GOLD EXTRACTION
Leveraging
the lixiviants
The extraction of gold has become increasingly complex over
the last few decades, leading to the development of several new
technologies able to effectively recover gold while, at the same
time, meeting the needs for more environmentally friendly
processing options. Dan Gleeson profiles some of these
old may dominate when it comes to the
number of mines currently in operation
across the globe, but, if analysts are
correct, we could soon hit a mine supply peak.
There is a simple explanation for this: one,
the easy-to-find deposits in favourable
jurisdictions have been discovered and
exploited, meaning development costs for new
mines can be high; two, and related, the
complexity associated with processing gold
orebodies has significantly increased.
Brian Howlett, CEO of Dundee Sustainable
Technologies (DST), a company that has devised
alternative gold processing methods to aid
mining companies faced with metallurgy,
recovery and environmental challenges, is all
too aware of this.
“Most of the ‘easy gold’ in the world has
been found; we are seeing a lot more complex
concentrates in the market, whether that be
arsenopyrite-types, or copper with gold,” he
said.
David Kratochvil, President and CEO of BQE
Water, says his company, which helps miners
avoid the negative interference of base metals
in the extraction of precious metals through
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44 International Mining | AUGUST 2019
processes such as sulphidisation, acidification,
recycling and thickening (SART), concurs.
“There seems to be fewer and fewer ‘clean
gold’ deposits of any significance discovered,”
he told IM. “Consequently, the ounces of gold
produced are increasingly being replaced by
ounces from more complex gold deposits that
feature a mix of gold and base metals.”
It is not only metallurgy and gold being
‘locked up’ in, for example, refractory orebodies
that is reducing the amount of yellow metal
likely to be produced in the future.
Environmental regulations and the negative
perceptions associated with existing gold
processing technology is holding back the
development of various gold deposits.
The use – or potential use – of cyanide has
had a negative effect on permitting at, for
example, the Rosia Montana gold-silver deposit
in Romania; an open-pit development that has
the potential to be Europe’s biggest gold
producer, but remains on hold awaiting a
parliamentary decision on the potential use of
the controversial lixiviant.
“Cyanide is becoming more of an issue every
day,” Howlett said, explaining places such as
Commercialisation of the ‘Going for Gold’
process technology occurred in June, not too
long after the thiosulphate process devised by
CSIRO had produced Australia’s first gold using
a non-toxic chemical process
China, Eastern Europe and the US have either
implemented, or plan to implement, bans on its
use.
The perceived risk of continuing to operate
mines that use cyanide into the future is also
leading some companies to reassess existing
process routes, according to Howlett.
“We have spoken to major miners that tell us
– and they are looking five-to-10 years ahead – if
cyanide were to be banned overnight for some
unknown reason (I’m not saying that is likely),
they could lose the ability to operate the
majority of their mines,” Howlett said.
It is these considerations shaping the way
gold miners, developers and explorers continue
to do business in the gold space.
Cyanide alternatives
Alternatives to cyanide in the gold processing
flowsheet have received much attention in
recent years largely driven by the health, safety
and environmental risks associated with its use.
Professor Jacques Eksteen Director, Gold
Technology Group and Chair, Extractive
Metallurgy Western Australia School of Mines,
Curtin University, Australia, summed up the
situation nicely in an abstract to his ‘Fit-for-
purpose precious metals leach systems: