BACKGROUND OF THE INVENTION
This invention relates generally to the separation of material into fractions of different densities.
"Jigging" is one method whereby minerals of different densities are separated from one another. A jig typically consists of a chamber whose bottom is a screen and which is open above. The material to be separated is fed into the chamber at one end and the separated products are removed at an opposing end.
The separation process involves the repeated suspension of a bed of particles in the chamber which is brought about by an upward flow of water, followed by a short hindered-settling phase, followed by a suction stroke. The differences in the hindered-settling velocities of the phases of various densities cause the phases to stratify with the denser fractions lowermost and progressively less dense fractions above.
In "through-the-bed" jigging the apertures of the screen are greater in size than the largest particles in the feed. The bed is prevented from falling through the screen by a layer of particles whose density is between those of the two minerals to be separated. These particles are referred to as "ragging".
The denser mineral works its way through the ragging and into the chamber,
below the screen, which is called the hutch. The less dense particles overflow
a tailings weir at an end of the bed.
Through-the-bed jigging is used typically for finer particles eg -6mm. For the separation of coarse particles, "on-the-bed" jigging is normally used. In this process the screen is finer than the finest particles thereby preventing the bed from falling into the hutch. The denser particles are removed from the bed by a gate in the screen and the lighter particles overflow the tailings weir.
The type of gate used in an on-the-bed jig includes a chamber at an end of the bed into which the denser fraction falls. The rate of release of the denser fraction is controlled by the gate with the aperture of the gateway being regulated electronically or mechanically according to the position of a float which tracks the height of the interface between the lighter and heavier fractions. In one design the gate area is quiescent while in another a separate jigging action is applied in order to maintain the separation. Both designs are similar in principle in that the denser fraction changes its direction of motion from a horizontal movement to vertically downwards once it enters the gate area.
The aforementioned gate designs have been found to give problems in practice in that the flow of material into the gateway causes light material to be drawn
down into the denser fraction. Pulsing of the gate area is not always effective in
restoring the separation especially where the density difference is small as in
ores with a range of densities.
SUMMARY OF THE INVENTION
The invention provides, in the first instance, a method of extracting a desired fraction from a jigging separator which includes a housing in which is formed at least one compartment, the method including the step of allowing the desired fraction to flow substantially horizontally from the compartment.
The desired fraction may be allowed to flow from the compartment at or above the level of a bed of the compartment.
The fraction which is extracted may be the denser fraction.
The denser fraction may be extracted from the housing at a plurality of locations each of which is associated with a respective compartment in the housing.
The invention also extends to a method of operating a jigging separator which includes the steps of introducing material into a compartment of the separator, stratifying the material at least into a relatively denser fraction and a less dense
fraction, allowing the less dense fraction to flow from the compartment over an
overflow weir, and causing the relatively denser fraction to flow substantially
horizontally from the compartment through a discharge opening at least part of
which is higher than a bed of the compartment.
The invention also provides a jigging separator which includes a housing in which is formed at least one compartment and a bed for the compartment, and means forming a discharge opening, from the compartment, higher than the bed.
Preferably the separator includes a wall on a side of the compartment, with the discharge opening being formed in the wall.
The wall may form at least part of an overflow weir from the compartment.
In one form of the invention a plurality of the compartments are formed in the housing, and the separator includes a plurality of the said walls each wall being located on a side of a respective compartment and forming an overflow weir into a successive compartment and, in the case of the last compartment, from the housing.
A gate of any suitable kind may be provided for controlling discharge through the discharge opening.
In one embodiment the gate is rotatably mounted and includes a concave outer
surface which faces the compartment.
This type of gate may include a plurality of gate sections which are rotatably movable relatively to one another to a limited extent.
Alternatively the gate is a slide gate.
The separator may include a detector which is responsive to the position of an interface between different density fractions in the compartment and which controls movement of the gate.
The invention also provides a jigging separator which includes a housing in which is formed at least one compartment, a bed for the compartment, a wall which is located on a side of the compartment and which forms an overflow weir from the compartment, a discharge opening, at least part of which is higher than the bed, being formed in the wall, and a gate which is mounted in the discharge opening.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is further described by way of examples with reference to the
accompanying drawings in which:
Figure 1 is a plan view of portion of a jigging separator according to one form of
the invention,
Figure 2 is a cross sectional view of the separator of Figure 1 taken on the line
2-2,
Figure 3 is an end view of the separator of Figure 1 taken on the line 3-3,
Figure 4 is a plan view of a separator which includes a plurality of gates along the
length of the separator,
Figure 5 is a cross sectional side view of the separator of Figure 4 taken on the
line 5-5,
Figure 6 is a side view of a separator according to a different form of the
invention, and
Figures 7, 8 and 9 are respectively views from the side, in plan and from an end,
of a modified radial gate for use in the jigging separator of the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Figures 1, 2 and 3 illustrate the construction of a jigging separator 10 according to a first form of the invention which is adapted to remove a denser fraction through a gateway in a vertical end wall of a jig.
The separator includes a housing 12 with a base or bed 14 which underlies a chamber or compartment 15, an overflow weir which is formed by a vertically extending side wall 16, a float mechanism 18 and a radial gate 20.
The jig bed 14 is made from a screen in a conventional manner. Similarly the float mechanism 18 is based on the use of known techniques and is adapted to sense or detect the interface between the denser and lighter fractions which are produced during operation of the separator.
The radial gate 20 is mounted for rotatable movement in a discharge opening 21 through which material from the compartment 15 can be discharged into a hopper 22.
The radial gate is movable by means of a hydraulic cylinder 24 which acts through a crank 26 to cause rotation of the gate.
In operation of the separator the material to be treated is fed into the left side of
the compartment 15.
In this instance the housing 12 forms a narrow jig bed with a maximum width which equals the length of the radial gate 20, of approximately 500mm. If the jig bed is wider then the number of hydraulic cylinder actuators can be increased, if necessary, by adding additional components along the length of the gate. The actuators could then, for example, operate from above the bed, lifting the gate by means of a short lever.
The cylinder 24 is under the control of the float mechanism 18.
It is to be understood that the present invention relates to the provision of the gate and not to the operation of the jigging separator in other respects. For this reason the manner in which a pulsating action is achieved in the liquid inside the compartment 15 is not described herein. Suffice it to say that by means of the process described in the preamble to the specification, or any equivalent process, the material in the compartment 15 is stratified and thereby divided into superimposed underlying more dense and overlying less dense fractions which are positioned over the bed 14.
The lighter fraction flows over the weir which is formed by the upper end of the
vertical side wall 16. The heavier fraction is allowed to flow from the
compartment, substantially horizontally, through the discharge opening 21 which
is normally closed by the radial gate 20. The extent to which the gate is raised,
and hence the size of the aperture through which the heavier fraction is
discharged into the hopper 22, is varied according to the height of the denser
fraction on the bed, which is sensed by the float mechanism 18.
It is found that the sideways movement of the heavier fraction, which takes place at or slightly above the level of the bed, reduces the extent to which the lighter fraction is entrained in the heavier fraction during discharge. Thus the two fractions are separated more effectively.
The hydraulic actuator 24 is given merely by way of example and it is to be understood that the gate could be actuated using electric motors via a radial or other gearbox, or by means of any other suitable actuator.
Figures 4 and 5 illustrate the principles on the invention applied to a separator 10A which includes a housing 12A divided into a number of compartments 28A, 28B, etc.
Each compartment has a respective side wall 16A, 16B, etc and a respective
radial gate 20A, 20B, etc is mounted in the associated side wall. In this way the
less dense fraction which overflows a preceding weir is treated in a succeeding
compartment and, in each compartment, the denser fraction is removed by
actuating the associated radial gate to the appropriate extent in a manner which
is analogous to what has been described with reference to Figures 1, 2 and 3.
The radial gates shown in Figures 1 to 5 are preferred to other gates, such as slide gates, in that the radial movement reduces the vertical height through which the gates are moved, when they are opened, as opposed to the vertical height through which a slide type gate is moved. Nonetheless it is possible in certain applications to make use of a slide type gate in the manner shown, for example, in Figure 6.
Figure 6 illustrates a slide type gate 34 mounted in a wall 36 which forms an overflow weir and which is positioned on one side of a compartment 38 formed in a housing 40, with an underlying bed 42.
Movement of the gate is controlled by means of a hydraulic cylinder actuator 44 which is responsive, in the manner described hereinbefore, to a float mechanism 46 which in turn is responsive to the height of the interface between the denser and less dense fractions of the material in the compartment of the separator.
The gate is moved vertically upwardly or downwardly to vary the height of the
discharge aperture through which the denser fraction flows into a discharge hopper 48.
Again it is to be noted that the discharge of the denser fraction is achieved by permitting sideways or substantially horizontal flow of the denser fraction into the discharge hopper. As before, the extent to which the lighter fraction is entrained into the flow of the emerging denser fraction, is reduced and consequently a more effective separation into more dense and less dense fractions is achieved.
The efficiency of the invention is evident from the following table in which column A relates to a prior art system, and column B relates to the prior art system modified to incorporate the structure shown in Figures 1, 2 and 3, and hence operating in accordance with the principles of the invention.
Recovery of Ferrochrome (-20mm to +3mm) from Slag
(Table Removed)
When use is made of a radial gate of the type shown in Figures 1 to 3 the gate, as it closes, may rotate onto a particle of the material which is being separated. If the particle is trapped by the gate then the particle will hold the gate partly open and, depending on the size of the particle and the length of the gate, a gateway opening of considerable size may be formed through which the material can flow, without prior stratification taking place. This adversely affects the mass yield in the concentrate, ie the effectiveness of the recovery.
To reduce the effect of this type of occurrence the single radial gate can be divided into a number of smaller radial gates, designated 50A, 50B, 50C and 50D in Figures 8 and 9 which are plan and end views respectively of the radial gate arrangement which is shown from the side in Figure 7.
Each of the gates 50 is mounted on a respective support arm 52 which extends from an axle which is rotatably mounted, at opposed ends, in bearings 56.
Spacers 58, between adjacent pairs of support bases 60A to 60D on the axle 54,
position the gates correctly side-by-side one another.
A swivel arm 62 is centrally mounted to the axle and is connected to an actuator, not shown, which is similar to the actuator 24 of Figure 3.
Each of the support bases 60 includes a flexible rubber section 64 which is mounted to the axle 54. The rubber section normally causes the respective arm 52 to move in unison with the axle, when the axle rotates, but is sufficiently resilient to permit the axle to rotate relatively to the respective arm if, for any reason, movement of the arm is blocked.
When the actuator is moved in one direction the gates 50A to 50D are raised in unison whereas, with movement of the actuator in the opposite direction, the gates are lowered.
If an ore pebble or particle is trapped by a descending gate then the remaining gates are able to pivot downwardly and close off their respective sections of the gateway aperture. The trapped gate is held open by the pebble and its resilient rubber section 64 deforms and permits relative rotation of the axle and the other gates. Consequently the area through which un-stratified material can flow is reduced.

WE CLAIMS
1. A jigging separator which includes a housing in which is formed at least one compartment and a bed for the compartment, and means forming a discharge opening, from the compartment, higher than the bed.
2. A separator according to claim 1 which includes a wall on a side of the compartment, with the discharge opening being formed in the wall.
3. A separator according to claim 2 wherein the wall forms at least part of an overflow weir from the compartment.
4. A separator according to claim 3 wherein a plurality of the compartments are formed in the housing, and which includes a plurality of the said walls, each wall being located on a side of a respective compartment and forming an overflow weir into a successive compartment and, in the case of the last compartment, from the housing.
5. A separator according to any one of claims 1 to 4 which includes a gate for controlling discharge through the discharge opening.
6. A separator according to claim 5 wherein the gate is rotatably

mounted and includes a concave outer surface which faces the compartment.
7. A separator according to claim 6 wherein the gate includes a plurality of gate sections which are rotatably movable relatively to one another to a limited extent.
8. A separator according to claim 5 wherein the gate is a slide gate.
9. A separator according to any one of claims 5 to 8 which includes a detector which is responsive to the position of an interface between different density fractions in the compartment and which controls movement of the gate.
10. A jigging separator which includes a housing in which is formed at least one compartment, a bed for the compartment, a wall which is located on a side weir from the compartment, a discharge opening, at least part of which is higher than the bed, being formed in the wall, and a gate which is mounted in the discharge opening.
11. A method of extracting a desired fraction from a jigging separator which includes a housing in which is formed at least one compartment,
the method including the step of allowing the desired fraction to flow substantially horizontally from the compartment.
12. A method according to claim 11 wherein the desired fraction is allowed to flow from the compartment at or above the level of a bed of the compartment.
13. A method according to claim 11 or 12 wherein the desired fraction is a relatively denser fraction.
14. A method according to claim 11, 12 or 13 wherein the desired fraction is extracted from the housing at a plurality of locations each of which is associated with a respective compartment in the housing.
15. A method of operating a jigging separator which includes the steps of introducing material into a compartment of the separator, stratifying the material at least into a relatively denser fraction and a less dense fraction, allowing the less dense fraction to flow from the compartment over an overflow weir, and causing the relatively denser fraction to flow substantially horizontally from the compartment through a discharge opening at least part of which is higher than a bed of the compartment.
16. A jigging separator substantially as herein described with
reference to and as illustrated in the accompanying drawings.
17. A method of extracting a desired fraction from a jigging
separator substantially as herein described with reference to the
accompanying drawings.
18. A method of operating a jigging separator substantially as
herein described with reference to the accompanying drawings.