GB2105617A - Magnetic separation - Google Patents

Abstract

A method of separating relatively magnetic particles from relatively non- magnetic particles comprising allowing a mixture of the magnetic and non-magnetic particles to fall, under at least the influence of gravity in a three dimensional stream in a common path closely adjacent to a wall of a channel S nearest a magnet 10 which is arranged and designed to produce a strong magnetic field force in a horizontal direction, the horizontal component being greater than the vertical component which is less than that of gravity, the free fall of the particles being interrupted at 24 as they pass adjacent the magnet to cause them to move away from the magnet whereafter the magnetic particles M move back towards the magnet whereas the non-magnetic particles NM are not drawn away from their diverted path. The magnetic separator has one or more bumps, ridges, ramps or the like 24 to divert the particles away from the magnet. <IMAGE>

Description

SPECIFICATION Improvements in and relating to magnetic separators This invention relates to a magnetic separator for minerals separation and to methods of minerals separation.

The invention is particularly concerned with a separation system in which the material to be separated is allowed to fall freely past a high strength magnet. The relatively magnetic material is attracted towards the magnet and the relatively non-magnetic material continues in a relatively straight path. Splitter members may be used to separate the two streams.

One problem which has been encountered is that if all the material falls in a relatively low magnetic field and the magnetic material which is attracted to the magnet only reaches the high field region when it has already been separated from the non-magnetics. On the other hand, if the material all falls closely adjacent the magnet wall, then the non-magnetic material falls down with the magnetic material and there is not sufficient relative movement of the magnetic material to achieve separation.

A magnetic separator in accordance with this invention solves this problem by providing means at or closely adjacent the inner wall of the separation channel and extending down over at least a part of the portion of the separation channel which extends past the magnet to divert the particulate material to be separated substantially horizontally away from the magnet.

The diversion means may comprise a bump, hump or ridge, preferably having a smooth upper surface so as to avoid re-mixing of the material. A sharp step causes mineral to be bounded at random and this may cause a degradation in the quality of separation. Several bumps or humps may be provided one above the other.

Alternatively the diversion means may take the shape of a chute or "ski" ramp having a profile extending in the direction of free fall, outwardly from the magnet, followed by a necked portion.

The use of the particle diversion means enables the ore to be fed adjacent the inner wall of the separation channel i.e. that nearest the magnet and in the region of maximum field strength for the channel. Some separation takes place above the said diversion means, but this is limited. When the stream of particles is diverted by the said means, away from the magnet, the non-magnetic particles are thrown out well clear of the magnet and then continue to fall in their diverted path. The magnetic particles on the other hand are drawn back towards the magnet immediately after being diverted and thereafter follow the wall of the channel.

The two streams then pass on either side of an appropriately positioned splitter plate.

The magnet for the separator is preferably cryogenic and may have a circular coil or coils or may be the linear magnet described and claimed in our co-pending Application No. 8219259 filed simultaneously herewith.

Typically, the stream of ore is 3 to 6 mm in thickness and the ridge or bump 24 projects 4 to 10 mms from the surface of the wall. It is desirable that the shape is smooth on the upper side so as to avoid re-mixing of the mineral. A sharp step causes mineral to be bounced at random and this may cause a degradation in the quality of separation.

The materials are reseparated at each successive ridge or bump.

The invention will now be further described by way of example with reference to the accompanying drawings in which: Figure 1 is a part section through one embodiment of a magnetic separator in accordance with the invention showing one form of diversion means and Figure 2 is a diagram illustrating alternative forms of diversion means.

Referring to Figure 1 of the drawings the separator comprises a linear dipole superconducting cryogenic magnet generally indicated at 10 and a flat substantially rectangular cross section separation channel S formed between a wall 1 6 of the magnet and an outer wall 1 5.

The material to be separated is fed from a hopper 20 through an adjustable choke feed to fall adjacent the wall 1 6 of the magnet in a stream about 10 mm thick.

The magnetic force is adjusted, depending on the ore to be separated so that the ore 22 falls down the side of the magnet under the influence of gravity, the magnetic portion of the ore being drawn towards the magnet and held against the wall. This tends to reduce the falling velocity and increase the residence time for separation. A smooth bump 24 (or its equivalent) is provided on the wall 1 6 extending across the width of the channel wall, which causes the ore falling against or adjacent the wall and especially the nonmagnetic fraction, to be diverted horizontally away from the wall to increase the physical dispersion of the magnetic and non-magnetic fractions.

Substantially non-magnetic mineral is diverted away from the magnetic mineral which tends to be re-attracted by the magnet back towards the wall 1 6. Finally, the relatively magnetic material falls adjacent the magnet and the relatively nonmagnetic material away from the magnet, the two streams M and NM being separated by an adjustable flat splitter member 26 whose position can readily be adjusted towards or away from the flat wall 16.

To feed the mineral into the channel a simple linear choke feed is required.

The feed channel can, if desired, be divided into a horizontal series of thin vertical channels, e.g.

each 30 mms deep, each receiving a stream of crushed ore to be separated, instead of one broad channel, given that the magnetic field is of sufficient extent (say 100 mm) to encompass all the channels For example, if a second channel is used on both sides, this will be positioned outwardly of the channel shown in Figure 4, where the magnetic field is weaker. A first pass of the material may be made through this second channel and then a final or second pass through the first channel adjacent the magnet where the field is stronger.

As an example of the separation achieved tests were made on phosphate mineral containing about 14% apatite mineral and analysing as 5.8% P2O5. In the separation at a modest magnetic field of 24,000 gauss at a flow rate of 9 ton/hour per metre of magnet length ore was passed over two bumps of 10 mm projection from the magnet face.

The ore has a free fall of 100 mm from the linear hopper during which fall it was held against the face of the channel adjacent to the magnet by the magnetic field. Below each bump the ore was split into magnetic and non-magnetic fractions. The magnetics from the first bump were passed over the second bump, the two non-magnetic fractions were combined for retreatment at a higher field.

The splitter below each bump was positioned 30 mm away from the magnet face and 70 mm below the centre of the bump. The non-magnetic product was 36% of the mass. The magnetic product was discarded as waste mineral. The recovery of apatite was 77% in the non-magnetic product. This product was then retreated at a higher field of 31000 gauss.

Again the mineral was passed over two bumps of 10 mm projections after a 100 mm free fall. The splitter was set at 20 mm from the magnet wall and 70 mm below the bump. The non-magnetic product from the first bump analysed at 38.3% P205 or 90.3% phosphate. Magnetic measurement of the susceptability indicated 93% phosphate.

The non-magnetic product from the second bump represented 32.4% P205 or 76% apatite. The recovery of this second double stage of separation was 78%. The final product is of sufficient commercial grade.

Referring to Figure 2, a "ski" ramp having the shape of either a) or b) may be used instead of the rounded top humps or bumps to cause the particles to be thrown or moved out away from the magnet during their free fall path.

The dimension of the two "ski" ramps shown in Figure 2a and 2b are as follows: Shape No. a; Length CE 1 8.9 cm; depth D 1.25 cm; angle x = 1680 Shape No. b: Length CE' 1 5.3 cm; depth D' 1.5 cm; angle x = 1610.

Shape No. b is mainly used for the first or cleaning pass whilst shape No. a is mainly used for the final separation step(s). The "ski" ramp shown in Figures 2a and 2b illustrate the actual dimensions of the "ski" ramps used.

Although the applicants are unable to state with accuracy what the maximum free-fall velocity is at which the "ski" ramps still operate effectively, it may be mentioned that the aforementioned tests were carried out under conditions where the ore fell for a distance of approximately 11 5 mm before it reached the separation point of the "ski" ramp. With the aid of a high-speed camera, it has been determined that the free-fall velocity of the particles is then 1.5 m:s. At this velocity acceptable metallurgical results were obtained.

Poor metallurgical results were obtained when the ore was allowed to free-fall for a distance of approximately 1000 mm, reaching a velocity of approximately 4.5 m/s. It is believed that even poorer metallurgical results would be obtained at velocities greater than 4.5 m/s.

Claims (7)

1. A method of separating relatively magnetic particles from relatively non-magnetic particles comprising allowing a mixture of the magnetic and non-magnetic particles to fall, under at least the influence of gravity in a three dimensional stream in a common path closely adjacent to a wall of a channel nearest the magnet which is arranged and designed to produce a strong magnetic field force in a horizontal direction the horizontal component being greater than that of the vertical component which is less than that of gravity, the free fall of the particles being interrupted as they pass adjacent the magnet to cause them to move away from the magnet whereafter the magnetic particles move back towards the magnet whereas the non-magnetic particles are not drawn away from their diverted path.

2. A magnetic separator comprising a superconducting magnet and at least one particle separation channel adjacent the magnet, means for feeding particles in a stream adjacent the wall of the channel nearest the magnet and means at or adjacent the said wall of the channel and extending down over at least a part of the portion of the separator channel which extends past the magnet to divert the particles away from the magnet.

3. A magnetic separator as claimed in Claim 2 in which the diversion means comprises one or more bumps. ridges or the like extending across the inner wall of the channel.

4. A magnetic separator as claimed in Claim 3 in which the bump, ridge or the like has a smooth upper surface to cause a gradual acceleration or horizontal velocity away from the magnet.

5. A magnetic separator as claimed in Claim 2 in which the diversion means has the shape of a chute or "ski" ramp having a profile which, extending in the direction of free fall, is outwardly from the magnet.

6. A magnetic separator substantially as hereinbefore described with reference to the accompanying drawings.

7. A method of magnetic separation substantially as hereinbefore described with reference to the accompanying drawings.