MATERIAL FEED PROCESS AND ASSEMBLY FOR A ROTARY MAGNETIC SEPARATOR

Abstract

The invention provides a material feed process for magnetically separating magnetic and non-magnetic particles from a material feed by means of a magnetic roller separator wherein the process is characterised therein that particle separation is independent of centrifugal force, and where the process can equally well be applied to both wet and dry particle separation. The process specifically provides feeding the particles at an incident zone above the horizontal axis centre line, and separating the magnetic and non-magnetic particles at opposite rotational sides of the roller.

Claims

1. A material feed process for magnetically separating magnetic and non-magnetic particles by means of a magnetic roller separator wherein the process is characterised therein that primary particle separation is independent of centrifugal force, the process comprising the steps of— providing a magnetisable roller [30] which rotates about an axis of rotation [32], and at least one magnet [34] which is configured to create a magnetic field [X] on the roller surface [42] for at least a portion of the roller surface [42], the magnetic field [X] being characterised therein that it is created at least partially to one side of the roller circumference relative to a vertical axis centre line [33] and opposite to the rotation direction [35]; providing a feed hopper [36] and accompanying feed chute [38] for feeding material at an angle onto the roller surface [42]; feeding the material directly into the magnetic field [X] on the roller surface [42] from one side of the roller [30], at an incident zone [α] which is above a horizontal axis centre line [39], such that primary particle separation occurs where feed particles first meet the roller surface [42] in that the non-magnetic particles [18] fall from the roller surface [42] at the point of impact, under the influence of gravity, at one side of the roller [30]; while the magnetic particles [20] are trapped within the magnetic field [X] and carried over in the magnetic field [X] in the direction of rotation [35] towards an opposite side of the roller [30] and fall from the roller surface [42], under the influence of gravity, once they move outside of the magnetic field.

2. The material feed process according to claim 1 wherein the incident zone [α] is 0°-45° above the horizontal axis centre line [39].

3. The material feed process according to claim 1 wherein the roller [30] rotates in an anti-clockwise direction and the magnet [34] is arranged such that the magnetic field [X] is created on the roller circumference at least at a position of between approximately twelve-o'-clock and three-o'-clock relative to the axis of rotation [32].

4. The material feed process according to claim 3 wherein the feed material is introduced onto the roller surface [42] at the incident zone [α] so that the material is fed directly into the magnetic field [X] on the roller circumference, the arrangement being such that particle separation occurs at the point of impact where particles meet the roller surface [42] and non-magnetic particles [18] fall from the roller surface [42], under the influence of gravity, at a clockwise-side of the roller [30], while the magnetic particles [20] are carried over in the magnetic field [X] towards an anti-clockwise side of the roller [30] and fall from the roller [30], under the influence of gravity, as soon as they move outside of the magnetic field [X].

5. The material feed process according to claim 1 wherein the roller [30] rotates in a clockwise direction and the magnet [34] is arranged such that the magnetic field [X] is created on the roller [30] circumference at least at a position of between approximately nine-o'-clock and twelve-o'-clock relative to the axis of rotation [32].

6. The material feed process according to claim 5 wherein the feed material is introduced onto the roller surface [42] at the incident zone [α] so that the material is fed directly into the magnetic field [X] on the roller circumference, the arrangement being such that particle separation occurs at the point of impact where particles meet the roller surface [42] and non-magnetic particles [18] fall from the roller surface [42], under the influence of gravity, at an anti-clockwise side of the roller [30], while the magnetic particles [20] are carried over in the magnetic field [X] towards a clockwise side of the roller [30] and fall from the roller [30], under the influence of gravity, as soon as they move outside of the magnetic field [X].

7. The material feed process according to claim 1 wherein the process further comprises the step of positioning the feed chute [38] at an angle relative to the incident zone [α].

8. The material feed process according to claim 7 wherein the feed chute [38] is positioned at an angle of between 50° to 70° to the horizontal, and preferably at an angle of 60°.

9. The material feed process according to claim 1 wherein the feed chute [38] terminates in a feed chute outlet [40], which is angularly offset from a longitudinal axis of the feed chute [38], and the process provides configuring the feed chute outlet [40] such that the feed material is introduced onto the roller surface [42] at an incident angle of between approximately 10° to 20° relative to the horizontal.

10. The material feed process according to claim 9 wherein the feed chute outlet [40] terminates at a gap distance [D] of between 10 mm to 20 mm from the roller surface [42] so as to allow non-magnetic particles [18] to fall through the gap between the roller surface [42] and the feed chute outlet [40] at the point of impact.

11. The material feed process according to claim 1 wherein the process further comprises the step of feeding the feed material under free-fall conditions from a hopper [36] onto the feed chute [38] so as to reduce static friction between the to feed material and the feed chute surface.

12. The material feed process according to claim 11 wherein the vertical free-fall distance between the hopper [36] and the feed chute [38] is between 50 mm and 100 mm.

13. The material feed process according to claim 1 wherein the process further comprises the step of introducing the feed material particles onto the feed chute [38] by means of a vibrating feeder [37] in order to increase the final velocity with which material particles meet the roller surface [42].

14. The material feed process according to claim 1 wherein the magnetic roller [30] separator is a REDS with a non-magnetic roller shell rotating about an array of static magnets [34] which are configured relative to the roller [30] such that the magnetic field [X] is created on the roller surface [42] at least at a position of between approximately twelve-o'-clock and three-o'-clock relative to the axis of rotation [32] of the roller [30], but can be positioned such that the magnetic field [X] is created at between approximately nine-o'-clock and three-o'-clock relative to the axis of rotation [32], but either way such that it creates an incident zone of between 0° and 45° relative to the horizontal axis centre line [39], such that when feed material is introduced onto the roller surface [42], non-magnetic particles [18] fall from the roller surface [42] at the point of impact, under the influence of gravity, at one side of the roller [30], while the magnetic particles [20] are retained by the magnetic field [X] of the roller surface [42] and are carried over to an opposite side of the roller [30], where they fall from the roller surface [42] under the influence of gravity, as soon as they move outside of the magnetic field [X].

15. The material feed process according to claim 1 wherein the magnetic roller [30] separator is a RERS with a rotating magnet [34] being installed at a tail roller [30] of a short belt conveyer [28] such that the magnetic field [X] is created at least at a position of between approximately twelve-o'-clock and three-o'-clock relative to the axis of rotation [32] of the tail roller [30], but either way such that it creates an incident zone at between 0° and 45° relative to the horizontal axis centre line [39], such that when feed material is introduced onto the belt conveyer, non-magnetic particles [18] fall from the tail roller [30] at the point of impact, under the influence of gravity, at one side [30A] of the tail roller [30], while the magnetic particles [20] are retained by the magnetic field [X] of the tail roller [30] and are carried over to the head roller [30], where they fall from an opposite side [30B] of the head roller [30], under the influence of gravity, as soon as they move outside of the magnetic field [X].

16. The material feed process according to claim 15 wherein a rotating magnet [34] is additionally installed at a head roller [30] of the short belt conveyer to provide a secondary separation functionality, additionally to the primary separation functionality of the tail roller [30], such that when feed material is introduced onto the belt conveyer, non-magnetic particles [18] are predominantly separated out at the tail roller [30] under the influence of gravity, while the magnetic particles [20] and any non-magnetic particles [18] that might not have separated out at the tail roller [30] are carried over in the magnetic field [X] to the head roller [30] where the non-magnetic particles [18] are dispelled from the head roller [30] under centrifugal force, while the magnetic particles [20] fall from an anti-clockwise side [30B] of the head roller [30], under the influence of gravity, as soon as they move outside of the magnetic field [X].

17. The material feed process according to claim 1 wherein the process is adapted for wet separation and provides the steps of feeding the feed material in a slurry from the hopper [36] down the inclined chute [38] towards the magnetic drum [30] such that when the slurry reaches the end of the chute [38], the magnetic particles [20] are attracted to the drum surface [42] by the magnetic field [X], allowing non-magnetic ore particles [18] and carrier water to fall from the magnetic drum surface [42] at the point of impact, under the influence of gravity, at one side [30A] of the magnetic drum [30]; while the magnetic particles [20] are trapped within the magnetic field [X] and carried over in the magnetic field [X] in the direction of rotation [35] towards an opposite side [30B] of the magnetic drum [30].

18. The material feed process according to claim 17 wherein at the opposite side [30B] of the roller [30], the magnetic particles [20] are scraped off the magnetic drum surface [42], at which position a stronger magnet section is fitted to squeeze water out of the magnetic particles, increasing density of recovered medium.

19. The material feed process according to claim 17 wherein the process provides the step of providing a tank [48] with three outlets installed under the magnetisable roller [30]—one outlet [48.1] for ore with some water, one outlet [48.2] for densified medium with some water, and one outlet [48.3] for water with some medium that carried over with the water.

20. A material feed assembly for feeding particle material from a hopper [36] onto a magnetisable roller [30] of a magnetic roller separator for magnetically separating magnetic and non-magnetic particles from the material feed, the material feed assembly comprising— a magnetisable roller [30] which rotates about an axis of rotation [32], and at least one magnet [34] which is configured to create a magnetic field [X] on the roller surface [42] for at least a portion of the roller circumference, the magnetic field [X] being characterised therein that it is created at least partially to one side of the roller circumference relative to a vertical axis centre line [33] and opposite to the rotation direction [35]; a feed hopper [36] and accompanying feed chute [38] for feeding material onto the roller surface [42], the feed chute [38] being disposed at an angle relative to the roller surface [42] such that material is fed directly into the magnetic field [X] on the roller surface [42] from one side of the roller [30], offset from the horizontal; the arrangement being such that primary particle separation occurs where feed particles first meet the roller surface [42] in that the non-magnetic particles [18] fall from the roller surface [42] at the point of impact, under the influence of gravity, while the magnetic particles [20] are trapped within the magnetic field [X] and carried over in the magnetic field [X] in the direction of rotation [35] towards an opposite side of the roller [30] and fall from the roller surface [42], under the influence of gravity, once they move outside of the magnetic field [X].

Description

SPECIFIC EMBODIMENT OF THE INVENTION

[0050] Without limiting the scope thereof, the invention will now further be described and exemplified with reference to the accompanying drawings wherein—

[0051] FIGS. 1-5 illustrate prior art configurations as discussed in the Background to the Invention;

[0052] FIG. 6 is a schematic illustration of a dry material feed process and assembly of the invention where the magnetic roller separator is a REDS;

[0053] FIG. 7 is a schematic illustration of a dry material feed process and assembly of the invention where the magnetic roller separator is a RERS;

[0054] FIG. 8 is a schematic illustration of a RERS, such as in FIG. 7, but where a rotating magnet is additionally (and optionally) installed at a head roller of the short belt conveyer to provide a secondary separation functionality;

[0055] FIG. 9 is a schematic illustration of REDS, such as in FIG. 6, but illustrating the incident angle, chute angle and vertical distance between a hopper outlet and the incident zone;

[0056] FIG. 10 is an enlarged schematic illustration of the REDS of FIG. 9, more clearly illustrating the incident angle;

[0057] FIG. 11 illustrates a preferred configuration of the magnets on the roller; and

[0058] FIG. 12 is a schematic illustration of a wet material feed process and assembly of the invention where the magnetic separator is a Wet drum LIMS.

[0059] The material feed process according to the invention for magnetically separating magnetic and non-magnetic particles by means of a magnetic roller separator is characterised therein that primary particle separation is independent of centrifugal force. The process comprises the steps of providing a magnetisable roller [30] which rotates about an axis of rotation [32] and which is operatively associated with at least one magnet [34] which is configured to create a magnetic field [X] on the roller surface [42] for a portion of the roller circumference. The magnet [34] is arranged such that the magnetic field [X] is created at least partially to one side of the roller circumference relative to vertical axis centre line [33] and opposite to the rotation direction [35].

[0060] The process provides feeding the material directly into the magnetic field [X] on the roller surface [42] from one side of the roller [30], at an incident zone [α] which is above a horizontal axis centre line [39], such that primary particle separation occurs where feed particles first meet the roller surface [42] in that the non-magnetic particles [18] fall from the roller surface [42] at the point of impact [44], under the influence of gravity, while the magnetic particles [20] are trapped within the magnetic field [X] and are carried over in the magnetic field [X] in the direction of rotation [35] towards an opposite side of the roller [30] and fall from the roller surface [42], under the influence of gravity, once they move outside of the magnetic field [X].

[0061] In the illustrated embodiments of the invention the roller [30] is rotating in an anti-clockwise direction and the magnet [34] is arranged such that the magnetic field [X] is created on the roller circumference at least at a position of between approximately twelve-o'-clock and three-o'-clock relative to the axis of rotation [32]. Feed material is introduced onto the roller surface [42] at the incident zone [α] so that the material is fed directly into the magnetic field [X] on the roller surface [42], the arrangement being such that primary particle separation occurs at the point of impact [44] where particles meet the roller surface [42] and non-magnetic particles [18] fall from the roller surface [42], under the influence of gravity, at a clockwise-side [30A] of the roller [30], while the magnetic particles [20] are carried over in the magnetic field [X] towards an anti-clockwise side [30B] of the roller [30] and fall from the roller [30], under the influence of gravity, as soon as they move outside of the magnetic field [X].

[0062] In a preferred embodiment of the invention the incident zone [α] is between above the horizontal axis centre line [39].

[0063] The process further comprises the step of positioning the feed chute [38] at an angle relative to the incident zone [α], and specifically at an angle of between approximately 50° to 70° to the horizontal. The material feed assembly further provides for configuring a feed chute outlet [40] such that the feed material is introduced onto the roller surface [42] at an incident angle [γ] of between approximately 10° to 20° relative to the horizontal, and preferably 15°. The feed chute outlet [40] terminates at a gap distance [D] of between approximately 10 mm to 20 mm from the roller surface [42] so as to allow non-magnetic particles [18] to fall through the gap [D] between the roller surface [42] and the feed chute outlet [40] at the point of impact [44].

[0064] The process further comprises the step of feeding the feed material under free-fall conditions from a hopper [36] onto the feed chute [38] so as to reduce static friction between the feed material and the feed chute surface. The vertical free-fall distance between the hopper and the feed chute [38] is between 50 mm and 100 mm.

[0065] The process further comprises the step of introducing the feed material particles onto the feed chute [38] by means of a vibrating feeder [37] in order to increase the final velocity with which material particles meet the roller surface [42]. It will be appreciated that when feed material slides down the inclined chute [38], the velocity of the particles upon exiting the feed chute [38] is calculated as [Sqr 2×9.81×sin angle×chute length] (units are metres and seconds). However, if the initial velocity is increased through a vibrating feeder [37], the square root of this initial velocity is added to the final velocity calculation.

[0066] In a process of the invention where the magnetic roller separator is a REDS (refer FIG. 6), a non-magnetic roller [30] shell rotates about an array of static magnets [34] which are configured relative to the roller [30] such that the magnetic field [X] is created on the roller surface [42] at least at a position of between approximately twelve-o'-clock and three-o'-clock relative to the axis of rotation [32] of the roller [30], but can be positioned such that the magnetic field [X] is created at between approximately nine-o'-clock and three-o'-clock relative to the axis of rotation [32], but either way such that it creates an incident zone [α] at between 0° and 45° above the horizontal axis centre line [39]. When feed material is introduced onto the roller surface [42], non-magnetic particles [18] fall from the roller surface [42] at the point of impact [44], under the influence of gravity, at a clockwise-side [30A] of the roller [30], while the magnetic particles [20] are retained by the magnetic field [X] of the roller surface [42] and are carried over to an anti-clockwise side [30B] of the roller [30], where they fall from the roller surface [42] under the influence of gravity, as soon as they move outside of the magnetic field [X].

[0067] In a process of the invention where the magnetic roller separator is a RERS (refer FIG. 7), a rotating magnet [34] is installed at a tail roller [30] of a short belt conveyer [28] such that the magnetic field [X] is created at least at a position of between approximately twelve-o'-clock and three-o'-clock relative to the axis of rotation [32] of the tail roller [30], but either way such that it creates an incident zone [α] at between 0° and 45° above the horizontal axis centre line [39]. When feed material is introduced onto the belt conveyer [28], non-magnetic particles [18] fall from the tail roller [30] at the point of impact [44], under the influence of gravity, at a clockwise-side [30A] of the tail roller [30], while the magnetic particles [20] are retained by the magnetic field [X] of the tail roller [30] and are carried over by the belt [28] to the head roller [26], where they fall from an anti-clockwise side [30B] of the head roller [26], under the influence of gravity, as soon as they move outside of the magnetic field [X].

[0068] Referring to FIG. 8, in the process of the invention where the magnetic roller [30] separator is a RERS, a rotating magnet [34] additionally and optionally may be installed at a head roller [26] of the short belt conveyer [28] to provide a secondary separation functionality, additionally to the primary separation functionality of the tail roller [30], such that when feed material is introduced onto the belt conveyer [28], non-magnetic particles [18] are predominantly separated out at the tail roller [30] under the influence of gravity, while the magnetic particles [20] and any unwanted weakly magnetic particles [18] that might not have separated out at the tail roller [30], are carried over in the magnetic field [X] to the head roller [26], where the unwanted weakly magnetic particles [18] are dispelled from head roller [26] under centrifugal force, while the magnetic particles [20] fall from an anti-clockwise side [30B] of the head roller [26], under the influence of gravity, as soon as they move outside of the magnetic field [X]. The process of the invention provides for the possibility of installing a magnetisable tail roller [30] into an existing RERS without the need to replace the magnetisable head roller [26].

[0069] In one embodiment of the invention, the magnetic configuration on the magnetisable tail roller [30] comprises a plurality of small, permanent magnets [34] installed very close to each other, with their magnetic polarities [46] oriented at alternate north-south orientation.

Experimental Results

[0070] In order to test the material feed process and assembly of the invention, the applicant configured a RERS assembly with a material hopper [36], vibrating feeder [37], inclined feed chute [38], magnetic tail roll [30], non-magnetic head roll [31] and a thin belt [28] of 0.13 mm. The inclined chute [38] was adjustable to make an acute angle alpha [α] with the magnetic roll [30]. The magnetic roll [30] comprised a carbon steel tube to which was attached small rectangular rare-earth neodymium permanent magnets [34]. The final diameter of the roll [30] with the magnets was 225 mm. The magnets [34] were arranged north-south (N-S) around the roll circumference, such that the magnetic force was the strongest where the N-S magnets abutted each other. Magnetic material attached to the strong magnetic lines formed across the roll face. The shorter the pitch was between the magnets, the more magnetic lines appeared to carry away the magnetic material.

Test 1

[0071] The applicant tested a feed material comprising 99.5% sand and 0.5% hematite in a process according to the invention. Feed material was introduced onto the belt surface at an incident zone [α] of 35° from the horizontal, a feed chute angle [β] of 70°, and a feed chute outlet angle [γ] of 18°. The separator was run at a roller speed of 10 rpm and a belt speed of 0.12 m/s. Feed material was fed onto the separator at a feed rate of 6 t/h/m. For comparison, the same feed material comprising 99.5% sand and 0.5% hematite was run through a conventional RERS. The comparative results are depicted below with Table 1 depicting the test results of the prior art RERS process, and Table 2 depicting the test results of the RERS material feed process according to the invention.

[0072] The prior art material feed process (Table 1) provided a 99.74% separation of sand and 90% separation of hematite. However, this separation was only achieved after three passes (i.e. after the material was sent through the separator three times). In addition, this separation could only be achieved at a material feed rate of 2 t/h/m, and at a roller speed of 100 rpm and a belt speed of 0.52 m/s. The prior art magnetic roller comprised a series of neodymium permanent magnets sandwiched between steel discs (poles), diameter 100 mm. The capacity of 2 t/h/m for a 300 mm diameter roller can be scaled up using the diameter ratio as described in the Background to the invention, page 5, according to the equation Sqr 3/1=1.73×2 t/h/m=3.46 from (Jakobs 2016) not more than 4 t/h/m.

[0073] By comparison, the material feed process according to the invention (Table 2) provided a 99.89% separation of sand and 90% separation of hematite. However, this separation was with a single pass, at a higher material feed rate of 6 t/h/m, and at a roller speed of only 10 rpm and a belt speed of 0.12 m/s. Accordingly, the process of the invention was proven to provide the same separation efficiency at a significantly higher feed rate and capacity, while at the same time running the RERS at a lower roller speed and belt speed, thus reducing wear and tear typically associated with such separators.

Test 2

[0074] The applicant tested a feed material comprising 95% ilmenite and 5% sand in a process according to the invention. Feed material was introduced onto the belt surface at an incident zone [α] of 0° from the horizontal, a feed chute angle [β] of 70°, and a feed chute outlet angle [γ] of 18°. The separator was run at a roller speed of 100 rpm and a belt speed of 1.12 m/s. In this test, the applicant included a magnetised head roller [26]. Feed material was fed onto the separator at a feed rate of 6 t/h/m. For comparison, the same feed material comprising 95% ilmenite and 5% sand was run through a conventional RERS. The comparative results are depicted below with Table 3 depicting the test results of the prior art RERS process, and Table 4 depicting the test results of the RERS material feed process according to the invention.

[0075] The prior art material feed process (Table 3) provided a 99.8% separation of ilmenite and 90% separation of sand. However, this separation was only achieved after two passes (i.e. after the material was sent through the separator twice). In addition, this separation could only be achieved at a material feed rate of 2 t/h/m.

[0076] By comparison, the material feed process according to the invention (Table 4) provided a 98.42% separation of ilmenite and 99% separation of sand. However, this separation was with a single pass, at a higher material feed rate of 6 t/h/m.

[0077] The roller [30] of the invention used neodymium magnets [34] for paramagnetic (weakly magnetic) minerals, but can work with ferrite magnets for ferromagnetic (strongly) magnetic material also.

[0078] The material feed process and assembly according to the invention may be adapted for both dry and wet magnetic separation. During wet separation, as illustrated in FIG. 12, the feed material is carried in a slurry and falls from a feed box [36] down the inclined chute [38] towards the magnetisable drum [30]. As the slurry reaches the end of the chute [38], magnetic particles will be attracted to the drum surface [42] by the magnetic field [X]. Non-magnetic ore and carrier water fall from the drum surface [42] at the point of impact, under the influence of gravity, at one side of the drum; while the magnetic particles are trapped within the magnetic field [X] and carried over in the magnetic field [X] in the direction of rotation towards an opposite side of the drum [30]. At the opposite side, the magnetic particles may be scraped off the drum surface [42]. As the magnetic particles are not pulled through moving slurry, the drum surface magnetic field strength can be lower than that used in prior art wet separators. At the position where the magnetic particles are scraped off the drum, a strong magnet section can be fitted. The strong magnet will squeeze water out of the magnetic particles, increasing the density of the recovered medium. A tank [48] with three outlets may be installed under the drum—one outlet [48.1] for ore with some water, one outlet [48.2] for densified medium with some water, and one outlet [48.3] for water with some medium that may be carried over with the water.

[0079] It will be appreciated that other embodiments of the invention are possible without departing from the spirit or scope of the invention as defined in the claims.