Macroscopic and microscopic fluorescence spectra of coal and coal components

Fluorescence spectra, from 540 nm to 700 nm, were obtained from the major microscopically identifiable components of a high volatile and a medium volatile coal. The liptinite spectra of both coals were blue shifted with respect to the vitrinite spectra. The inertinite spectra of the medium volatile coal had a similar form to the associated vitrinite spectra, although at a lower intensity. The signal response from the high volatile coal inertinite was so low as to be indistinguishable from noise. The clay component fluoresced more intensely than liptinite (sporinite), vitrinite and intertinite macerals. Further, it exhibited spectra which mimicked the shape of the liptinite spectra, suggesting an organic source for the fluorophore in the clay. Approximately one half of the total fluorescence of the medium volatile coal was from the clay minerals. The shape of the composite microfluorescence spectrum of the medium volatile bituminous coal closely paralleled the macrofluorescence spectrum obtained from laser-induced fluorescence excitation of a large measurement area (3 cm 2) of crushed coal. Petroleum bitumen addition to kaolinite resulted in a brighter than additive fluorescence output. It is thought that the kaolinite acted as a wavelength-shifting fluorescence ‘sensitiser’; the fluorescence being much greater than the sum of the parts. A similar effect is thought to occur in coal.