Mine excursion
processed through drum processing
(a coarse drum and a medium drum),
while another two fractions are
processed via cyclones (a coarse cyclone
plant and a fine cyclone plant). In
addition, there is a minus two fraction,
processed through an upcurrent
classifier (the latest addition to the
plant), which gives the plant its fifth
fraction.
The DMS uses ferrosilicone to prepare
the medium in which the separation
takes place at an operating density of
3.6t/m3. The product sinks, while the
waste floats. The very fine waste material
is further crushed down at a fourth
crushing stage, where another saleable
product can be screened out.
The various products are eventually
stacked onto product beds, where they
are also blended, and loaded at three
load-out stations. Two of these loading
stations are for the lumpy product,
and one of them is for the fines. The
product is loaded onto 140 wagons, one
rake at a time.
The finer material (minus 200
microns) is thickened before it is
pumped out to the slimes and tailings
dams, where the water is recovered.
Currently, the recovery rate is on
average between 60% and 70% of the
water, which is used for reprocessing.
The minus 25mm fractions are
discarded on the coarse discard dump.
Sishen’s second plant is a JIG plant,
which in general processes B-grade
material, while A-grade material is put
through the DMS plant. B-grade material
was previously regarded as waste that
couldn’t be processed in the DMS. The
difference between these technologies is
the cut point, which in a DMS is 3.6t/m3,
while it is 4t/m3 in the JIG plant.
The JIG plant has three crushing
stages: the primary jig crusher,
secondary jig crusher, and the tertiary
crusher circuit. The minus 25mm
product, previously discarded but for
which there is now a market, is stacked
onto ROM beds. The product needs to
be homogeneous to prevent blockages
in the JIG beneficiation circuit.
The product is reclaimed from the
ROM beds, and then the JIG ROM
is processed through the JIG plant.
Boasting 24 modules, the JIG plant
at Sishen is the biggest in the world
and produces both lumpy material and
fines. It operates with water and air
that is pumped through the JIG and
creates a pulsation. After pulsation, the
heavy particles (product) will settle at
the bottom and t he lighter material is
discarded over the top of the JIG.
The new UH DMS technology is
able to process the JIG discards, which
was previously unheard of. In the past,
the JIG discards were transported to
the tailings dumps. However, today,
it reports to the new modular UH
DMS, which has the ability to cut
at a higher grade of 4.2t/m3 (bear in
mind that the normal DMS cut point
is 3.6t/m3). The modular plant, which
now consists of three modules, is
undergoing an expansion process and a
lot of construction is taking place. It is
processing about 3.2Mt of JIG discards
at the moment, and the yield varies.
Despite tough times, Sishen remains
a prime producer of iron ore — and
it will retain this position for the
foreseeable future. Using cutting-edge
technology and good leadership,
Kumba is striving to extend the life
of mine beyond the current 13 years
and continue to play a significant role
in the economy of the Northern Cape
and South Africa. b
AUGUST 2018 MINING MIRROR
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