GB2042936A - Method of and Apparatus for Electrodynamic Separation of Nonmagnetic Free-flowing Materials - Google Patents

Abstract

Electrodynamic separation of nonmagnetic free-flowing materials is accomplished by feeding the flow of a material into the region of maximum intensity of a variable nonuniform magnetic field for inducing eddy currents in electrically conducting particles of the material being separated and producing electromagnetic forces which deflect the moving electrically conducting particles 3 from the direction of feed of the material being separated. The variable nonuniform magnetic field is generated by an electromagnet 1 having a closed magnetic core 5 with a magnetic air gap defined by pole pieces 2. The electromagnet pole pieces 2 are symmetrically divergent from the pole axes in a plane substantially perpendicular to the direction of feed of the material being separated. <IMAGE>

Description

SPECIFICATION Method of and Apparatus for Electrodynamic Separation of Nonmagnetic Free-flowing Materials The present invention relates to the art of separating materials according to their electromagnetic properties and in particular to methods of and apparatuses for electrodynamic separation and classification of nonmagnetic freeflowing materials according to their electrical conductivity and density.

According to one aspect of the invention, there is provided a method of electrodynamic separation of nonmagnetic free-flowing materials based on interaction between a variable nonuniform magnetic field and eddy currents in electrically conducting particles of a material to be separated, the method comprising directing a flow of particles of the material to be separated into the region of maximum intensity of the variable nonuniform magnetic fields so as to induce the maximum eddy currents in the electrically conducting particles of the material to be separated and thus produce the maximum electromagnetic forces, which deflect the moving electrically conducting particles from the direction of feed of the material to be separated.

Such a method of electrodynamic separation of nonmagnetic free-flowing materials makes it possible to enhance the efficiency separation of the materials at the same power consumption as that required for known separation methods. This is attained owing to the fact that the separation process is accomplished in the region of the maximum intensity of the variable nonuniform magnetic field.

In separating heavy metals, the material particles to be separated may be exposed to additional electro-magnetic forces directed oppositely to the gravity forces acting on the electrically conducting particles so as to partially counterbalance the gravity forces and so as to increase the angle of deflection of the direction of fall of the electrically conducting particles away from the vertical under the action of the main electromagnetic forces. Increasing the angle of deflection of the direction of fall of the electrically conducting particles from the vertical allows the heavier electrically conducting particles to be more efficiently separated from electrically nonconducting particles and particles with a lower specific electrical conductance.

When separating a material containing spatially asymmetrical particles, before being fed into the region of maximum intensity of the variable nonuniform magnetic field, the particles may be oriented in space with their maximum cross-sectional areas substantially perpendicularly to the magnetic lines of force of the variable nonuniform magnetic field. This technique considerably enhances the efficiency of separating spatially asymmetrical particles by creating the conditions for emergence of the maximum possible electromagnetic forces at essentially the same intensity and degree of nonuniformity of the variable magnetic field.

Such an orientation of electrically conducting particles of the material being separated may be accomplished by directing the freely falling flow of the material into the region of a variable uniform magnetic field whose magnetic lines of force are substantially perpendicular in space to the magnetic lines of force of the variable nonuniform magnetic field.

The orientation of electrically conducting particles of the material being separated may also be effected by directing the flow of the material by a vibrating trough disposed in the region of the maximum intensity of the variable nonuniform magnetic field. This technique makes it possible to orient the spatially asymmetrical particles substantially in a horizontal plane in the course of their feed.

According to another aspect of the invention, there is provided an electrodynamic separator for separating nonmagnetic materials, comprising an electromagnet having an excitation winding connected to an alternating current source and a closed magnetic core with a magnetic air gap defined by pole pieces of the electromagnet, the pole pieces being symmetrically divergent from the pole axes in a plane substantially perpendicular to the flow of the material when supplied for separation, there being further provided a loading means, a means for feeding the flow of particles of the material to be separated into the region of the variable nonuniform magnetic field produced by the poles of the electromagnet, and a receiving means for holding separated material.

Such a construction of the electrodynamic separator enables the energy of the variable magnetic field of the electromagnet to be utilized to the maximum extent owing to concentration of the magnetic field at the centre of the magnetic air gap between the pole pieces which allow for passage of the particles being separated in the region of the maximum intensity of the variable magnetic field.

The electromagnet pole pieces may be wedgeshaped with their opposite edges disposed in a vertical plane.

The electromagnet pole pieces may also have curved surfaces of the second degree whose generatrices are disposed vertically.

The opposite surfaces of the pole pieces may be arranged with respect to each other at an angle whose vertex points downwardly. This arrangement produces an additional electromagnetic force directed oppositely to the gravity forces acting on the particles being separated, which increases the angle of deflection of individual particles from the direction of feed of the initial material and enhances the efficiency of separating heavy electrically conducting particles.

The opposite surfaces of the pole pieces may be arranged at an angle of from 0 to about 450 with respect to each other. When the pole piece surfaces are arranged at an angle of 00, no additional electromagnetic force directed oppositely to the particle gravity force is produced, and their arrangement at an angle of 450 considerably reduces the intensity of the variable magnetic field in the top portion of the separation zone.

Preferably, there is provided means for orientation of spatially asymmetrical particles of the material to be separated before feeding them into the region of the maximum intensity of the variable nonuniform field so that the maximum cross-sectional areas of the particles are arranged in space substantially perpendicularly to the magnetic lines of force of said electromagnet.

Such an orientation of the spatially asymmetrical particles before feeding them into the region of the maximum intensity of the variable nonuniform field enhances the efficiency of extracting such particles from the initial mixture.

The means for orientating the spatially asymmetrical particles of the material being separated may be placed above the electromagnet and made in the form of an additional electromagnet having a closed magnetic core with a magnetic air gap defined by pole pieces whose opposite planes are parallel to each other and perpendicular in space to the pole of the said electromagnet.

The means for orienting the spatially asymmetrical particles of the material to be separated may also be made in the form of a vibrating trough inclined to the horizontal, disposed between the electromagnet pole pieces, and provided at the material discharge end with ribs serving to divide and guide the material to be separated; in this case, the electromagnet has to be installed so that the axis of its poles is arranged in a vertical plane.

The invention will be further described, by way of example, with reference to the accompanying drawings, wherein identical parts are denoted by identical reference numerals, and wherein: Figure 1 diagrammatically represents the principle of electrodynamic separation of nonmagnetic free-flowing materials; Figure 2 is a general diagrammatic view of a preferred electrodynamic separator; Figure 3 is a top view of Figure 2; Figure 4 is a side elevation view of Figure 2, partially sectionalized to show the direction of motion of the separated material; Figure 5 illustrates an example of pole pieces with convex curved surfaces of the second degree; Figure 6 is a similar view to Figure 5, but with concave surfaces of pole pieces;; Figure 7 is a diagrammatic representation of an electromagnet, wherein the opposite surfaces of its pole pieces are arranged at an angle with respect to each other; Figure 8 is a diagram of the principal forces acting on an electrically conducting nonmagnetic particle in accordance with Figure 7; Figure 9 is a diagrammatic representation of the electrodynamic separator with a means for orientation of spatially asymmetrical particles in the form of an additional magnet which, as well as the electromagnet, is partially broken away for a better illustration of the separation zone; Figure 10 is a diagrammatic representation of the electromagnetic separator with a means for orientation of spatially asymmetrical particles in the form of a vibratory trough; and Figure 11 is a diagram of the forces acting on electrically conducting particles in accordance with Figure 1 0.

There is described a method of electrodynamic separation of nonmagnetic free-flowing materials, based on interaction between a variable nonuniform magnetic field and eddy currents induced in electrically conducting particles of the material being separated.

The method is accomplished by feeding a flow of nonmagnetic free-flowing materials into the region of nonuniform variable magnetic field produced by an alternating-current electromagnet 1 (Figure 1) with a magnetic air gap defined by pole pieces 2.

The flow of the free-flowing material being separated is fed into the region of the maximum intensity of the variable nonuniform magnetic field so as to induce in electrically conducting particles 3 the maximum eddy current so as to deflect the moving electrically conducting particles from the direction of feed of nonmagnetic particles 4 of the material being separated.

The method of electrodynamic separation of nonmagnetic free-flowing materials is effected an electrodynamic separator. The electrodynamic separator comprises the electromagnet 1 (Figure 2) which is a magnetic core 5 with an excitation winding 6 (Figure 3) connected to a highfrequency alternating-current source (not shown).

The magnetic core 5 has a magnetic air gap (Figure 3) defined by the pole pieces 2 (Figures 1 and 2) which produce a variable nonuniform magnetic field. The material being separated is fed into the separation zone by a loading means in the form of a hopper 7 and a belt conveyor 8 disposed adjacent thereto. To hold the separated material, a receiving means is provided in the form of a hopper 9 divided into sections 10 (Figure 4), each of the sections being intended to receive the corresponding material.

The pole pieces 2 of the electromagnet 1 (Figures 1, 3) are symmetrically divergent from the pole axis in a plane substantially perpendicular to the direction of feed of the material being separated.

The pole pieces 2 (Figures 1, 3) of the electromagnet 1 are wedge-shaped with their opposite edges 11 (Figures 1, 4) disposed in a vertical plane.

According to another embodiment of the invention, the pole pieces 2 of the electromagnet 1 have curved surfaces of the second degree whose generatrices are disposed vertically. Figure 5 iliustrates the pole pieces 2 having convex surfaces of the second degree, and Figure 6, the pole pieces 2 with concave surfaces of the second degree.

According to still another embodiment of the invention, the opposite surfaces of the pole pieces 2 (Figure 7) are arranged with respect to each other at an angle of from 0 to about 450 whose vertex points downwards.

The electrodynamic separator has a means (Figure 9) for orientation of spatially asymmetrical electrically conducting particles of the material being separated, installed above the electromagnet 1 and made in the form of an additional electromagnet 14. The additional electromagnet 14 is installed above the electromagnet 1 and has a closed magnetic core 1 5 with a magnetic air gap defined by pole pieces 16 whose opposite planes are parallel to each other and perpendicular in space to the axis of the poles of the electromagnet 1.

According to another embodiment of the invention, the means 1 3 for orientation of spatially asymmetrical particles of the material being separated is essentially a vibratory trough 1 7 Figure 10 having a vibratory drive (not shown).

The vibratory trough 1 7 is disposed between the pole pieces 2 of the electromagnet installed so that the axis of its poles is oriented perpendicularly to the surface of the trough 1 7.

The end of the vibratory trough 1 7 in the direction of material discharge is provided with guide ribs 18 arranged substantially parallel to the axis of the vibratory trough 17.

The above-described electrodynamic separator functions as follows.

The initial free-flowing material which is a mixture of at least two nonmagnetic materials differing in electrical conductance is delivered from the loading hopper 7 onto the belt of the conveyor 8, which carries the material being separated to the centre of the magnetic air gap of the electromagnet 1. The flow of the material being separated freely falls from the belt of the conveyor 8 into the air gap defined by the pole pieces 2 of the electromagnet 1.

Because the pole pieces 2 defining the magnetic air gap are symmetrically divergent from the pole axis, a region of the maximum intensity of the nonuniform variable magnetic field is formed in the air gap (i.e., in the separation zone).

Thus, in the course of the free fall of the flow of the material being separated, the maximum eddy currents are induced in the particles of the material which differ in electrical conductance, the magnitude of the currents being directly proportional to the specific electrical conductance of a particle.

Interaction between the variable nonuniform magnetic field and the eddy currents induced in the electrically conducting particles produces electromagnetic forces which push out the particles in the direction of degrease in the magnetic field intensity.

The particles are deflected from the direction of feed of fall of the material being separated through different angles depending on their electrical conductance and density. Heavier particles and particles with a lower electrical conductance are deflected through a smaller angle, and conversely, lighter particles and particles with a higher electrical conductance are deflected through a greater angle.

The use of the pole pieces 2 (Figure 5) with convex surfaces of the second degree is advisable when the throughput rate of separation is to be increased and when no restriction is imposed on the power consumption. With this configuration, increasing the current through the excitation winding 6 of the electromagnet and thus stepping up the magnetic induction in the separation zone makes it possible at a lesser degree of nonuniformity of the variable magnetic field to attain the same magnitudes of the electromagnetic forces in a larger volume.

Concentration of a variable nonuniform magnetic field 1 9 with convex shaped pole pieces is diagrammatically shown in Figure 5.

Figure 6 diagrammatically shows concentration of a variable nonuniform magnetic field 20 with the pole pieces 2 having concave surfaces of the second degree. Such a configuration is recommended when a high quality of separation is required with no demands placed upon the throughput rate and the power consumption. Concentration of the magnetic field in the central portion of the magnetic air gap (separation zone) with a high degree of the field nonuniformity is attained in this case at an insignificant increase in the power consumption.

For the wedge-shaped pole pieces 2 (Figure 1), the above-specified conditions can be attained by varying their wedge angle.

When the opposite surfaces of the pole pieces 2 (Figure 7) are arranged at an angle with respect to each other, separation of nonmagnetic freeflowing materials occurs as follows.

The variable nonuniform magnetic field induces eddy currents in the electrically conducting particles 3 of the material being separated in the separation zone. Interaction between the variable nonuniform magnetic field and the eddy currents results in that the electrically conducting particles 3 are acted upon by two electromagnetic forces (Figure 8): F1, conditioned by the magnetic air gap diverging in a plane perpendicular to the flow of the material being separated, and F2, conditioned by the magnetic air gap diverging in the direction opposite to that of the electrically conducting particule gravity force F3.

Interacting with the field, the electrically conducting particles 3 under the action of the resultant force F which is equal to F=(F3-F2)2+F21 (1) are deflected through an angle a and fall into the section 10 for the electrically conducting particles of the receiving hopper 9, while the electrically nonconducting particles 4 freely with no deflection from the vertical (i.e. from the direction of feed of the flow being separated) into the appropriate section 10.

Thus, owing to counteraction of the electromagnetic forces F2 to the gravity forces F3, the velocity of fall of heavy particles is slowed down and they are deflected by the resultant force in the direction of decrease in the intensity of the variable nonuniform magnetic field. Such a separation technique is useful in beneficiation of heavy minerals, such as gold, platinum, etc., i.e.

when the separation efficiency greatly depends on the density of the electrically conducting particles.

When there is the means for orientation of spatially asymmetrical particles in the form of the additional electromagnet 14, the process of separation proceeds as follows. While falling freely, the flow of the material being separated enters the magnetic air gap of the additional orienting electromagnet 14, and eddy currents are induced in the electrically conducting particles of the material being separated. Interaction between the eddy currents and the uniform variable magnetic field causes the electrically conducting particles 3 to turn so that their maximum cross-sectional areas become arranged along the magnetic lines of force of the additional orienting electromagnet 14.

While freely falling the flow of the material being separated whose electrically conducting particles 3 are now oriented in the above manner enters the magnetic air gap of the electromagnet 1, i.e. the separation zone, or the region of the maximum intensity of the nonuniform variable magnetic field, where separation of the initial material occurs. Owing to the fact that the maximum cross-sectional areas of the particles are arranged substantially perpendicularly to the magnetic lines of force, the maximum eddy currents are induced in the particles.Interaction between the maximum eddy currents and the nonuniform variable magnetic field causes an increase in the electromagnetic forces acting on the particles and hence an increase of the angle of deflection of the electrically conducting particles from the free fall direction and a decrease of the probability of collision of the particles with one another. Thus, the quality of separation of a material with spatially asymmetrical particles is improved and the throughput rate of separation increased.

Example 1 Finely divided wastes of electrical cables in the form of a copper-lead mixture with a particle size of 2 to 3 mm at a weight ratio of 1:1 was separated. The shape of particles was close to spherical.

Separation was accomplished in an electrodynamic separator whose wedge-shaped pole pieces 2 (Figure 1) of the electromagnet had a wedge angle of about 1350, the magnetic air gap between the edges of the pole pieces being about 7 mm. The electromagnet excitation winding 6 was fed from a high-frequency current source. The maximum value of magnetic induction at the centre of the magnetic air gap was about 0.07T.

Electrodynamic separation yielded the following results: The copper concentrate contained 99.9% copper and 0.1% lead; the lead concentrate contained 99.4% lead and 0.6% copper.

Separation of the above-specified copperlead mixture with the use of the pole pieces 2 (Figure 7) whose opposite surfaces were arranged at an angle of about 1 00 to each other yielded the same results as in the above-described case, but the appearance of an additional electromagnetic force directed oppositely to the particle gravity forces made it possible to reduce the magnetic induction to 0.06T, which naturally cut down the power consumption.

Example 2 Auriferous mixtures containing, according to the analysis of averaged samples, about 95% gold and 5% associated minerals with a low electrical conductance, such as pyrite, and electrically nonconducting minerals, such as hematite, cassiterite, garnet, scheeiite, etc. were separated. The gold particles were predominantly of a splintery nature in the form of disks with a diameter of about 1 to 2 mm.

Separation was accomplished in an electrodynamic separator whose wedge-shaped pole pieces 2 (Figure 1 ) of the electromagnet had a wedge angle of about 90 , the magnetic air gap between the edges of the pole pieces 2 being about 4 mm.

The magnetic induction at the centre of the magnetic air gap between the pole pieces was 0.07 T.

The extraction of gold into the concentrate by electrodynamic separation amounted to about 24%. Such a low extraction of gold into the concentrate may be attributed to a random orientation of gold particles entering the separation zone.

When the above-specified auriferous mixture was separated in an electrodynamic separator provided with the additional electromagnet 14 (Figure 9) for orientation of gold particles, the degree of extraction rose to 80% with a content of gold in the concentrate of up to 99.8%.

Example 3 Auriferous mixtures containing 74% gold and 36% associated heavy-concentrate minerals with a low electrical conductance were separated.

Gold particles were of a splintery and an oblate shape and of 1 to 2 mm in size.

The particles were fed into the separation zone by the vibratory trough 1 7 (Figure 10) of the electrodynamic separator.

When being fed by the vibratory trough 17, the particles were repeatedly tossed up, with the result that they became dispersed over the surface of the vibratory trough 1 7 and contacted the latter by their maximum-area surfaces. On reaching the separation zone, the particles became exposed to the action of the electromagnetic forces F4 (Figure 11) directed perpendicularly to the direction of movement of the material being separated, and a rearrangement of the particles on the vibratory trough 1 7 took place: gold particles moved to the sides of the vibratory trough 1 7, while particles of heavy-concentrate minerals, unaffected by electromagnetic forces, concentrated at the central portion of the vibratory trough 1 7. Thus, as the particles moved further, gold particles were directed into the sections 10 of the hopper for holding electrically conducting particles, while electrically nonconducting particles fell into the section 10'.

Example 4 An aluminium-lead mixture with the particles of 2 to 3 mm in size at a weight ratio of 1:1 was separated. The shape of particles was close to spherical.

Separation was accomplished in an electrodynamic separator with wedge-shaped pole pieces, the wedge angle being 1350, and an air gap of 10 mm.

The degree of aluminium extraction by electrodynamic separation was about 99.7%.

Example 5 A mixture containing 60% aluminium and 40% zinc was separated. The size of particles in the mixture varied from 2 to 4 mm.

To separate said mixture, the particles were classified into two fractions, from 2 to 3 mm and from 3 to 4 mm.

Separation was accomplished in an electrodynamic separator with the wedge-shaped pole pieces 2, the magnetic air gap therebetween being about 10 mm. The wedge angle of the pole pieces was about 1200.

The maximum induction in the separation zone was 0.04T in separating the 3 to 4-mm fraction material and 0.048T in separating the 2 to 3-mm one.

The degree of aluminium extraction amounted to about 98% for the particles of 3 to 4 mm in size and to 96.5% for those of 2 to 3 mm in size.

Example 6 Inasmuch as the electromagnetic force acting on an electrically conducting particle in a variable nonuniform magnetic field depends on the particle size, particles of one and the same metal can be classified according to their size.

Thus, classification of spherical aluminium particles of different size namely of 2 to 6 mm in diameter, was accomplished in an electrodynamic separator whose electromagnetic had wedgeshaped pole pieces with a wedge angle of 1200.

Separation of the particles according to their size proved to be successful at the maximum magnetic induction of 0.03T. The maximum curving of the path in passing through the separation zone took place for 6-mm diameter particles, while the path of smaller-size particles, i.e., those with a diameter of up to 2 mm, was aimost unaffected, and 3 to 5-mm particles exhibited an intermediate curving of the path, with the result that large-diameter 6-mm particles were coilected in the outer sections of the receiving hopper; small-diameter particles, in the centre section; and intermediate-size particles, in the sections adjoining the centre one, i.e., disposed between the centre section and the outer sections of the receiving hopper.

An averaged degree of concentration of particles according to their size of 97% was attained in each of the sections, respectively.

Claims (14)

Claims

1. A method of electrodynamic separation of nonmagnetic free-flowing materials based on interaction between a variable nonuniform magnetic field and eddy currents in electrically conducting particles of a material to be separated, the method comprising directing a flow of particles of the material to be separated into the region of maximum intensity of the variable nonuniform magnetic field so as to induce the maximum eddy current in the electrically conducting particles of the material to be separated and thus produce the maximum electromagnetic forces, which deflect the moving electrically conducting particles from the direction of feed of the material to be separated.

2. A method as claimed in claim 1 for separating heavy metals, in which the material particles to be separated are exposed to additional electromagnetic forces directed oppositely to the gravity forces acting on the electrically conducting particles so as to partially counterbalance the gravity forces and so as to increase the angle of deflection of the direction of fall of the electrically conducting particles from the vertical under the action of the main electromagnetic forces.

3. A method as claimed in claim 2, for separating material containing spatially asymmetrical particles, in which, before being fed into the region of the maximum intensity of the variable nonuniform magnetic field, the particles are oriented in space with their maximum crosssectional areas substantially perpendicular to the magnetic lines of force of the variable nonuniform magnetic field.

4. A method as claimed in claim 3, wherein the orientation of the electrically conducting particles of the material to be separated is accomplished by directing the freely falling flow of the material into the region of a variable uniform magnetic field whose magnetic lines of force are substantially perpendicular in space to the magnetic lines of force of the variable nonuniform magnetic field.

5. A method as claimed in claim 3, wherein the orientation of the electrically conducting particles of the material to be separated is accomplished by directing the flow of the material by a vibrating trough disposed in the region of the maximum intensity of the variable nonuniform magnetic field.

6. An electrodynamic separator for separating nonmagnetic materials, comprising an electromagnet having an excitation winding connected to an alternating current source and a closed magnetic core with a magnetic air gap defined by pole pieces of the electromagnet, the pole pieces being symmetrically divergent from the pole axes in a plane substantially perpendicular to the flow of the material when supplied for separation, there being further provided a loading means, a means for feeding the flow of particles of the material to be separated into the region of the variable nonuniform magnetic field produced by the poles of the electromagnet, and a receiving means for holding separated material.

7. An electrodynamic separator as claimed in claim 6, wherein the electromagnet pole pieces are wedge-shaped with their opposite edges disposed in a vertical plane.

8. An electrodynamic separator as claimed in claim 6, wherein the pole pieces of the electromagnet have curved surfaces of the second degree whose generatrices are disposed in a vertical plane.

9. An electrodynamic separator as claimed in claim 6, wherein the opposite surfaces of the pole pieces are arranged with respect to each other at an angle whose vertex points downwardly.

10. An electrodynamic separator as claimed in claim 9, wherein the opposite surfaces of the pole pieces are arranged with respect to each other at an angle of from 0 to 450.

11. An electrodynamic separator as claimed in any one of ciaims 6 to 10, wherein there is provided means for orientation of spatially asymmetrical electrically conducting particles of the material to be separated disposed above the electromagnet and made in the form of an additional electromagnet having a closed magnetic core with a magnetic air gap defined by pole pieces whose opposite planes are parallel to each other and perpendicular in space to the pole axis of the said electromagnet.

12. An electrodynamic separator as claimed in any one of claims 6 to 10, wherein there is provided means for orientation of spatially asymmetrical particles comprising a vibratory trough disposed between the pole pieces of the electromagnet and provided at the end where the material to be separated is discharged with ribs serving to divide and guide the material to be separated, the electromagnet being installed so that the axis of its poles is perpendicular to the surface of the vibratory trough.

13. A method of electrodynamic separation of nonmagnetic free-flowing materials, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

14. An electrodynamic separator substantially as herein described with reference to and-as illustrated in the accompanying drawings.