High intensity Magnetic Separators
In beneficiation plant like hematite, Separating
paramagnetic or weakly magnetic particles requires a higher flux density. This
higher density is achieved by designing electromagnetic circuitry that can
generate a magnetic force of up to 2 tesla. For example, in a silica sand processing plant, these
separators are used to remove weakly magnetic iron-bearing particles.
Induced-roll
Magnetic Separator
Induced-roll dry magnetic separators are widely used to remove trace
impurities of paramagnetic substances from feedstocks such as quartz, feldspar,
and calcite. The machine contains laminated rolls of alternating magnetic and
nonmagnetic discs. A magnetic flux on the order of 2 tesla is obtained, and
very high gradients are obtained where the flux converges on the sharp edges of
the magnetic laminations. A thin stream of granular material is fed to the top
of the first roll. The magnetic particles are attracted to the roll and are
deflected out of their natural trajectory (Figure 1). Selectivity is obtained
by varying roll speed and magnetic flux. A rather closely sized material must
be treated if high selectivity is required. An industrial induced-roll magnetic
separator consists of several rolls and can treat up to 10 tph (Figure 2).
Lift-type magnetic separators are used on granular and powdered material
that is dry and free flowing. This type of separator produces a clean magnetic
product because the magnetic particles are lifted out of the stream against the
force of gravity, which minimizes entrapped particles (Figure 3). The
selectivity of the lift-type separator is superior to that of induced-roll
separators. Their main limitation is lower capacity. The cross-belt separator,
a type of lift magnetic separator, has been used to some extent in processing
ilmenite, garnet, and monazite in beach sands.
Jones
Separator
The Jones separator is a wet high-intensity separator built on a strong
main frame made of structural steel (Figure 4). The magnet yokes are welded to
this frame, and the electromagnetic coils are enclosed in air-cooled cases. The
actual separation takes place in the plate boxes that are on the periphery of
the one or two rotors attached to the central shaft. The feed, which is a
thoroughly mixed slurry, flows through the separator by means of fitted pipes
and launders and into the plate boxes. The plate boxes are grooved to
concentrate the magnetic field at the tips of the ridges. Feeding is continuous
as a result of the rotation of plate boxes and the rotors, and the feed points
are at the leading edges of the magnetic fields. Each rotor has two
symmetrically placed feed points.
The feebly magnetic particles are held by the plates, whereas the
remaining nonmagnetic slurry passes straight through the plate boxes and is
collected in a launder. Before leaving the field, the entrained nonmagnetic
particles are washed by low-pressure water and are collected as a “middlings product.”
When the plate boxes reach a point midway between the magnetic poles, where the
magnetic field is essentially zero, the magnetic particles are washed out under
high-pressure scour water sprays of up to 5 bars of pressure. Field intensities
greater than 2 tesla can be produced in these machines. They are widely used to
recover iron minerals from low-grade hematite ore. Some other common
applications
include removing magnetic impurities from cassiterite concentrate,
removing fine magnetics from asbestos, and purifying talc.
Frantz
Isodynamic Separator
The Frantz Isodynamic Separator, introduced in the early 1930s, is the
most efficient magnetic separator for separating minerals with
field-independent magnetic susceptibilities. The isodynamic field, generated by
a bipolar magnet with special pole tip profiles, provides constancy of the
product of the field and the field gradient. However, mineral separation in an isodynamic
magnetic field is limited to minerals that have a constant susceptibility at the
laboratory scale. Only this category of mineral then experiences a constant
force throughout the isodynamic area.
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