MINERAL SEPARATION
“Sorting technology has definite advantages
before the mineral is milled,” he said. “Eriez has
equipment for the recycling industry that will be
applicable to the mining industry with
modifications.”
Eriez also has eyes on making in-roads into
another hard-rock market that has been
expanding.
Marin explained lithium producers have been
facing challenges with metallic contamination in
their final product. Even though Eriez already has
a piece of equipment that can significantly reduce
this contamination, the company is developing a
higher capacity product to reduce the number of
units required to handle demand for current and
future high-purity lithium products.
“It is common to see more than half a dozen
The Eriez Dry Vibrating Magnetic Filter is already
significantly reducing metal contamination in
high-purity lithium and other hard-to-flow
powder applications, but more developments
are coming
uses gravity to concentrate gold will have to deal
with the steel from wear and tear of the mills.
Thus, the benefits of employing low intensity wet
metal generated in the mill, mills end up
overworking because they must mill the chips as
well as the ore,” he said.
A trunnion magnet offers significant advantages
in the mining industry that some operators just
don’t appreciate, according to Marin. “Many prefer A leading designer and manufacturer of
magnetic separators for the mineral processing,
mining and ceramic industries, Bunting has
European manufacturing facilities in Redditch and
further and more cost-intensive processing.
Marin said Eriez has participated in many
projects that effectively reduced the amount of ore
going to the rod mills in such applications. “This
can save mining companies thousands of dollars,”
he said, adding that the savings can be even more
substantial if the gangue mineral is quartz, as this
is one of the hardest minerals.
34 International Mining | MAY 2020
stages of separation.
Disc 1 is set to first produce 7,000 gauss on the
surface of the belt (separation stage one) and
the feed direction. The black mineral rich fraction
is used as a source for titanium oxide. The 8,000-
gauss rear removes any remaining and smaller-
Still within magnetic separation, Bunting’s latest
three-stage Magnetic Disc Separator (MDS) has
recently been used for processing and separating
key minerals from a beach sands deposit in Africa.
the wet concentrating plant.”
Dry cobbing, in this instance, relates to the dry
low-intensity magnetic separation of materials
with the aim of producing an enriched iron ore
concentrate and a low-grade reject feed ahead of
of around 1-2 mm to generate two slightly
different magnetic fields at the front and rear of
each disc. Subsequently, there are six separate
intensity magnetic separator to process high
purity, very finely milled products. “This
development could guarantee lithium producers
can deliver their products with less than 50 parts continuously, according to Marin.
“Another example is a typical copper plant. If
that plant does not use trunnion magnets to
reduce the damaging steel and some of the fine
before) the mill.
“Pre-concentration or pre-sorting is not a
foreign concept in iron ore,” he says. “It is very
common to see dry cobbing before the ore goes to
Each magnetic disc produces a different magnetic
force to separate a specific group of minerals. In
addition, each magnetic disc is positioned at a tilt
8,000 gauss at the rear (separation stage two),
with the former removing larger iron-bearing
particles, including the highly paramagnetic
ilmenite into the first collection area to the left of
per billion of metallic contamination,” he said.
benefit they offer.”
Marin is convinced the applications for
magnetic separation can expand beyond (or
separation stages, according to the company.
In operation, the beach sands mineral mix is
evenly fed via a vibratory feeder onto a conveyor
belt that passes under all three magnetic discs.
units processing lithium carbonate in a typical
plant,” he explained. “The higher capacity unit will
reduce maintenance and operational costs.”
In addition, Eriez is looking at a stronger high drum magnetic separation is typically tied to the
removal of the steel and magnetite before a
gravity concentrator so the machine can operate
to deal with the problem in flotation, which adds
significant operating costs,” he said. “The
payback of a trunnion magnet is short for the
mineral processing laboratory. The controlled tests
determined the magnetic power required at each
stage to produce a successful separation.
The production-scale MDS has six distinct
Six stages of separation
Berkhamsted, in the UK.
MDSs enable accurate separation of minerals
with varied magnetic susceptibilities, according to
the company. Typically, they feature up to three
high-intensity electromagnetic discs, each set at a
different height from a feed conveyor. The first disc
will be set the furthest from the feed material in
order to extract only the most magnetically
susceptible particles. The second and third discs
are set at lower gaps, increasing the magnetic
force at each disc and separating different grades
of magnetic material. Magnetic intensity can be
further adjusted by varying the current of each coil
to suit the client’s specific mineral separation
requirements, Bunting said.
Bunting has a designated coil for each magnetic
disc: “The coil and magnetic disc relationship
enable precise adjustment of the magnetic field at
each stage and ensures accurate generation of the
optimum magnetic field,” the company says.
In this latest project, the beach sands mineral
mix included ilmenite, garnet, monazite, silica
sand, rutile, and zircon. Prior to determining the
specification of the production-scale MDS,
Bunting undertook material tests at its Redditch
sized particles of ilmenite, with the combined
recovery rate from Disc 1 more than 95%,
according to Bunting.
Disc 2 rotates in a counter-clockwise direction
to the conveyor feed and focuses on recovering
minerals of medium magnetic susceptibility.
Separation stage three uses a magnetic field of
13,000 gauss to recover pink and red minerals
such as almandine garnet. At the rear, the
magnetic disc is generating a higher field of
14,000 gauss to recover any remaining almandine
garnet. The recovered garnet, in this case, is sized
for use as an abrasive grit media in shot-blasting
applications.
The third and final magnetic disc rotates in a
clockwise direction in relationship to the feed and
is set to produce fields of 16,000 gauss
(separation stage five) and 22,000 gauss
(separation stage six). Separation stage five is for
the recovery of the weakly paramagnetic orange-
brown mineral monazite with stage six recovering
smaller monazite particles. Through the two
separation stages, recovery is plus-95%.
Monazite is a phosphate mineral that contains
rare earth elements – in this case, including
neodymium, cerium, lanthanum and
praseodymium – a highly valued raw material
source for rare earth magnet manufacture.
The remaining non-magnetic, cream-coloured
mineral fraction is a mix of silica sand, rutile and
zircon sand, which is separated using
electrostatics, froth flotation and density
separation.
The ability of the Magnetic Disc Separator to
produce six different fractions from one source,
Bunting says, makes the technology suitable for
many varied applications. IM