Ra. Creelman et Cr. Ward, A SCANNING ELECTRON-MICROSCOPE METHOD FOR AUTOMATED, QUANTITATIVE-ANALYSIS OF MINERAL MATTER IN COAL, International journal of coal geology, 30(3), 1996, pp. 249-269
Quantitative mineralogical analysis has been carried out on a series o
f nine coal samples from Australia, South Africa and China using a new
ly-developed automated image analysis system coupled to a scanning ele
ctron microscope. The image analysis system (QEMSEM) gathers X-ray sp
ectra and backscattered electron data from a number of points on a con
ventional grain-mount polished section under the SEM, and interprets t
he data from each point in mineralogical terms. The cumulative data in
each case was integrated to provide a volumetric modal analysis of th
e species present in the coal samples, expressed as percentages of the
respective coals' mineral matter. Comparison was made of the QEMSEM
results to data obtained from the same samples using other methods of
quantitative mineralogical analysis, namely X-ray diffraction of the l
ow-temperature oxygen-plasma ash and normative calculation from the (h
igh-temperature) ash analysis and carbonate CO2 data Good agreement wa
s obtained from all three methods for quartz in the coals, and also fo
r most of the iron-bearing minerals. The correlation between results f
rom the different methods was less strong, however, for individual cla
y minerals, or for minerals such as calcite, dolomite and phosphate sp
ecies that made up only relatively small proportions of the mineral ma
tter. The image analysis approach, using the electron microscope for m
ineralogical studies, has significant potential as a supplement to opt
ical microscopy in quantitative coal characterisation.