whereas acid functional groups were the predominant species formed in the latter. Important structural differences in the inorganic phases between the fresh and crop coals were due to oxidation of pyrite, leaching of calcite, and incorporation of some ion-exchangeable metal cations such as calcium in the crop coals. No such differences were observed in the composition of the ash from the fresh and laboratory-oxidized coals.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology
- Organic Chemistry