Mine excursion
Coal samples that enter the lab as solid core samples are
ground down to a fine dust to reveal its numerous qualities.
In other cases, the coal sample is
sent in and crushed to different sizes
in the laboratory’s jaw crushers and
then further analysed, beginning
with the sink/float process. The core
needs to be crushed to exactly the size
that will enter the mine’s processing
plant — the sample needs to be plant
specific. According to Carstens, the
standard size of coal is 25mm, but
this is not always the case. “Most coal
that is fed into plants in Mpumalanga
is 25mm,” Carstens informs. After
crushing the coal, during what is
known as the pre-treatment phase,
the samples are put through the sink/
float washability dense medium
separation, where the coal is separated
into different density fractions.
“Here we separate the coal into
different densities before we start
preparing it for a range of tests,
including moisture, ash, volatiles,
calorific values, percentage sulphur,
and many more. There are special
instruments for each different
test, and each fraction is tested
individually,” Carstens explains.
Through a series of analyses and tests,
the original core sample that arrived
at the laboratory wrapped in plastic,
is reduced to only a fraction of the
original size. The powder that emerges
after this intensive process can best be
described as a recorded history and a
book about the future of a core sample,
retrieved by a geologist in the field.
Looks can be deceiving though, and no
matter how insignificant the powder
might appear, it tells a story and it is
an indispensable aid to exploration
companies. Carstens emphasises the
importance of a good geologist.
“When you do coal exploration,
the key is to use a reputable and good
geologist. If it is a greenfields project
and there is no plant yet, the geologist
is your most important asset. Anybody
can drill a hole, extract coal, analyse
it, and start mining. But it’s not that
easy. You need to plan properly and to
do that, you need a proper geologist. If
you have an existing operation with a
plant, the most important people are
the geologists, plant operators, and
plant designers. And it is critical that
these people speak to each other and
formulate a strategy and plan before
they come to us,” Carstens advises.
Although this highly skilled and
experienced team at Bureau Veritas
can tell you the difference between
Waterberg coal and Mpumalanga
coal, or coking and thermal coal,
they cannot make recommendations,
and it is up to the mining team
to make the final decisions.
A few hours in the laboratory with
coal experts is probably not enough to
decipher the true mysteries of coal. It
is enough, though, to realise the limits
of our own knowledge about this finite
and inconspicuous resource, and that
it takes more than just digging a hole
to consider yourself a coal miner. b
MARCH 2018 MINING MIRROR
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