CENTRIFUGAL SEPARATION OF INTERMIXED PARTICULATE MATERIALS BY SPECIFIC GRAVITY TO FORM A HIGH CONCENTRATION OF THE HEAVIER MATERIALS

This invention relates to a method for centrifugal separation of intermixed particulate materials of the type in which a bed is formed of the separated heavier materials and in which the bed when formed is discharged periodically for collection and particularly to a method by which the concentration of the heavier materials can be improved. BACKGROUND OF THE INVENTION In U.S. Patents 4,608,040, 4,776,833 and 5,222,933 of the present inventor are shown various embodiments of a batch processing system for centrifugal separation of intermixed particulate materials of different specific gravities.

In these patents, the present inventor has shown a centrifuge bowl having a plurality of axially spaced, annular recesses around the peripheral wall of the bowl extending from the base of the bowl to an open mouth of the bowl. Feed materials are deposited into the bowl at the base and run over the peripheral wall so that heavier materials collect within the recesses and the lighter materials carried by a fluidizing liquid are discharged over the open mouth of the bowl.

In each recess in effect forms a collection bed with the separation of the heavier material from the lighter materials occurring within the bed and particularly at the inner surface of the bed where the materials flow across the

inner surface. The separation is enhanced by the injection of fluidizing liquid into each of the recesses through the peripheral wall.

The separation continues until the quantity of collected heavier materials in each of the recesses is sufficient that the separation becomes inefficient and heavier materials begin to be lost with the lighter materials over the open mouth. At this time the batch process is halted and the collected bed, that is the material within the recesses, is discharged from the bowl through a discharge opening at the base of the bowl and is collected. The heavier materials collected in the recesses forms only a proportion of the total material collected so that the result end product from the batch of material process constitutes a further mixture in which the concentration of the heavier materials is increased but certainly does not approach 100% of the batch collected.

Machines of this type can be used in a serial processing system having a first set of machines acting as primary machines from which the batch concentrates are collected and fed to secondary machines which act to carry out a further concentration.

Even after the further concentration of the secondary machine the concentration of heavier materials within the batch is generally insufficient to allow the concentrate to be passed to final processing and yet further concentration techniques are required before final processing can take place.

It is also known from a number of prior patents such as US Patents 1557672 (Doener), 1684870 (Lewis), 3732979 (Gilkey) and 1530758 (Coleman) that a bed of mercury can be located in a centrifuge bowl to effect amalgamation simultaneously with the separation of the heavy particles. However mercury is of

course a toxic compound which should not be released into the lighter materials escaping from the bowl and in addition the mercury cannot be kept in a bowl of the type with fluidizing openings since it will escape outwardly through the openings. SUMMARY OF THE INVENTION

It is one object of the present invention, therefore, to provide an improved concentration method using the batch processing type method described above which reduces the amount of unwanted material in the concentrate and may therefore increase the concentration or percentage of heavier materials in the output product from the concentration method.

According to one aspect of the invention there is provided a method of separating intermixed particulate materials of different specific gravity comprising: providing a centrifuge bowl having a peripheral wall; defining on the peripheral wall at least one axially localized area for collecting heavier materials; rotating the bowl about a longitudinal axis so as to rotate the peripheral wall around the axis to generate centrifugal forces on the intermixed particulate materials at the localized area; arranging the localized area on the peripheral wall such that, when the intermixed particulate materials are fed to the bowl, the intermixed particulate materials pass over the peripheral wall causing heavier particulate materials from the intermixed particulate materials to collect in the localized area on the

peripheral wall while lighter particulate materials pass over the localized area for discharge from the bowl; arranging the localized area on the peripheral wall such that the heavier particulate materials collecting therein form a bed of the heavier particulate materials having an inner surface over which the intermixed particulate materials, when fed, pass and in which separation of the intermixed particulate materials occurs in response to the different specific gravities under the centrifugal forces; prior to feeding the intermixed particulate materials into the bowl, feeding into the bowl a particulate base material in a quantity substantially sufficient to form the bed; subsequent to forming the bed of the particulate base material, feeding the intermixed particulate materials into the bowl so as to effect separation thereof in the bed and so as to collect the heavier particulate materials in the bed while displacing some of the particulate base material and leaving a remaining portion of the particulate base material; continuing to feed the intermixed particulate materials into the bowl to form a batch of the collected heavier particulate materials in the bed with the remaining portion of the particulate base material; and discharging from the bowl the batch of the collected heavier particulate materials in the bed and the remaining portion of the particulate base material for collection.

In one arrangement, the particulate base materials may have similar physical properties to the intermixed particles.

In this arrangement, the particulate base materials may be the final product of the same ore and therefore the centrifugal separator product consists of the collected heavier particulate materials and the remaining portion of the particulate base material where further separation of collected heavier particulate materials and particulate base materials is not necessary, or it may be a byproduct of the same ore.

Thus the seeding can be carried out using the final concentrate so that no separation s necessary. Thus the seeding material can be any one of a number of possible alternatives including silica, and/or garnet and/or course ore and/or the final concentrate.

An example of preloading where further separation is required can be a gold ore where most of gold is fine. The selected preloading material is coarse.

An example of preloading where no further separation is required can be a copper gold ore. Final copper concentrate is used for preloading and the product does not require further separation.

Both methods are applicable for any say type of ore. A study of product recovery, costs, and ease of operation determines which method is more suitable. According to a second aspect of the invention there is provided a method of separating intermixed particulate materials of different specific gravity comprising: providing a centrifuge bowl having a peripheral wall;

defining on the peripheral wall at least one axially localized area for collecting heavier materials; rotating the bowl about a longitudinal axis so as to rotate the peripheral wall around the axis to generate centrifugal forces on the materials at the localized area; arranging the localized area on the peripheral wall such that materials fed to the bowl pass over the peripheral wall causing heavier materials from the intermixed materials to collect in the localized area on the peripheral wall while lighter materials pass over the localized area for discharge from the bowl; arranging the localized area on the peripheral wall such that materials collecting therein form a bed of the materials having an inner surface over which the fed materials pass and in which separation of the materials occurs in response to the different specific gravities under the centrifugal forces; prior to feeding the intermixed materials into the bowl, feeding into the bowl a particulate base material in a quantity substantially sufficient to form the bed; the particulate base material having a character such that it is different from the intermixed materials and such that it is readily separated from the heavier materials using a readily effected separation technique;

Subsequent to forming the bed of the particulate base material, feeding the intermixed materials into the bowl so as to effect separation thereof in the bed and so as to collect the heavier materials in the bed while displacing

some of the particulate base material and leaving a remaining portion of the particulate base material; continuing to feed the materials into the bowl to form a batch of the collected heavier materials in the bed with the remaining portion of the particulate base material; discharging from the bowl the batch of the collected heavier materials in the bed and the remaining portion of the particulate base material for collection; and separating the particulate base material from the collected heavier materials using said separation technique to form a concentrate having a high concentration of the heavier materials.

Preferably the particulate base material is of a character such that it has no binding effect with the heavier materials.

Preferably the particulate base material has a physical characteristic different from specific gravity which allows said readily effected separation technique to be effected without gravitational forces.

Preferably the physical characteristic is ferromagnetism and the separation technique includes applying magnetic forces to the collected materials. Preferably the physical characteristic is particle size and the separation technique includes passing the collected materials through a filter screen.

Preferably the particulate base material separated from the heavier materials is collected and is returned to the bowl to form a bed for a next batch of the heavier materials.

Preferably the axially localized area includes an annular recess in the peripheral wall and wherein the bed is fluidized by the injection of fluidizing liquid through the peripheral wall into the recess.

Preferably the axially localized area includes a plurality of axially spaced, annular recesses in the peripheral wall and wherein the bed is fluidized by the injection of fluidizing liquid through the peripheral wall into the recesses. In a particularly important use of this principle, the particulate base material is a metal ore for use in separation of a metal and the metal ore is shipped to a remote location for smelting such that the material shipped contains primarily the heavier particulate material and the metal ore with a reduced content of gangue. Thus in a metal mine such as copper where ore is produced with contains significant amounts of gold, the gold can be separated using the conventional batch concentration machines such as that manufactured by Knelson Concentrators and in a last one of the concentrators of the process line, the bowl is seeded with the metal ore before operation so that the resulting concentrate contains the gold with the metal ore and only a small proportion or at least a reduced proportion of gangue. This allows the mine to ship for smelting the concentrate which is mainly ore required for smelting rather than gangue thus avoiding shipping materials which are valueless at high shipping cost.

In one preferred arrangement, the metal ore and the collected heavier particulate material are separated at the remote location during smelting using known metallurgical processes.

In many cases the particulate base material is a metal sulphide concentrate and the collected heavier particulate material is gold. However the heavier material may be other high value metals.

In a particular example, the particulate base material is a copper sulphide ore for use in production of copper. BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the invention will now be described in conjunction with the accompanying drawings in which:

Figure 1 is a schematic illustration of the method according to the present invention utilizing a vertical cross sectional view of an example of a machine, the cross sectional view being taken from U.S. Patent 5,222,933 of the present inventor.

Figure 2 is a radial cross sectional view on an enlarged scale of one part only of the bowl of Figure 1 showing schematically the separation of the materials.

Figure 3 is a schematic illustration of a first example of the separator step of Figure 1.

Figure 4 is a similar schematic illustration of a second example of a separator step of Figure 1.

In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION

The details of the machine shown in Figure 1 are available from the above patent and therefore the following description will refer only to the main features of the machine for the convenience of the reader. The machine therefore comprises a bowl 10 mounted for rotation about a longitudinal axis 11 and driven by a drive system 12 which includes bearings carrying a main shaft supporting the bowl. The bowl includes an inner bowl section 13 and an outer bowl section 14. Between the inner and outer bowl sections is provided a chamber 15 which is fed with fluidizing water from a duct 16 within the shaft. The inner bowl 13 has a metal outer wall and a molded inner liner 17 defining a plurality of annular, axially spaced grooves or recesses 18 extending from a base of the bowl to an open mouth 19 of the bowl. The feed duct 20 directs feed material toward the base 21 of the bowl, from which the feed material passes over the open mouths of the grooves 18 to the open mouth. A housing 22 defines a first launder 23 for collecting material discharging from the open mouth for communication to discharge and a second launder 24 for collecting material discharged through an opening 25 at the base of the bowl.

Each recess is fluidized with additional liquid, generally water which passes from the chamber 15 through openings 26 in the peripheral wall of the inner bowl and breaking out at the base of each respective groove. The holes are arranged at angularly spaced positions around the groove.

The supply of intermixed materials is generally indicated at 30 and the materials are screened through a screen 31 to provide a suitable particle size for effective separation. It will of course be appreciated that the intermixed

materials include lighter particles and heavier particles, the latter generally including metals with intention that the heavier particles including the metals be separated out into a concentrate for collection in the launder 24.

In operation the machine is fed with a supply of intermixed particulate materials in slurry form, that is mixed with a fluidizing liquid generally water. The intermixed materials pass through the feed duct 20 and then pass over the peripheral wall of the bowl and particularly over the mouths of the grooves such separation occurs by centrifugal action causing heavier materials to collect within the grooves and lighter materials and liquid to pass over the open mouth of the bowl to discharge.

After a period of time, the separation has reached a point that some heavier materials can no longer collect within the grooves and begin to escape from the bowl with the lighter materials. When the situation is reached, the separation action is halted, the supply closed off and the bowl halted so that the materials collected within the grooves are washed down from the peripheral wall through the opening 25 in the base for collection in the launder 24. This washing action is enhanced by the water flowing through the holes 26.

The above description is a brief description of the operation of the machine and further details can be obtained from the above patent. The above machine is modified by the addition of the following points. A particulate base material is supplied in a supply container 40 fed from a hopper 41. A valve 42 can be operated so that the feed tube 20 receives either the base material 40 or the intermixed materials 30 depending upon the selected position of the valve 42.

The base material 40 is selected so that it is of a particulate nature which can thus be readily collected within the grooves 18. The particulate material is selected so that it does not have any binding characteristics relative to the heavier materials but is simply a particulate material which can therefore be admixed with the heavier materials. The particulate size is selected so that it is compatible with the separation process. The particulate material is selected so that it has a physical characteristic which may be of a metallurgical nature which allows it to be readily separated from the heavier particles using a simple readily operable physical separation technique which does not require operation of a centrifuge.

Thus in one example the particulate base material is formed to a particle size larger than that from the screen 31. Thus the base material can be separated from the heavier particles simply by a screening process as shown schematically in Figure 3. As another example the base material can be ferro magnetic so that it can be separated from the heavier materials by a magnetic separation system schematically indicated in Figure 4.

Other metallurgical methods well known to a person skilled in this art may also be used. In operation, with the bowl emptied from a previous discharge of concentrate from the grooves 18, the valve 42 is operated so that the first material fed through the duct 20 is the base material without any intermixed materials included. The base material then enters the bowl and then fills the grooves 18 sufficient of the base material supply so that the grooves are

substantially wholly filled. The base material can be supplied to the bowl in dried form or can be supplemented with water to allow improved flow characteristics. As soon as the grooves are filled the feed of the base material is halted by operation of the valve 42. In this condition, therefore, the grooves are filled with a base material and the bowl is rotating with the base material maintained within the grooves by the centrifugal forces tending to force the base material into the grooves. This position is shown in Figure 2 where the base material 40 is shown filling each of the grooves up to a surface 45 which is at the mouth of the grooves, that is on a line joining top edges 46, 47 of each groove. With the liquid flow through the openings 26 operating, the liquid is injected to the grooves so as to tend to fluidize the material 40 within the groove and form a fluidized bed of the material. At this time the feed of the intermixed materials is commenced for operating the valve 42 so that the intermixed materials flow over the surfaces 45 and tend to form a separation zone at the surface 45 and partly into the respective grooves so that the materials slowing over the surfaces 45 and flowing within the groove in the fluidized bed tend to form a separation system allowing the heavier particles to move outwardly into the groove under the high centrifugal forces of the rotation of the bowl. The heavier particles are indicated at 50 and the lighter particles indicated at 51 flowing with the liquid 52 toward the open mouth.

The separation is continued in a batch processing system with the heavier particles tending to migrate toward the base of the grooves. However it is not possible to completely fill the grooves with the heavier particles before the

presence of a high number of heavier particles at the surface 45 and cause the loss of some of the heavier particles with the liquid 52.

When this stage is reached, therefore, the batch processing must be halted and at this time a significant portion of the material within the grooves is constituted by the base material 40.

As previously described the feed of intermixed particles is then halted and the bowl halted causing the concentrate within the grooves to be washed down for collection in the launder 24. The concentrate from the launder 24 is then passed to the separator 70 shown schematically in Figure 1 and shown in two examples in Figures 3 and 4. The separator thus using the simple physical separation process generates an output 71 of a concentrate which is substantially wholly formed by the heavier particles and an output 72 which is substantially wholly formed by the base material which is then recycled to the supply 40 of the base material. Alternatively the separation may take place at a remote location using metallurgical processes for example used in smelting of the ore. In this case there will be no recycling of the particulate seeding material since it will be consumed in the process. However the seeding is effected by using the readily available ore which is on site such as metal sulphide or in particular copper sulphide in a copper mining situation.

In Figure 3, the separator 70 comprises a screen 80 which can be vibrated by a drive system 81 and over which the concentrate from the launder 24 is passed allowing the smaller particles defined by the heavier particles to

pass through the screen 80 to a collector 82 while the base material is discharged from the end of the screen into the recycle 72.

In Figure 4 is shown another example of the separator 70 in which the concentrate from the launder 24 is passed over a conveyor 90 with the base material extracted from the conveyor by an electromagnet 91. The base material which is of course ferro magnetic in this example is then removed from the electro magnet so that the concentrate is discharged from the conveyor for collection.

This system, therefore, allows an end product from the above machine which has a concentration greater than that which can be obtained on the conventional process in which the additional material within the grooves is defined by lighter particles which are not readily separable from the heavier particles except by the centrifugal action.

Although the method of the present invention is shown used with the particular example of the above machine, it is also possible to use this technique with any centrifugal machine which includes a separation bed with the separation occurring preferentially within the bed. The use of grooves in the bowl is therefore not essential.

Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without departing from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.