BACKGROUND TO THE INVENTION

This invention relates to an apparatus and method for mineral beneficiation. In particular, but not exclusively, the invention relates to an apparatus and method for mineral beneficiation using a foreign component in a jigging process.

Jigs are well-known and often used in a mineral separation process. A jig is a piece of equipment used to process a mass of material containing particulates or components of different density, size and shape with the objective of separating these particles into product streams according to their density. The separation is achieved by creating a bed of the particles on a screen immersed in fluid, which is usually water although air is also used in pneumatic jigs. Some mechanism is used to cause the fluid in the bed to pulse up and down in a regular patter, which is referred to as the jigging motion. This motion causes the bed of particulates to expand and to consolidate in a cyclical manner resulting in particle segregation by density. The size and shape of particles affect the nature of this segregation. If the segregation is sharp enough, clear strata form that consist primarily of particles with different densities. Particle segregation in a jig can be illustrated by referring to the concentration and density profiles such as those shown in Figures 1 and 2. Figure 1 shows an example of a concentration profile wherein the x axis is the volumetric concentration (C) of particles having a particular density and size and lying in a very thin layer located at a relative height h from the bottom of the bed. In this figure h is defined as H _L ayer/H _B ed where H _Lay er is the height of the layer from the bottom of the bed and H _Be _ is the height of the top of the bed measured from the bottom. Figure 2 shows the density profile corresponding to the concentration profile shown in Figure 1. In Figure 2 the x axis is the average density, which is typically represented as specific gravity, of the layer at relative height h.

In a jigging process the density difference is generally the driving force behind the density segregation of the particles in the jig. The larger the difference between the densities of different components, the smaller the degree to which their profiles overlap and the sharper the degree to which they will be segregated from one another in the jig bed. This is illustrated in Figure 3 which shows the concentration profiles for binary particle mixtures for increasingly larger values of Δ, which is the difference between the density of the heavy particles (Phea y) and the density of the light particles (Plight)- Figure 3 shows that, in binary systems, a large density difference leads to a highly segregated bed with a small zone in the bed where the two profiles overlap. This region or zone of overlap is commonly referred to as a mixed zone. With a small mixed zone, very clean products can be obtained by splitting (also referred to as slicing or cutting) the bed at the appropriate height. For example, see the small mixed zone for Δ = 1.05 in Figure 3 which is indicated by the greyed area. If the bed is split somewhere in the mixed zone the upper part of the bed will form a light product in that it consists primarily of the particles with a lighter density and the lower part of the bed will form a heavy product in that it consists primarily of particles with a heavier density. Further, when Δ decreases the segregation in the bed becomes increasingly poorer and the mixed zone becomes increasingly larger so that the concentration profiles of the light and heavy components increasingly overlap. Consequently, the light and heavy product streams will have increasingly larger proportions of misplaced particles, i.e. light particles in the heavy product and/or heavy particles in the light product. Accordingly, a decrease in Δ results in product streams produced by the jigging operation that are less clean in that they contain a high concentration of misplaced particles. However, if the bed is split above or below the mixed zone, clean products can be produced using a jig. As can be seen from Figure 3, when the specific gravity (SG) differences are below about 0.1 , the mixed zone becomes so large that little if any clean product can be produced. Even in the situations where very little if any clean product can be produced it is still possible to obtain significant segregation of the different density components. From Figure 3 it can be seen that even when the SG difference is as small as 0.05, or even 0.02, some segregation is evident in that the concentration of a component in a layer changes noticeably from the top to the bottom of the bed.

A person familiar with the jigging process will know that particles segregate by size as well as by density. For example, smaller, lighter particles may percolate into layers of larger, heavier particles or smaller, heavier particles may move upwards in the jig to mix with larger, lighter particles. To minimize these size effects, jig operators generally screen particles into relatively narrow size ranges and process the different size ranges in different jigs. Typically the feed to a jig will have a particle size ratio between the largest to smallest particle of about 2 to 3 to one. Experience has shown that the narrower the size range in the feed material, the smaller the size effects confounding particle segregation by density. When the size range is less than about 1.4 to one, the size effect seems to be negligible.

Particle shape also influences segregation in a particle bed. Typically, the more spherically shaped particles tend to migrate more towards the bottom of the bed, while the flatter more sheet-like particles tend to migrate towards the top of the bed. A person familiar with the art of jigging will be familiar with the different types of jigs that are currently being used. Industrial jigs are generally designed to operate in a continuous mode, i.e. they receive feed material continuously, pulsate the bed continuously and split off products continuously. These continuous industrial jigs are therefore referred to as continuous jigs. On the other hand, batch jigs, which are currently used only in laboratories or in small scale operations, are designed and operated differently in that they are charged with a specific batch of feed material. The jig bed is then pulsated to bring about the desired segregation before the bed is split or cut into products by removing horizontal sections from the bed starting from the top.

A jigging operation may produce two or more products. In order to produce two products, the jig bed is split horizontally by selecting a cut height, h _cut , such that all particles in the bed above that height are removed as the light product, i.e. comprising primarily particles of lighter density, and all particles below that height are removed as the heavy product, i.e. comprising primarily particles with heavier densities. The same principle applies to situations where a jig, or a combination of jigs, splits the feed material into three or more products. Two cut points are required to produce three products from a jig, or, more generally, n cut points are required to produce n+1 jig products.

Predominantly, jigs are operated to produce two products. When three products are required, i.e. a light and a heavy product, and a product with densities intermediate between that of the light and heavy products, the usual configuration is to use two jigs in series. The product which has the intermediate densities is typically referred to as a middlings product. When operating two jigs in series the first jig produces the heavy product and the light and middlings product mixed together. The second jig then operates to split this mixed product into a light and a heavier product, the latter constituting the middlings product. ln mineral beneficiation processes such as dense medium separation (DMS) and jigging, the density of a particle is used as a proxy for properties that relate more directly to processing economics. For example, in the iron ore industry the density is used as a proxy for %iron, in that iron-bearing minerals have densities much greater than the gangue minerals from which they need to be separated. As such, the beneficiation process aims to separate the ore into two products, namely a first product comprising of all particles with density greater than the target density, also referred to as the cut density, and an iron content greater than the associated target % iron, and a second product comprising of all particles with a lower density and a lower iron content. In the coal industry, density is a proxy for %ash (and other properties) in that ash-bearing minerals are denser than coal.

However, the proxy is frequently not exact. For example, the relationship between density and %iron in an iron ore becomes blurred if the ore contains two or more iron-bearing minerals that have different compositions and different densities. Similarly, the relationship between density, %ash and other coal properties is complex and is frequently variable because it changes as mining progresses and different parts of the mineral deposit are mined. The same is true about the extent of liberation that is achieved when processing iron ore, or coal, or any other ore, i.e. the relationship between density and the liberation characteristics of a coal or iron ore is complex and variable. The result of either or both of these factors is that specifying the cut density for the beneficiation process is both a design and an operating variable and the beneficiation process must be able to vary the cut density from time to time in order to respond to changes in the characteristics of the feed material and to strive for technical and production efficiency.

Many factors influence the technical performance of a jig. Invariably, the nature of density segregation in a jig bed and the splitting of that bed into two or more products is not perfect or ideal, with some of the lighter components reporting to the heavy product and some of the heavy components reporting to the light product. As such, it is not appropriate to think in terms of separation of the components of different densities, but rather their recovery to a particular product. Recovery is defined as the proportion of that component that reports to a particular product. A high recovery of a light component to the light product corresponds to efficient performance, i.e. an efficient 'separation', and a high recovery of a heavy component to the heavy product similarly corresponds to efficient performance.

In minerals processing, however, operational interest is not limited to just one density component, but to all components with densities below a reference or target density (if the lighter components are the value-bearing ones such as is the case in coal processing for example) or to all components with densities above a reference or target density (if the values are associated with the heavier fractions as in iron ore processing for example). Accordingly, one measure of the quality of jig performance is the recovery of all components above or below the reference or target density. A jig operator aims to obtain a high recovery of that composite component to the appropriate jig product.

A second measure of the quality of jig performance is the composition of the value-bearing product, i.e. its grade. The grade is defined as the proportion of that product that consists of the component or components of interest. The grade also indicates the quality of the product in that the higher the grade of the value-bearing components the greater the quality of the product. As with recovery, operational interest focuses on all density components having densities below or above a reference or target density.

Control of the jig performance is exercised most directly by where the bed is cut, i.e. by the cut height h _cut . If the cut height is increased, the recovery of lighter fractions to the light product decreases. However, recovery of the heavier fractions decreases proportionally to a greater extent which means that the grade of the light product increases. Accordingly, by varying the cut height, the grade of the jig product and the recovery of the targeted components can be varied but with the variation being in tension in that recovery increases at the expense of grade and grade increases at the expense of recovery. Accordingly, the most fundamental indication of the performance of a jig is the grade-recovery relationship or curve which plots the grade and recovery achieved at any particular bed height. An example of a grade-recovery curve is illustrated in Figure 4.

Also shown in Figure 4 are different ways in which improved performance might manifest, namely an improved recovery at the same grade, an improved grade at the same recovery or an improvement in both grade and recovery.

There are several aspects to notice about the performance curve of a jig as illustrated in Figure 4. Firstly, the grade-recovery curve constitutes the operating line or performance curve of a jig, i.e. the range of possible operating points achievable in a jig processing a given feed material. Each point on the curve corresponds to a particular cut height, h _cu t, and to the grade and recovery that would be achieved if the jig bed was cut at that specific height. What that height might be can be determined by referring to curves that show how the grade and recovery in a particular jig product would vary with cut height. Secondly, associated with each point on the grade-recovery curve, i.e. with each cut height, is a cut density, which is the density at which the jig is cutting the feed material into two products. The cut density is defined technically as the density of that density component that has a 50% recovery to one or other of the two products. A third aspect of the performance curve to be noticed is that, if the feed material to a jig changes, its performance curve and the kind of segregation that will occur may also change. A fourth aspect of the performance curve is that both grade and recovery refer either to the cumulative or composite density component -p _ref (meaning all components with density less than p _re f) or to +Pref (meaning all components with densities greater than p _re f).

Another factor that influences the performance of the jigging process is whether the feed material has a discrete or continuous density distribution. The feed material delivered to a jig used in the recycling industry has a discrete density distribution as illustrated in Figure 5 because it consists of well-defined, essentially liberated components such as specific metals, plastics, glass, stone etc, each of which is associated with a specific density. In contrast, the feed material delivered to a jig used in the minerals beneficiation industry invariably is not completely liberated and so has a continuous distribution because it consists of a very large number of different particle classes with different densities over the complete range from the density of the heaviest mineral component to the density of the lightest mineral component. The continuous nature of the density distributions of material processed by jigs in minerals beneficiation is illustrated in Figure 5.

Another factor that affects the performance of a jig is the proportion of near density (ND) or very near density (VND) material in the feed to a jig. ND material is defined as particles that have a density that is close to the cut density in separations based on density differences. Technically, ND is commonly defined as the percentage of a material that has densities in a range of ±0.1 g/cc of the cut density. VND is commonly defined as material having a density in the range ±0.05 g/cc of the cut density. Referring again to Figure 3 it is evident that the concentration profiles of density components that constitute ND and VND components will overlap considerably because they have densities that are only slightly different from each other. For example, the Δ values will be much smaller than 0.1. As a result, the mixed zone associated with these components will be quite extensive making it difficult to separate these components from each other.

When the feed material being processed in a jig has a continuous density distribution all the density components will have adjacent components, i.e. components with densities that are only slightly different. As a result, there will be considerable overlap between the profiles of these components and a large mixed zone of all these components. A large mixed zone in the region of the cut density is a major concern because the segregation of the components in that region is poor and separation of these components when the bed is split in this mixed zone is poor. The situation becomes worse as the proportion of ND or VND material increases. Therefore the % of ND or VND material in the feed to a jig is a useful metric of the degree to which poor segregation and poor separation of density components is to be expected. For example, in the iron ore industry, jigging performance typically becomes problematic if the %ND exceeds about 10%. Typically, South African coal has around 50% ND and separations are so poor that jigs are not commonly used to beneficiate coal in this country. Instead, coal is beneficiated in this country using dense medium separation (D S) which is a more operationally costly process option but produces more precise density separations than conventional jigging.

Another factor to be taken into account when determining jig performance is the bed segregation. The cut height as the primary variable for controlling the performance of a jig is only able to determine where on the grade/recovery curve a jig will operate. The cut height determines the balance struck between grade and recovery. However, the grade-recovery curve itself is determined by the degree to which the bed is segregated according to density. A well segregated bed will achieve a higher grade and recovery combinations than a more poorly segregated bed. To improve jig performance, the segregation in the bed has to be improved. As explained earlier, the nature of the segregation achieved in a jig bed can be assessed by referring to the concentration profiles of the density components in the jig bed. Figure 6 represents an example of the concentration profiles in a jig bed that consisted of 6 discrete components. (The figure is derived from Woollacott et al (2015) and represents simulated data that fits experimental data very well.)

From Figure 6, several points of discussion are noted. Firstly, the concentration profiles are very well defined. This means that the concentration of each component in the thin layer at h is reproduceable, occurs over a well-defined region of the bed, i.e. over a specific range of h, and the profile can be simulated quite accurately, at least for particles that are all the same size. Secondly, it is misleading to think in terms of different density components forming layers or strata within the jig. As can be seen, each component forms a distinct profile that varies in a well- defined way as h varies so that the concentrations of component over that region change in a well-defined way. From Figure 6 it can be seen that as h increases, the concentration of the lightest components increases from zero to its highest value at the top of the bed. The concentration of the densest component in turn decreases from its highest value at the bottom of the bed to a value of zero. The components of intermediate density increase to a peak value and then decrease. Thirdly, when a jig bed is poorly segregated, the problem is not that turbulence or disturbances occur within the jig (which can happen, particularly in continuous jigs) or that the turbulence or disturbances result in mixing or contamination of layers. Instead, the problem is that the profiles of different components, distinct as they are, overlap one another. Fourthly, the feed material of Figure 6 consists of only six discrete components the profiles of which overlap considerably. If the feed material had a continuous density distribution it would consist of a very large number of components each with only slightly different densities. The associated number of profiles and the degree to which they overlap would be very extensive and far greater than the situation shown in Figure 6 where only six discrete components are present. Where the feed material has a continuous density distribution, adjacent components, i.e. those whose densities are only slightly different from each other, would be poorly segregated from each other to an extent similar to the density profiles for systems with Δ = 0.005 as shown in Figure 3.

Some known jigging methods use a foreign component in an attempt to improve jig performance. In these known jigging methods a foreign component is a component that is additional to the feed material which the jig is to process and separate into two or more products. In particular, a known jigging method which uses a through-the-screen concept may employ a ragging which is a foreign component that consists of particles that are significantly larger in size than the particles in the jig feed so that they form a layer at the bottom of the particle bed that allows small heavy particles to pass through the screen supporting the particle bed. This application is not relevant to this invention which relates to over-the-screen jigging applications. Another known jigging method which uses a foreign component is described in detail in de Jong and Dalmijn (1997). The jigging method of de Jong makes use of the concept of utilising a foreign component to form an intermediate layer between the light and heavy fractions in a jig used for processing shredded vehicle scrap, which clearly consists of discrete components.

Although De Jong and Dalmijn suggest that their method of jigging could also be used in the minerals processing industry, they provide no indication as to how this would be achieved. It is imperative to realise that there is a very significant difference between feed material of a jig used in the recycling industry and the feed material of a jig used in the mineral beneficiation industry, something which De Jong and Dalmijn failed to do. The use of a foreign component to improve the performance of a jig in the minerals processing industry requires conditions that are different from those required to improve the performance of a jig in the recycling industry. De Jong and Dalmijn were not aware of and did not disclose what these conditions should be. They also did not have the more advanced conceptual understanding available today about segregation dynamics in a jig that is necessary for identifying what those conditions should be. As a result, aspects of their conceptualization of these dynamics are misleading. For example, the idea that components form layers in the bed, and that these can be separated by using an intermediate foreign component. Consequently, the approach they suggest for using a foreign component to enhance jig performance in the minerals beneficiation is inadequate for a viable implementation of a foreign component to enhance jigging performance in that industry, i.e. for an implementation that is properly grounded conceptually and technically and has the operational flexibility needed to achieve a reliable and consistent improvement in the recovery and/or grade of the jig product. The jigging process proposed by de Jong and Dalmijn is therefore simply not adequate for use in a minerals beneficiation process. It is an object of this invention to alleviate at least some of the problems experienced with existing apparatuses and methods for mineral beneficiation.

It is a further object of this invention to provide an apparatus and method for mineral beneficiation that will provide useful alternatives to existing apparatuses and methods for mineral beneficiation.

SUMMARY OF THE INVENTION

According to the invention there is provided a mineral beneficiating method, in particular a method for producing different product streams from a feed material, which has a continuous density distribution, using a jig, the method including:

adding at least one foreign component to the feed material in the jig, the foreign component being particulate and having a density that is selected to improve the segregation in a particle bed in the jig so that the bed can be cut at a specific height in order to achieve a desired particulate quality in the product stream;

determining the height in the particle bed at which the density in the bed has a value corresponding to the required cut density

removing at least one of the product streams from the feed material by cutting the particle bed in the jig at the determined height; and

removing the foreign component from the cut product stream.

The method may include selecting the foreign component based on the density profile in the particle bed in the jig. Selecting the foreign component may include simulating the density profile in the particle bed and then selecting the foreign component based on the simulated density profile.

Preferably, selecting the foreign component includes the following steps:

i. selecting a reference density; ii. selecting a target cut density;

iii. selecting a density for one foreign component (FC1);

iv. selecting the volumetric proportion of the particle bed that will consist of FC1 ; and

v. simulating the expected density profile for the feed material and volumetric proportion of FC1 , and examining the density profile and the related grade-recovery curve for the resultant product stream.

Selecting the foreign component may further include the following steps:

vi. conducting further simulations with different values of the volumetric proportion of FC1 to optimize the size of this plateau region; and/or

vii. conducting simulations to investigate how the use of more than one foreign component improves the operational flexibility of the jigging operation.

The method may include removing a number of product streams from the particle bed in the jig by cutting the particle bed a corresponding number of times at different cutting heights each of which is indicated by at least one foreign component, and recovering the foreign component from each of the product streams.

Preferably, the foreign components each have a different density in order to obtain product streams of different qualities.

The method may also include using more than one foreign component, each with a different density, to enhance segregation in the region of each cutting height.

The step of recovering the foreign component(s) from the product stream(s) may be carried out by means of at least one material property that differentiates the foreign component(s) from the product stream(s). The at least one material property that differentiates the foreign component(s) from the particles in the product streams may be particle size such that the foreign component(s) is/are removed from the product streams by means of a screening process. The particulate size of the foreign component may be between about 10 to 15% larger than the largest particle size of the particles in the feed material.

Alternatively, the at least one material property that differentiates the foreign component(s) from the product stream(s) may be its/their magnetic property such that the foreign component(s) is/are recovered by means of a magnetic separation process. There is also provided for the at least one material property that differentiates the foreign component(s) from the product stream(s) to be an optical property, such as colour for example.

The method may also include using a dense medium as the jigging fluid. The method may further include maintaining a steady upflow of dense medium through the jig so that particles with a density less than that of the dense medium can be removed as a float product stream. The dense medium may be an aqueous suspension of magnetite or Ferro-Silicon, or a puddle comprising an aqueous slurry of fine ore or non-magnetic mineral particles.

The volumetric percentage of foreign component(s) in the jig is preferably between about 30% and 90%.

The method is preferably carried out using a batch jig.

The step of cutting the particle bed in the jig to remove the product stream(s) may include making one or more horizontal slices through the jig. A product stream may be removed with each horizontal slice through the jig. Consecutive slices are preferably made in different directions so as to remove product streams from different locations on the jig.

The method may also include using more than one batch jig.

There is also provided for the method to be carried out using a continuous jig. More than one continuous jig arranged in series one after the other could also be used. According to the invention there is also provided an apparatus for producing different product streams from a feed material, the apparatus including:

a chamber for housing the feed material,

a screen located in the chamber so as to form a floor of the chamber on which a particle bed is, in use, carried;

means for imparting a jigging motion to the particle bed in the chamber such that the particulates in the particle bed segregate according to their densities;

means for cutting the segregated particulates in the chamber in order to remove a product stream;

and

means for moving the screen of the chamber so that one or more cuts can be made at the desired heights through the particle bed in the chamber so as to achieve the desired quality of particulates in the cut product stream.

The apparatus may include means for determining the average density of the particles at a particular height in the particle bed in the chamber.

The means for cutting the segregated particulates in the chamber is a scraper which is movable in a substantially horizontal direction across the chamber.

The apparatus may have a number of chutes extending from the chamber in which the particulates that have been cut by the scraper is conveyed away from the chamber, thereby allowing multiple product streams to be removed from different locations on the chamber.

In one embodiment the apparatus includes two chutes which are arranged substantially in line and on opposite sides of the chamber so that consecutive cuts are made in substantially opposite directions by moving the scraper in the opposite directions across the chamber, thereby removing product streams from substantially opposite locations on the chamber.

In the preferred embodiment of the apparatus the screen can be raised or lowered with respect to the chamber so as to adjust the height at which each cut is made through the particle bed by moving the screen inside the chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows an example of concentration profiles in a jig bed;

Figure 2 shows an example of a density profile associated with the concentration profiles of Figure 1 ;

Figure 3 illustrates how horizontal strata may intersect the concentration profiles to produce (a) light and heavy products or (b) light, heavy and middling products;

Figure 4 illustrates the grade-recovery relationship

fundamental indication of jigging performance

Figure 5 illustrates discrete and continuous density distributions;

Figure 6 illustrates the concentration profiles in a six component jig bed having specific densities ranging from 1.4 to 2.1 ;

Figure 7 shows a perspective view of a batch jig in accordance with the invention; Figure 8 shows a side view of the jig of Figure 7;

Figure 9 shows a diagrammatic illustration of the top view of the screen cage and slice box indicating the slicing action;

Figure 10 shows a diagrammatic illustration of the side view of slice box indicating the slicing action;

Figure 11 shows diagrammatic illustrations of the front view and corresponding top view of the batch jig of the invention indicating the slicing sequence;

Figure 12 shows a diagrammatic illustration of an alternative embodiment in which the batch jig of the invention has four chutes;

Figure 13 illustrates how the foreign components force apart the concentration profiles of three density fractions so that each fraction concentrates above, below or in-between the zones of highest foreign component concentration to give cleaner products not contaminated by the other density fractions;

Figure 14 illustrates how increasing the proportion of the foreign component forces apart the concentration profiles of other components;

Figure 15 illustrates the effect of bed splitting position; Figure 16 illustrates the relationship between the concentration and density profiles in a foreign component Jig of the invention; illustrates a density probe for determining the density of foreign component in a foreign component jig according to the invention; shows a flow diagram for the foreign component jigging process in accordance with the invention; and shows a process for preparing foreign component particles for a mode 1 foreign component jigging operation that treats material in the size range digest to d _sma iiest in accordance with the invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Referring to the drawings, in which like numerals indicate like features, a non-limiting example of an apparatus in accordance with the invention is generally indicated by reference numeral 10.

Figure 7 shows a perspective view of a schematic representation of the apparatus 10. It is envisaged that the apparatus 10 would be particularly useful in producing different product streams from a feed material which has a continuous density distribution. An example of a feed material which has a continuous density distribution which can be processed by the apparatus 10 is suitably prepared coal or mineral bearing ores. The invention is however not limited to this particular application and could be used in producing product streams from any suitable feed material.

The apparatus 10 shown in Figures 7 and 8 is a high capacity batch jig. The jig 10 has a chamber 12 for housing the feed material from which the product streams are to be separated. A screen cage 14 is located movably inside the chamber 12. The screen cage has a jig screen 14.1 which is supported by two sides 14.2 and 14.3. Referring in particular to Figure 8 it can be seen the screen 14.1 forms the floor of the chamber 12 and, accordingly, carries the bed of particles, in use. The jig screen 14.1 is permeable so as to allow a fluid to pass through it in order to impart the jigging action to the bed. The screen cage 14 fits loosely inside the chamber 12 such that the two sides 14.2 and 14.3 of the screen cage enclose the particle bed on opposite sides and the walls of the chamber 12 enclose the particle bed on the other two sides. As described shortly, the screen cage is able to be lifted into a slicing zone carrying the particle bed with it and allowing slices to be cut from the particle bed as described shortly. However, such movement is only made once the particle bed has been segregated by the jigging action in the jig. Such jigging action generally occurs when the screen cage 14 is in its lowest position within the jigging chamber 12.

In this embodiment of the invention the feed material is typically fed into the chamber 12 on a batch basis to form the particle bed that is to be segregated and split into product streams. The fluid used to facilitate the segregation through the jigging motion is introduced into the chamber 12 so that the particle bed is partially or fully immersed in the fluid.

The batch jig 10 further has means 16 for imparting the jigging action to the feed material in the chamber 12 such that the particulates in the feed material segregate according to their densities. The means 16 for jigging the feed material is mounted below the chamber 12 housing the feed material, in use. In the illustrated embodiment the means for jigging the feed material includes a reciprocating actuator 18 driving a deformable bellows-like connector 20 which is connected to and in fluid communication with the chamber 12. In use, the reciprocating movement of the actuator 18 causes deformation of the connector 20 so that the expansion and contraction of the connector imparts a jigging motion on the fluid and thereby to the feed material inside the chamber 12. It should be understood that the permeability of the jig screen 14.1 allows the jigging motion to be transferred to the feed material in the chamber 12 above the screen 14.1. It is envisaged that the means for generating the pulsing action in the fluid in the jigging chamber 12 in a large, commercial scale embodiment of the invention could be an air chamber located below the screen 14.1 into which and from which air can be introduced or partially exhausted in a regular pattern (the jigging action) and by so doing cause the fluid in the chamber to rise and fall in the same way as is caused by the actuator and bellows system described above.

A person familiar with jigging processes will know that the jigging motion acts to segregate or stratify the particles in the feed material according to their density, the segregation also being influenced by the size and shape of the particles. More about this is said below. However, the stratification is exploited to produce separate product streams which have different material properties by removing horizontal sections of the particle bed. To remove at least one of the desired product streams from the chamber 12 after the feed material inside the chamber 12 has been jigged for a sufficient amount of time, the jig 10 includes a rapid product-removal system having means for cutting the segregated particulates in the chamber 12. The rapid product-removal system allows the batch jig 10 to be used as a high capacity jig in an industrial scale operation. The means for cutting the settled particulates in the chamber 12 is in the form of a scraper 22 which is movable in a substantially horizontal direction across the chamber. The scraper 22 is movable linearly back and forth across the chamber 12. The cutting or slicing action is illustrated by the schematic representations in Figures 9 to 11.

In the schematic representations of Figure 10 the scraper 22 is illustrated as a slice box. The slice box has a central ram plate 22.1 which acts as a two-sided plough or scraper such that as the box moves horizontally backwards or forwards it forces slices from the bed to move over the sidewalls of the chamber 12 and into the product receiving chutes 24.1 and 24.2. The slice box has two side plates 22.2 and 22.3 which run parallel to the ram plate 22.1. The gap between the ram plate 22.1 and each of the side plates 22.2, 22.3 is substantially equal to the width of the chamber 12. When the screen cage 14 is being lifted one of the side plates 22.2, 22.3 is aligned with the top of the chamber and prevents particles from sliding out of the slicing zone. Only when the slice box 22 is moved across the chamber 12 will particles be forced into one of the product receiving chutes 24.1 , 24.2. It can be seen from Figure 10 that the combination of the ram plate 22.1 and one of the side plates 22.2; 22.3 effectively extends upwards the chamber 12. After a slice has been removed, i.e. the slice box 22 has been moved across the bed, the other side plate aligns with the top of the chamber. This is illustrated in Figure 10.

By moving the scraper across the chamber 12 the segregated particulate matter at the height of the scraper and above are removed from the chamber 12. A number of chutes are connected to the chamber 12 and located so that the particulate matter that has been removed from the chamber 12, i.e. the cut product streams, is conveyed away from the chamber by the chutes. In the illustrated embodiment of the batch jig 10 there are two chutes 24.1 and 24.2 which extend from the chamber 12 at two aligned and substantially opposite locations of the chamber 12. The two chutes 24.1 and 24.2 allow two separate product streams to be removed from the chamber by making two consecutive cuts in substantially opposite directions. In the illustrated embodiment of the batch jig 10 the two consecutive cuts are made by moving the scraper 22 in opposite directions across the chamber, thereby removing product streams from substantially opposite locations on the chamber.

In order to remove the desired product streams from the chamber 12 the particle bed must be cut at the specific height as dictated by operating conditions. More about this is said below. To do this, the screen cage 14 with the particle bed it carries is lifted to a height such that the top of the chamber 12 aligns with the desired cut height in the bed. If multiple cuts need to be made this process is repeated so that the screen cage 14 is lifted progressively to each of the cut heights corresponding to the desired cuts. To adjust the height at which a cut is made across the chamber 12 the screen 14.1 is movable with respect to the chamber 12 and scraper 22 using means for moving the jig screen. In the illustrated embodiment of the batch jig 10 the means for raising and lowering the jig screen 14 is in the form of an electric motor 26 driving a threaded bar 28. The threaded bar 28 is connected to the screen cage 14 carrying the screen 14.1. Rotation of the threaded bar 28 in one direction moves the screen cage 14 upwards while rotation in the opposite direction moves the frame and jig screen downwards. Movement of the screen cage 14 inside the chamber 12 allows each cut to be made at the desired level in the chamber so as to achieve the desired quality of particulates in the cut product stream. In larger scale implementations of the batch jig 10 a hydraulic system will typically be used to move the screen 14.1.

Returning now to the illustrated embodiment, during the jigging cycle, the screen cage 14 is generally seated in its lowest position such that jigging can proceed normally to stratify the particles in the bed. When sufficient time has elapsed for the bed to stratify as required, jigging is stopped and the screen cage 14 is lifted into the slicing zone. Because two sides of the screen cage 14 are open, the particle bed will scrape along the sidewalls of the chamber 12 as the screen cage 14 is raised. (To facilitate easy movement of the screen cage 14 as it is raised, the jigging cycle or a minimised version of it, may be continued until the screen cage 14 is in position for slicing to be carried out. Once in the appropriate position in the slicing zone, the scraper or slice box is able to move horizontally between the two sidewalls of the screen cage 14.

Although the illustrated embodiment of the batch jig 10 only has two chutes for removing product streams it is envisaged that in an alternative embodiment not shown in the accompanying drawings there could be more than two chutes. This multiple chute system allows multiple product streams to be removed from different locations on the chamber 12. In such an alternative embodiment, the design of the screen cage 14 and the slice box 22 would need to be modified so as to allow slicing actions in multiple directions. For example, in an embodiment which includes four chutes such as the one illustrated in Figure 12, the scraper is movable along two axes of movement which are substantially perpendicular to one another. In the embodiment of Figure 12, the scraper 22 is forwards and backwards as described above with reference to the jig 10 as well as sideways at right angles to the forwards and backwards movement so that products can be sliced into any chute on the four sides of the chamber 12. It is also envisaged that moveable deflector plates could be added to any of the chutes to divert material scrapped into the chutes in different directions.

Referring again to Figures 9 to 11 , the product removal sequence is a stepwise procedure. First the screen cage 14 is lifted to a position such that the topmost slice, of the appropriate thickness, can be sliced off. The scraper 22 then moves across the bed to remove that slice. The screen cage 14 is then lifted further to a position such that the second slice can be removed and so on. The procedure is repeated until all the particles have been removed from the bed after which the screen cage 14 returns to its lowest position to receive the next batch of particles and the beneficiation process is repeated.

Although the scraper 22 has been described as being movable, it should be understood that the cutting height at which the scraper operates could be adjusted by either moving the scraper downwards or by lifting the particulate bed upwards to and through the cutting zone.

Although it has been stated that the screen cage 14 should be in the lowermost position during the jigging cycle, less vertical movement of the screen cage and more rapid turn-around times between the processing of successive batches of feed material can be achieved if the screen cage 14 is positioned, before each batch of feed material is charged to the chamber 12, at a height corresponding to the anticipated cut height needed to produce the lightest product. This would mean that the slice box 22 would function as a vertical section or extension of the jig chamber 12 and that jigging would occur in this extended chamber. This arrangement would shorten the time needed to lift the screen cage to the appropriate cut height for the first cut to be taken from the particle bed.

In the accompanying representations the horizontal cross-section of the bed depicted in the jig 10 is square. Increased jigging capacities or more efficient operation would be achieved by using circular cross-sections or a combination of circular and square cross-sections. It is envisaged that a circular cross-section would require a rotating plough or scraper to remove slices from the bed.

To facilitate the re-use and recycling of foreign components (which is described below), the jig 10 can be fitted with a recycling compartment on one side that can discharge back into the chamber 12 after the screen cage 14 has been returned to its bottommost position for the next round of jigging. The recycling compartment is positioned such that the scraper 22 discharges the foreign component or the section of the particle bed that contains a high proportion of foreign component into it on one side of the jig. In this embodiment, the compartment for the foreign material could replace one of the chutes.

In use, a foreign component is added to the feed material inside the chamber 12 in order to obtain the desired segregation of particulate matter inside the chamber 12. The foreign component is particulate and has a density that is selected to facilitate the formation of an appropriate density profile in the particle bed so that the segregated feed material can be cut to achieve the desired particulate quality in the cut product stream. More about this is said below. Although the apparatus can be employed without the use of a foreign component, the use of a foreign component is particularly appropriate when the feed material has a continuous density distribution.

A foreign component is a specially prepared component which, either before or during the operation of the jig 10, is added to the chamber 12 separately from or with the feed material being processed. The presence of a foreign component in the jig 10 means that the separating environment is semi-autogenous in nature because that environment is determined both by the components in the feed material and by the foreign component that are added to the chamber 12 of the jig 10.

Each foreign component has the following characteristics:

a) It is particulate in nature, i.e. it comprises of particles.

b) It has a very particular density selected according to the cut densities required for the separation. The exact value of a foreign component density is a design and operational variable as discussed below.

c) The foreign component is foreign to the feed material being separated in the jig in that it is derived and prepared elsewhere. d) The foreign component comprises particles that have sizes that are either (in mode 2 operation) similar to those of the particles to be separated in the jig or (in mode 1 operation) are slightly larger than the largest particles in that material. The different modes of operation are discussed below.

e) The foreign component has one or more separability properties. The separability property is described in greater detail below.

In the preferred method the foreign component is selected to obtain the appropriate density profile in the particle bed in the chamber 12, the appropriate grade-recovery relationship, and the appropriate cut height to achieve product streams of the desired quality. It should therefore be understood that the foreign component is added to improve segregation in the particle bed so as to obtain improved jigging performance. After the product stream has been cut from the chamber 12 the foreign component is removed (separated) from the other particulate material in the cut product stream. More about the recovering of the product stream is said below.

If the feed material being processed has a discrete density distribution, the selection of the density of the foreign component is straight forward: a single foreign component is needed for each cut and its density must be intermediate between the densities of the discrete components that are to be separated. In addition, the density of the foreign component must be adjusted according to its size relative to the average size of particles in the feed material being processed. The size adjustment procedure is described below.

If the feed material has a continuous density distribution, as is invariably the case in minerals beneficiation, the method of selecting the foreign component is more difficult and requires decisions with regard to the number of foreign components that should be used, the density of each foreign component, the proportion of each foreign component relative to each of the other foreign components, and the proportion of all the foreign components relative to the feed material being processed. The factors that influence these decisions include the typical density distribution of the feed material, the proportion of near density and very near density material in the feed, the number of products which the jig must produce and the type of jigging operation being undertaken. In addition, the decisions about the densities of the foreign components must be adjusted if the sizes of the particles of the foreign components are significantly different from the average size of the particles of the feed material being processed.

The method for making these decisions is based on the density profile that is achieved in the particle bed in the chamber 12 when all the relevant operational factors are taken into account. One way of estimating what this density profile will be and what the grade-recovery relationship that will result from that density profile will be is to use a simulation procedure such as the one reported by King (2001). Once the density profile of the particle bed in the chamber has been simulated, the foreign component having the appropriate material properties to achieve the desired segregation of particulate matter in the chamber 12 can be selected. The method of selecting the foreign component typically includes the following steps:

a) Selecting a reference density - p _ref : This is the density used to define the composite density component relevant to the mineral beneficiation operation, i.e. the operation is focused on processing the feed material to produce products with a high proportion of the +p _ref particles in one product stream and a low proportion in the other product streams while at the same time maximizing the recovery of those particles to the relevant product stream. (Alternatively, the same can be said with regard to the -p _ref composite component.)

b) Selecting a target cut density - p _cut : This is the standard cut density that is expected to provide the optimum balance between grade and recovery for the material being processed. In most cases, p _cut will be quite close to p _ref .

c) Selecting a density for one foreign component (FC1) - p _F ci: Initially this density will be equal to or close to p _cut .

d) Selecting the %FC1 , i.e. the volumetric proportion of the particle bed that will consist of FC1 : This proportion will depend on the relative proportion of ND and VND in the typical feed material to be processed. Typical initial values would be 30% to 40%, such as 35% for example.

e) Simulating the expected density profile for the typical feed material and %FC1 and examining the density profile and the related grade- recovery curve for the component -p _ref (or +p _ref )- Referring to Figure 16, experimental and simulated results suggest that in order to obtain good enhancement of jig performance there should be a 'plateau' region in the profile corresponding to the zone of highest concentration of FC1 particles such that the average density in the thin layer at h (i.e. the y axis) does not change very much over a significant region of h.

f) Conducting further simulations with different values of %FC1 to optimize the size of this plateau region. The trade-off to bear in mind here is that while a larger plateau region is obtained with larger values of %FC1 the processing capacity of the jig decreases as %FC1 increases.

g) Having selected a value of p _F ci and %FC1 , conducting simulations to investigate how the use of more than one foreign component per cut can improve the operational flexibility of the jigging operation: As described in the background section, the characteristics of the feed material are likely to change both in the short, medium and longer term of operations. The required operational flexibility is achieved by varying the cut height appropriately and not by varying the proportion and density of the foreign components in the jig. Therefore, the values of p _FC i and %FC1 selected initially may not provide the appropriate operational flexibility or optimum performance and/or additional foreign components may lead to better jig performance.

Three options are available. (These options are discussed in more detail in the section headed Experimental Results Using the Batch Jig of the Invention) The first option is to use two foreign components with densities p ₁ and p ₂ . This spreads the range of possible cut densities from p-t and p ₂ (and a little above and below those densities). The ratio p^ to p ₂ can be skewed towards either pi or p ₂ to suit operating circumstances. The second option is to use three foreign components which have densities, in increasing order, from p p ₂ and p ₃ . This has a similar effect to that achieved by using two foreign components in that the range of possible cut densities is spread from pi to p ₃ (and a little above and below those densities). However, the component with a density p ₂ is the primary component and is in greatest proportion and the variation in cut density will centre on p ₂ . The other two components allow the range of possible cut densities to be spread out from p ₂ in both directions and the extent of this variation can be manipulated by the relative proportion of the other two foreign components. The third option is to use more than three foreign components. This adds little material benefit to the control of the cut density that can be exercised by using three foreign components but may be beneficial in some circumstances.

As mentioned above, the invention is not limited to producing a single product stream. A number of different product streams can be cut from the segregated particulate matter in the chamber 12 by using a number of different foreign components. Typically, in order to cut n number of products from the chamber 12, n-1 number of foreign components are added to the feed material inside the chamber 12. What has been said above about selecting foreign component/s for one cut also applies to each additional cut to be made from the particle bed in chamber 12. From the above description, and in particular the three options discussed above in respect of selecting the foreign component, it should be clear that more than one foreign component could be used per cut. In other words, the foreign component could include a sub-set of foreign components so as to cut each product stream using a sub-set of foreign components of slightly different densities. For example, in the three options mentioned above, the sub-sets included two, three or more than three foreign components each with slightly different densities.

In use, when slicing a product stream from the segregated particulate matter in the chamber 12, some of the foreign component may end in the cut product stream. The method in accordance with the invention therefore includes the step of removing (i.e. separating) the one or more foreign components from the cut product stream. In the event that multiple product streams are cut it would typically be required to recover the one or more foreign component from each of the cut product streams. Irrespective of the number of cut product streams, it is envisaged that the foreign components could be recovered by imparting at least one differentiating material property that differentiates the foreign components from the particulate matter in the product streams. For example, the differentiating material property could be particulate size such that the foreign components are recovered by means of a screening process. By selecting a foreign component which is larger than the largest particle size in the feed material, the product streams could be run through a screen which allows the particulates from the desired product stream to pass to the screen undersize product while removing the larger particulates of the foreign component to the screen oversize product. It is envisaged that the particulate size of the foreign component could be between about 10 to 15% larger than the largest particle size of particles in the feed material.

In the event that particle size is used as differentiating material property the foreign component particles should be only slightly larger so that the size difference does not cause any significant change in the segregation patterns within the jig because of the size effect discussed above. Here the rule of thumb mentioned in the background to the invention is relevant, namely that differences in the size of particles in a jig affects density segregation very little provided the size ratio of large to small particles is less than about 1.4. However, the size of the foreign component particles must be sufficiently larger than the particles being processed in the jig so that the separation of foreign component from other components in the product streams from the jig does not present too difficult a screening operation.

An alternative material property that could be used as the differentiating material property that differentiates the foreign component from the product streams could be its magnetic property. By selecting a magnetic material for the foreign component it can be recovered from the product stream using a magnetic separation process. It should be clear that, for the purposes of removing the foreign component, a magnetic foreign component can only be used where the product stream is non-magnetic. In the event that the product stream includes magnetic particulates that should be retained therein, another differentiating material property has to be used. An example of such other material property is an optical property such as its appearance or texture, and particularly its colour for example. It is envisaged that the application of a contrasting colour to the foreign component will provide a quick and easy method of differentiating between the foreign component and the product stream. For example, where the product stream is in the form of a coal particulate matter the foreign component could be easily identifiable if it is white in colour. An automated separation process could then be used to separate the foreign component from the product stream. It is envisaged that if the foreign component particles are manufactured particles they can be engineered to possess a number of different separability or differentiating properties. In addition to the material properties mentioned above the foreign component could also be different in appearance with respect to fluorescence or non-optical wavelengths in the electromagnetic spectrum. This property could be used as the primary separability property of the foreign component (e.g. instead of being magnetic) or simply as a second separability property that enables a scavenging separation to back up the primary separation of foreign component from other particles in the light or heavy product streams. An additional separability property that could be engineered into such foreign component particles is to make them sensitive to a radiometric detector as a safety measure to prevent loss of any of foreign component particles that may slip through the primary (and secondary) separation processes. Such detection could be used to either stop the belts taking product streams away from the jig or to activate a deflector plate so that the section of the stream in which the detected foreign component particle is located is deflected into a reject bin for later recovery of the foreign component particles.

It should further be understood that the recovery of the foreign component not only purifies the product stream but also allows for the recycling of the foreign component. The recovered foreign component could be re-used in the chamber 12 of the batch jig 10. The recovered foreign component could either be fed back into the chamber 12 continuously or could be batch delivered to the chamber.

The inventor has also identified that the jigging process using one or more foreign components could be improved further by using a 'dense medium' as the fluid in the jig. Such a 'dense medium' is typically a slurry of water mixed with finely ground, high density, magnetic solids such as magnetite or Ferro-Silicon for example. However, a slurry of water and fine particles of any mineral or mineral mixture, such as the ore itself, can also function as a dense medium although it is better to refer to it as 'puddle'. The dense medium or the 'puddle' functions in all ways as the fluid in the chamber 12 mixing with the feed material in the chamber 12 and imparting the jigging action to the particle bed. The dense medium or puddle acts to improve the segregation in the particle bed and hence a better grade-recovery relationship can be obtained for each of the products cut from the particle bed in chamber 12. However, an additional improvement can be obtained if the density of the dense medium or puddle is greater than densities of some of the components in the feed material. In this case, the particulates in the bed which have a density that is less than that of the dense medium or puddle are caused to float, i.e. to separate from the particle bed and float on the surface of the medium in the same way as occurs in dense medium separators. If a continuous flow of dense medium up through the chamber 12 is maintained, those particles that float in this way will overflow from the chamber and can be removed as a float product. The particulates which have a specific gravity that is greater than that of the dense medium will not float in this way but will segregate according to density in the normal way but with a greater degree of segregation because, for example, of the effect of the dense medium or puddle on the 'hindered settling ratios' of particles of different density as explained below.

The hindered settling ratio (HSR) of two particles designated 1 and 2 that have different sizes, d1 and d2 respectively, and different densities, p-, and p ₂ respectively, is given by Equation 1. Equation [1]

In Equation 1 , p _f , is the density of the fluid in the jig and n is an exponent with a value between 1 and 0.5. As can be seen, if the fluid density p _ff is increased, the HSR becomes greater which translates into sharper segregation in the jig. Equation 1 is also useful as a basis for calculating what the effective density of a foreign component would be in a bed of particles that have a different size from the foreign component.

The inventor has also identified the possibility of using more than one batch jig 10 either in series or parallel. Multiple batch jigs 10 could be used to produce multiple product streams or to improve the quality of a particular product stream by reprocessing it in a second jig in which the jigging conditions are different. Such an embodiment is described more fully below.

It is also envisaged that the method of jigging using a foreign component in accordance with the invention could be used in a continuous jigging process. The method in accordance with the invention as described above is therefore not limited to being used in the batch jig 10. In a continuous jig the feed material is fed into the chamber of the jig continuously instead of the batch delivery described above with reference to the jig 10. The foreign components may be added along with the feed material. Again, it should be understood that more than one continuous jig could be used, typically in series one after the other.

From the above description of the invention several aspects to the invention have emerged and will be highlighted below.

According to a first aspect of the invention a foreign component is used in the jig 10 to create a semi-autogenously separating environment. The purpose of the foreign component in the chamber 12 of the jig 10 is to form discrete foreign component zones in the bed such that mineral particles fed into the jig stratify according to their densities and the different density fractions in the feed material concentrate generally above, below and in between the zones formed by the particles of the foreign component. For example, if it is desired to cut a feed material with three discrete components such as 1.3 SG, 1.5 SG and 1.7 SG into three density fractions, then two foreign components could be used such that the 1.3 SG fraction concentrates above the least dense foreign component, the 1.5 SG fraction would concentrate between the two foreign components, and 1.7 SG fraction would concentrate below the more dense foreign component. The principle is illustrated in Figure 13.

By selecting the number and density of the foreign components appropriately, the unavoidable mixed zones that develop in a jig can be engineered such that the mixing that happens in the mixed zones is primarily between the relevant density fraction and the adjacent foreign component particles. In this way, the majority of each density fraction could be removed from the jig in its own product stream that contains only the foreign component particles mixed with it and, importantly, very little if any of the other density fractions mixed with it. Accordingly, after the foreign component particles are removed from that product stream (by exploiting its separability property), the product stream is a clean product and has a high recovery of that density fraction. Figure 13 illustrates the point.

According to a second aspect of the invention it is important that the proportion of foreign component particles in the chamber 12 of the jig is sufficient to force apart the concentration profiles of the density fractions above and below the density of the foreign component. The proportion of the bed that is occupied by foreign component particles must be sufficiently large that the mixed zones in the jig contain primarily and ideally only one of the desired density fractions, obviously mixed with one or more foreign components. In essence, the inclusion of the foreign component particles in the jig forces apart the concentration profiles of mineral components at a particular density so that the profiles of components with a density less than the foreign component's density overlap less with the profiles of components with a density greater than the foreign component's density or overlap to only a small extent. Figure 14 illustrates how an increase in the proportion of foreign component particles in the jig increases the extent to which the concentration profiles of the mineral fractions are forced apart and the extent of the mixed zone decreases. According to a third aspect of the invention the jig bed is split in the region where targeted concentration profiles do not overlap or overlap only a little. The proportions and densities of the foreign component particles determines the stratification patterns in the jig and the extent to which the concentration profiles of the targeted density fractions have been forced apart. The bed is then split to achieve the optimum separation of the required density fractions taking into consideration the balance between a high recovery of a density fraction and the grade or quality of the product stream, i.e. the concentration of that density fraction in the product stream and the degree to which the product stream is not contaminated by the other density fractions. The selection is made according to the density profile in the bed as discussed in greater detail below with reference to the fifth aspect of the invention below. Figure 15 illustrates how the strategy for splitting the bed affects the composition of the jig product streams and the associated recovery of the various components.

Referring to Figure 15, it can be seen that as foreign component particles are subsequently removed from the product streams (as described with reference to the fourth aspect of the invention) the quality of the product streams is assessed by ignoring the foreign components because these are removed from the product streams. Accordingly, cutting at the different positions will achieve the following results:

Cutting at position A: Achieves a 100% grade but 85% recovery of 1.3 SG to the upper layer.

Cutting at position B: Achieves a 100% recovery of 1.3 SG but with some 1.5 SG that reduces the grade.

Cutting at position C: Achieves a middle/upper product free of 1.7 SG but loses some 1.5 SG to the lower layer

Cutting at position D: Achieves a 100% grade of 1.7 SG in the lower layer but some is lost to the middle layer

The fourth aspect of the invention covers the removal of the foreign component particles from the product streams by exploiting the separability property of foreign component particles. As a result of the foreign component being an additional component added to the system, it is possible to engineer a separability property into the foreign component that enables it to be separated from the mineral components in the jig products.

In some situations the contamination of the jig product streams with the foreign component particles may be acceptable in which case, no separation of foreign component particles from other particles is necessary after the jigging process.

The foreign component particles that are separated from other components in the jig product streams should be recycled, i.e. reused if it is a batch operation, or routed back to the jig feed if it is a continuous operation. To minimize the extent of this recycle in continuous jigging, the jig should be operated so as to retain within an intermediate zone in the jig (i.e. the zone between the light product and the heavy product) as much of the foreign component as possible consistent with operational practicalities as described with reference to the seventh aspect below.

According to a fifth aspect of the invention the desired bed splitting position is located by referring to the density profile in the bed. Figure 16 illustrates the relationship between the concentration and density profiles in a foreign component jig in accordance with the invention. Because a large proportion of the bed is occupied by foreign component particles and each foreign component has a unique density, the density profile has one or more characteristic plateaus which correspond to the density of each foreign component. Accordingly, the location of each foreign component and the identification of the optimum splitting position can be determined if the density profile, or key points on that profile, can be determined. This could be achieved by using a density probe as described below with reference to the sixth aspect of the invention.

The sixth aspect of the invention involves the measurement of the density profile of the jig bed by means of a pressure probe. A density profile measuring system that is based on pressure measurement is shown in Figure 17. It includes a vertical tube filled with water that is connected to a pressure gauge. The pressure at any position H from the top of the bed will vary between p _wgH (when the bed is fully consolidated and the particle mass is supported by the screen) and p _be d at H g (H + ΔΗ) (when the bed is fully expanded and fluidized). Here p _w is the density of water and p _be d at H is the density of the bed above H when it is fully fluidized. The latter density is a function of the density of the particle bed above H, p _be d, the packing density of that bed, the density of water, and the amplitude of the jig cycle, ΔΗ. From a knowledge of the jig cycle and its amplitude, the packing density variation in the bed, and the pressure signal from the device, it is possible to determine the density of the bed above H. The density profile can then be determined by moving the probe up and/or down (or both) step wise and taking the required pressure measurements at each step.

Although an alternative method of determining the density profile could be to use X-rays this would be expensive and could be accompanied by an unnecessary health hazard.

A seventh aspect of the invention relates to the use of a continuous jigging process in which one or more zones of foreign component are maintained in the jig to minimize the contamination of jig product streams with foreign component particles and to minimize the recycling of foreign component particles. Foreign component jigging in accordance with the invention requires that the jig bed has a large proportion of foreign component particles. If the bed is split into two parts then all the foreign component particles in the two product streams would need to be separated and recycled. This could mean that a very large recycle relative to feed would need to be maintained. The magnitude of this recycle could be reduced significantly in a continuous operation. Typically, a continuous jig is operated so that a heavy layer is maintained at the bottom of the jig and the heavy component is removed from that layer, sometimes only periodically, in such a way that the thickness of this layer is maintained between an upper and lower limit. Control of the layer thickness could be achieved by means of the density probe discussed above which detects where the top of the heavy layer is in the jig. The lighter components flow over the chamber wall at the product end of the jig. In this mode of operation, an intermediate zone is maintained in the jig that comprises particles with densities intermediate between the density of heavy components withdrawn from the heavy layer and the light components that flow over the chamber wall to form the light product stream. In essence, the light product stream is peeled off the top layers at the product end of the jig and the heavy product is removed from the heavy layer, and an intermediate layer exists between the two that is not intentionally removed as a product at all. However, particles of intermediate density will tend to build up in this layer as jigging progresses and ultimately will either penetrate into the heavy layer and exit with the heavy product, or will be swept up with the lighter particles into the light product.

In order to minimize the contamination of the light and heavy products with foreign component particles, the thickness of the intermediate layer needs to be controlled. Control of the depth of the heavy layer provides, by definition, control of the bottom bound of the intermediate layer. Control of the top of the intermediate layer should be exercised by means of a second density measurement and by withdrawing material from the intermediate layer in order to keep the top of the layer within desired bounds. If material is withdrawn from the layer in the region where the concentration profile peaks, then the intermediate product will have a high concentration of foreign component particles and so could be recycled without separating out other components from the product.

The eighth aspect of the invention relates to the design of a high capacity batch jig for industrial scale operation. Batch jigs such as the jig 10 described above have a number of advantages over continuous jigs. They produce more sharply defined segregation, require far less fluid, allow multiple and more accurate slicing of the bed, can be operated to a true equilibrium condition, and do not suffer from the problem of remixing of layers near the dam at the product end of the jig. In addition, the jig cycle can be varied during the jigging period to optimize segregation and the approach to an equilibrium condition. Further, unlike in continuous jigs, all layers in the batch jig have the same residence time and are subjected to the same jig cycle for the same period of time.

The disadvantage of a conventional batch jig is that the operation is batch- wise and, for large scale operation, a complex system is required to split the bed efficiently into appropriate products. The batch jig 10 in accordance with the invention addresses this disadvantage by using a slicing box structure to remove layers from the bed starting from the top of the bed.

Implementational features of using foreign component particles in jigs a) Process flow diagram and the recycling of foreign component particles: Figure 18 shows a process flow diagram including recycling of foreign component particles. As mentioned above one of the key aspects of foreign component jigging is the removal and recycling of foreign component particles from the various product streams. In a batch jig, this can be done by retaining and reusing the separated foreign component particles. In continuous foreign component jig, a recycling conveyor would be needed as suggested in the flow diagram of Figure 18. b) Modes of operation: it is envisaged that there are four different ways or modes of implementing foreign component jigging. The four different modes are as follows:

i. Mode 1 - when the separability property used for the primary separation of foreign component from other particles in the product stream is screening, i.e. the foreign component particles are larger than the particles being processed in the jig. The preparation of these particles is described in (c) below. ii. Mode 2 - when the separability property used for the primary separation of foreign component particles from other particles is something other than particle size. iii. Mode 3 - mode 2 but with foreign component particles being larger than the particles being processed in the jig. In effect this is a combination of modes 1 and 2.

iv. Mode 4 - no separability property is built into the foreign component particles because the jigging operation does not need them to be separated from other particles in the jig products. (The next section (c) explains this application.)

Preparation of the foreign component feed for Mode 1 operation: foreign component jigging relies on the separability of the foreign component particles so that they can be easily removed from any of the jig product streams produced by the foreign component jig. When foreign component particles are artificial particles which are manufactured elsewhere, the associated separability property, such as magnetism, is built into the particles as part of the manufacturing process. When the separability property is size and the foreign component particles are derived from the mineral feed material being processed, the foreign component must be prepared before that material is fed to the main jigging plant. An appropriate configuration for such a preparation plant is shown in Figure 19.

Continuous foreign component Jigging: it is envisaged that in order to apply foreign component jigging in accordance with the invention to continuous jigging would require firstly that the product streams be processed to remove the foreign component particles which they will inevitably contain. This means that recycling of foreign component particles is required, see Figure 18 for example. To minimize the recycling of the foreign component, and accordingly the expense associated therewith, as much of the foreign component can be retained in the jig as is consistent with processing realities and conditions. This can be done by maintaining and carefully controlling as much as possible of the particles in the foreign component zones in the jig. e) The use of a foreign component jig in accordance with the invention as a dense-medium jig separator: There are references (de Jong & Dalmijn, 1997; Manouchehri, 2007) in the literature that talk about using an intermediate layer so that the jig operates in effect as a dense medium separator. It is possible to describe the foreign component jig of the invention in these terms when only one foreign component is utilised. However, the concept behind foreign component jigging is much more sharply and realistically defined. First, it recognizes that particles with different densities form concentration profiles and that these profiles overlap to an extent determined by the difference in their densities. This is very different from the float/sink idea associated with dense medium separations where all less-dense particles should float and all dense particles should sink. Second, the understanding of stratification, i.e. the nature of the concentration profiles, is based on a model of the stratification process which can predict the extent of overlap of these profiles and hence the quality of separations that can be achieved. Thirdly, the separation of lower- from higher-density particles is understood not only in terms of manipulating the concentration profiles in a jig by introducing foreign component particles to force apart the profiles of the lower/higher density particles but also to use the measured density profile in the bed along with the model's interpretation of that profile in order to provide the set points for the product removal (jig bed slicing) systems. This provides a control capability that is more sophisticated and flexible than is the case with conventional jigging and also with actual dense medium separations.

Applications of the invention a) The basic process application: The basic application of the invention is to separate a feed material ideally so that particles of different densities report to different products or product streams. Figures 18 and 19, aspect 7 and section (d) above describe how this would be done for a continuous operation. Each product from the jig is processed to separate and recycle foreign component particles from the material being processed. In a batch jig of the invention, each slice from the jig bed is processed to separate foreign component particles from the jig products so that the foreign component particles do not contaminate the products and so that they can be re-used.

The washability application - Fractionating a material into density classes: This is best done in a batch jig such as the jig 10 described above where segregation in the jig bed can be optimised and the bed can be split most accurately with little or none of the mixing across layers that occurs in a continuous jig. A suite of foreign component particles is required, each foreign component set having a different density in much the same way that a suite of dense liquids is used to fractionate a material in float-sink analysis. The density of each foreign component will define one density class boundary in the fractionation process. The jig bed will be formed with a very high proportion of the lowest density foreign component (about 30% to 90%, preferably more than 70%), the rest being the feed material to be processed. A high proportion of foreign component particles is needed so that a very high proportion of all components in the jig that have a density greater than the foreign component density segregate well below the zone of the foreign component. The bed is then jigged to equilibrium, typically for 10 to 30 minutes. The density profile needs to be measured in some way to establish the position of the foreign component layer as depicted in Figure 16. This could be done either by using a calibrated X-ray measurement of the jig bed, by the kind of density probe immersed in the bed that is typically utilized in continuous jigs, or by a suitably designed density probe. The bed is then split at a preselected point well into the foreign component layer and the foreign component particles are removed from the top slice. This can be done precisely by raising the jig bed by for example using the screen cage 14 described above. The procedure will require some calibration work to establish exactly how far into the foreign component layer the cut should be made. This product then constitutes the +FC (foreign component) density fraction. The process is then repeated using foreign components with progressively higher densities until the material has been fully fractionated.

This fractionating procedure would be best conducted in a series of jigs. It is more laborious and time consuming than conventional float- sink analysis but has the advantage that it is not restricted in the range of densities that can be fractionated. Typically, for fractionation above about an SG (specific gravity) of 3, float-sink fractionation is difficult and, above 4 or 4.5, it is not possible as heavy liquids or liquid suspensions with such densities are not generally available.

The continuous fractionation system for pre-process fractionation and for process auditing: In this application, it is envisaged that foreign component jigs could be used, either in batch or continuous operation, to fractionate large samples of the feed material which is fed to the main jigging plant. It is believed that this could be done for one of three purposes, namely preparing large quantities of foreign component particles for a main jigging plant as described in implementation feature (c), determining the washability of the feed material to the main jigging plant, and for conducting process audits of the main plant by determining the washability of products from the main plant.

Operation as a cleaner jig: It is envisaged that in this application, conventional or foreign component jigs could be used as roughers and foreign component jigs in accordance with the invention could be used as cleaners acting on the light, and/or heavy and/or middlings products from the roughers. EXPERI ENTAL RESULTS USING THE JIG OF THE INVENTION

Based on the above description it should be clear that the performance of a jig can be improved, i.e. an improved recovery and/or grade of the valuable product streams can be obtained, by including in the chamber, along with the feed material being processed, one or more foreign components of the appropriate kind and in the appropriate proportion. The kind and proportion of the foreign component such that it improves the density segregation in the chamber by manipulating and controlling the density profile in the chamber so that the segregated matter can be cut at an appropriate height to obtain a recovery and/or grade that is significantly higher than would be obtained without the use of the foreign component. The method for selecting the type and proportion of the foreign component is dependent on a number of operational factors. These operational factors include increasing the degree of density segregation, the trade-off between improved segregation and the production capacity of the jig, designing for an appropriate cut density, and facilitating flexibility in the control of the cut density. Each of these factors will now be described in greater detail below.

Increasing the degree of density segregation

The presence of the foreign component modifies the concentration profiles in the chamber so that the profiles of those components which are eventually cut into the product streams are forced apart so that they overlap less than they would in the absence of the foreign component. For this to happen, the densities of the foreign component lie between the densities of those components. Where more than one type of foreign component is to be used per cut, at least one of them has to have this intermediate density.

The degree by which those component profiles are forced apart or segregated depend both on the difference in their densities and on the proportion of foreign component in the chamber, i.e. the foreign component volumetric percentage referred to above. It is also worth noting that near density (ND) and very near density (VND) components in the chamber will have densities close to each other, close to the cut density, and also close to the density of the foreign component (if only one foreign component is used) or to at least one of the foreign components (if more than one foreign component is used). Consequently, the foreign component will force apart the concentration profiles of the ND and VND components only to a small extent. In addition, the profiles of these components and the foreign component will intermingle and overlap extensively in the region where the bed is to be split. If the proportion of the foreign component in the bed is increased, the region where this intermingling occurs will increase so that the ND and VND components are more spread out vertically in the jig bed in the region where the bed is to be split. This provides a means of manipulating the distribution of the ND and VND particles between the product streams cut from the bed. Making the cut higher in the bed will reduce to some degree the concentration and recovery of the heavier ND and VND components in the light product stream cut from the jig. Making the cut lower in the bed will reduce to some degree the concentration and recovery of the lighter ND and VND components in the heavy product stream cut from the jig.

The way the foreign component influences density segregation in the bed can be manipulated by selecting more than one foreign component per cut. The foreign components have slightly different densities. The mix of the multiple foreign components will be dictated by the nature of the feed material to be processed by the jig. For example, a foreign component with a density close to p _ref , the reference density defining the composite component to be recovered from the jig feed, i.e. the component '-ρ _Γβ or '+p _ref ', could be used to establish the cut density of the jig in the region of Pref; while a second component with density less than p _re f could be added to force components lighter than p _ref higher up in the jig bed; while a third foreign component with a density greater than p _ref could be added to force components more dense than p _ref lower down in the jig bed. There is no inherent restriction on the number of foreign components that could be used, but using more than three foreign components does not appear to offer the potential for enhancing density segregation in the bed to an extent greater than can be achieved using three foreign components.

It has been established that by increasing the proportion of foreign component in the bed in order to manipulate the distribution of ND and VND components will also result in an increase in the degree to which the component profiles in the bed are forced apart.

Trade-off between improved segregation and the production capacity of a iia

It follows naturally that an increase in the proportion of the foreign component in a jig bed reduces the amount of material which a jig can process in a given period of time. This affects the number of jigs required to achieve a given production capacity. The minimum proportion of the foreign component in a jig for any significant enhancement of jig performance depends on the %ND and %VND components in the feed material and is typically between about 30% and 40%, such as 35% for example, by volume.

Designing for an appropriate cut density

Because there are many 'adjacent components' in the region where the bed is to be cut into two or more products, and because improvement in jig performance is based on achieving improvements in recoveries and grades, it does not follow that the optimum cut density for a jig should coincide with the reference density that defines the composite component, p _ref . In other words, if a jig operation aims to recover the -p _ref component at a high grade it does not mean that the cut density should be p _ref . It may very well be the case that the cut density achieved should be greater than the reference density (to increase the grade achieved), or less than the reference density (to increase the recovery achieved). Facilitating flexibility in the control of the cut density

Because density is a proxy property and because the characteristics of the material processed by a jigging facility may change in the short term, it must be possible to vary the cut density achieved by the jig, i.e. cut density must be an operating variable. It is not practical in the short term to provide this flexibility by changing the mix of the foreign component in the jig. It is possible to manipulate the proportion of the foreign component in the bed in the medium term but this is not an appropriate means for manipulating the cut density on an ongoing operational basis. Ongoing operational manipulation of the cut density is achieved by controlling the cut height in the bed. This means that varying the height in the bed has to lead to a meaningful shift in the cut density. Such a shift will always occur as it is an inherent feature of the nature of the concentration profiles in the jig bed. However, this inherent shift may be insufficient to provide the kind of operational flexibility that a jigging operation may need, especially when using very high proportions of the foreign component in the bed, and additional measures may be needed to provide that flexibility. It can be provided by choosing the number and density of the foreign components appropriately. Four qualitatively different options are available. The first option is to use a single foreign component which has a density pi close to the desired cut density. This limits the control of the cut density to the inherent variation of cut density around pi that can be obtained by varying the cut height. The second option is to use two foreign components with densities i and p ₂ . This spreads the range of possible cut densities from p _! and p ₂ (and a little above and below those densities). The ratio ρ to p ₂ can be skewed towards either pi or p ₂ to suit operating circumstances. A third option is to use three foreign components which have densities, in increasing order, from p^ p ₂ and p ₃ . This has a similar effect to that achieved by using two foreign components in that the range of possible cut densities is spread from p-, to p ₃ (and a little above and below those densities). However, the component with a density p ₂ is the primary component and is in greatest proportion and the variation in cut density will centre on p ₂ . The other two components allow the range of possible cut densities to be spread out from p ₂ in both directions and the extent of this variation can be manipulated by the relative proportion of the other two foreign components. The fourth option is to use more than three foreign components. This adds little material benefit to the control of the cut density that can be exercised by using three foreign components. However, more than three foreign components may be dictated by other operational factors (specifically the impact of these components on the nature of segregation in the bed) and a side effect of this choice is its effect on the range of control of the cut density ion the jig.

REFERENCES

de Jong, T. P. R., & Dalmijn, W. L. (1997). Improving jigging results of non- ferrous car scrap by application of an intermediate layer. International Journal of Mineral Processing, 49, 59-72.

King, R. P. (2001). Modeling and Simulation of Mineral Processing

Systems. Boston, Oxford: Butterworth Heinmann.

Manouchehri, H. R. (2007). Looking at Shredding Plant Configuration and Its Performance for Developing Shredding Product Stream (An Overview): Jemkontorets Forskning.

Woollacott, L. C, Bwalya, M., & Mabokela, L. (2014). A validation study of the King stratification model, in press.