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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