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DIAMONDS
March 2017
MODERN MINING
31
The combination of a
dewatering cyclone cluster
and a Derrick HI-G dewater-
ing machine in a diamond
tailings application.
come into their own, as
they can efficiently extract
recyclable water from the
desired end-product of
mining, as well as from
tailings or waste. Excessive
water in the end-product
or tailings also makes it
expensive – and in many
cases problematic – to
transport, and in the case of
some commodities penal-
ties are applied.
“There are a number of
commodities which have to
be dried to a certain degree
before they are acceptable
to the customer, making
dewatering an operational
imperative,” Schoepflin says. “In terms of
waste product or tailings, the material must be
dry enough to be transported on a conveyor to
be stacked.”
What the dewatering screen is able to accom-
plish is to drain ‘free moisture’ from a wet
slurry through the screen media while retain-
ing as much of the fine particle material in the
screen bed, creating a product that can be con-
veyed and stockpiled with minimal handling
and environmental impact. The drained mois-
ture can then be re-used by being recirculated
into the processing plant.
The key principle at work in a dewatering
vibrating screen is the entrapment of solid fine
particles in a thick layer on the screen, creating
a ‘cake’ that acts as a filtration bed. The incom-
ing feed forms a pool in the angle between the
back of the screen and the slightly upward-
sloping deck, where most drainage takes place
until the feed particles form a cake.
The G-forces resulting from the screen’s
action enhance the adherence of the particles to
one another, effectively squeezing water out of
the material. At the same time, the linear action
of the screen conveys the cake up the slightly
inclined deck – which on Kwatani dewatering
screens can be up to a 5 degree angle.
“At Kwatani, we achieve higher G-forces by
generating an ideal combination of stroke and
speed, which in turn squeezes more water out
of the bed,” she says. “We also ensure that the
material is retained for sufficient time on the
deck of the screen – requiring a more vertical
stroke angle and an alignment of the exciter
drive’s speed. At the same time, we ensure the
required tonnage passes across the deck.”
To enable mines to recover more water and
reduce the need to pump slurry onto slimes
dams, Kwatani offers fine screening solutions
by Derrick Corporation, whose dewatering
screens can be used as a precursor to thick-
eners and filter presses. This technology from
Derrick has been successfully used in a number
of dewatering applications for diamond mines,
as well as in a diverse range of other commodi-
ties worldwide.
Derrick’s HI-G performance, linear motion
dewatering screen is able to recover solid mate-
rial including particles as small as 25 microns.
This allows slurry to be successfully screened,
releasing valuable water resources while con-
verting the slurry into material dry enough to
be conveyed and stacked.
These screens are designed for high volu-
metric capacity, which they achieve through
the use of two 2,5 horsepower vibrating motors
rotating at 1 750 rpm in opposite directions,
creating high G-forces. The effectiveness of this
solution is enhanced by using very high open
area, patented Polyweb urethane screen panels.
“The open area of the screen is critical for
successful dewatering, and the high open area
of these panels results in a superior dryness
of up to 90 % solids in the oversize,” says
Schoepflin. “The lifespan of these products is
lengthened by the urethane panels’ resistance
to abrasion. At the same time the sealed-for-
life Derrick vibrators ensure low maintenance
operation.”
The benefits of effective dewatering impact
positively not only on the financial bottom
line, but help mines to manage a range of
environmental risks associated with water man-
agement. As environmental controls tighten in
various countries, dewatering screens are likely
to become a valuable element of mines’ tailings
and water recycling strategies.
“There are
a number of
commodities
which have to be
dried to a certain
degree before they
are acceptable
to the customer,
making dewatering
an operational
imperative.”