MINERAL SEPARATION
The Rare Earth Roll Magnetic Separator features
a high intensity permanent neodymium iron
boron magnet head pulley on a short conveyor
Three designs of high intensity magnetic
separator are commonly used when processing
dry minerals, Bunting said; The Rare Earth Roll
Magnetic Separator, Induced Roll Magnetic
Separator and Magnetic Disc Separator (MDS).
The Rare Earth Roll Magnetic Separator and
Induced Roll Magnetic Separator purify non-
metallic minerals, removing fine iron and
paramagnetic minerals, while the MDS is widely
used to ensure an accurate separation of dry
minerals that have varied magnetic
susceptibilities.
The former features a high intensity
permanent neodymium iron boron magnet head
pulley on a short conveyor. The magnets and
interspacing steel poles are aligned to produce
intense magnetic forces at points across the
whole width of the pulley, according to Bunting.
Bunting said the system is suited to handle
materials with a particle size range between 15
mm and 75 microns, although optimum
separation is achieved by having a material with
a narrow particle size distribution.
The Induced Roll Magnetic Separator,
meanwhile, uses electromagnetically-generated
high intensity magnetic fields to continuously
separate small paramagnetic particles from
materials with a particle size range between -2
mm to 45 microns. It is comprised of an electro-
magnetically induced steel roll positioned
between a bridge bar and pole piece.
Typically, an MDS features up to three high-
intensity electromagnetic discs, each set at a
different height from a feed conveyor. Disc one
will be set the furthest from the feed material to
extract only the most magnetically-susceptible
particles, while discs two and three are set at
lower gaps to increase the magnetic force at
each disc and enable the separation of different
grades of magnetic material.
“The magnetic intensity can be further
adjusted by varying the current of each coil. This
allows each MDS to be designed and set-up for
22 International Mining | MAY 2019
an individual mineral
ore,” Bunting said.
All three produce
high intensity magnetic
fields to separate ferro-
and para-magnetic
minerals, but Bunting
says their application
suitability through
controlled tests at its
Master Magnets
Redditch laboratory.
Bunting concluded:
“Many mineral
processing companies
are now mining reserves with lower purities.
However, they are also faced with environmental
restrictions that hinder the use of technology
such as flotation.
“High intensity magnetic separation
technology is key to the realisation of these
reserves.”
Iron contamination is one of the biggest
problems the minerals industry faces, leading to
structural and cosmetic defects in the manufactured
product, such as in ceramics and glass.
Contamination can be natural or inadvertently
introduced. Iron-bearing minerals such as
magnetite, hematite, chalcopyrite, and ilmenite
appear in many of the raw materials used for
ceramics. Most of these minerals are removed
during preparation, but contaminants may pass
to the fine grinding stages. Contamination can
also be introduced to processes through milling,
screening and plant deterioration.
The most effective way to address the problem
of iron contamination is to remove it before it
gets into the plant (from the raw material in-
feed), according to Eriez Europe. “Once the
material has been mixed, milled and screened, it
is ready to be passed through a magnetic
separator.”
The Eriez High
Intensity Filter (HI
Filter), a high gradient
magnetic separator, is
capable of capturing
fine ferrous and
paramagnetic particles
in liquids and slurries,
according to the
company. It generates a
background magnetic
field of around 5,000
gauss, which, when
intensified in the matrix,
increases to 15,000 to
18,000 gauss – enough
attraction to draw fine
and weakly magnetic particles and provide the
highest level of iron separation possible.
The unit is automatic, ensuring optimum
magnetic separation can be guaranteed at all
times, and has proven results of over 90%
reduction in product defects attributable to iron
contamination, according to the company.
Eriez Europe has installed over 280 HI Filters
in the minerals industry to purify ceramic glaze
and body, and for the treatment of mineral
slurries such as silica and felspathic sands.
Historically, sand slurry beneficiation has
involved a series of processes including flotation
to purify the sand to meet the strict
specifications of the glass industry.
The development of the HI Filter changed the
industry’s perception of magnetic separation
technology, according to Eriez. “For sand
purification, HI Filters are often installed in pairs
to maintain a constant production of sand and
prevent sedimentation in the feed pipework –
when one HI Filter is processing sand, the other
is cleaning.”
All HI Filter projects begin with extensive
testing at the Eriez Europe laboratory in the UK,
with the response of individual minerals to the
implied magnetic field determining the
separation performance.
Eriez’s Rare Earth Roll is more commonly used
to process dry materials such as feldspar and
silica sand. This consists of a head roll
constructed with strong rare earth permanent
magnets and a conveyor belt. Material is fed
from a feed conveyor belt onto a vibratory feeder
before cascading down a chute and into the
magnetic field. Magnetically susceptible particles
are attracted to the field, resulting in a change in
their trajectory, enabling the separation. Non-
magnetic particles are unaffected and cascade
normally. This self-cleaning system is a simple
and effective method of magnetic separation,
according to Eriez.
Eriez has two different designs of Rare Earth
HI Filters are often installed in pairs to maintain
a constant production of sand and prevent
sedimentation in the feed pipework