CYANIDE REDUCTION/REPLACEMENT
Testing to verify the process has been
conducted at the Fairview operation, in South
Africa, according to van Niekerk, with a
demonstration ahead of a full-scale installation
resulting in the 50% cyanide consumption
reduction highlighted.
While Fairview has been the only operation to
trial the new process on a continuous basis, batch
test work had been completed on several other
concentrates, all of which had produced similar
benefits, van Niekerk said.
The highest operating cost benefits – brought
about by the reduction in cyanide consumption –
will be realised at those plants where ores
typically require high cyanide doses for effective
metal extraction via bio-oxidation, according to
van Niekerk.
“We’ve got some plants with a normal
mesophile BIOX plant where the cyanide
consumption isn’t really that high, so we wouldn’t
expect to see that level (50%) of cyanide
consumption reduction,” he said. “Whereas, we
have some plants that have higher cyanide
consumption than Fairview; that is where you will
expect an even higher potential saving.”
van Niekerk concluded: “Cyanide consumption
has always been considered a negative aspect of
bio-oxidation, so I think this will be a step change
in the applicability of the process.
“We’re also seeing an increase in the number of
high sulphur concentrates coming through and
being tested, and I think that is really where the
technology will find its niche. Higher sulphur
concentrates are typically harder to break down
and tend to consume more cyanide.
“The new process will have a big impact on the
economics of processing those concentrates.”
Cyanide recycling
GreenGold Technology’s ReCYN process looks to
reduce cyanide consumption through an
innovative recycling process.
The Jakarta-based company has recently been
making waves, with its biggest ReCYN resin-based
technology build nearing completion and several
new projects on the horizon.
The ReCYN technology reduces cyanide
consumption by up to 50% by capturing free
cyanide from plant tailings and recycling it back
into the leach circuit while recovering metal
complexes and making them available for sale,
according to the company. In the process, it
detoxifies the tailings stream and guarantees
100%-compliant clean water discharge.
Such technology is in serious demand
considering the industry’s operational cost focus,
increased stakeholder pressure around the use of
cyanide, the need to recycle and replace as much
water as possible, and a necessity to improve
project economics through the recovery of all
payable metals.
On top of this, new and existing gold projects
are becoming difficult to process through
conventional means with problems around byproducts
such as copper often proving the
difference between a sub-economic and economic
mine development proposition.
The ReCYN process is based on the use of a
functionalised resin bead, pre-treated to allow the
dual duty of recovering free and complex cyanide
ions from solution with a high degree of efficiency.
GreenGold works with local construction
companies to customise treatment plants for each
operation to match the various solution
chemistries and throughputs, it says.
“The two areas of cyanide recovery and metal
detoxification are balanced to achieve the desired
compliance levels,” GreenGold says. “Equally
applicable to slurries and solutions, the process is
technically and economically superior to all others
currently available for the detoxification of gold
plant tailings.”
The company currently has four ReCYN options
for clients, according to Commercial Director, Peter
Mellor.
ReCYN I is for active (free) cyanide reduction,
while ReCYN II has been devised to include detox
applications to recover cyanide complexes such as
copper. ReCYN III adds gold recovery as a
“secondary function” to the mix.
The fourth option (ReCYN IV) includes gold
recovery as a primary option, Mellor told IM,
explaining that the development of a plant
offering in this configuration could remove the
need for a carbon-in-leach treatment plant in
some applications.
It is a ReCYN II installation the company is
currently putting the finishing touches to at PT
Agincourt Resources’ Martabe gold-silver
operation in Sumatra, Indonesia.
The application of the technology, which will
detoxify tailings and recover cyanide and copper,
was previously estimated by Whittle Consulting to
provide a $126.9 million upside to the project.
Speaking to IM earlier this year, Mellor said the
company was just over a month away from
completing the plant at Martabe before COVID-19
restrictions hit progress. He was confident the
company would be back commissioning it before
the end of the year.
By far the biggest ReCYN installation of the
technology, the ReCYN II plant at Martabe will fit
into the 5.5 Mt/y circuit and treat around 1.2 t/d of
copper, Mellor said. It will have benefits in terms
of reduced cyanide consumption and reduced
cyanide detoxification costs, he added.
While work in Indonesia is currently on hold,
the company is making significant progress
elsewhere.
Mellor said GreenGold had started detailed
engineering for a plant in the Ivory Coast, while it
had also completed an economic study on a
legacy gold operation in Australia that showed
compelling economics and the potential for a
ReCYN IV installation for processing gold-bearing
tailings.
The company also has some 40 projects it is
working on in the laboratory – from Australia to
the US – with client awards expected this year.
Sulphidisation, acidification, recycling and
thickening (SART) technology also has
applications in cyanide reducing projects, with
GoGold Resources’ recently commissioned SART
plant at the Parral tailings facility in Chihuahua,
Mexico, a prime example.
The plant is providing important economic and
technical benefits to the Parral facility, according
to the Toronto-listed company. This includes the
recovery of a high-grade saleable copper sulphide
product, the re-generation of cyanide – the largest
single operating cost at Parral – and an
improvement in the leaching efficiency of the
heap.
The company announced back in June 2019 that
it had retained BQE Water to design, construct and
commission the SART plant at Parral. This contract
followed on-site testing and preliminary
assessment of SART integration into the
metallurgical process at Parral that BQE
completed earlier that year.
Brad Langille, President and CEO of GoGold,
said: “Our team at Parral has successfully adapted
agglomerated heap leaching to old mined waste
at Parral, and the SART is a further optimisation of
this innovation.”
The SART plant commissioning phase began in
late January, and steady production was reached
in early March, GoGold said. The plant is currently
operating as intended, producing copper sulphide
precipitate and re-generating cyanide.
Its introduction reduced the need for purchased
cyanide by more than 20%, or around C$200,000
($140,378) in the month of March, according to
the company, with the revenue attributed to the
copper sulphide precipitate offsetting the costs of
operation of the SART plant. In the March quarter,
GoGold produced copper by-product from the
SART plant equating to 9,509 oz of silverequivalent.
More SART plants could be on the way, too.
BQE said in its March quarter results that
engineering design for the construction of two
new plants to be integrated into the respective
gold metallurgical processing facilities for
Shandong Zhongkuang Group and Zhaojin Group
in China had been carried out.
The company has also submitted a SART plant
engineering design for the feasibility study
assessment of tailings re-processing using carbonin-pulp
at an existing mine in Mexico, while
preliminary technical assessment of integrating
SART into an existing gold heap leach operation in
Mexico has been conducted. IM
14 International Mining | JULY/AUGUST 2020