GB2217632A - Magnetic separator - Google Patents

Abstract

A magnetic separator has the magnet 2 positioned at an angle to the vertical and a belt 4 arranged to carry a mixture of magnetic and non-magnetic particulate material past at least part of the magnet adjacent the face thereof into the region of highest magnetic field at the same inclination to the vertical as the magnet. A second belt 10 may be provided which moves past the magnet between the magnet and the mixture of particulate material. The arrangement ensures that all the particulate material experiences the highest magnet force, which increases the purity of separation. The two belts may move in the same or opposite directions (Figs 2 & 3). A superconducting magnet may be used. <IMAGE>

Description

IMPROVEMENTS IN AND RELATING TO MAGNETIC SEPARATORS The invention relates to a magnetic separator for minerals and is particularly concerned with systems in which a strong magnet is used to separate magnetic particles from non-magnetic particles. In the simplest form of such a system the magnet is passed across a layer of ore or vice-versa, the magnetic particles being attracted towards and becoming attached to the magnet.

This method suffers from the disadvantage that it is not continuous and several passes are needed to complete the separation.

A continuous process which has been developed comprises allowing a stream of mineral to fall vertically some distance from the high field region of a magnet, the magnetic fraction of the mineral being deflected towards the magnet. However, this has the disadvantage that the stream of mineral never experiences the maximum magnetic force and consequently, the separation is not as effective as it should be. Moreover, in order to prevent capture of the magnetics on the magnet, the mineral has to be dropped from a height so that the vertical momentum is sufficient to carry the strongest magnetic particles through the high field region This reduces the degree of deflection of the weakest magnetics, decreasing even further the purity of the separation.

A solution to these problems and forming the subject of our co-pending International Application No PCT/GB87/00915 is a magnetic separator where the magnet is arranged at an angle to the vertical, means being provided for feeding the mineral at or closely adjacent the magnet in the region of high magnetic field. The non-magnetic particles fall vertically under the influence of gravity whereas the magnetic particles are diverted towards the magnet and fall in a parabolic path away from the non-magnetic particles. The arrangement has several advantages. Firstly, the inclination of the magnet gives good physical separation of the non-magnetics and magnetics and consequently the feed point can be close to the magnet face which means that the mineral at least initially falls through the region of high magnetic field strength.The angle of inclination can be varied to give optimum results for a given mineral and the magnet can, for example, be arranged either so that the strongest magnetics fall along the face of the magnet but do not adhere thereto so preventing clogging or so that even the weakest magnetics are diverted to give a very pure non-magnetic portion. In the latter case, a belt is preferably provided which moves across the face of the magnet and carries away the magnetics to prevent clogging. The risk of capture of a magnetic particle in the non magnetics is greatly reduced since the particulate material can be fed at a low speed because it is not necessary for the magnetic particles to have sufficient momentum to carry them past the magnet without being captured by it and, therefore, clogging the separation zone as is the case with known methods.Finally, the separator gives good results even when the mineral is separated according to degree of magnetic susceptibility, that is into three or more different fractions.

However, even with this arrangement, the maximum magnetic force is not fully utilised. since although the mineral is fed close to the magnetic face, the separation between the stream of mineral and the magnet increases as it falls because of the inclination of the magnet. Consequently, the weakly-magnetic particles may not be removed from the mineral stream A magnetic separator in accordance with the invention comprises a magnet positioned at an angle to the vertical and a belt which carries a mixture of magnetic and non-magnetic particulate material past at least part of the magnet into the region of highest magnetic field at the same inclination to the vertical as the magnet and then allows the material to fall under gravity.

The advantage of this is that the particulate material is held close to the magnet and therefore, has the longest possible residence in the region of highest magnetic field. Consequently, the full magnetic force is utilised and high separation purity with high capacity is achieved.

The belt permits the speed at which the particles pass the magnet to be high so that for a given supply rate the thickness of the mineral stream is reduced. This results in firstly, the risk of entrapment of magnetic particles in the non-magnetics being reduced ,indeed, the magnetics can be physically lifted out of the particulate material. Secondly, fewer non-magnetics are carried over to the magnetic stream because of the decreased number of particle collisions. Consequently for a given supply rate a cleaner product is acheived or for a given grade of product the feed and production rate is higher.

Very preferably a second belt is provided which moves past the magnet between the particulate material and the magnet, magnetic particles which are attracted towards the magnet being captured by the second belt which carries them out of the region of high magnetic field until the gravitational force exceeds that exerted by the magnet and the particles fall from the belt.

Preferably the second belt moves parallel to and either in the same or the opposite direction to the first belt.

The second belt serves to carry away magnetic particles and, thereby prevents clogging of the magnet.

If the second belt moves in the opposite direction to the first belt the strongly magnetic particles are carried right away from the mixture to give an extremely clean separation.

Suitably, splitters are provided in the falling particles paths. These serve to separate the non-magnetic particles which fall vertically under gravity from the magnetic particles which follow a parabolic path under the dual influence of gravity and the magnetic force. Since the path followed by the particles depends on the magnetic force exerted on them, particles of different magnetic susceptibilities will follow different paths and several splitters may be provided to allow separation of the particles according to degree of magnetic susceptibility. The splitters also serve to separate the particles which fall from the first belt from those which fall from the second belt.

Suitably, a superconducting type magnet is employed.

The invention will now be further described by way of example with reference to the accompanying drawings in which: Figure 1 is a sketch of a magnetic separator in accordance with the invention; Figure 2 is a sketch of another embodiment of the magnetic separator of Figure 1; Figure 3 is a sketch of a further embodiment of the magnetic separator of Figure 1, and Figure 4 is a graph showing the results of separations carried out with different types of magnetic separators.

The magnetic separator shown in Figures 1 to 3 comprises a magnet 2 inclined at an angle to the vertical and a belt 4 which moves past and closely adjacent to at least part of the magnet at the same angle to the vertical. Particulate material 6 is carried by the belt 4 past the magnet 2.

The magnet 2 is arranged to provide a strong magnetic field in a direction at right angles to the magnet.

The dry particulate material 6 is fed onto the belt 4 by supply means which may be,for example,a hopper 8 or a vibrating table, and is carried thereby past the magnet through the region of high magnetic field. The particulate material is acted on by gravity vertically downwards and by the magnetic force in a direction at right angles to the face of the magnet. The magnetic force will depend on the magnetic susceptibility of a particular particle. The direction of the resultant force on a particle will consequently depend on its magnetic susceptibility and the angle of which the magnet 2 is inclined to the vertical. The magnet can, therefore, be arranged so that the most strongly magnetic particles follow a path parallel to the face of the magnet, thereby preventing clogging.

However, when the constituents of an ore are not known with a great degree of precision, a second belt 10 is preferably provided which moves past and closely adjacent the face of the magnet 2 between the particulate material and the magnet. Magnetic particles which are attracted towards the magnet and which would become attached thereto are captured by the second belt 10 which carries them through the magnetic field until the gravitational force exceeds that exerted by the magnet and they fall under gravity. Non-magnetic particles or those which are not so strongly magnetic that they are captured by the second belt 10 are carried by the first belt 4 until it turns back on itself, at which point they fall under gravity.

The second belt 10 may move either in the same direction as the first belt 4 (Figures 1 and 2) or in the opposite direction thereto (Figure 3). In the former case the strongly magnetic particles will fall some distance away from the weakly or non-magnetic particles and the two streams of falling particles can be separately collected. In order to ensure good physical separation of the magnetic and weakly or non-magnetic particles, the first belt is preferably arranged so that it carries the particulate material past only part of the magnet and then allows the material remaining thereon to fall.

When the second belt 10 moves in the opposite direction to the first belt 4 the strongly magnetic particles have their direction of movement reversed.

They are carried backwards and, when the gravitational force exceeds the magnetic, they fall from the second belt 10, and may be collected via a plate 11. The weakly and non-magnetic particles continue in their original direction and then fall from the belt. The inclination of the magnet to the vertical, however, allows a second separation to take place that is of the mixture which falls from the first belt 4. The non-magnetic particles fall vertically from the belt 4 whilst those which are weakly magnetic are deflected due to the combination of the gravitational and magnetic forces. They, therefore, follow a parabolic path and may be separated from the vertically falling non-magnetic particles by a splitter 12 provided in the lower portion of the falling particles' paths.As discussed above the path followed by a particle will depend on its magnetic susceptibility and further splitters may be provided to separate the particles according to degree of susceptibility.

If the first belt 4 changes direction as it brings the particulate material into proximity with the magnet, as is the case in the seperators shown in Figures 2 and 3, a plate 14 is preferably provided in the region of the change of direction. This serves to keep all the material travelling parallel to the magnet and prevents any non-magnetics from becoming trapped amongst the magnetics, in perticular, when the second belt moves in the opposite direction to the first belt.

The plate 14 is made from non-magnetic material such as aluminium plate or stainless steel.

The angle at which the magnet is inclined to the vertical can be arranged for a given ore so that even the weakest magnetics are attracted towards the magnetic and are captured and carried away by the second belt 10. The separator can therefore be very successfully employed when it is desired to separate out the non-magnetic portion of a particular ore. By physically lifting out the magnetic portion, a very clean separation is ensured.

The magnet employed is preferably a cryogenic magnet in particular a linear dipole magnet of the type described in International Parent Application No.

PCT/GB87/00915. Such magnets are very strong and consequently give good clean separations. They have a single magnetic separation zone on one side and are therefore particularly suitable for a separator as described above.

The improvement which can be achieved in purity of separation with a separator as described above is illustrated by Figure 4. This shows separation results obtained using various types of separator with a phosphate ore. The x axis represents the percentage mass removal as non-magnetics, whilst the y axis represents the percentage P205 loss in the magnetics.

The results achieved with an induced magnetic roll separator of the type commonly employed in industry and with a 'ramp' separator, that is a separator where the particulate material falls vertically parallel to the magnet and is directed away therefrom by a ramp in the falling particles' paths, the magnetics being pulled back towards the magnet, are shown by lines A and B. In each case the results depicted are those obtained after four passes. Band C shows the results achieved with an inclined magnet separator of the type described in International Patent Application No. PCT/GB87/00915 and discussed above in a single pass. Finally, curve D shows results achieved in a magnetic separator as described above again in a single pass. Clearly a magnetic separator as described above gives much better results than known separators without any necessity for repeated passes.

The very significant improvement is due to carrying the particulate material through the high magnetic field before allowing it to fall under gravity. By supporting the material on the belt the full magnetic force is utilised and the risk of a magnetic particle being trapped within non-magnetic particles is greatly reduced by using a fast moving thin flow of material. This is particularly the case when the magnetic particles are actually lifted out of the mixture and carried away by the second belt. It is envisaged that other forms of feed means rather than a belt could be employed for example a plate or a vibrating table.

Claims (9)

CLAIMS:

1. A magnetic separator comprising a magnet positioned at an angle to the vertical and a belt arranged to carry a mixture of magnetic and nonmagnetic particulate material past at least part of the magnet adjacent the face thereof into the region of highest magnetic field at the same inclination to the vertical as the magnet and then allow the material to fall under gravity.

2. A magnetic separator as claimed in Claim 1 wherein a second belt is provided which moves past the magnet between the particulate material and the magnet so that magnetic particles which are attracted towards the magnet are captured by the second belt which carries them out of the magnetic field until the gravitational force exceeds that exerted by the magnet and the particles fall from the belt.

3. A magnetic separator as claimed in Claim 2 wherein the second belt moves in the same direction as the first belt.

4. A magnetic separator as claimed in Claim 2 wherein the second belt moves in the opposite direction to the first belt.

5. A magnetic separator as claimed in any one of Claims 2 to 4 wherein the second belt moves in a path parallel to the first belt.

6. A magnetic separator as claimed in any preceding Claim wherein at least one splitter is provided in the falling particles' paths.

7. A magnetic separator as claimed in Claim 6 where two or more splitters are provided in the falling particles' paths to separate the magnetic particles according to the degree of magnetic susceptibility.

8. A magnetic separator as claimed in any preceding Claim wherein the magnet is a superconducting magnet.

9. A magnetic separator as herein described with reference to the accompanying drawings.