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The Multotec Pachuka Valve are
used as
aerators and/or agitators to keep material in
suspension or to introduce air into media. |
Multotec Pachuka Valves Solve Problem In Gold Reduction
In the past conventional aerator
systems used in the operation of Pachuka vessels in
gold leaching have not worked acceptably. Multotec
developed and successfully field tested a multi
aerator that addresses this 30-year-old problem.
“As more mines move away from mechanical and
compressed air agitation systems because they are
maintenance intensive, the Multotec Pachuka Valve
has gained popularity. Compressed air is introduced
at the bottom of the Pachuka tank to aerate the
media. When air flow is stopped for whatever reason,
slurry settles into the compressed air lines and
causes severe blockage,” Fritz Schoeman, engineer at
Multotec Wear Linings, says. “This will prevent the
system from being restarted and necessitates
draining of the Pachuka vessel, which results in
production losses and unscheduled maintenance
costs.”
Schoeman says that Multotec Pachuka Valves are used
as aerators and/or agitators to keep material in
suspension or to introduce air into media.
The design uses a composite of high
alumina ceramics, polyurethane, stainless steels and
PTFE components to withstand abrasion and corrosion
and to provide mechanical strength and overall
process efficiency. |
Most modern gold recovery processes depend
on gold’s ability to dissolve in dilute solutions of
cyanide. Pachuka vessels are large tanks that typically hold
between 450 and 600 m3 of a pulp comprising milled gold
bearing ore and a diluted lime and cyanide solution and are
continually agitated either by mechanical means or
compressed air.
In the latter, air is injected into the pulp at the bottom
of the Pachuka through the Multotec Pachuka Valve. This has
a two-fold purpose, firstly to break up the air into
extremely fine bubbles so that oxygen, which facilitates the
gold leaching reaction, is absorbed by the slurry, and
secondly to prevent passage of slurry into the air pipes in
the vent of loss of air supply.
Slurry densities in the Pachuka tanks run to between 1.3 and
1.7, and if agitation stops a huge mass of corrosive gold
bearing material settles out in the area of the aerator.
With conventional aeration systems, denser particles settle
into the open air pipes. Air lines are blocked with settled
material and tons of potentially highly profitable material
has to be washed out of the large tanks manually. This means
that the whole plant process has to be diverted, resulting
in substantial losses through additional labour costs,
wasted reagents and gold concentrate and slow startup times
of an average of three days per event.
Essentially, the Multotec dual-action non-return air
aerator, or Multotec Pachuka Valve, has eliminated the
conventional systems of the past and adapted them into a
most effective unit using to modern materials. The aerator
closes automatically if air inlet pressure falls below a
preset 1 bar air pressure, and reopens as soon as aeration
is resumed. Air consumption is about one third of the amount
used when operating without a Multotec Pachuka Valve.
Due to the layout of the aerator no slurry particles are
able to enter the air line or the valve and blockages are
avoided. There are no practical pressure limits either.
Despite the high pressure of the settled slurry above the
valve and the 6 bar air pressure on the inlet side, the
aerator opens without any delay, even after a long
settlement period, and agitates the slurry to full
suspension within minutes after startup.
The design of the aerator imparts a dynamic, centrifugal
movement of the rising air bubbles, promoting improved
dispersion of bubbles and greater leaching efficiencies.
“This has resulted in a tangible and recordable increase in
the levels of productivity and profitability wherever the
Multotec Pachuka Valves have been installed,” Schoeman
concludes.
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