GOLD EXTRACTION
Under the agreement, MPS will receive a
royalty for the use of the technology based on
an NSR from future revenue flows of projects
where the technology is applied. As an early
adopter of the technology, Gindalbie has
secured a significant discount to standard
market royalty rates. Any other fees paid to MPS
will be based on a standard schedule of rates
for test work.
Gindalbie Chief Executive Officer Chris Stevens
said that the agreement provides “a fantastic
option to use this innovative Australian
developed processing technology at Mt Gunson
as well as globally in other potential Gindalbie
projects. We are delighted to be working with
MPS who not only bring their GlyLeach technology
but also a wealth of knowledge and expertise in
the field of mining and mineral processing.”
MPS Managing Director, Ivor Bryan
commented: “MPS has had a long association
with the Mt Gunson project and is delighted that
Gindalbie is coming on board to help fund and
progress the feasibility of the project.”
The GlyLeach process was invented by
Professor Jacques Eksteen and Dr Elsayed
Oraby, from Curtin University’s Western
Australian School of Mines. Curtin has awarded
MPS an exclusive global licence to the process.
According to Eksteen, the process has a
number of immediate applications including
leaching of low grade ores, differentially
leaching copper and gold ores, upgrading
concentrates, and tailings retreatment.
The major reagent in the process is glycine
which is the simplest and cheapest of the amino
acids, and is available in bulk ranging from food
to technical grade. It has a number of attractive
chemical and physical properties that gives it
significant advantages over any other copper or
gold lixiviant:
n Environmentally safe and stable reagent
n Biodegradable and easily metabolised in
most living organisms
n Active as a selective leach agent only when
used in an alkaline based circuit between pH
8 and 12
n Step change in copper leaching with
enhanced solubility of copper ions in
aqueous solutions and forms stable
complexes with copper
n Effective leaching agent for almost all copper
minerals except chrysocolla - a copper
silicate mineral
n Easily recovered and recycled (apart from
normal process losses expected at less than
5%); keeping operating costs low.
MPS Technical Director, Frank Trask stated
that GlyLeach is a simple process requiring no
new equipment to be designed, has low
operating costs due to regeneration of the
principal reagents, and is expected to provide
36 International Mining | A UGUST 2017
Lime / cement
Feed ore
Agglom
Glycine makeup
Heap leach
Stage 2
Heap leach
Stage 1
Cyanide
Lime
Bleed
Solvent Extraction
Carbon
adsorption
Electrowinning
high recoveries with almost all copper minerals,
even chalcopyrite (long considered the ‘Holy
Grail’ of copper leaching). It will also offer the
gold industry a non-toxic method of leaching
gold, something that is becoming more
important in many jurisdictions around the
world.
MPS has also entered into an agreement with
Curtin and a major ASX- listed mining company
to support a collaborative project to research
specific aspects of glycine leaching of gold
dominated polymetallic ores. This will be a
three-year, A$800,000 program. Curtin
University (Gold Technology Group, WASM) will
be the Chief Investigating Partner with MPS
being a sponsor and collaborative partner.
Rapid Oxidative Leach (ROL)
As gold deposits become increasingly complex
to treat and grades continue to deteriorate in
known reserves, treatment solutions for
refractory ores gain in importance. Some 15-
20% of current world gold production involves
refractory ores that must be pre-treated prior to
downstream recovery by cyanidation.
Ores are refractory for many reasons but
commonly because gold occurs as tiny
inclusions or submicroscopic gold within a
sulphide mineral matrix. This mineral matrix
must be physically and chemically altered to
liberate the gold for subsequent leaching.
Mike Woloschuk, FLSmidth’s Global Industry
Director for gold says there are many
undeveloped gold deposits where the resource
head grade is simply too low to be economically
viable using current refractory processing
technologies. “The industry needs a step
change in technology that will significantly
reduce processing cost, thereby lowering cut off
grades for refractory resources. We believe ROL
for gold has this potential.”
FLSmidth is pioneering Rapid Oxidative Leach
(ROL), which is a mechano-chemical pre-
treatment process for refractory gold ores. Sally
Cu cathode
Rocks, Senior R&D Chemist believes her team
has made an extraordinary breakthrough which
will have a profound effect on the industry. “We
have discovered an economically viable method
to process low-grade stockpiles and low-grade
refractory gold deposits.”
“Initially, we are targeting refractory gold-
bearing iron sulphides where the gold is locked
inside the sulphide mineral matrix and cannot
be recovered without pre-treatment.”
Unlike other refractory processing techniques
that require ultrafine grinding or high
temperatures and pressures, the FLSmidth ROL
gold process uses the application of mechanical
energy coupled with oxidation under
atmospheric conditions.
The process relies on Stirred Media Reactors
(SMRt) to accelerate the oxidation of sulphide
minerals. “Other technologies have relied on
ultrafine grinding to increase the surface area of
the particles. While ultrafine grinding is
sometimes effective, it also requires a lot of
energy and thus incurs a very high cost. We have
successfully engineered a new low-energy process
without having to ultrafine grind,” she explains.
In the ROL process, the abrasion of the
particle surfaces which occurs when the SMRt is
activated is balanced to match the leach rate of
“Judicious use of mechanical energy allows us
to accomplish chemical reaction rates that are
otherwise impossible without the use of high
temperatures or pressures. The end result is a
process that uses simple equipment and low-
cost operating conditions for refractory gold pre-
treatment.”
At present, the main refractory gold
processing methods include ultrafine grinding,
pressure oxidation (POX), roasting, or
bioleaching.
Pressure oxidation, roasting and bioleaching
have been successful in oxidising refractory
sulphide minerals to expose gold in solid
solution that cannot be recovered by ultra-fine
grinding alone.