MINERAL SEPARATION
Roll Separator. The difference is simply the
diameter of the head magnetic roll – RE300 (300
mm diameter) and RE100 (100 mm diameter).
The RE300 Rare Earth Roll enables over 40%
extra capacity per metre than the original 75 mm
diameter model developed by Eriez. For a mineral
processor, this means fewer units are required
for a plant, resulting in less maintenance and
less spares, Eriez said.
DMS hydrocyclones
Hydrocyclones are effective devices for
classifying, separating or sorting particles in a
liquid by density with Cavex ® one of the bigger
names in this sector.
Now under the Weir Minerals umbrella, Cavex ®
hydrocyclones use a proven design to deliver
maximum efficiency, capacity and longer wear
life than conventional feed designs, according to
the company.
These hydrocyclones were recently put to the
test at a diamond mine in South Africa’s Northern
Cape Province, proving the technology can be
applied in dense medium separation (DMS)
plants treating diamondiferous material,
according to the company.
In a presentation to the Southern African
Institute of Mining and Metallurgy diamond
conference, in Johannesburg, in 2018, Weir
Minerals Africa’s Senior Process Engineer,
Boitumelo Zimba, said the hydrocyclones in
question improved plant efficiency and produced
40% more tonnage than the mine’s target.
“As the Cavex ® hydrocyclone is tried and
tested in hard-rock mining and coal
classification, the Cavex ® 360° laminar spiral
inlet profile was used as a basis for the
development of a dense medium cyclone,” Zimba
said. “Individual casting patterns were
developed and produced in order to fabricate the
Cavex ® dense medium hard chrome cyclone with
the exact laminar spiral feed chamber that exists
when moulded out of rubber.”
The customer required a solution that could
offer at least six months wear life, and a
probable error of separation (Ep) of no greater
than 0.08 at a cut density of 3.1 t/m³. Tracer tests
were used to monitor the efficiency of the
separation achieved by the Cavex ®
hydrocyclones to ensure all of these
requirements were met.
“Ep values achieved were 0.042 for the 4 mm
tracer tests and 0.035 for the 8 mm tracer tests,
which were below the set maximum target of
0.08 from the mine,” Zimba said. “This
highlighted the benefits and improved
efficiencies of the Cavex ® laminar spiral feed
inlet.”
The lower the Ep – or probable error of
separation – the more efficient the separation; it
is defined as half the difference between the
24 International Mining | MAY 2019
density at which 75% is recovered to sinks, and
that at which 25% is recovered to sinks, Weir
said.
“The customer’s tracer tests on the Cavex ®
hydrocyclones showed that cut points of 3.08
t/m³ were achieved for both the 4 mm and 8 mm
tracers,” Zimba said. “This was within the
performance levels of 3.1 t/m³ that the customer
had specified.”
Initially, the hydrocyclones were
commissioned to treat only fines at the diamond
plant – the minus 8-+1 mm material. Later,
however, the mine decided to run a combined
DMS, after which the full DMS size range of
minus 20-+1 mm was treated through all the
fines DMS hydrocyclones.
“The unique design of the laminar spiral inlet
geometry delivers sharper separation and
maximises capacity while delivering a longer
wear life than conventional involute or tangential
feed inlet designs,” Weir said of the Cavex ®
hydrocyclones. “By providing a natural flow path
into the hydrocyclone body, the design allows
the feed stream to blend smoothly with the
rotating slurry inside the chamber, reducing
turbulence and improving separation efficiency.”
Zimba explained: “Combining our cone and
spigot components in the hard-metal range is an
important contribution to the reduction in
turbulence. Another vital factor is the Cavex ®
inlet design with 360° scroll; this design was
proven through extensive computational fluid
dynamics analysis as well as our multiple
installations to date.”
Separation by spirals
Spirals have become a useful tool at many mine
sites around the world, upgrading metal
concentrates and removing deleterious elements
penalised by potential end users.
One of the major suppliers of spirals
technology is Minerals Technology, an Australia-
based outfit owned by the Downer Group.
Earlier this year, Minerals Technology became
a recipient of government funding, through the
METS Ignited Collaborative Project Funds. The
company was granted A$1 million ($709,235)
through the scheme, matching funds already
contributed by its partner Roy Hill, for an
innovative automation project the two are
working on.
Mineral Technologies and Roy Hill’s project is
focused on automating the gravity separation
spiral process used in Roy Hill’s iron ore
beneficiation plant in the Pilbara of Western
Australia to optimise the concentration of lower-
grade ore into higher-value ore for export.
Downer’s General Manager, Process and
Engineering, Jess Maddren, said: “The project
funding along with Roy Hill’s contribution is a
significant investment and will ensure that
Mineral Technologies can resource the
automation project.”
It is not just iron ore where spirals are being
applied for product improvements.
Multotec Process Equipment recently reported
that its spiral technology has been enjoying
success at copper mines in the Democratic
Republic of Congo, Zambia and Zimbabwe.
The South Africa-based company said its
equipment is upgrading product from 1-3% Cu
run-of-mine to 20%-plus Cu concentrate.
“These mines can achieve an upgraded
product which can be sold as copper
concentrate,” Graeme Smith, Application
Engineer at Multotec Process Equipment, said.
“Spirals can also be applied as a bulk reduction
strategy to achieve a higher-grade material for
more efficient leaching.”
Smith says this is a fraction of the mining
companies benefitting from such technology.
“A number of customers mining minerals such
as copper, lithium, tin and tantalite are already
benefiting from using spirals to upgrade the
value of their concentrate, either replacing their
conventional processing technique or
augmenting it,” Smith said.
Spirals are proving their worth in helping
producers become more efficient, potentially
raising output levels while cutting the cost
involved in downstream processing, according to
Smith.
“This upgrading of the value of mined material
also contributes to lower transportation costs
and higher revenues earned,” Multotec added.
Working with tin producers in countries
including Morocco, the DRC and Spain, Multotec
spirals have been able to raise initial head
grades of 1-3% Sn to levels of over 50% Sn in
concentrate, according to the company. Treating
tantalite from a tailings operation in the DRC,
spiral technology has also performed massive
bulk reduction and upgrading, while shaking
tables clean the final product, the company
said.
“This allows existing downstream processes to
become more productive, and to ramp up
production by maximising recoveries and
reducing rand per tonne costs,” Smith said.
In test work in its extensive Spartan
manufacturing and research facility, near
Johannesburg, Multotec has also succeeded in
separating elements of lithium using spiral
technology, aiming for 80% concentration of the
element petalite, it said.
Smith highlighted the value of the company’s
experience in modular plants, allowing spiral
applications to be conveniently containerised for
transport to and commissioning at remote sites.
“Our mobile plants – capable of treating 20 t/h
– can be moved in two standard containers – one of
12 m in length and the other of 6 m,” he said. IM