GB1590034A - Vertical rotor-type high intensity wet magnetic separator with countercurrent flushing - Google Patents

Description

(54) VERTICAL ROTOR-TYPE HIGH INTENSITY WET MAGNETIC SEPARATOR WITH COUNTERCURRENT FLUSHING (71) We, JONES FERRO-MAGNETICS, INC., a Swiss Company of Unterbösch 2, CH-633 1 Oberhünenberg, Switzerland, (Assignee: JERZY ANTONI BARTNIK), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a high intensity wet magnetic separator capable of separating magnetic materials from non-magnetic materials.

Magnetic separation has long been known as a valuable technique in mineral separation and it has been particularly useful in the separation of strongly magnetic materials, from non-magnetic materials.

Although the greatest commercial use of magnetic separators has been found in dry separation processes, recently new types of magnetic separators have been very successfully used under wet conditions.

In the past, magnetic separators have generally been in the form of an axially rotatable drum having disposed interiorly thereof a plurality of fixed magnets. These magnets are normally placed in close proximity to the desired area of the interior surface of the drum so that when magnetic particle-carrying material is fed against the peripheral portion of the drum overlying the fixed magnets, the magnetic particles adhere to the drum and are then carried to a discharge position. The nonmagnetic material unaffected by the mag netic field normally is permitted to fall under the force of gravity for separate collection. When such equipment is employed for wet separating processes, a slurry or pulp of the material to be separated either is fed to the periphery of the.drum in the same manner as dry material or, the rotating drum may be partially sub merged in a liquid slurry.

More recently for wet separation there has been developed the so-called high in tensity wet magnetic separator and the most commercially successful of these is the so-called " Jones Separator". A typical design of the Jones separator is described in U.S. Patent No. 3,326,374, issued June 20, 1967. It was of circular design with a series of vertically oriented grooved plates mounted in an annular ring which rotated horizontally through alternating magnetic fields. In this manner a magnetic field was introduced in the grooved plate sections as they passed a magnetic pole, then reached a point of zero magnetic field between the poles of opposite polarity and a high magnetic field at the next magnetic pole. A feed slurry was fed into the grooved plates in the region of a magnetic pole so that magnetic particles adhered to the plate walls.A water flush was applied to help wash away the non-magnetic materials and then at a point of low or zero magnetic field the magnetic particles were released from the plates with the assistance of high pressure water scouring. The magnetic and non-magnetic particles were collected in separate launders. Magnetic pole pieces were usually provided on opposite sides of the grooved plate sections and, in order to obtain strong magnetic fields, these were usually in the form of electromagnets.

Such flow through separators were designed with a horizontal rotor having a ring carrying the grooved plates and this rotor was mounted for rotation on a vertical axle. From a mechanical standpoint, particularly with very large machines, the mounting bearings for such a vertical axle represent a significant problem. Moreover, unless great care was taken to remove all materials from the grooved plates during each cycle, there was a tendency for some material to collect between the plates and thus decrease the efficiency of the machine.

Also, unless great care was taken to assure that all particulate material being separated was below a certain minimum particle size, e.g. less than lmm, other difficulties could be encountered since the oversized particles would either remain on top of the grooved plate section or become jammed between the plates.

One attempt to overcome some of these problems can be found in Carpenter, U.S.

Patent No. 3,375,925, issued April 2, 1968.

It provides for a plurality of loose, unattached, individually movable pole pieces, such as vertically positioned helical rods or ball bearings. However, it was found in use that because of problems of rusting and the collection of deposits that within a quite short time these pole pieces became fused together, thereby totally defeating the purpose of having loose, unattached pole pieces.

Various attempts have also been made to provide a system in which a rotor is mounted for rotation in a vertical plane.

Such a system is described in U.S. Patent No. 3,690,454, issued September 12, 1972.

Here again soft iron balls are being used as induced pole pieces with the idea being that these balls are free moving except when they are under the influence of the magnetic field. In theory, the balls are picked up in the magnetized region of each rotation of the drum. However, the actual operation of these machines has been observed in U.S.S.R. and it has been found necessary to provide a separate elevator to deliver the steel balls to an upper region where they are delivered by a trough into contact with a magnetized region of the rotating drum.

It is, therefore, an object of the present invention to provide an improved design of wet magnetic separator which will avoid or at least reduce the above difficulties.

According to this invention, there is provided a magnetic separator for separating solid magnetic particles from a fluid in which they are suspended comprising: a rotor mounted for rotation on a horizontal axis, said rotor having an annular separator portion formed by a pair of spaced side walls, at least one of which is an annular wall, and a series of radial dividers of nonmagnetic material extending between said side walls thereby forming a series of magnetically isolated separator compartments with open inner and outer ends, induced pole pieces disposed within said compartments to permit passage of particulate material therethrough, said pole pieces being in the form of magnetically permeable steel grooved plates or in the form of a plurality of magnetically permeable steel balls held within the compartments by inner and outer retaining screens, at least one magnet positioned immediately adjacent an uper or lower region of a said annular side wall for producing a magnetic field within each compartment passing the magnet, inlet means for feeding a slurry feed downwardly into said compartments through open ends thereof while within the magnetic field of said magnet, inlet means for delivering a flushing fluid downwardly into said compartments at a point remote from said magnet whereby said flushing fluid passes through said compartments in a direction countercurrent to the direction of slurry feed into the compartments, first collecting means for granular non-magnetic material disposed below said compartments while in the magnetic field and second collecting means for granular magnetic material disposed below the compartments at a point below the inlet means delivering the second flushing fluid.

Advantageously, the feed inlet is positioned at the leading edge of the magnetic field whereby the magnetic particles immediatly adhere to the induced pole piece surfaces while non-magnetic particles pass through the compartment. Collecting launders can be positioned beneath the compartments in this region to collect the non-magnetic particles passing through.

The inlet means for the first flushing fluid is preferably in the form of a low pressure water wash and it serves to remove nonmagnetic material which is trapped by the adhering magnetic particles. Collecting launders can also be positioned beneath the compartments in these regions to separately collect a middlings product. This middlings product may contain some magnetic particles which can be recycled into the feed slurry.

The inlet means for the second flushing fluid is preferably provided at a location about 1800 from the magnet where the magnetic field is substantially zero for delivery of the second flushing fluid to an upper open end of a compartment. This is preferably in the form of high pressure water spray or air-water spray which assists in removing magnetic particles from the induced pole piece surfaces. Collecting launders can also be positioned beneath the compartments in these regions to separately collect the magnetic products.

In order to accommodate the launders, etc. adjacent the inner ends of the compartments, the annular separator portion can be connected to the rotor hub by means of an axially off-set web portion.

For example, the hub may be connected to one side wall of the annular separator portion by means of a disc-like web or radial spokes.

Since the magnet or magnets are adjacent, the flat annular end portions of the rotor, the magnet pole pieces can have flat faces adjacent the rotor. The magnets can be placed on one or both sides of the rotor and can be mounted at either an upper or a lower region. Preferably, the magnets are mounted in pairs with opposite poles on each side of the rotor and with the opposite poles joined by a mild steel yoke to complete the magnetic circuit.

The magnets can be either electromagnets or permanent magnets and the use of permanent magnets with this apparatus is greatly simplified because of the flat pole end faces. A particularly advantageous permanent magnet for this use is a ceramic permanent magnet, such as that made from barium ferrite. According to a preferred feature, a ceramic permanent magnet can be used having on the same side north and south polarity.

For efficient operation, the non-magnetic dividers should have considerable thickness, preferably an inch to several inches.

This provides for sufficent separation of magnetic effects in individual compartments so that each compartment can function substantially independent of adjacent compartments.

As mentioned above, the magnet or magnets can be positioned adjacent either an upper portion of the annular ring or a lower portion of the ring. When the magnets are located at the upper portion of the ring, the slurry is fed through the top outside arcuate region of the ring with the non-magnetic material discharged through an inner arcuate region while the magnetics are attracted to the induced pole pieces within the separator compartment.

When the compartment turns to the lower position outside the magnetic field, the magnetic particles are flushed out by water spray or air-water jet entering from an inner arcuate region. Thus, it will be seen that the flushing off of the magnetic particles is always countercurrent to the feed flow. The high magnetic material which may accumulate on the top of the induced pole pieces during feeding of slurry will when the ring rotates 1800 be in a bottom position so that this accumulated material will be flushed out first. Hence, any plugging of the separator by highly magnetic particles is greatly reduced. Moreover, any coarse material which is too large to pass through the spaces between the induced pole pieces would be flushed away during removal of the magnetic fraction.

The present separator is capable of separating a wide variety of different materials and for instance, it may be used for making a magnetic concentrate when the magnetic material is the required product, e.g. concentration of relatively low magnetic susceptibility ores such as hematite or chromite. Alternatively it can be used for the collection and removal of magnetic impurities from non-magnetic materials, e.g. removal of magnetic contaminants, such as brolite, garnet or iron oxides, from ceramics, chemicals, oils and steel plant effluents. It is particularly advantageous for removing weakly magnetic contaminants from industrial effluents. For this purpose a permanent magnet is uniquely suitable because it permits extremely low operational costs.

Also, any large contaminant particles in such industrial effluents will not interfere with the operation of the machine since they will always be removed by the counterflow separation of the magnetic particles.

The invention is described further hereinafter by way of example with reference to the accompanying drawings, in which: Figure 1 is a side elevation in partial section of a separator in accordance with the invention; Figure 2 is an end elevation of the separator; Figure 3 is a vertical section through the annular ring; Figure 4 is a side elevation in partial section of an other embodiment of separator in accordance with the invention; Figure 5 is a sectional view taken along line 5-5 of Figure 4; Figure 6 is a top plan view showing details of another embodiment; Figure 7 is a sectional view through the embodiment shown in Figure 6, Figure 8 is a schematic view of Figure 6 showing flux lines.

Figure 9 is a vertical section through a further embodiment of the separator; and Figure 10 is a side elevation in partial section of the embodiment shown in Figure 9.

As will be seen from Figures 1, 2 and 3, the first embodiment has a rotor 10 mounted for rotation on a horizontal axle 11. The rotor includes a pair of spaced annular mild steel plates 12 between which are fixed a series of radial truncated wedgeshaped dividers 13 of non-magnetic material, thereby forming a plurality of magnetically isolated separator compartments "C". These dividers can, for instance be made from "300 series" stainless steel, aluminum, copper, etc. The compart- ments have open outer ends 32 and open inner ends 31. Spaced inwardly from outer ends 32 are screen mesh portions 15 and spaced inwardly from inner ends 31 are screen mesh portions 14. These screens 14 and 15 retain therebetween a plurality of steel balls 16. These steel balls can conveniently be ordinary ball bearings having diameters ranging between 1/4" and 1".

They form a magnetic collecting zone and represent induced pole pieces when under the influence of a magnetic field.

As can be seen from Figure 3, the compartments "C" are not entirely filled by the balls 16. Thus, at the slurry feeding position the balls 16 are resting on outer screen 15 with a space adjacent inner screen 14. Then, at the magnetic particle discharge position the balls 16 have moved within the compartment so that they are resting on inner screen 14 with a space adjacent outer screen 15. This is an important feature in the use of balls as induced pole pieces. The balls create a tortuous path for the feed slurry passing through and this provides for a very efficient collecting of magnetic particles.

However, if the balls are left resting in this position during all stages of the process, they quickly become bonded together by material from the feed slurry which is trapped in the small crevices between the balls. With the present apparatus, the balls go through considerable movement during each revolution of the rotor and this prevents any build-up of material in crevices between adjacent balls. As a result, the efficiency of the separation is improved from the outset and this high separation efficiency can be maintained for long periods of operation.

Additional dividers are provided radially on each side of the dividers 13, these being the outward divider 18 and the inward divider 19. These can be simple radial plates as shown in Figure 1 or they may be of triangular cross-section to assist in the smooth delivery of slurry and scouring water into the compartments.

The annular separator ring section of the rotor is mounted on a hub portion 20 which is offset such that there is a clear area adjacent inner compartments ends 31. The hub 20 is mounted on rotatable shaft 11 which is in turn supported in a bearing mount 21. This can be driven by an electrical motor (not shown) by way of a sprocket 22.

A permanent magnet assembly 23 is mounted at a lower region of the rotor 10 with a north pole permanent magnet block 24 at one side and a south pole permanent magnet block 25 at the other side.

The pole faces are positioned to provide a small gap between the pole faces and the sides of the rotor. A mild steel yoke 26 joins the poles 24 and 25 while leaving a space 27 between the yoke and the sides of the poles. The yoke serves to close the magnetic circuit and thereby improve the flux intensity in the gap between the poles.

A hole 28 is provided in the yoke to allow water and non-magnetic particles to pass through and deflector plates 58 are mounted within space 27 for directing the material emerging from the rotor through the hole 28.

A feed inlet pipe 29 is connected to a feeder head 30 which directs the feed into the compartments C via inner ends 31 at approximately the lowermost position in the rotation. The feed should enter in the region of the leading edge of the magnet 23 and as the feed passes down through the compartment C, the magnetic particles adhere to the steel balls 16 while the liquid and non-magnetic material passes directly through the compartment and out through outer end 32 where it is collected in a non-magnetic collecting launder 33 and is carried away via a conduit 34. A low pressure water spray head 35 is also mounted adjacent open compartment end 31 in a lower region and this is arranged to supply flushing water which helps to wash away non-magnetic material on the magnetic particles as well as such material trapped by the magnetic particles.This should be supplied while still under the direct influence of the magnets 23 so that the flushing will not remove magnetic particles. The flushing water is in this embodiment shown to also be collected by launder 33 but it will be readily appreciated that if it is desired to separately collect a middlings product, a separate launder and outlet can be provided for this purpose below spray head 35.

At the side of the rotor diametrically opposite the magnet 23 are high pressure water sprays or compressed air and water jets 36. These are at a region of minimum influence from the magnetic field created by the magnets 23 where the magnetic particles can be easily removed from the steel balls 16. The scouring water and removed magnetic particles are collected in a launder 56 and are carried away from the machine through a conduit 57.

Figure 4 show a second embodiment of the separator in which the magnets 37 are located adjacent an upper region of the rotor diametrically opposite the location in Figure 1. These magnets comprise a north pole permanent magnet block 38 at one side of annular ring 10 and a corresponding south pole 39 at the opposite side. The poles are joined by a mild steel yoke 40 with a space 41 between the yoke and the sides of the magnets. With this arrangement the feed inlet pipe 42 and feeder head 43 are positioned at the top of the ring 10 at the leading edge of the magnet with the head 43 extending through an opening in the yoke whereby the feed is fed in through outer open ends 32 and the nonmagnetic materials and water comes out through inner open ends 31 to be collected by launder 58 and conduit 60. The flushing water head 53 is also positioned at the upper region of the ring 10 within the field of the magnet 23 and extends through the yoke so that this water passes in through outer end 32 and out through inner end 31 to be collected by launder 59. If desired, the launder 59 can be replaced by a pair of side-by-side launders with one of these beneath feeder 43 to collect non-magnetic particles and the other beneath flushing water head 53 to collect middlings. The scouring water or water-air high pressure sprays 46 are in this embodiment positioned in the inner region at the lower side of the ring 10 whereby the scouring water is sprayed downwardly in through inner ends 31 and flows out with the magnetic particles through outer end opening 32 and into launder 44 where it is carried away by conduit 45.

With the wide dividers 13, it may also be desirable to provide wedge-shaped flow deflectors adjacent the ends of the dividers.

For instance, they may include an outer wedge-shaped deflector 54 and an inner wedge-shaped deflector 55, as shown in Figure 4. These are preferably made of the same material as the dividers and serve to direct the flow into the compartment C, as well as decreasing splashing and preventing build-up of material on the ends of the dividers.

Figures 6, 7 and 8 show another arrangement of magnets and induced pole pieces in which the magnets can be placed at either an upper or a lower region of the ring 10. Once again the magnets are placed on opposite sides of the ring 10 and each of these magnets is in the form of a block of oriented barium ferrite. Each block is oriented such that one-half of the block is a south pole 47 and the other half is a north pole 48. A permeable steel backing plate 49 is fixed to each magnetic block to complete the magnetic circuit and this arrangement creates magnetic flux lines as schematicaly illustrated in Figure 8. A magnetic arrangement of this type can produce a magnetic circuit of about 8,000 Gauss in the region between the induced pole pieces.

With this arrangement of magnets, in order to prevent short-circuiting of the magnetic flux, it has been found to be advantageous to utilize grooved plates 51 as the induced pole pieces. Grooved plates are, of course, well known and are illustrated in detail in U.S. Patent 3,830,367.

The plates are arranged in plate boxes separated by non-magnetic separators 50.

The material being separated flows down the gap 52 between the plates 51, with the magnetics being collected on the grooved faces of the plates. It will, of course, be understood that all of the other components of the separator including the feeding and washing devices and the product removal devices can be the same as those described in Figures 1 to 5.

With special configuraion of the permanent magnets as shown in Figure 6, when the feed flows in through the feeding head the magnetic particles come under the influence of the south pole and orient themselves on the grooved plates under the south pole influence. As the compartment moves into the influence of the north pole, the magnetic particles reorient themselves under this new influence and this reorientation of the magnetic particles assists in the flushing away of nonmagnetic particles, particularly those which may be trapped by the adhering magnetic particles.

Figures 9 and 10 show a further embodiment with the magnets at an upper region of the rotor. This arrangement has a rotor mounted for rotation on a horizontal axle 61. The rotor includes a mild steel plate member 62 fixed to the end of axle 61 and an annular ring 65 spaced from an outer portion of plate rnember 62 so as to form an annular separator compartment 64 therebetween. This compartment has outwardly flared annular portion 66 forming an enlarged entry 67. The compartment is divided into a series of separate compartments by means of radial dividers 71.

Each compartment contains steel balls 68 retained within the compartment by means of a screen 69 at the outer end and a screen 70 at the inner end. A pair of magnets 63 are mounted at each side of the sepatrator compartments and, as shown in Figure 10, they are positioned on an incline downstream of the vertical centerline of the rotor.

The region below the magnets is enclosed by means of an enclosure 72 having an outlet 73 at the bottom thereof. Immediately above the magnets 63 in an inlet hood 74 within which is mounted a feed inlet pipe 75.

Beneath the inlet 75 is non-magnetics collector 76 to receive the non-magnetic material which does not adhere to the balls 68 within the field formed by the magnets 63. High pressure water sprays 77 are positioned to spray downwardly through the separator compartments (from inner end to outer end) when the compartments are remote from the magnetic field. These sprays assist in washing the magnetics from the steel balls 68 and out through discharge hole 73. Additional water sprays may also be provided in the regions of the magnets.

While the above detailed description has related entirely to devices using magnets of the permanent type, it will be readily appreciated by those skilled in this field that any of these permanent magnets can be readily replaced by electromagnets of known type, for example those shown in U.S. Patent 3,830,367.

The invention is further illustrated by the following examples: Example I A test was carried out using a separator of the design shown in Figs. 9 and 10.

The feed was an uranium ore containing brannerite and uraninite as the principal auranium ores. The ore was ground to - 150 mesh (U.S. sieve) with 90.4% being -325 mesh. It contained 0.081% U,Os.

A slurry of this ground ore was formed containing 25% solids and this was the feed stream to the separator. The ore was separated into 13.7% magnetics and 86.3% non-magnetics. The magnetics stream contained 0.493% Use,, or 83.4% of the U3Os contained in the feedstream. The nonmagnetics stream contained 0.0156% of or or 16.6% of the U308 contained in the feedstream.

Example 2 The same separator used in Example 1 was used to separate iron-bearing minerals from bauxite. The ore being processed contained over 60% - 10 micron solids with an iron content of 9.4% (Fe208). The main impurities were siderite, ferro-titanium oxides, iron oxides, biotite, muscovite, garnet, etc.

This ore was fed to the separator as a slurry containing 20% solids. The ore was separated into 14.0% magnetics and 86.0% non-magnetics, with the magnetics stream containing 48.2% Foe203, or 71.7% of the Foe203 contained in the feed. The nonmagnetic stream contained only 3.10/c Fe203, or 28.2% of the Fe2O3 contained in the feed.

WHAT WE CLAIM IS: - 1. A magnetic separator for separating solid magnetic particles from a fluid in which they are suspended comprising: a rotor mounted for rotation on a horizontal axis, said rotor having an annular separator portion formed by a pair of spaced side walls, at least one of which is an annular wall, and a series of radial dividers of non-magnetic material extending between said side walls thereby forming a series of magnetically isolated separator compartments with open inner and outer ends, induced pole pieces disposed within said compartments to permit passage of particulate material therethrough, said pole pieces being in the form of magnetically permeable steel grooved plates or in the form of a plurality of magnetically permeable steel balls held within the compartments by inner and outer retaining screens, at least one magnet positioned immediately adjacent an upper or lower region of a said annular side wall for producing a magnetic field within each compartment passing the magnet, inlet means for feeding a slurry feed downwardly into said compartments through open ends thereof while within the magnetic field of said magnet, inlet means for delivering a flushing fluid downwardly into said compartments at a point remote from said magnet whereby said flushing fluid passes through said compartments in a direction countercurrent to the direction of slurry feed into the compartments, first collecting means for granular nonmagnetic material disposed below said compartments while in the magnetic field and second collecting means for granular magnetic material disposed below the compartments as a point below the inlet means delivering the second flushing fluid.

2. A magnetic separator as claimed in claim 1, including further inlet means for delivering a flushing fluid downwardly into said compartments downstream of said feed inlet but still within the magnetic field.

3. A magnetic separator as claimed in claim 2 wherein said flushing fluid inlet means remote from the magnet or magnets is positioned about 1800 from the magnet or magnets.

4. A magnetic separator as claimed in claim 1, 2 or 3 wherein said compartment dividers are wedge-shaped, forming substantially rectangular separator compartments therebetween.

5. A magnetic separator as claimed in any of claims 1 to 4, wherein two collectors are disposed below said compartments while in the magnetic field, one of said collectors being located below the slurry feed inlet to collect non-magnetic material and the other being located below said first flushing fluid inlet to collect a middlings product.

6. A magnetic separator as claimed in any of claims 1 to 5 wherein a pair of electromagnets are positioned on opposite sides of the annular separator portion.

7. A magnetic separator as claimed in any of claims 1 to 5, wherein a pair of permanent magnets are positioned on opposite sides of the annular separator portion.

8. A magnetic separator as claimed in claim 7, wherein the magnets are joined by a magnetically permeable steel yoke.

9. A magnetic separator as claimed in claim 7, wherein each magnet is permanently oriented whereby one-half is a south pole and the other half is a north pole.

10. A magnetic separator as claimed in any of claims 1 to 9, wherein the magnet or magnets are positioned immediately adjacent an upper region of the rotor on the vertical axis thereof.

11. A magnetic separator as claimed in any of claims 1 to 9, wherein the magnet or magnets are positioned immediately adjacent a lower region of the rotor on

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. of the design shown in Figs. 9 and 10. The feed was an uranium ore containing brannerite and uraninite as the principal auranium ores. The ore was ground to - 150 mesh (U.S. sieve) with 90.4% being -325 mesh. It contained 0.081% U,Os. A slurry of this ground ore was formed containing 25% solids and this was the feed stream to the separator. The ore was separated into 13.7% magnetics and 86.3% non-magnetics. The magnetics stream contained 0.493% Use,, or 83.4% of the U3Os contained in the feedstream. The nonmagnetics stream contained 0.0156% of or or 16.6% of the U308 contained in the feedstream. Example 2 The same separator used in Example 1 was used to separate iron-bearing minerals from bauxite. The ore being processed contained over 60% - 10 micron solids with an iron content of 9.4% (Fe208). The main impurities were siderite, ferro-titanium oxides, iron oxides, biotite, muscovite, garnet, etc. This ore was fed to the separator as a slurry containing 20% solids. The ore was separated into 14.0% magnetics and 86.0% non-magnetics, with the magnetics stream containing 48.2% Foe203, or 71.7% of the Foe203 contained in the feed. The nonmagnetic stream contained only 3.10/c Fe203, or 28.2% of the Fe2O3 contained in the feed. WHAT WE CLAIM IS: -

1. A magnetic separator for separating solid magnetic particles from a fluid in which they are suspended comprising: a rotor mounted for rotation on a horizontal axis, said rotor having an annular separator portion formed by a pair of spaced side walls, at least one of which is an annular wall, and a series of radial dividers of non-magnetic material extending between said side walls thereby forming a series of magnetically isolated separator compartments with open inner and outer ends, induced pole pieces disposed within said compartments to permit passage of particulate material therethrough, said pole pieces being in the form of magnetically permeable steel grooved plates or in the form of a plurality of magnetically permeable steel balls held within the compartments by inner and outer retaining screens, at least one magnet positioned immediately adjacent an upper or lower region of a said annular side wall for producing a magnetic field within each compartment passing the magnet, inlet means for feeding a slurry feed downwardly into said compartments through open ends thereof while within the magnetic field of said magnet, inlet means for delivering a flushing fluid downwardly into said compartments at a point remote from said magnet whereby said flushing fluid passes through said compartments in a direction countercurrent to the direction of slurry feed into the compartments, first collecting means for granular nonmagnetic material disposed below said compartments while in the magnetic field and second collecting means for granular magnetic material disposed below the compartments as a point below the inlet means delivering the second flushing fluid.

2. A magnetic separator as claimed in claim 1, including further inlet means for delivering a flushing fluid downwardly into said compartments downstream of said feed inlet but still within the magnetic field.

3. A magnetic separator as claimed in claim 2 wherein said flushing fluid inlet means remote from the magnet or magnets is positioned about 1800 from the magnet or magnets.

4. A magnetic separator as claimed in claim 1, 2 or 3 wherein said compartment dividers are wedge-shaped, forming substantially rectangular separator compartments therebetween.

5. A magnetic separator as claimed in any of claims 1 to 4, wherein two collectors are disposed below said compartments while in the magnetic field, one of said collectors being located below the slurry feed inlet to collect non-magnetic material and the other being located below said first flushing fluid inlet to collect a middlings product.

6. A magnetic separator as claimed in any of claims 1 to 5 wherein a pair of electromagnets are positioned on opposite sides of the annular separator portion.

7. A magnetic separator as claimed in any of claims 1 to 5, wherein a pair of permanent magnets are positioned on opposite sides of the annular separator portion.

8. A magnetic separator as claimed in claim 7, wherein the magnets are joined by a magnetically permeable steel yoke.

9. A magnetic separator as claimed in claim 7, wherein each magnet is permanently oriented whereby one-half is a south pole and the other half is a north pole.

10. A magnetic separator as claimed in any of claims 1 to 9, wherein the magnet or magnets are positioned immediately adjacent an upper region of the rotor on the vertical axis thereof.

11. A magnetic separator as claimed in any of claims 1 to 9, wherein the magnet or magnets are positioned immediately adjacent a lower region of the rotor on

the vertical axis thereof.

12. A magnetic separator substantially as hereinbefore particularly described with reference to and as illustrated in any of Figs. 1 to 8 of the accompanying drawings.

13. A magnetic separator substantially as hereinbefore particularly described with reference to and as illustrated in Figs. 9 and 10 of the accompanying drawings.