WO2000025929A1

WO2000025929A1 - Magnetic separation method and apparatus

Info

Publication number: WO2000025929A1
Application number: PCT/IL1999/000590
Authority: WO
Inventors: Raphael Smolkin; Michael Smolkin; Eduard Smolkin
Original assignee: Technomag Ltd.
Priority date: 1998-11-04
Filing date: 1999-11-04
Publication date: 2000-05-11
Also published as: IL126878A0; AU1071900A

Abstract

A method and apparatus for magnetic separation are presented for separating a first component having predetermined magnetic properties from a mixture containing the first component and at least a second component having relatively weak magnetic properties as compared to those of the first component. A magnetic field source is aligned along the circumference of a drum, which is rotated in a certain direction with a predetermined speed. The magnetic field source creates a magnetic field region in the vicinity of the drum. The mixture is fed into a separation channel, which is stationary mounted in the vicinity of the drum and extends along a circumferential portion of the drum. The rotation of the drum causes the movement of the first component along the separation channel in a direction opposite to the direction of the rotation of the drum. The first and second components are discharged through opposite ends of the separation channel.

Description

Magnetic Separation method and Apparatus

FIELD OF THE INVENTION

This invention is in the field of magnetic separation techniques and relates to a method and apparatus for separating components having different magnetic properties. The present invention is particularly useful for recovering precious metals and stones by separating them fϊom various ores.

BACKGROUND OF THE INVENTION

Magnetic separators have been used for many years for separating desired materials from compounds containing them, by passing the compound through a magnetic field generated by permanent magnets or electromagnets. These magnetic separators are generally of two kinds, utilizing, respectively, so-called "dry" and "wet" separating techniques.

Magnetic separation techniques are disclosed, for example, in Author Certificates Nos. 782870 and 1577839, RU Patent No. 2067887, all by the inventor of the present application. The disclosures in these Author Certificates relate to, respectively, the "wet" separation utilizing a magneto-gravimetric technique, and the "dry" separation utilizing high magnetic induction and high gradient magnetic fields.

RU Patent No. 2067887 discloses a three-stage separation technique. The first and second stages are "dry" processes utilizing, respectively, a magnetic field of relatively low induction value and gradient and a magnetic field of relatively high induction value and gradient. The third stage presents a "wet" process utilizing a magneto-gravimetric technique. However, this disclosure has no indication as to any optimal implementation of any of these stages. It is known to use so-called "drum-type" separators for separating strong magnetic fractions by a relatively weak magnetic field. For this purpose, a magnetic field system includes stationary magnets and a drum that is rotated with respect to the magnets. Compounds containing products to be separated are fed into a magnetic field region and magnetic fractions contained in the compounds are adhered to the surface of the rotating drum in the vicinity of the magnets, while non-magnetic fractions continue their flow away from the magnetic field region. The adhered products are removed from the magnetic field region by the rotation of the drum and are duly discharged while leaving the magnetic field region. Such drum-type magnetic separators are disclosed, for example, in Bulletin no.H26 of Dings magnetic Group, pp. 1-3, and Handbook 390 "Laboratory and Pilot Size Materials Testing and Handling Equipment for the Process Industries", pp. 67-68.

A common problem of all conventional techniques of the kind specified is that associated with the undesirable effect of "flocculation", described as follows. When magnetizable material passes through a magnetic field region, it becomes magnetized. Each small particle of such material presents a separate magnet having opposite pole pieces. Magnetic forces occurring between these particles cause their conglomeration, trapping non-magnetic material therebetween. This reduces the quality of the separation. In such cases, at least one additional stage of magnetic separation is required. Alternatively, in some applications, separation of the materials is usually performed manually to simply visual recognition of pieces of different materials, and to manually separate these materials.

It is needless to say that the expense of manual separation is considerable, especially in the case of small pieces, for example, used in production of micro-electronic components, such as miniature resistors, capacitance, active elements, etc. As for the manual separation of small ferromagnetic balls (media) used in the Nickel coating process from Nickel coated electronic components (chips), the use of a microscope is unavoidably required. SUMMARY OF THE INVENTION

There is accordingly a need in the art to improve conventional magnetic separation techniques by providing a novel method and apparatus capable of more effective and less expensive separation of a material having certain magnetic properties from a mixture containing this material.

It is a major feature of the present invention to provide such an apparatus, which has a relatively simple construction and provides high quality separation, and in which the above-indicated flocculation-related problem is eliminated or at least significantly reduced. The main idea of the present invention consists of the following. A rotatable drum carries a magnetic field source radially aligned along the circumference of the drum. A separation channel is stationary mounted in the proximity of the rotatable drum and extends along a circumferential portion of the drum, such that a part of the separation channel is located in a magnetic field region defining a separation zone. The drum is rotated with a predetermined speed, and a mixture that should undergone separation is fed into the separation channel. The rotation speed is predetermined to be sufficient for creating a ponderomotive force of the magnetic field in the magnetic material contained in the mixture forcing it to move along the separation channel, in a direction opposite to the direction of rotation of the drum. Separated particles having different magnetic properties, i.e., particles affected and not affected by the magnetic field, are discharged at opposite ends of the separation channel, respectively.

It should be understood that the terms "affected" and "not affected" particles signify the following: the "affected" particles are those which are more affected by the magnetic field, as compared to that of the "not affected" particles.

To facilitate the discharge of the magnetic particles affected by the magnetic field, that end of the separation channel, through which these affected particles are to be discharged is slightly brought away from the circumference of the drum, i.e., away from the separation zone, as compared to the extension of the separation channel which is located in the separation zone. There is thus provided according to one broad aspect of the present invention, a method for separating a first component having predetermined magnetic properties from a mixture containing the first component and at least a second component having relatively weak magnetic properties as compared to those of the first component, the method comprising the steps of:

(a) rotating a drum that carries a magnetic field source aligned along the circumference of the drum in a certain direction with a predetermined speed, the magnetic field source creating a magnetic field region in the vicinity of the drum; (b) feeding said mixture into a separation channel, which is stationary mounted in the vicinity of the drum and extends along a circumferential portion of the drum, the rotation of the drum causing said first component to move along the separation channel in a direction opposite to said certain direction of the rotation of the drum; and (c) discharging the first and second components through opposite ends of the separation channel. The predetermined speed of the rotation of the drum is such as to create a ponderomotive force in the first component, and is preferably in the range of 30 to 1500 rpm and more. The changes of the magnetic field (caused by the rotation of the drum) within the separation channel, although it is stationary mounted, create a conveyer that conveys the first component in the direction opposite to the rotational direction of the drum. As for the second component, its flow towards the corresponding end of the separation channel due to its gravitational forces. To this end, the mixture is supplied into the separation channel at a location thereon higher than the corresponding end of the separation channel, through which the non-affected, second component is to be discharged.

Preferably, the magnetic field source is composed of a plurality of permanent magnets. The magnets are arranged along the circumference of the drum, and oriented such that each s-pole is enclosed between «-poles. To this end, the 5-poles and rø-poles may be aligned in parallel rows, respectively, extending parallel to the axis of the rotation of the drum. Alternatively, the s- and n-poles may be arranged in a so-called "chess-board order" within the circumference of the drum. The separation channel may be of a so-called "closed-type", namely a hollow housing in the form of a pipe opened at its opposite ends through which the first and second components are discharged. Alternatively, the separation channel may be of a so-called "open-type", namely in the form of a belt.

The "open-type" separation channel can be used for both, the "dry" and "wet" separation modes. The "dry" separation mode is preferred when dealing with materials containing high concentrations of magnetic particles. When using the "wet" separation mode, a discharge launder is located at that end of the belt through which the first (magnetic) component is discharged, and a water flow is supplied along the long axis of the launder. This discharge launder may either be coupled to the corresponding end of the belt, or be a separate unit accommodated between this end of the belt and a corresponding discharge vessel.

Thus, according to another broad aspect of the present invention, there is provided a magnetic separator for separating a first component having predetermined magnetic properties from a mixture containing the first component and at least a second component having relatively weak magnetic properties as compared to those of the first component, the separator comprising:

(i) a drum carrying a magnetic field source aligned along the circumference of the drum, wherein said magnetic field source creates a magnetic field region in the vicinity of the drum; (ϋ) a driver coupled to the drum for providing its rotation in a certain direction with a predetermined speed;

(iii) a separation channel stationary mounted in the vicinity of the drum and extending along a circumferential portion of the drum; (iv) a feeding means for feeding said mixture into the separation channel; wherein the rotation of the drum with said predetermined speed causes said first component to move along the separation channel in a direction opposite to said certain direction of the rotation of the drum, the separated first and second components being discharged through opposite ends of the separation channel, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Fig. 1 schematically illustrates the main components of a magnetic separator constructed according to one embodiment of the invention;

Figs. 2a and 2b are schematic illustrations of two different examples, respectively, of magnetic poles' arrangement suitable for use in the magnetic separator of Fig. 1; Fig. 3 schematically illustrates a magnetic separator according to another embodiment of the invention; and

Figs. 4a and 4b illustrate two different examples, respectively, of a mechanism for discharging separated magnetic fractions suitable for "wet" separation.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to Fig. 1, there is illustrated a magnetic separator, generally designated 1, for separating particles of relatively strong magnetic fractions, such as magnetite, ferromagnetic scrap, etc., contained in a supplied material, generally at Mo. The mixture Mo containing the component to be recovered flows through the separator 1, where the relatively strong magnetic fractions are separated from the remaining portion of the mixture containing relatively weak magnetic and non-magnetic fractions. The supplied material Mo is a mixture containing particles Mi and M₂ having different magnetic properties. In general, the component of interest, i.e., to be recovered from the entire material Mo, may be and may not be formed by particles of a magnetic fraction. If the component to be separated has weak magnetic or non-magnetic properties, the remaining portion of the mixture will then undergo a further separation stage. In other words, the passage of the mixture Mo through the separator 1 may represent the first separation stage of the entire separation process, in which case the separator 1 forms a constructional part of the entire separation system, which is not specifically shown. The magnetic separator 1 includes such main constructional parts as a feeder

2, a magnetic assembly 4, a separation channel 6, and a discharge assembly 8. The feeder 2 may include a vibrating element. In the present example of Fig. 1, the feeder 2 is composed of a hopper 2a and a connecting pipe 2b which is coupled to the separation channel 6 via an opening 9. The magnetic assembly 4 comprises a plurality of permanent magnets 10

(constituting a magnetic field source) mounted on the outer surface of a rotor or drum 12 so as to be rotated together with the dram 12. Poles of the magnets 10 are radially aligned along the circumference 12a of the drum 12, as will be described further below with reference to Figs. 2a and 2b. The drum 12 is driven by a suitable driving means (not shown) for rotation in the direction Di.

The separation channel 6 is located inside a hollow housing 14 accommodated proximate to the outer surface 12a of the drum 12 and extending above a circumferential portion thereof. Opposite ends 14a and 14b of the housing are opened serving thereby as outlet openings for discharging therethrough different fractions Mi and M₂ towards two vessels 16a and 16b, respectively, of the discharge assembly 8.

As shown, the housing 14 is mounted in such a manner that its end 14b is gradually led away from the circumference of the dram 12. The housing 14 is made of non-magnetic material, and preferably also non-conductive material, in order to prevent the induction of eddy currents. For example, a ceramic or plastic material can be used. Generally speaking, the housing 14 is designed and oriented with respect to the magnetic field source 10 in a manner to define the separation channel 6 located within a magnetic field region created by the magnetic field source 10.

The magnetic separator 1 operates in the following manner. The mixture Mo containing the relatively strong magnetic fraction Mi and the relatively weak magnetic and non-magnetic fraction M₂, is fed from the feeder 2 towards the magnetic assembly 4, i.e., into the housing 14 defining the separation channel 6. The magnetic field source 10 is rotated with the drum 12. The rotation of the magnets creates a rotating composite magnetic field within the separation channel 6. The mixture of particles Mi and M₂ enters the separation channel 6 and becomes located within the rotating magnetic field region (gap). Non-magnetic and weak magnetic particles M₂ are not affected by the magnetic field and, therefore, due to the gravity force, move downwards, i.e., towards the outlet opening 14a to be received by the corresponding vessel 16a. As for the strong magnetic particles Mi, both the gravity force and the magnetic field affect them. The magnetic field effect results in the adherence of the particles Mi to the inner surface of the housing 14. Due to the appropriately adjusted speed of rotation of the dram 12, these adhered particles move in the direction opposite to that of the rotation of the dram 12 (clockwise in the present example). The dram 12 is preferably rotated at a speed ranging from 30 to 1500 rpm and more.

To cause the movement of the magnetic particles Mi in the direction opposite to the direction of rotation of the drum 12, appropriate changes in the magnetic field parameters (i.e., induction and gradient) should be provided. Preferably, the magnetic particles Mi are forced to move with the speed of 0,01-0,001% of the linear speed of the dram. In order to obtain a desired value of the magnetic field induction, the permanent magnets 10 are preferably made of Ferrous-Barium, or rare-earth metals. These materials allow for constructing a strong magnet having the magnetic induction in the vicinity of the magnet's surface of 0.16- LOT. The magnets 10 may be shaped like a flat, "domino-like", rectangular block and may be either affixed to a magnetic soft-iron core or substituted by electromagnets. The outer surface of each magnet 10 facing the separating material may be flat, cylindrical, spherical, etc. Hence, the rotation of the magnets 10 conveys the particles Mi along the separation channel 6 in the direction D₂ opposite to the direction of rotation of the dram towards the outlet opening 14b. The particles Mi ensuing from the separation channel through the opening 14b flow into the corresponding discharge vessel 16b. As shown, in order to facilitate the discharging of the magnetic particles Mi from the separation channel 6, the corresponding end 14b of the housing is taken away from the dram 12.

As more specifically illustrated in Figs. 2a and 2b, the magnets 10 are arranged along the circumference of the drum 12, and oriented such that each 5-pole is enclosed between a pair of t?-poles. According to the example of Fig. 2a, the s-poles and «-poles are aligned in two parallel rows 10a and 10b, respectively, extending parallel to the axis of rotation of the drum 12. In the example of Fig. 2b, the s- and n-poles are arranged in a so-called "chess-board order" within the circumference of the dram 12.

In the example of Fig. 1, the separation channel 6 is of a so-called "closed-type" or "isolated type". This allows for avoiding an undesirable effect of "jumping aside" of the separated particles.

Fig. 3 illustrates a magnetic assembly 104 utilizing an "open-type" separation channel 106, which is suitable to be used in the apparatus 1. The assembly 104 is constructed generally similar to the assembly 4, and the same reference numbers identify the common components in assemblies 4 and 104. In the assembly 104, a stationary mounted belt 20, extending in a manner similar to that of the housing 14 in the assembly 4, defines the separation channel 106 along the outer surface of the belt 20. The non-magnetic and weak magnetic fractions M₂ are discharged into a corresponding vessel (not shown) at one end 20a of the belt 20, while the relatively strong magnetic fraction Mi is discharged at the opposite end 20b.

Similarly to the "closed-type" separation channel, the "open-type" separation channel could be made of a non-magnetic or a dia-magnetic material, which material is preferably also nonconductive to prevent induced eddy currents, e.g., ceramic or plastic material.

The "open-type" separation channel 106 can be used with a "dry" separation mode when dealing with materials containing high concentrations of magnetic particles, but is particularly useful for a "wet" separation mode. Figs. 4a and 4b more specifically illustrate two possible examples of discharging the fraction Mi with the "wet" separation. A discharge launder 22 is provided at the end 20a of the belt 20, and a water flow F is supplied along the long axis of the launder 22. In the example of Fig. 4a, the discharge launder 22 is either integral with or coupled to the end 20a of the belt 20. According to the example of Fig. 4b, the discharge launder 22 is a separate unit accommodated between the end 20a of the belt 20 and the discharge vessel 16a. The provision of the discharge launder 22 facilitates the discharging of the separated magnetic particles Mi, owing to the fact that the launder 22 is taken away from the magnetic field region. In both examples, the long axis of the launder 22 is slightly inclined towards the discharge vessel 16a, and the water flow F flushes the magnetic particles Mi out of the discharge launder 22, directing them to the discharge vessel. It should be noted that the gap defined by the magnetic and non-magnetic discharge vessels 16a and 16b may be adjustable for different sizes of separated particles or pieces. Turning back to the example of Fig. 3, an experimental magnetic separator of this kind was constructed and tested for separating small ferromagnetic balls used in a process of Nickel coating from electronic components with this coating. Fourteen rows 10a and 10b of permanent magnets were used, each row comprising a pair of radially oriented Ferrous-Barium permanent magnets. The magnets were shaped like flattened rectangular blocks, each of about 135mm length, about 90mm height and 110-120mm width. The outer diameter of the magnetic dram 12 was about 704mm, and the width (the height of the drum-cylinder together with its supporting frame) was about 500mm. The shape of the part of the conveyor belt 20 forming the magnetic discharge end 14b that gradually keeps away from the rotating dram 12, can be described by the following equation:

(X/360) ² + (Y/340) ² = 1 wherein X and Y are coordinates along, respectively, the horizontal X-axis and vertical Y-axis in the figure plane.

The mixture Mo of the ferromagnetic balls and electronic components was supplied to the separation channel 106 by a vibrating feeder. The dram 12 is rotated in the counter-clockwise direction and performs 235 revolutions per minute.

Almost complete separation of the ferromagnetic balls from the electronic components was achieved.

The same separator was used for recovering gold from the mixture Mo containing 65% of magnetite, i.e. magnetic fraction Mi. The dram 12 carrying twenty-two rows of radially oriented permanent magnets 10 and having the outer diameter of lm performed 300 revolutions per minute. As a result, about 98,5 % of magnetite were separated.

Those skilled in the art will readily appreciate that various modifications and changes may be applied to the preferred embodiment of the invention as heretofore exemplified without departing from the scope of the invention as defined in and by the appended claims.

Claims

CLAIMS:

1. A method for separating a first component having predetermined magnetic properties from a mixture containing the first component and at least a second component having relatively weak magnetic properties as compared to those of the first component, the method comprising the steps of:

(a) rotating a dram that carries a magnetic field source aligned along the circumference of the dram in a certain direction with a predetermined speed, the magnetic field source creating a magnetic field region in the vicinity of the dram; (b) feeding said mixture into a separation channel, which is stationary mounted in the vicinity of the dram and extends along a circumferential portion of the dram, the rotation of the dram causing said first component to move along the separation channel in a direction opposite to said certain direction of the rotation of the dram; and (c) discharging the first and second components through opposite ends of the separation channel.

2. The method according to Claim 1, wherein said predetermined speed of the rotation of the drum is such as to create a ponderomotive force in the first component. 3. The method according to Claim 2, wherein said predetermined speed is in the range of 30 to 1500 rpm and more.

4. A magnetic separator for separating a first component having predetermined magnetic properties from a mixture containing the first component and at least a second component having relatively weak magnetic properties as compared to those of the first component, the separator comprising:

(i) a dram carrying a magnetic field source aligned along the circumference of the dram, wherein said magnetic field source creates a magnetic field region in the vicinity of the drum; (ii) a driver coupled to the dram for providing its rotation in a certain direction with a predetermined speed; (iii) a separation channel stationary mounted in the vicinity of the drum and extending along a circumferential portion of the drum; (iv) a feeding means for feeding said mixture into the separation channel;

5. The separator according to Claim 4, wherein the magnetic field source is composed of a plurality of magnets.

6. The separator according to Claim 4, wherein said magnets are permanent magnets. 7. The separator according to Claim 4, wherein said magnets are electromagnets.

8. The separator according to Claim 6, wherein said permanent magnets are made of Ferrous-Barium.

9. The separator according to Claim 6, wherein said permanent magnets are made of rare-earth metals.

10. The separator according to Claim 5, wherein said magnets are arranged along the circumference of the drum, and oriented such that each s-pole is enclosed between a pair of «-poles.

11. The separator according to Claim 10, wherein the 5-poles and n-poles are aligned in parallel rows, respectively, extending parallel to the axis of the rotation of the dram.

12. The separator according to Claim 10, wherein the s- and n-poles are arranged in a "chess-board order" within the circumference of the dram.

13. The separator according to Claim 4, wherein the separation channel is of a "closed-type", being a hollow housing opened at its opposite ends through which the first and second components are discharged.

14. The separator according to Claim 4, wherein the separation channel is of an "open-type", being in the form of a belt.

15. The separator according to Claim 14, and also comprising a discharge launder located at that end of the belt through which the first component is discharged, and a water flow is supplied along the long axis of the launder.

16. The separator according to Claim 15, wherein the discharge launder is coupled to said end of the belt.

17. The separator according to Claim 15, wherein the discharge launder is a separate unit accommodated between said end of the belt and a discharge vessel.

18. The separator according to Claim 16 or 17, wherein the discharge launder is slightly inclined along the axis of the water flow.

AMENDED CLAIMS

[received by the International Bureau on 21 March 2000 (21.03.00); original claims 1 and 4 amended; remaining claims unchanged (3 pages)]

(a) rotating a drum that carries a magnetic field source aligned along the circumference of the drum in a certain direction with a predetermined speed, the magnetic field source creating a magnetic field region in the vicinity of the drum;

(b) feeding said mixture into a separation channel, which is stationary mounted in the vicinity of the drum and extends along a circumferential portion of the drum such that the end portion of the separation channel at which said first component is to be discharged is gradually led away from the circumference of the drum, the rotation of the drum causing said first component to move along the separation channel in a direction opposite to said certain direction of the rotation of the drum; and

(c) discharging the first and second components through opposite ends of the separation channel.

2. The method according to Claim 1 , wherein said predetermined speed of the rotation of the drum is such as to create a ponderomotive force in the first component.

3. The method according to Claim 2, wherein said predetermined speed is in the range of 30 to 1500 rpm and more.

4. A magnetic separator for separating a first component having predetermined magnetic properties from a mixture containing the first component and at least a second component having relatively weak magnetic properties as compared to those of the first component, the separator comprising: (i) a drum carrying a magnetic field source aligned along the circumference of the drum, wherein said magnetic field source creates a magnetic field region in the vicinity of the drum;

(ii) a driver coupled to the drum for providing its rotation in a certain direction with a predetermined speed;

(iii) a separation channel stationary mounted in the vicinity of the drum and extending along a circumferential portion of the drum, such that the end portion of the separation channel at which said first component is to be discharged is gradually led away from the circumference of the drum: and

(iv) a feeding means for feeding said mixture into the separation channel.

6. The separator according to Claim 4, wherein said magnets are permanent magnets.

7. The separator according to Claim 4, wherein said magnets are electromagnets.

10. The separator according to Claim 5, wherein said magnets are arranged along the circumference of the drum, and oriented such that each s-pole is enclosed between a pair of n-po es.

11. The separator according to Claim 10, wherein the s-poles and rø-poles are aligned in parallel rows, respectively, extending parallel to the axis of the rotation of the dram.

12. The separator according to Claim 10, wherein the s- and π-poles are arranged in a "chess-board order" within the circumference of the drum.