REPROCESSING AND RETREATMENT
Quarter turn valves such as plug and ball
valves generally have a reduced port, which
increases the velocity and can become scratched
and end up leaking with every turn, according to
Corflex. “Knife gates generally have blades that
are far thinner than blank flanges for the same
pressure and, at high pressure, can leak or form
dished ends,” the company added.
But, pinch valves for high pressures have to
be built with both safety and performance in
mind. “To build a 450 mm pinch valve sleeve for
higher pressures, special tooling had to be
designed and built to enable the use of larger
gauge wire reinforcement in the flange area,”
Corflex said.
“The development of this tooling enabled a
450 mm pinch valve to be built for a working
pressure up to 35 bar, a test pressure of 70 bar
and a calculated burst of 105 bar,” Corflex said.
“The force required to close and seal a 450 mm
pinch valve at 25 bar is 77 t with no extra to
ensure an adequate seal. To build a 450 mm
pinch valve suitable for 25 bar, a special valve
had to be designed and built in every respect
similar to the 500 mm high pressure Corflex
Pinch Valve.”
The 450 mm valves at ETRP are fitted with four
160 mm hydraulic cylinders which, at a hydraulic
pressure of 200 bar, would seal the valves
against a pressure of +/34 bar, giving a sealing
safety factor in excess of 30%, Corflex said.
“The hydraulic power pack to operate the
valves has a constant recharge system to ensure
that the valves stay closed and do not creep
open,” the company said.
Although not required for this project, the
hydraulic power pack could have been built to
automatically close the pinch valves in the event
of an electrical power failure, according to the
company. This would allow the valves to be used
as open/close and non-return valves. “Typical
non-return valves in slurry pipelines are not
always reliable, so this system has excellent
advantages,” Corflex said.
Cyanidation
Elikhulu has also become a reference case for
enhancing cyanidation in gold processing, with
Maelgwyn Mineral Services (MMS) having
employed its Aachen Shear reactors at the
operation.
As MMS said, the reprocessing of old gold
tailings dams has a significant operating cost
advantage over run of mine ores, but projects
also come with lower head grades and increased
reagent costs; particularly cyanide and oxygen;
which could represent up to 50% of the
operational cost.
MMS believes employing its Aachen Shear
reactor can provide a cost-effective solution to
enhance cyanidation in gold processing, with
10 International Mining | MAY 2019
benefits including:
n Enhanced kinetics;
n Reduced cyanide consumption;
n Reduced lime consumption;
n Increase in gold recovery, and;
n Downstream benefits for carbon plants due to
steeper leach profile.
MMS said: “The Aachen shear reactor is
essentially a highly efficient mass transfer device
developed and refined over many years out of
experience with Maelgwyn’s Imhoflot flotation
technology.”
Imhoflot flotation technology is characterised
by high selectivity in terms of grade versus
recovery relationship, efficient recovery of small
(<20 μm) and coarse (>350 μm) particles, small
cell volumes and small flotation plant footprint,
no moving parts, and a lower energy requirement
due to there being no rotor/stator required to
keep the pulp in suspension.
The versatility of the Aachen reactor is evident
by the growing list of different process
applications, MMS said.
For the direct cyanidation of gold ores, Aachen
reactors are used in two different ways, the
company said:
n Mild pre-oxygenation to reduce cyanide
consumption through oxidation of cyanide
consuming species combined with efficient
oxygen use, and;
n Aachen assisted leaching (AAL): As a highly
efficient mass transfer device, and also a shear
reactor, Aachen reactors are finding increasing
applications within gold and silver leach
circuits to accelerate leach kinetics, reduce
cyanide consumption and reduce surface
passivation.
MMS said: “Currently there are over 60
Aachen reactors installed across various
operations for a combination of pre-oxidation
and AAL including the majority of Barrick Gold’s
African operations.”
And the Aachen reactors have also recently
found a home at Elikhulu, which operates a
conventional carbon-in-leach circuit including the
The conventional carbon-in-leach circuit at
Elikhulu includes Maelgywn Mineral Systems’
proprietary Aachen pre-oxidation process
proprietary Aachen pre-oxidation process.
“Having achieved the nameplate processing
target of 1.2 Mt/mth of tailings, the low-cost,
long-life Elikhulu project is expected to reduce
the group’s average all-in cost of production,”
MMS said. “The three tailings facilities will, after
processing, be consolidated into a single
enlarged Kinross facility, thus reducing Evander
Mines’ environmental footprint and associated
environmental impact.”
Aachen units can be manufactured in a range
of sizes to suit the site-specific flow rate
requirements up to a maximum flow of 800
m³/hr for a single reactor and enable efficient
oxygen dispersion under high shear (velocities of
up to 10 m/s within the unit) and pressure (3 to 6
bar) generated by the feed pump, according to
MMS.
“Furthermore, the shear exposure reduces
boundary layer resistances that influence most
solid/liquid reaction rates,” the company said.
“This can enhance the reaction kinetics
tremendously and enable process options not
feasible otherwise. Essentially, all of the
requirements of Elsner’s equation governing gold
leaching are met ensuring that rapid dissolution
of gold can take place.”
Peñasquito plant tailings
The Pyrite Leach Project (PLP) at Goldcorp’s
Peñasquito precious metal operation, in Mexico,
reached a major milestone last year.
Commissioning of the PLP commenced in the
September quarter with the plant now
commercial and processing 100% of the existing
plant tailings.
David Garofalo, President and Chief Executive
Officer of Goldcorp, said the project was a major
investment decision for the company and he was
pleased to see it completed both ahead of
budget and schedule.
The PLP is part of Goldcorp’s $420 million