Abstract
The surface analytical techniques X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOFSIMS), and laser ionization mass analysis (LIMA) were used to characterize coal dust and cleaved coal surfaces from the Young Wallsend and Whybrow seams, Hunter region, New South Wales, Australia. XPS provided a quantifiable measure of the surface composition of coal dust samples which was correlated with chemically specific mass spectral data for cleaved coal surfaces produced by TOFSIMS. TOFSIMS molecular and atomic ion images were used to investigate modes of occurrence and spatial associations of mineral species. A rapid mineral fingerprinting technique for individual mineral grains (∼1 μm diameter) in coal was developed using LIMA, in which high energy ions are preferentially collected and mass analyzed. This method provides relatively simple mass spectra which can be readily assigned to mineral types. The small analysis area (∼2 to 3 μm) allows many discrete mineral species to be characterized in a complex sample. The dominant mineral species found on Young Wallsend coal surfaces were carbonates and aluminium and silicon in the form of aluminosilicate clays and quartz. TOFSIMS indicates the presence of spatially associated mixed clays and carbonates or more complex clays. A discrete mineral species containing strontium, barium, and calcium, probably in the form of a complex carbonate, was also observed. LIMA mass spectral analysis of Whybrow coal surfaces was used to identify a series of discrete clay, sulfide, sulfate, and carbonate mineral species. The interfacial chemistry of quartz particles occluded in vitrinite was also investigated. A thin organic phase at the interface, similar to liptinite, was shown to contain a significant concentration of sulfur. The use of these complementary techniques allows the surface composition and reactivity of mineral species in coal to be studied from both an elemental and a chemical perspective.