Magnetic
separation:
All materials possess
magnetic properties. Substances that have a greater permeability
than air are classified as paramagnetic;
those with a lower permeability are called diamagnetic.
Paramagnetic materials are attracted to a magnet; diamagnetic
substances are repelled. Very strongly paramagnetic materials can be
separated from weakly
or nonmagnetic
materials by the use of low-intensity magnetic separators. Minerals
such as hematite,
limonite, and garnet
are weakly magnetic and can be separated from nonmagnetics by the use
of high-intensity separators.
Magnetic
separators are widely used to remove tramp
iron from ores being crushed, to remove contaminating
magnetics from food and industrial products, to recover magnetite
and ferrosilicon
in the float-sink methods of ore concentration, and to upgrade or
concentrate ores. Magnetic separators are extensively used to
concentrate ores, particularly iron ores, when one of the principal
constituents is magnetic. See
also
Mechanical
separation techniques;
Ore
dressing.
Principle of operation:
When
minerals are placed in a magnetic field, there are three reactions
which may occur. First, they are attracted to the magnetic field.
Second, they are repulsed by the magnetic field. And third, no
noticeable reaction to the magnetic field occurs.
Particles that are attracted to the magnetic field are called magnetic. But, there are two classifications of magnetic particles, strongly magnetic particles, such as iron and magnetite, and weakly magnetic particles, such as rutile, ilmenite, and chromite. Strong magnetic particles may be easily separated with a separator having a low intensity magnetic field of 400 - 600 gauss. Paramagnetic particles (weakly magnetic) require a higher intensity magnetic field to separate them, generally ranging from 6,000 to 20,000 gauss.
Particles that are repulsed by a magnetic field are called diamagnetic. A line of separators called Eddy Current Separators, takes advantage of the diamagnetic particles, separating them from other material. One of the largest uses currently is in the recycling industry, where wire and metals made from copper and aluminum are separated from plastics. When product, such as aluminum, passes over the eddy current , the spinning magnets inside the shell generate an eddy current in the aluminum thus creating a magnetic field around the piece of aluminum. The polarity of the magnetic field of the aluminum is the same as the rotating magnets, causing the aluminum to be repelled away from the separator. Product such as plastic, glass, or other process materials simply fall off the end of the separator. An eddy current is defined as the currents caused by voltages induced by changing flux, and tend to oppose the change of the flux.
Non magnetic particles, such as gold, quartz, and pyrite, are not amenable to magnetic separation, but some magnetic material may be removed from the feed. For instance, in a few situations, plants using gravity concentration for recovering gold, used magnetic separators to remove the high concentration of magnetite that was recovered with the gold, prior to further processing.
Magnetic separation is generally a low cost method of recovery, unless high intensity separators are required. The electro-magnetic high intensity separators that produce 20,000 gauss, tend to be expensive. However, the rare earth magnetic separators are relatively inexpensive and can produce magnetic fields around 6,000 gauss. So, when looking for a process to recover valuable minerals, magnetic separation should not be overlooked, if some of the material is magnetic or para-magnetic.
Particles that are attracted to the magnetic field are called magnetic. But, there are two classifications of magnetic particles, strongly magnetic particles, such as iron and magnetite, and weakly magnetic particles, such as rutile, ilmenite, and chromite. Strong magnetic particles may be easily separated with a separator having a low intensity magnetic field of 400 - 600 gauss. Paramagnetic particles (weakly magnetic) require a higher intensity magnetic field to separate them, generally ranging from 6,000 to 20,000 gauss.
Particles that are repulsed by a magnetic field are called diamagnetic. A line of separators called Eddy Current Separators, takes advantage of the diamagnetic particles, separating them from other material. One of the largest uses currently is in the recycling industry, where wire and metals made from copper and aluminum are separated from plastics. When product, such as aluminum, passes over the eddy current , the spinning magnets inside the shell generate an eddy current in the aluminum thus creating a magnetic field around the piece of aluminum. The polarity of the magnetic field of the aluminum is the same as the rotating magnets, causing the aluminum to be repelled away from the separator. Product such as plastic, glass, or other process materials simply fall off the end of the separator. An eddy current is defined as the currents caused by voltages induced by changing flux, and tend to oppose the change of the flux.
Non magnetic particles, such as gold, quartz, and pyrite, are not amenable to magnetic separation, but some magnetic material may be removed from the feed. For instance, in a few situations, plants using gravity concentration for recovering gold, used magnetic separators to remove the high concentration of magnetite that was recovered with the gold, prior to further processing.
Magnetic separation is generally a low cost method of recovery, unless high intensity separators are required. The electro-magnetic high intensity separators that produce 20,000 gauss, tend to be expensive. However, the rare earth magnetic separators are relatively inexpensive and can produce magnetic fields around 6,000 gauss. So, when looking for a process to recover valuable minerals, magnetic separation should not be overlooked, if some of the material is magnetic or para-magnetic.
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