Petrological characterization of coal: an evolving science
JM Richards, G Naude, SJ Theron, M McCullum
For most of the 20th century optical petrography has been the
primary petrological and mineralogical tool used to characterize coal.
The development of quantitative SEM-based techniques, e.g.
QEMSCAN®, for coal began only about a decade ago. The application
of these techniques for coal lagged behind other commodities, but
they are currently being developed with the aim to provide ‘one
complete analysis’ for coal. Quantitative SEM-based techniques are
supplemented by quantitative X-ray diffraction (XRD).
Recent indications are that these more modern techniques cannot
replace the ‘standard’ petrographic and chemical evaluations, but
rather complement them where and when required. The great
advantage of quantitative SEM-based techniques is that they are very
rapid, with the result that large volumes of samples can be processed
on a routine basis. This is ideal for coal type identification, since the
results can be used in the creation of ‘intelligent’ composites. This can
lead to the more speedy evaluation of coal deposits by reducing the
number of samples on which detailed metallurgical and characterization
test work is required, without an increase in the overall
statistical error of the resource model.
Coal petrography, however, remains important for the prediction
of the coking characteristics of certain coals and coal products. As a
consequence it is therefore important that any coal laboratory be able
to produce data with confidence. This requires strict quality control
and assurance protocols that adhere to international standards.
Keywords: coal petrography, coking strength, scanning electron microscopy,
QEMSCAN®.