Kemix (Pty) Ltd (Kemix) in conjunction with Anglo
American Corporation (AAC) developed the Mineral
Processing Separating (MPS) and Mineral Processing
Separating (Pumping) (MPS(P)) Interstage screens.
The development of the MPS(P) Interstage screen
was instrumental in the ultimate development of the
Pumpcell. The formation of the Pumpcell concept was
based on the supposition that improved carbon
performance could be achieved by employing the
carousel mode of operation.
The Pumpcell is in essence a complete CIP plant
incorporating a Pumpcell mechanism and launder
system enabling the carousel mode of operation to be
employed. The carousel mode of operation involves
keeping the carbon in a discreet batch within each
contactor and rotating the pulp feed and discharge
positions.
The pulp feed and tailings discharge positions are
rotated in such a manner that the counter current
movement of carbon relative to pulp is simulated
without physically having to pump carbon through the
circuit. The benefit associated with the carousel mode
of operation is that backmixing associated with
conventional counter current CIP circuits is
eliminated.
Coupled to the carousel configuration, the Pumpcell
design and operating philosophy is based on the fact
that the circuit is operated at increased carbon
concentrations and reduced residence time relative to
conventional counter current CIP circuits.
The design of the Pumpcell circuit allows all
contactors to be placed at the same elevation, in
contrast to the stepped arrangement used for
conventional cascade CIP adsorption plants.
Furthermore, the potential capital and operating cost
benefits coupled with the operational advantages of a
carousel Pumpcell circuit is considered to offer an
attractive alternative to the conventional cascade CIP
process.
There is no standard Pumpcell design, each
application is evaluated with the aim of optimizing the
active volume of the cell, the number of the
adsorption stages required, the carbon concentration
and the carbon elution rate (loading cycle).
Of the Pumpcell plants installed, the active volume of
the cells range from 10 m3 to 330 m3 providing an
approximate residence time of 15 minutes per stage.
The number of stages installed typically varies from
six stages for lower grade operations (<6 g/t Au) to
eight stages for the higher grade operations (> 6 g/t
Au). Carbon concentrations vary between 30 - 60 g/l.
Pumpcell Mechanism Description
The MPS screen incorporates a cylindrical
wedge wire basket (screen) attached to the
underside of the volute.
The volute also houses the drive unit and
includes a discharge launder.
Rotating around the periphery of the screen is a
cage and pulse blades.
The rotating cage sets up a pulse and
sweeping action around the periphery of the
screen. This reduces the possibility of carbon
and near size material pegging in the screen’s
apertures which in turn ensures that pulp
flowrate through the screen is maintained.
The drive shaft of the cage is surrounded by
a stationary pipe, which extends up beyond the
slurry operating level. This pipe is referred to as
the hydraulic seal, which ensures that pulp and
carbon can not by-pass the screen, thus
providing an effective seal having no moving
parts.
The hydraulic seal is attached to the bottom of
the screen by means of hydraulic seal base.
Around the stationary hydraulic seal is a hollow
(outer) shaft, which is attached to the drive
shaft above the top of the hydraulic seal. This
hollow shaft rotates along with the main drive
shaft and has a pitch blade turbine (PBT)
attached which provides the agitation inside the
screen basket.
The PBT blades in turn cause an upwards
movement of the pulp inside the screen thus
maintaining the pulp in a suspended state. This
also aids in keeping the internal wedge wire
area clean.
The hollow (outer) shaft of the Pumpcell
Mechanism also houses the up-pumping
impeller.
The pumping impeller is a mixflo type, specially
designed to handle high flowrates at low tip
speeds.
The up-pumping impeller elevates the pulp from
inside the screen and deposits it in the launder
higher than the level of the pulp in the
adsorption contactor in which the screen is
operating and imparts horizontal velocity. Thus,
the Pumpcell Mechanism is able to generate
pulp height and horizontal velocity sufficient to
overcome the pressure drop around the screen,
thus overcoming the need to have a series of
cascade adsorption contactors.
Attached to the bottom of the drive shaft is a
down pumping hydrofoil. This hydrofoil is
situated in the cell to ensure that an efficient
high velocity flow pattern is achieved and
maintained thus reducing the possibility of pulp
and carbon settlement occurring within the cell.
A single gearbox and electric motor drive the entire
mechanism.
The Pumpcell Mechanism is attached to the internal
launder of the adsorption tank by means of a hookon arrangement such that the complete mechanism
can be removed from the tank without having to
loosen bolts.
Pumpcell Description
The Pumpcell tank is comprised of an internal
launder system, discharge and feed pipes, launder
gate and plug valves. The internal launder is
arranged such that it facilitates the individual
functions of feeding pulp to the Pumpcell,
discharging pulp from the Pumpcell and bypassing
the Pumpcell in the event of taking the particular
Pumpcell off line. This launder also connects the
adjacent Pumpcells together. The nature of this
launder arrangement enables the carousel mode of
operation to be employed.
Pulp should be screened prior to the CIP circuit to
remove grit or fibrous material thus preventing the
ingress of this material into the Pumpcell circuit. The
screened pulp exiting the leach circuit either
gravitates or is pumped to the Pumpcell feed launder
arrestor box.
The head Pumpcell receives fresh pulp from the feed
launder located above the Pumpcell top platform.
The feed launder valve arrangement directs the flow
of pulp into the desired Pumpcell. The pulp enters
the Pumpcell via a feed pipe and is directed to an
area below the down pumping hydrofoil, thus
reducing the possibility of short circuiting with the
Pumpcell.
The pulp flows through the Pumpcell Mechanism to
the subsequent tank. Once the Pulp has passed
through all the stages in the Pumpcell train the pulp
exits the last Pumpcell in the carousel sequence and
is directed via a residue valve and manifold to the
residue screen.
When the gold on carbon loading in the head
Pumpcell has reached the predetermined value, the
head Pumpcell is isolated and the feed material will
be directed to the second Pumpcell in the carousel
sequence.
When the content of the original head Pumpcell has
been drained, that Pumpcell is brought back on line
as the new tail Pumpcell.
During the draining of the head Pumpcell the entire
Pumpcell plant operates with one Pumpcell less in
the carousel sequence.
