GOLD EXTRACTION
other gold-bearing sulfides) and copper-gold
ores.
MAXGOLD chemistry is a sustainable
alternative to the traditionally used sulphide
collectors such as xanthates. One of the major
benefits of MAXGOLD chemistry is that they are
highly concentrated liquids, which afford greater
flexibility and lower dosages.
Aachen reactor versatility
Weir Minerals’ Warman ® advanced centrifugal
froth pump with Continuous Air Removal
System (CARS)
to decrease both head and efficiency, causing air-
binding.
As a result, poor froth pumping performance
normally leads to overflowing hoppers and the
loss of valuable concentrate.
As flotation performance is greatly influenced
through the on-going development of new and
improved reagents, companies producing mining
chemicals are continually striving to develop
“super performing chemicals”. Collectors are
being developed to further increase the
separability of the hydrophobic and hydrophilic
particles, while froth advancements aim to create
more stable froths to increase flotation kinetics
and allow for improved drainage of entrapped
gangue material.
To meet the demands of flotation plants that
exhibit complex and tenacious froth conditions,
Weir Minerals has developed the heavy duty
Warman ® AHFC froth pump with Continuous Air
Removal System (CARS) technology.
“Our Warman AHFC froth pump technology is
purposely designed for flotation processes that
produce medium froths, and very tough froth
concentrate transfer applications that produce
long lasting, tenacious froth conditions,” states
Taylor.
The pump has open inducer vanes that
protrude into the large intake throat area,
designed to create a strong swirling air core,
while drawing the froth air bubbles into the
impeller-eye. This process separates the valuable
concentrate from the tenacious froth bubbles.
Weir Minerals’ CARS technology is then able to
expel a vast amount of air into the atmosphere,
enabling more efficient froth concentrate pumping.
“Our enhanced froth pump technology, CARS,
is expertly designed for heavy duty slurry froth
42 International Mining | AUGUST 2017
pumps and is successfully operating in a number
of gold plants around the world,” says Taylor.
To support optimum froth pump performance,
froth hopper design and geometry is absolutely
critical.
“Every one of our froth hoppers is uniquely
designed to suit both the application and the
chosen Warman AHFC froth pump. Froth hoppers
must be designed to enhance the efficiency of
the froth transfer system by reducing ‘froth
generation’ turbulence inside the hopper, while
ensuring that the froth slurry concentrate is
effortlessly induced into the AHFC inlet,” explains
Taylor.
As some degree of flotation plant instability is
always to be expected, especially during plant
start-up, it is likely that under extreme, adverse
conditions the froth hopper may overflow.
Anticipating this instability, Weir Minerals has
innovatively designed large overflow launders
with a large down-pipe feeding directly into the
spillage handling system to minimise the loss of
valuable froth concentrate.
“Successful froth concentrate transfer projects
are only achievable through detailed process
plant reviews, involving a team of process
engineers and froth pump application
engineering consultants. We always partner with
our customers to deliver an autonomous flotation
process,” Taylor concludes.
Solvay continues to develop collectors
designed for the flotation recovery of precious
and base metals from primary and secondary
ores. This family of collectors is based on the
novel chemistry, MAXGOLD™. This chemistry is
offered under the name AERO ® MAXGOLD 900
promoter and mineral-specific formulations. The
AERO MX-900 promoter series, developed using
FLOTATION MATRIX 100™ is for flotation recovery
of gold values from primary gold ores (free gold,
auriferous pyrite, auriferous arsenopyrite and
One of the problems many gold operations face
is how to manage the transition from oxide
material to more refractory sulphide material. As
the orebody changes from free milling oxide
through transitionary material to full sulphide,
recovery levels begin to drop. The drop off in
recovery is often associated with reduced oxygen
levels. Whilst a lance system may be adequate
for a low oxygen demand free milling orebody it
cannot address the higher oxygen demand and
other process issues such as passivation which
are associated with more aggressive orebodies.
This problem can be solved through the flexibility
of the Aachen reactors whereby initially when
oxide material is treated only a light pre-
oxidation and downstream oxygen boost would
be applied but then as the material becomes
more refractory the oxygen levels can be
increased through a combination of an increased
throughput through the reactors combined with
additional reactors. Assuming the ore is
amenable to flotation then Imhoflot flotation
could be introduced due to its improved
cost/performance benefits over conventional
tank flotation to produce a flotation concentrate
which would then be subjected to ultra-fine
grinding as the circuit migrates into the Leachox
process. As the ore becomes increasingly
refractory then a fully oxidative process such as
pressure oxidation can be pursued.
The above approach allows for a phased
capital approach and minimises upfront capital
expenditure allowing the operation to generate
revenue and reduce risk as process problems can
be rectified without major capital investment.
The ‘secret’ to the Aachen shear react or’s
success is the high amount of shear generated
within the reactor which in addition to the high
oxygen levels generated removes passivating
films which can otherwise stall the leach reaction.
The shear at the mineral surface thins the
boundary layer of the bulk solution enhancing
kinetics. Importantly unlike a lance system or
partially mixed reactor the Aachen reactor is
designed so that all of the slurry passes through
the Aachen reactor at least once so that every
slurry particle is exposed to a combination of high
shear and very high dissolved oxygen level.
Maelgwyn Mineral Services (MMS) has
significantly increased the number of
installations of its Aachen shear reactors and