Magnetic Separators to Improve Mineral Cleaning

Magnetic Separators to Improve Mineral Cleaning

The strongest magnetic roll separator available on the market enhances certain industrial minerals purity to levels not reached previously. Exceptionally strong forces can also be utilized for processing relatively fine particles at feed rates several times greater than for prior art electromagnetic induced roll separators. Since the unique machine does not work with an air-gap, coarser particles than what has been considered practical can be separated at rates up to 20 tph per single machine unit and 40 tph for a double machine unit.

To maximize the magnetic force acting on paramagnetic materials means optimizing the product of magnetic flux density (H) and the magnetic field gradient (grad H), matching the resulting “force field” to the particle size of the material to be separated. The following simplified formula illustrates the importance of this product of factors generated by a magnetic separator:

FM = C·X·V·H·Grad H.

Where FM is the magnetic force, C a constant, X the magnetic susceptibility of the paramagnetic material, V the particle volume and the magnetic field factors as shown above.

While all matrix-type separators in commercial use are designed for slurry processing, the IMR separators have been successfully applied to dry processing to produce high- quality (i.e. low-iron) materials for the glass and ceramic industry. They often constitute the final, polishing part in the flowsheet because greater magnetic forces and less competitive forces are inherent in the operation of such machines compared to matrix-type separators in the same price class. The IMR separators have relatively small capacity per unit, which means that for even moderately sized plants, multiple units must be used. Also, the narrow air-gap associated with generating as high field strength as possible does limit the practical upper particle size in the feed. The advance of the unique PERMROLL separator makes even greater magnetic forces available as well as very high unit capacity, processing of a wide range of particle sizes while enhancing separation selectivity (improving product recovery) and reducing installation costs and operation costs.

Ferrous Wheel Magnetic Separator Design and Operation Principle

The first version of the Ferrous Wheel separator was constructed a decade ago under a contract to develop an inexpensive dry beneficiation machine for iron ore. Even though the results were satisfactory the project was not commercialized. After conversion to a wet separator it was used for several wet iron ore applications with promising results. However, the potential for cleaning industrial minerals was not explored until just recently.

The matrix with the collected magnetic product may be rinsed while it is in the magnetic zone to displace nonmagnetic particles, but often the matrix is drained only and excessive amount of nonmagnetic particles washed out at a different location, see below. As the ring continuously moves out from the magnetic zone, the magnetic product remains in the matrix pocket until it is washed out at the top position.

PERMROLL Magnetic Separator Design and Operation Principle

The development and design of the PERMROLL separator have been reported previously. In summary, a magnetic roll consisting of numerous high-energy permanent magnet discs interleaved with magnetically soft iron discs is the main component. For easy removal of magnetic particles the roll is enveloped by a relatively thin belt supported by a second (idler) roll.

Technical Features

The Ferrous Wheel has been shown to be relatively insensitive with regards to matrix blocking that can be caused by occasional oversize particles and trash in the feed. The reason is, of course, the washing of magnetics and middlings in the opposite direction compared to the feed flow.

Another attractive feature is insensitivity for modest amounts of ferromagnetic particles. Little flux leakage and the matrix characteristics are the main reasons. It is well known that almost all electromagnetic wet high-intensity magnetic separators (WHIMS) are prone to be plugged due to difficulties in removing the problem particles such as magnetite, pyrrhotite and tramp iron.

A large number of technical advantages have been discussed in some detail previously. Besides the capability for processing coarse particles, of importance for several refractory raw materials, there are two areas of particular importance that will be highlighted here: high purity; and high separation selectivity.

Industrial Minerals Applications

Calcite: Preliminary tests show that for one calcite sample it was possible to remove most of the dark minerals. No assay data has been made available.

Clay: Tests with several clay samples show that some respond well to the Ferrous Wheel magnetic separator. A filler type kaolin clay sample was upgraded 2 brightness points at relatively high capacity. This brought it up to a saleable quality.

Glass Sand: A glass sand with Cr2O3 contamination as the main problem was tested with the results shown in Table 1.

The advantage for processing relatively coarse quartz is that in some cases only fine crushing is required, eliminating expensive grinding. In other cases the removal of contaminants before grinding to required product size requires less installed magnetic separator capacity, since finer size particles reduce the permissible feed rate for achieving adequate separation. Tables 2, 3, and 4 illustrate this reasoning.

Kimberlite—Several machines have been delivered for kimberlite (i.e. diamond) applications. Depending on ore nature, 50 to 90 percent, in one case more, may be rejected as a diamond-free waste. Tables 5 and 6 give examples on performance with different materials.

Limestone—Plant feed up to 15 mm (¾ – inch) was processed in full scale tests with excellent rejection of dark contaminants. High quality filler can be produced by dry methods only if graphite-bearing zones are avoided.







N.B. Diamond recovery was maintained at 100%.



At 8.5 tph the Cr2O3 % rose to 0.0003








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too new magnetic separators improving industrial minerals cleaning