GOLD EXTRACTION
“No pre-elution of copper or regeneration of
the resin was undertaken which significantly
simplified the resin elution process,” the authors
said. “This gold product was retorted to recover
mercury (some of the mercury entrained with the
ore when it was previously treated in the battery
is dissolved and recovered along with the gold)
and then smelted to produce gold doré.”
The barren leach solution (BLS) was recycled
back into the leach process with reagent top-up
as needed to replace that consumed or lost in
the process. The leach tails were rinsed with
process water to reduce the loss of any residual
gold and reagents in the solution exiting the
process with the solids, the authors said.
The recovery and recycling of BLS to minimise
gold and reagent losses, and maintain the
resultant water balance, is a vital aspect to the
application of this technology as the efficiency of
this stage influences the overall process
economics, according to the authors. “Hence,
this was a major focus of the demonstration.”
The authors concluded the technology
package, over the test period, successfully
demonstrated:
n A stable/reusable non-toxic leach reagent
having similar gold recovery rates to cyanide;
n Proven gold recovery plant and processes that
enable gold doré bar production on site;
n Feasible and simple processing plant enabling
small scale miners to recover fine gold without
toll treatment or the need to use cyanide;
n A mobile leaching plant that has a significantly
cheaper entry level cost compared with a
carbon-in-pulp/carbon-in-leach plant;
n A mobile modular plant design that is the
precursor to in-situ, heap, vat or tank leach
plant designs;
arlier this year, FLSmidth looked to broaden its gold processing
offering with the addition of Barrick Gold’s AuTec Innovative
Extractive Solutions. Dan Gleeson put some questions to Wayne
Douglas, Director of the FLSmidth Minerals Testing Center, to find out
more about the rationale for the acquisition.
E
IM: How will the acquisition of AuTec enable FLSmidth to cope with the
increasing complexity of gold-bearing orebodies?
WD: With AuTec as an integrated part of FLSmidth, we will continue to
work quickly and in an agile way to respond to each challenge as it is
presented by the industry. This will happen through using our advanced
mineralogical characterisation tools to develop the needed appropriate
metallurgical process. I believe we will continue to see an increase in the
refractory nature of new deposits. The AuTec acquisition brought over 100
years of experience pertaining to development and selection of the
optimum oxidation processes and downstream treatments required for
these complex gold ores.
More importantly, personnel have seen these processes from benchtop
test work, piloting, demonstration plants, through to commissioning and
optimisation of some of the largest refractory gold process plants. Adding
this expertise to the existing world-class flotation, leaching, separation,
comminution, and ore characterisation team allows FLSmidth to provide
practical solutions for any simple or complex gold ore.
This development comes at the same time as the game-changing Rapid
Oxidative Leach process (ROL) is reaching the milestone of a
demonstration-scale plant. ROL, in short, makes it possible to develop
mineral deposits containing arsenic for recovery of copper, gold, and
silver, while complying with stringent environmental regulations. ROL also
allows for recovery from waste streams, and piles containing arsenic can
be processed on site. This makes it possible to avoid potentially toxic
emissions to soils, air and water. In combination with the new expertise
from AuTec, this gives FLSmidth an unrivalled offering towards gold
customers.
IM: What technology/processes within AuTec will, for example, allow you
to provide advice or engineering on how to process sulphide-bearing
orebodies, or preg-robbing ores?
WD: The AuTec acquisition provides both the equipment and proven
expertise in full flowsheet development of both single and double
n An option for countries that have banned the
use of cyanide to recommence gold mining,
and;
n An option for countries that tolerate the use of
cyanide through lack of alternative, to
transition to a non-toxic leach process.
“The successful validation in the field at scale
of the leach reagent and technology has paved
the way for commercialisation,” the authors said.
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.
Clean Mining will deliver the new technology
solution to a global market of gold producers,
offering technology products and licences as well
as turn-key processing plant options, plus
equipment and product support throughout the
refractory gold orebodies. Capabilities include a pilot autoclave, benchtop
autoclaves, benchtop roasting, as well as downstream treatment and
leaching to maximise metals recovery in even the most complex orebodies
or novel flowsheets. Additional analytical instrumentation and methods
were obtained to provide the necessary support. Coupled with existing
FLSmidth Mineral Testing and Research Center capabilities, we can
provide full ore characterisation with metallurgical testing and plant
support from comminution through tailings.
IM: The use of cyanide within the gold processing field has become a hot
topic in the past decade or so, with many companies developing
alternative lixiviants or ways to recycle/reduce cyanide consumption: How
will AuTec help facilitate the move towards using less cyanide?
WD: There are various mineralogical and process conditions that create a
high cyanide consumption that require special attention to achieve
required efficient metal extractions. AuTec has utilised and helped
develop a few of these technologies to minimise cyanide usage. The
technical experts that have joined FLSmidth from AuTec have brought the
skillset to optimise current processes or develop new technologies to
address this issue.
It should also be noted that the AuTec group helped to develop, pilot,
and commission the thiosulphate leaching process being utilised by
Barrick Gold’s Goldstrike mine. Personnel have been involved with
examining alternate lixiviants for the last three decades. We look forward
to continuing to work with our customers as they look to meet their
challenges.
IM: How will the combination of AuTec and the existing gold extraction
capabilities of FLSmidth differentiate you from your peers?
WD: The combination of strengths will give customers a one-stop shop for
all their ore processing needs.
The addition of the AuTec team gives FLSmidth an unrivalled depth of
expertise in the gold and precious metals sectors. It allows us to provide
processing solutions to even the most challenging gold orebody, making
us partner of choice in providing solutions to the gold industry. Whether
undertaking test work to develop a new deposit, selecting the appropriate
equipment to meet production challenges, through to maximising
productivity of an operating site, FLSmidth has every base covered.
AUGUST 2019 | International Mining 49