WO1998058750A1

WO1998058750A1 - Particulate material separation

Info

Publication number: WO1998058750A1
Application number: PCT/AU1998/000470
Authority: WO
Inventors: John Michael Frederick Clout; Maureen Teresa O'connor
Original assignee: Commonwealth Scientific And Industrial Research Organisation
Priority date: 1997-06-20
Filing date: 1998-06-18
Publication date: 1998-12-30
Also published as: AUPO748997A0; ZA985361B

Abstract

An apparatus for separating particulate material includes supporting means for supporting a bed of the particulate material, means for inducing particle-particle interaction of particulate material in the bed whereby lower density particulate material migrates towards the top of the bed, and separation means for separating at least a portion of said lower density material from an upper portion of the bed.

Description

PARTICULATE MATERIAL SEPARATION

TECHNICAL FIELD

Particulate material can be separated by a variety of techniques which can be broadly classified as wet techniques and dry techniques . Wet techniques can be used in cases where water is required for subsequent processing. However, where that is not the case, the introduction of water into a separation process is undesirable because it drastically increases costs associated with materials handling, thickening, filtration, drying etc.

The present invention relates to an apparatus and method for the physical separation of particulate material. The present invention is primarily concerned with dry separation but it is to be understood that the present invention may be used as a wet technique. The present invention is particularly suited but is not limited to the separation of particles in the size range of lOμm-lOOmm, more particularly 100μm-50mm, on the basis of differences in density (specific gravity) .

The present invention has particular, although not exclusive, application to the separation of particulate material in the mining and related industries. BACKGROUND ART Various prior art separation techniques have been proposed in which a "fluidised bed" of the particulate material is formed by use of a fluidising or suspending agent such as air or water to achieve density separation. For example, US patent no. 3486620 discloses an apparatus for concentrating ore in which compressed air is upwardly directed through the particulate material and is arranged to lift lighter particles whilst having no or minimal affect on heavier particles. Australian patent application no. 10923/88 similarly teaches a method of dry separation of solids in which air is used as a fluidising agent.

Australian patent application no. 28485/92 discloses a sizing and concentrating apparatus which utilises a vibrating launder in which the bottom of the launder is formed of a plurality of spaced slats one plane of which is substantially horizontal to provide a stepped decline to produce a fluidised bed of particles of differing sizing and characteristics. The apparatus is said to be particularly useful in the case of particles in the range of minus 3mm and minus 75μm. The apparatus does not utilise a fluidising agent; however, it is said that the horizontal and vertical faces of each step of the stepped decline perform essential functions in particle transport and bed dilation. It is further said that the stepped decline which forms the particle bed base is vibrated such that the vibration promotes particle segregation and is essential for the proper functioning of the horizontal and vertical faces of each step.

In contrast to prior art techniques, the present invention utilises an analogous mechanism to fluidisation without the use of a fluidising agent by inducing particle-particle interaction of particulate material. As previously mentioned, the present invention may be used as a wet technique but it is to be noted that, where water is used in a wet technique, the water is not required as a fluidising agent. DISCLOSURE OF THE INVENTION In a first aspect, the present invention provides an apparatus for separating particulate material, the apparatus including: supporting means for supporting a bed of the particulate material, means for inducing particle-particle interaction of particulate material in the bed whereby lower density particulate material migrates towards the top of the bed, and separation means for separating at least a portion of said lower density material from an upper portion of the bed.

In a second aspect, the present invention provides a method for separating particulate material, the method including the steps of: forming a bed of the particulate material, inducing particle-particle interaction of particulate material in the bed whereby lower density particulate material migrates towards the top of the bed, and separating at least a portion of said lower density material from an upper portion of the bed.

Preferably, particle-particle interaction of particulate material in the bed is induced by subjecting the supporting means to vibratory motion. The supporting means may take the form of a trough mounted on a deck of a vibrating frame. The frame may be vibrated by a linear reciprocating motion which may be imparted to the frame at an angle to the plane of the deck. Alternatively, the frame may be vibrated by a non-linear motion, for example, a circular or elliptical motion. Non-linear motion may be imparted by a variable speed motor driving an out of balance flywheel. The vibratory motion may be a combination of a number of distinct vibratory motions. Preferably, the supporting means takes the form of a trough mounted on a deck which is in turn mounted on springs on a vibrating frame.

The bed of particulate material is "fluidised" by the means for inducing particle-particle interaction in the absence of a fluidising agent. The extent of fluidisation of the bed can be controlled by controlling a number of variables including the nature of the vibratory motion, the angle of the vibratory motion with respect to the supporting means, the amplitude of the motion, the frequency of the motion and the depth of the bed with the variables preferably optimised for a given sample of particulate material. The extent of fluidisation of the bed is largely determined by the amplitude of the motion which is preferably sufficient to induce particle-particle interaction of the particulate material allowing stratification of the bed but not so large as to induce too strong interaction between particles which obviates stratification and hence separation. The frequency of the motion largely affects the speed of interaction between particles within the bed and the rate at which lower density particles migrate upwardly through the bed. The bed depth is preferably at least about 5 particle diameters which has been found to be sufficient to enable particle-particle interaction to be established with upward displacement of lower density particles . Particulate material may be separated by batch or continuous operation with continuous operation being preferred. The separation means can take a variety of forms. For example, material may be raked from the top of the bed; lower density material may be caused to flow over a weir or through an aperture; or, at an intermediate level in the bed lower density and higher density material may be caused to be separated by encountering a standard scrapper bar or cutter plate.

The supporting means may be disposed substantially horizontally or may be inclined at an angle of up to about 45° and the nature of the motion from linear through elliptical to circular may be selected to optimise particle-particle interaction within the bed.

Inclination of the supporting means may assist separation of lower density material by enabling the lower density particles to flow under gravity over a weir or through an aperture in a lowered bed wall once they have migrated to an upper portion of the bed. The angle of inclination is preferably variable. A separation enhancing agent such as water or ferrosilicon particles may be added to the bed to enhance separation.

Separation may be effected on a continuous basis with the apparatus preferably including feed means for introducing particulate material into the bed for continuous operation. The feed means preferably takes the form of a vibratory or belt feeder which may introduce particulate material at a point or as a curtain, preferably evenly across the width of the supporting means .

A plurality of beds may be arranged to be used in series in accordance with the present invention. For example, particulate material separated from a first bed may be introduced to another bed arranged to provide either improved separation at the same density or further separation at a different density. It will therefore be appreciated that an apparatus according to the present invention can be used to separate a feed of particulate material into various fractions with the densities of the particles in the various fractions being variable.

Preferred embodiments of the present invention will now be described by way of example. Example 1

A batch test was conducted on a sample of iron ore in a rectangular trough 340mm wide by 260mm long by 60mm deep and mounted horizontally on a vibrating table in the form of a modified General Kinematics screen deck. The screen deck was modified by replacing the screens with the trough. The size range of the feed material was 13- 22mm. The test was conducted on an 8.3kg sample containing 4.6% gangue (SG<3.5) which formed a 50mm deep bed. The vibratory motion imparted to the trough was a linear reciprocating motion which was imparted at an angle of 30° to the horizontal at a frequency of 50 Hz and an amplitude of 1mm. Particle-particle ^' interactions were established in the bed resulting in fluidisation caused by the vibratory motion. Gangue migrated to the surface of the bed and accumulated in one corner from which it was manually collected and hence separated from the higher density particles (SG: 4.3-4.65). Notwithstanding that the trough was mounted substantially horizontally, the nature and angle of the vibratory motion to horizontal resulted in inclination of the upper surface of the bed. Approximately 90% of the gangue was separated from the feed material in approximately one minute . Example 2

A batch test was conducted on a sample of iron ore in the trough of Example 1 which was mounted on a modified Denver-Dillon screen deck at an inclination of about 8° to the horizontal. The screen deck was modified by replacing the screens with the trough. The 260mm sides of the trough were inclined at 8° with one of the 340mm rims being elevated with respect to the other of the 340mm rims. The size range of the feed material was 13-22mm. The test was conducted on an 8.0kg sample containing 6.4% gangue (SG<3.5). The vibratory motion imparted to the trough was circular with the plane of the motion substantially normal to the 340 rims of the trough at a frequency of 50Hz and an amplitude of 2mm. The circular vibratory motion was imparted by a variable speed motor driving a pair of standard out of balance flywheels connected by a drive shaft. Particle-particle interactions were established in the bed resulting in fluidisation caused by the vibratory motion. Gangue migrated to the surface of the bed and accumulated in one of the lower corners from which it was manually collected and hence separated from the higher density particles (SG: 4.3-4.65). Approximately 80% of the gangue was separated from the feed material in approximately 2 minutes. Example 3

A continuous test was conducted on a sample of iron ore (13 -22mm) in a rectangular trough 300mm wide by 705mm long by 300mm deep and mounted horizontally on the screen deck of Example 2. The sample was continuously fed from a vibratory feeder to a point adjacent a corner of the trough at a feed rate of 700kg per hour. One of the longer walls was formed with a tail aperture for removal of lower density (tail) material. The aperture was rectangular, centrally located in the longer wall, 390mm wide, and extended from the upper edge of the longer wall to a maximum depth of 280mm. The size of the aperture was adjustable by raising and lowering a sliding gate; the upper edge of which formed the lower edge of the aperture. The width of the aperture was also adjustable. Throughout the example the gate was positioned such that the tail aperture was 390mm wide by 170mm deep. A product aperture for removal of higher density (product) material was formed in the other of the longer walls . The product aperture was located in the bottom corner of the longer wall remote from the corner at which the product was fed to the trough and was of adjustable size by provision of a sliding gate. The product aperture was in the form of a quadrant of radius 70mm. Throughout the example the gate was positioned such that the product aperture was wide open. The vibratory motion imparted to the trough was elliptical with the plane of the motion substantially normal to the long sides of the trough at a frequency of 50Hz and an amplitude of l-2mm. The elliptical vibratory motion was imparted by a variable speed motor driving a pair of standard out of balance flywheels connected by a drive shaft with the screen deck weighted to modify the circular motion which would otherwise be induced. Particle-particle interactions were established in the bed resulting in fluidisation caused by the vibratory motion with lower SG material continuously collected from the tail aperture and higher SG material continuously collected from the product aperture .

Good upgrading was achieved yielding a product of 64.9% Fe_T0TAL, 3.25% Si0₂ and 1.06% Al₂0₃ from a feed of 64.3% Fe, 3.67% Si0₂ and 1.31% Al₂0₃ (Table 1). This product assay is close to the theoretical maximum as established from heavy liquid analysis of 65.5% Fe_T0TAL, 2.69% Si0₂ and 0.98% Al₂0₃ for 82% recovery (Table 2). Table 1 Quantitative Result Assay of Feed, Product and Tail

Table 2 Theoretical calculated assay based on removal of the gangue (SG<3.3)

Example 4

A continuous test was conducted on a sample of iron ore (6-30mm) in a rectangular trough 300mm wide by 600mm long by 300mm deep and mounted horizontally on the screen deck of Example 2. The sample was continuously fed from a vibratory feeder to the middle of the trough as curtain between the long sides of the trough and substantially parallel to the short sides of the trough at a feed rate of 500kg per hour. One of the longer wall-s was formed with a tail aperture for removal of lower density (tail) material. The aperture was rectangular, located adjacent a corner of the trough, 100mm wide, and extended from the upper edge of the longer wall to a maximum depth of 280mm. The size of the aperture was adjustable by raising and lowering a sliding gate; the upper edge of which formed the lower edge of the aperture. Throughout the example the gate was positioned such that the tail aperture was 100mm wide by 165mm deep. A triangular product aperture for removal of higher density (product) material was formed in the same longer wall as the tail aperture. The product aperture was located in the bottom of the longer wall adjacent the corner remote from the tail aperture and was of adjustable size by provision of a sliding gate. Throughout the example the gate was positioned such that the product aperture was a right angle triangle having a base of 100mm and a height of 120mm. The vibratory motion imparted to the trough was elliptical with the plane of the motion substantially normal to the long sides of the trough at a frequency of 70Hz and an amplitude of 0.5-lmm. The elliptical vibratory motion was imparted by a variable speed motor driving a pair of standard out of balance flywheels connected by a drive shaft with the screen deck weighted to modify the circular motion which would otherwise be induced. Particle-particle interactions were established in the bed resulting in fluidisation caused by the vibratory motion with lower SG material continuously collected from the tail aperture and higher SG material continuously collected from the product aperture.

The quantitative results for the total lump sample of iron ore indicated good ore recovery of 88%, with some upgrading of the feed (64.3% Fe_T0TAL, 3.46% Si0₂ and 1.36%

Al₂0₃) to the product (64.5% Fe_T0TAL, 3.11 Si0₂ and 1.26% Al₂0₃) being achieved (Table 3). Table 3. Quantitative Result - Assay of Product and

Tail

Example 5 A batch test was conducted on a 60g sample of a mixture of 75% by weight magnetite of SG 5.5 and 25% by weight silica of SG 2.65 in the rectangular trough of Example 1 mounted horizontally on the screen deck of Example 2 with a 3mm bed depth. The size range of the feed material was 100-300μm. The primary vibratory motion imparted to the trough was elliptical with the plane of the motion substantially normal to the long sides of the trough at a frequency of 50 Hz and an amplitude of 1mm. The elliptical vibratory motion was imparted by a variable speed motor driving a pair of standard out of balance flywheels connected by a drive shaft with the screen deck weighted to modify the circular motion which would otherwise be induced. A secondary linear reciprocating vibratory motion was also imparted to the trough. The secondary motion was a vertical motion at a frequency of 50 Hz and an amplitude of 1.5mm. Particle-particle interactions were established in the bed resulting in fluidisation caused by the vibratory motions. Two distinct bands were formed in the trough; the lower band (high SG) contained 95% by weight magnetite and 5% by weight silica and the upper band (low SG) contained 82% by weight magnetite and 38% by weight silica.

Claims

1. An apparatus for separating particulate material, the apparatus including: supporting means for supporting a bed of the particulate material, means for inducing particle-particle interaction of particulate material in the bed whereby lower density particulate material migrates towards the top of the bed, and separation means for separating at least a portion of said lower density material from an upper portion of the bed.

2. An apparatus as claimed in claim 1 wherein the means for inducing particle-particle interaction comprises means for inducing vibratory motion of the supporting means .

3. An apparatus as claimed in claim 2 wherein the means for inducing vibratory motion comprises means for inducing a linear reciprocating motion.

4. An apparatus as claimed in claim 2 wherein the means for inducing vibratory motion comprises means for inducing a circular or elliptical motion.

5. An apparatus as claimed in claim 2 wherein the means for inducing vibratory motion comprises means for inducing a circular or elliptical motion and means for inducing a linear reciprocating motion.

6. An apparatus as claimed in any one of claims 2-5 wherein the supporting means comprising a trough mounted on a frame arranged to be vibrated.

7. An apparatus as claimed in any one of claims 2-6 wherein the amplitude and frequency of the vibratory motion are variable.

8. An apparatus as claimed in any one of the preceding claims wherein the separation means is arranged for continuous separation of said lower density material and the apparatus further includes feed means for continuously introducing particulate material into the bed.

9. An apparatus as claimed in claim 8 wherein the feed means comprises a vibratory or belt feeder.

10. An apparatus as claimed in any one of the preceding claims wherein the separation means comprises a weir over which said lower density material flows in use or an aperture through which said lower density material flows in use.

11. An apparatus as claimed in any one of the preceding claims having a plurality of beds arranged in series whereby particulate material separated from one of the beds can be introduced into another of the beds for further separation.

12. A method for separating particulate material, the method including the steps of: forming a bed of the particulate material, inducing particle-particle interaction of particulate material in the bed whereby lower density particulate material migrates towards the top of the bed, and separating at least a portion of said lower density material from an upper portion of the bed.

13. A method as claimed in claim 12 wherein the bed is of a depth greater than 5 particle diameters .

14. A method as claimed in claim 12 or claim 13 which utilises an apparatus as claimed in any one of claims 1-11.

15. A method as claimed in any one of claims 12-14 wherein the particulate material is an ore.