AU657583B2

AU657583B2 - Magnetic separation of materials

Info

Publication number: AU657583B2
Application number: AU28520/92A
Authority: AU
Inventors: Gillis Johannes De Korte
Original assignee: Council for Scientific and Industrial Research CSIR
Current assignee: Council for Scientific and Industrial Research CSIR
Priority date: 1991-11-26
Filing date: 1992-11-20
Publication date: 1995-03-16
Anticipated expiration: 2012-11-20
Also published as: GB2261833A; AU2852092A; GB9125031D0; ZA928959B

Description

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AUSTRALIA

Patents Act 1990 P/00/011 Regulation 3.2

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT C t 00r Invention Title: MAGNETIC SEPARATION OF MATERIALS The following statement is a full description of this invention, including the best method of performing it known to us: Sii hi GH&CO REF: P22523-A:PJW:RK 1, i, 2 THIS INVENTION relates to a method of separating material susceptible to magnetism from material not susceptible to magnetism., and to a magnetic belt separator.

940# In accordance with the invention, there is provided a f: method of separating material susceptible to magnetism from material not susceptible to magnetism, including causing an upper run of a belt conveyor, a belt of which is non-magnetic, to move in a first direction; causing a feed stream of material to be separated to move along the upper run of the belt in a second direction opposite to the first direction i.e. against movement of the belt; generating, by means of a source located underneath the S. upper run of the belt, a strong magnetic field in a separation zone above the belt; subjecting the material moving along the belt in the separation zone to the strong magnetic field such as to check movement in the second direction of the material susceptible to magnetism and such as to cause the material susceptible to magnetism to move with the belt in the first direction; i I Li~ i T-T 3 recovering the material susceptible to magnetism at a first recovery station located in the first direction beyond the separation zone; and recovering or dumping the material not susceptible to magnetism at a second recovery or dumping station located in the second direction beyond the separation zone.

In a preferred method, the upper run may move upwardly along an incline of predetermined slope, the feed material and the material not susceptible to magnetism being caused to move downwardly along the belt under gravity.

The method may include pouring the feed stream onto the upper run of the belt from a feed station spaced above the upper run. Pouring the feed stream onto the upper run of the belt may be preceded by the method steps of charging the feed stream into a feed chamber, allowing the feed stream to flow over S a weir means downstream of the chamber and exhausting the feed stream from the feed station via an outlet directed onto the S upper run of the belt.

o a The method may include adjusting the speed of movement of the belt thereby to adjust the speed at which the material susceptible to magnetism is moved with the belt. Instead, or in addition, the method may include adjusting the incline of the upper run. Increasing the incline will increase the speed and decrease the thickness of the feed stream, and vice versa.

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Ti :i 4 The source for generating the magnetic field may include an electro-magnet. The method may then include adjusting the intensity at which the electro-magnet is energized, thus to adjust the strength of the magnetic field.

The method may include washing a liquid (conveniently water) along the upper run of the belt. The method may include spraying the liquid onto the upper run of the belt at a position toward or beyond an extremity, in the first direction, of the separation zone.

In the interest of efficiency, to optimize the strength of the magnetic field in the separation zone, the method may include spacing the upper run of the belt closely above the source of the magnetic field. This may be effected by supporting the belt by means of stationary support means having beneficial friction characteristics and being interposed between the belt and the source of the magnetic field. Then, the method may include lubricating by means of water) an interface between the belt and the support means.

instead, the belt may be supported by means of rollers.

Instead, the method may include allowing the belt to sag under its load in the separation zone, the source of the magnetic field being profiled complementally to a sag line of the belt.

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r o p.i; In accordance with a further aspect of the invention, there is provided a magnetic belt separator comprising an endless belt conveyor in which the belt is of a nonmagnetic material and which belt is arranged such that an upper run thereof will move upwardly in a first direction in use; a feed station arranged to feed material to be separated in a feed stream directed in a second direction opposite to the first direction onto the upper run of the belt; magnetic field generating means located underneath the upper run of the belt ard arranged to generate a st-ong magnetic field in a separation zone above the upper run of the belt, the arrangement being such that, in use, the feed stream will move downwardly along the belt in the second direction, i.e.

opposite to motion of the upper run of the endless belt, such that the movement of the material susceptible to magnetism in the second direction will be subjected to the strong magnetic field in the separation zone, such as to be checked and such as to be S moved with the belt in the first direction.

i€ The magnetic field generating means may be in the form of a magnet, e.g. a permanent magnet or an electro-magnet.

The belt may preferably have side walls to assist maintaining the material on the belt and thus to allow operation with the belt in a flat state when viewed in transverse section.

This enables a magnet having a correspondingly transversely flat upper surface to be used.

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6 The feed station may be spaced above the upper run and toward or beyond an extremity in the first direction of the separation zone.

The magnetic belt separator may include adjusting means to adjust the slope of the upper run. It may include a speed adjustable drive for the belt. When the magnetic field generating means includes an electro-magnet, the magnetic belt separator may include energizing means for the electro-magnet which energizing means is adjustable for intensity.

The magnetic belt separator may include support means for the upper run to support it closely above an upper surface of the magnet. The support means may be stationary and may be of a material having beneficial friction characteristics.

Advantageously, it may have lubricating means for providing lubrication at an interface between the belt and support means.

Instead, the support means may be in the form of ooeQ,: rollers.

Instead, the support means may be provided by means allowing the belt to sag under its load in the region of the magnet, and by having said upper surface of the magnet of predetermined concave shape.

The magnetic belt separator may include sprays for spraying a liquid onto the belt.

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7 The magnetic belt separator may include a recovery station located beyond an extremity in the first direction of the separation zone for recovering the material susceptible to magnetism and a dumping station located beyond an extremity in the second direction of the separation zone for recovering the material not susceptible to magnetism.

By way of development, the feed station may include a feed chamber into which the feed stream is charged in use; weir means downstream of the chamber to allow the feed stream to flow over a weir surface; an outlet passage downstream of the weir means; and an outlet at a downstream end of the outlet passage, which outlet is directed onto the upper run of the belt.

The weir means may include a plurality of weirs arranged in series.

Further, by way of development, the weir means or each 1 weir may allow an opening to be provided at a lower end thereof

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to allow an underflow of the feed stream to flow underneath the S weir means or each weir. This will prevent build-up of material on a floor of the feed chamber.

The invention is now described by way of example with reference to the accompanying diagrammatic drawings. In the drawings t-- F-

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8 1 Figure 1 shows, in three dimensional plan view, a magnetic V belt separator in accordance with the invention; Figures 2 and 3 show respectively in side view and in plan view, the belt separator of Figure 1; Figure 4 shows, fragmentarily, in side view, another embodiment of a magnetic belt separator in accordance with the invention; Figure 5 shows, in sectional side view, to a larger scale, Ii i a developed embodiment of feed means.

i With reference to Figures 1, 2 and 3 of the drawings, a magnetic belt separator in accordance with the invention is i generally indicated by reference numeral i The separator 10 comprises an endless belt 12 having an upper run 14. It is arranged for rotation about head and tail rollers 18, 20 and a pair of tensioners 22. It is arranged, as can best be perceived from Figure 2, at an incline and the direction of driving the belt is such that the upper run 14 moves

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in a first direction up the incline as indicated by reference numeral 16. The endless belt 12 has side walls 24 to enable it .i to hold a flowable material while being maintained in a transversely flat shape.

Intermediate the head and tail rollers 18, 20, there is provided a magnet pack 26 comprising a plurality of transversely arranged magnets 28 and a casing 30 surrounding the magnets 28. In this embodiment, the magnets 28 are permanent -I p.

9 magnets. In other embodiments, if desired, the magnets may be electro-magnets. In this embodiment, the magnets 28 are arranged in alternating polar orientation, ie. such that the positions of the north and south poles of adjacent magnets alternate.

The strength and size of the magnet pack will be predetermined to suit the application. If the magnet is in the form of an electro-magnet, its strength may conveniently be adjustable. Generally, the width of the magnet pack would correspond with the width of the endless belt 12.

The casing 30 is of a non-magnetic material which, in this embodiment, is a suitable stainless steel.

A feed station 32 is transversely located at a position spaced above the upper run 14 and toward the roller 20. The feed station 32 comprises an open topped casing in the form of a box 34 arranged to receive feed material e.g. from a. conveyor, a pipe, or the like. A lip 36 is provided above an exit cj ning 35. The lip and the exit opening 35 extend transversely along *41tsI the width of the endless belt 12. The lip 36 slopes downwardly from a wall of the box 34. The exit opening 35 faces in a second direction opposite to the first direction 16.

Extending from the exit opening 35 downwardly along the upper run 14, and corresponding to the width of the upper run 14, there is defined a separation zone identified by reference numeral 44 in Figure 3. Similarly, extending in the first r. I U -A 1 direction from the feed station 32 and transversely along the width of the upper run 14, there is provided a cleaning zone identified by reference numeral 46 in Figure 3. The magnet pack 26 extends intermediate the remote extremities of respectively the separation zone 44 and the cleaning zone 46.

A plurality of transversely spaced sprays 48 is provided above the upper r-n 14 in the cleaning zone 46, more specifically toward a lower extremity of the cleaning zone 46.

A scraper 50 is provided in association with the endless belt 12 at a position beyond the end of the upper run 14.

In association with the scraper 50, there is provided recovery means 54 which may be in the form of a chute or the like to receive material susceptible to magnetism as wil? be described hereinafter. If desired, in a direction in which the endless belt 12 rotates beyond the position of the scraper 50, there is provided a secondary cleaner 52 in the form of a plurality of sprays.

At a position beyond the start of the upper run 14, i.e. beyond its lower extremity, there is provided dumping means in the form of a chute or the like as indicated by reference num eal 56 to recover material not susceptible to magnetism as will be described hereinafter.

The upper run 14 slides over the magnet pack 26, more specifically over an upper face of the casing 30. Thus, the 4

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S AA 'Y ii i i.-i, F Luno-.u nUiJr-ll Q.aJ-rjvv S 037650 201192 I 11 material of the casing and the construction of the sheet at the top of the casing will be preselected or predetermined bearing in mind that it will form support means to support the upper run 14 closely above the magnet pack 26 in use. If desired, lubrication may be provided at the interface.

Instead, and with reference to Figure 4, in another embodiment, rollers 60 which will be of small diameter, may be interposed intermediate the upper run 14 and the casing 30 to support the upper run 14 without relative sliding.

In use, material comprising both material susceptible and material not susceptible to magnetism to be separated is introduced into the feed box 32 and thence via the exit opening 1 35 in a flow stream 38 onto the upper run 14 such that the material flows in a second direction opposite to the direction 16. Flow thus takes place against the direction of movement of I the upper run 14 and takes place under gravity, bearing in mind i the incline at which the upper run 14 is arranged.

I While the material flows throu.gh the separation zone 44, material susceptible to magnetism is checked by the magnetic field on account of the magnet pack 26. The material not susceptible to magnetism continues to flow in a flow stream in the second direction and is discarded as shown at 62 into the dumping means 56.

r t 2 The material susceptible to magnetism, after being checked by the magnetic field, moves with the upper run 14 in the direction 16 and passes underneath the feed box 32. In the cleaning zone 46, the material is washed by means of water sprayed onto the upper run 14 by means of the sprays 48. It is to be appreciated that also the clcaning zone 46 is subjected to the magnetic field exerc.sed by the magnet pack 26.

The material susceptible to magnetism continues to flow in a flow stream 42 in the direction 16 to be released as shown at 64 at the end of the uppsr run to fall into the recovering means 54. The scraper 50 ensures that all material susceptible to magnetism is removed from the belt 12.

If desired, the outermcst surface of the belt is cleaned by means of spraying as shown at 52.

It is to be appreciated that the invention can be applied generally to all applications making use of the I characteristic of magnetism to separate material susceptible to magnetism and material not susceptible to magnetism. More j specifically, it is envisaged that the invention can advantageously be applied in a primary or secondary magnetic separator in dense medium processing plants. The invention can also be applied to the benefication of fines by dense medium processing. The invention can be applied as a scavenger to recover magnetic material. The invention can also be applied in ore recovery where magnetic ores are to be recovered.

13 The Applicant is of opinion that apparatus in accordance with the invention has a number of advantages over known apparatus and processes.

First, the apparatus of the invention is of relatively simple construction and is thus of reduced weight and can be provided at reduced cost relative to known separators.

The Applicant is of opinion that a high efficiency of recovery of material susceptible to magnetism can be attained in accordance with the invention. In tests, in comparison to prior art drum type separators, the material susceptible to magnetism which was not removed by an apparatus in accordance with this invention, was only one fifth of the material passed by the prior art devices.

The invention can be applied to a feed in the form of aggregate, slurry or the like. In this regard, it is believed that magnetic material can be recovered even from very dilute suspensions.

It is to be appreciated that the invention does not utilize dynamic principles to effect separation. Thus, the invention operates well even during start-ups and shut-downs.

It is not dependant upon a specific level of feed being maintained in the separator as is the case in drum type separators. Thus level control is obviated.

14 Feeding of the apparatus is versatile. For example, it is of significance that the size of the feed opening has relatively little if any influence on the separating efficiency to the extent that the spacing between the material to be separated and the magnet pack is not dependent on the height of the feed opening. Thus, if desired, the feed opening can have a relatively large height to be able to pass relatively large chunks of material.

The form of the feed can vary between relatively coarse aggregate to slurry.

High slurry loading and surges in feed quantity and composition can be tolerated without detriment to recovery efficiency.

The relative proportions of material susceptible and material not susceptible to magnetisms in the feed can vary widely.

I, I '''CThe apparatus will generally not be damaged by oversize Sor tramp material provided that such material can clear the exit opening Operation of the separator can be controlled and adjusted in a number of ways e.g. by adjusting the angle of the incline, the speed of the belt, the intensity of the magnet (by adjusting the intensity of energizing in the case of an electromagnet and by adjusting the size of the magnet pack and the number of magnets it contains in the case of permanent magnets).

The position of the magnet pack can also be adjusted if desired.

The position where the material is concentrated, i.e.

immediately above the belt, is close to the surface of the magnet pack. This is conducive to effective utilization of the available magnetic field and can lead to an increased separating efficiency or a reduced requirement in respect of magnet strength or a combination thereof.

With reference to Figure 5, by way of development, another embodiment of feed means, generally indicated by reference numeral 132, is now described.

The feed means 132 comprises a casing 134 located immediately above the belt, a path of which is indicated by reference numeral 145.

*1 *tI At one end of the casing 134, an inlet passage 135 is formed. At an upper extremity thereof, it is bounded by means of a flange 137 which defines an inlet opening 139 via which a feed stream is fed into the feed means 132. An internal wall of the passage 135 terminates at a position spaced from a stepped floor 143 of the casing 134 to define a transfer passage 141 intermediate the inlet passage 135 and a cavity within the casing 134 which is herein referred to as a charging cavity.

16 In the charging cavity, there is provided a first weir 147 over which material being fed to the belt separator flows into a weir cavity 149. Downstream of the weir cavity 149, there is provided a second weir 151 leading into an outlet passage 153 and an outlet 155 directed onto the upper run of the conveyor belt.

In use, charging the feed means via the inlet opening 139 and exhausting the feed means via the outlet 155 will generally be such that a level of feed material will be maintained in the charging cavity which is above the weir surfaces of the weirs 147 and 151, and such that the transfer opening 141 is completely covered.

It is believed that the feed means 132 will cause a very stable feed to be transferred to the belt 12. For example, the feed stream exhausted via the outlet 155 will have purely downward flow and no speed component in the horizontal direction.

S Furthermore, because of flow into the charging chamber and over rILS, the weirs, variations in the rate of feed will be evened out.

I6 By way of development, both of the weirs 147 and 151 can be displaced upwardly if desired to allow a small underflow 157 to take place. This has the advantage of being able to clear the floor 143 of any material which may tend to build up.

17 A magnetic belt separator having feed means such as the feed means illustrated in Figure 5, will have the same advantages as those described with reference to Figures 1, 2, 3 and 4. In addition, it will have the advantages described with reference to Figure i i i t i i' -LI I L

Claims

1. A method of separating material susceptible to magnetism from material not susceptible to magnetism, including causing an upper run of a belt conveyor, a belt of which is non-magnetic, to move in a first direction; introducing a feed stream of material to be separated at a feed point onto the upper run of the belt and causing the feed stream to move along the upper run of the belt in a second direction opposite to the first direction i.e. against movement of the belt; generating, by means of a source located underneath the upper run of the belt, a strong magnetic field above the belt, the magnetic field extending continuously from a predetermined first positicn spaced in the first direc-t." n from the feed point to a predetermined second position spaced in the second direction from the feed point; subjecting the material moving along the belt in a separation zone which extends from the feed point in the second direction to said predetermined second position to the strong magnetic field such as to check movement in the second direction 9ei t of the material susceptible to magnetism and such as to cause the material susceptible to magnetism to move with the belt under the 1 influence of the strong magnetic field in the first direction at least to said predetermined first position; recovering the material susceptible to magnetism at'a Sfirst recovery station located in the first direction beyond the separation zone; and c' t 19 recovering or dumping the material not susceptible to magnetism at a second recovery or dumping station located in the second direction beyond the separation zone.

2. A method as claimed in Claim 1 in which the upper run moves obliquely upwardly along an incline of predetermined slope, the feed material and the material not susceptible to magnetism being caused to move obliquely downwardly along the belt under gravity.

3. A method as claimed in Claim 2 in which introducing the feed stream onto the upper run of the belt includes charging the feed stream into a feed chamber, causing the feed stream to flow over a weir means downstream of the feed chamber and exhausting the feed stream from the feed station via an outlet directed onto the upper run of the belt at said feed point.

4. A method as claimed in Claim 3 in which causing the 1 feed stream to flow over the weir means includes causing the feed C t t steam to flow over a plurality of weirs arranged in series. i A method as claimed in Claim 3 or Claim 4 including, selectively, opening a passage at a low level in the weir means to cause underflow to take place underneath the weir means.

6. A method as claimed in any one of Claim 1 to inclusive which includes adjusting the speed of movement of the J belt thereby to adjust the speed at which the material susceptible to magnetism is moved with the belt.

7. A method as claimed in Claim 2 which includes adjusting the incline of the upper run.

8. A method as claimed in any one of the preceding claims in which the source for generating the magnetic field includes an electro-magnet, the method including adjusting the intensity at which the electro-magnet is energized. S9. A method as claimed in any of the preceding claims which includes spacing the upper run of the belt closely above the source of the magnetic field. A method as claimed in Claim 9 which includes supporting the belt by means of stationary support means having beneficial friction characteristics and being interposed between the belt and the source of the magnetic field.

11. A method as claimed in Claim 9 which includes Ssupporting the belt by means of rollers. j

12. A method as claimed in Claim 9 which includes allowing the belt to sag under its load along the source of the magnetic 2n field, the source of the magnetic field being profiled complementally to a sag line of the belt. rtir 21

13. A magnetic belt separator comprising an endless belt conveyor in which the belt is of a non- magnetic material and which belt is arranged such that an upper run thereof will move obliquely upwardly in a first direction in use; a feed station arranged to feed material to be separated in a feed stream Oirected onto the upper run of the belt at a feed point; magnetic field generating means located underneath the upper run of the belt and arranged to generate a strong magnetic field which extends above the upper run of the belt continuously from a predetermined first position spaced in the first direction from the feed point to a predetermined second position space in the second direction from the feed point, the arrangement being such that, in use, the feed stream will move from the feed point obliquely downwardly along the belt in the second direction, i.e. opposite to motion of the upper run of the endless belt, such that the movement of the material susceptible to magnetism in the second direction will be subjected to the strong magnetic field in a separation zone which extends from the feed point in the second direction to said ao predetermined second position such as to be checked and such as to be moved with the belt under influence of the strong magnetic aetl field in the first direction, at least to said predetermined first position.

14. A magnetic belt separator as claimed in Claim 13 in which the feed station includes 4 1 22 a feed chamber into which the feed stream is charged in use; weir means arranged downstream of the feed chamber to allow the feed stream to flow over a weir surface; an outlet passage downstream of the weir means; and an outlet at a downstream end of the outlet passage, which outlet is directed onto the upper run of the belt at the *feed point. A magnetic belt separator as claimed in Claim 14 in which the weir means includes a plurality of weirs arranged in series.

16. A magnetic belt separator as claimed in Claim 14 or Claim 15 in which the weir means has passage means to allow a passage selectively to be opened at a low level to cause an underflow of the feed stream to flow underneath the weir means.

17. A magnetic belt separator as claimed in any one of Claim 13 to Claim 16 inclusive in which the magnetic field generating means is in the form of a composite magnet extending I J transversely generally along the width of the upper run and .o 20" longitudinally between said predetermined first and second *li, Sii positions.

18. A magnetic belt separator as claimed in Claim 17 in which the magnet is in the form of an electro-magnet, including 'I I':i 23 energizing means for the electro-magnet which energizing means is adjustable for intensity.

19. A magnetic belt separator as claimed in any one of Claim 13 to Claim 18 inclusive in which the belt has side walls to assist maintaining the material on the belt and thus to allow operation with the belt in a transversely flat state. A magnetic belt separator as claimed in any one of Claim 13 to Claim 19 inclusive which includes adjusting means to adjust the slope of the upper run.

21. A magnetic belt separator as claimed in any one of Claim 13 to Claim 20 inclusive which includes a speed adjustable drive for the belt. ift i i t o I 4444 orr 4 4* o e or 0* 4 Ir r I 44 It V2'

22. A magnetic belt separator as claimed in Claim 17 or Claim 18 which includes support means for the upper run to support it closely above an upper surface of the magnet.

23. A magnetic belt separator as claimed in Claim 22 in which the support means is stationary and is of a material having beneficial friction characteristics.

24. A magnetic belt separator as claimed in Claim 22 in which the support means is in the form of rollers. I" -r 24 A magnetic belt separator as claimed in Claim 22 in which the support means is adapted to allow the belt to sag under its load in the region of the magnet, said upper surface of the magnet being of predetermined concave shape.

26. A method of separating material susceptible to magnetism from material not susceptible to magnetism substantially as herein described and illustrated.

27. A magnetic belt separator substantially as herein described and illustrated. Dat this 7th day of December 1994 CSIR By their Patent Attorneys GRIFFITH HACK CO 4 4 I I C I I II I I 1 -L (Figure 2 for publication) ABSTRACT A magnetic separator 10 has an endless belt 12, an upper run 14 of which moves upwardly in use. A mixture of magnetic susceptible and material not susceptible to magnetism is poured in a flow stream 38 onto the upper run in a separation area where a magnetic pack 26 is provided closely underneath the run 14. Material not susceptible to magnetism 40 flows under gravity against movement of the run 14 to be dumped as shown at 62. Material susceptible to magnetism is checked by means of the magnetic pack 26 and then moves with the run 14, upwardly, against gravity, to be recovered as shown at 64. :t: