Laser-induced macrofluorescence of coal: oxidation and spectral effects

Exposure of Goonyella and Bulli seam coal to air at room temperature for 3 days reduced the 800 nm macrofluorescence by 5%. The macrofluorescence was reduced by 40% after exposure to air for 4 days at 105 °C. A 64% reduction in the 800 nm macrofluorescence of Goonyella coal resulted from treatment with 30% hydrogen peroxide solution for 1 h at 100 °C. This decrease in 800 nm macrofluorescence is associated with an increase in oxidation. A similar spectral change was noted across an oxidation line in the Goonyella seam by measuring the ratio of infrared to green intensity at 825 and 510 nm and correlating the ratio with core depth. Spectral measurements were made while illuminating the samples at 325 and 442 nm over relatively large surface areas (0.1–22 cm 2) with pressed fine coal samples and with lump coal. The method may be suitable for the on-line characterization of coal oxidation.