APPARATUS AND METHODS FOR THE SEPARATION OF PARTICULATE MATERIAL

This invention concerns apparatus and methods for the separation of particulate material, in particular, apparatus and methods for the separation of particulate material comprising a mixture of particles of different densities, sizes and/or shapes.

Separation of materials is an activity widely practiced across a range of processing industries. In general, processes are aimed at extracting valuable or useful components from a combination of components for utilization or for further processing.

Specialised methods for achieving this separation based on magnetic properties and electrical conductivity may be applicable in some cases.

However, the majority of separation processes rely on differences in particle size, density, or mass, either through differential behaviour in air using cyclones or other inertial classifiers, or by behaviour in dense-phase systems such as fluidised beds. "Wet" methods such as hydro-cyclones, sedimentation or froth flotation may also be used.

However, all of these processes fail to produce a complete separation within a narrow property range, certainly within a continuous process. At present the effectiveness of separation, particularly in a single process, falls considerably for particle sizes below about lOOμm for processing in air and about 50μm for wet processing.

Many processes result in the generation of large quantities of fine particulates, which are often treated as a waste stream since recovery of valuable components is often uneconomic, inefficient or technically challenging. However, increasing pressure on world resources is driving

the requirement to be able to extract valuable or useful components from increasingly fine materials. Therefore, there is a requirement for processes to be able to carry out separations of mixtures of fine particulates .

One approach to the separation of particulate mixtures, is the application of vibrations which cause the different types of particles in a mixture to separate into strata. There is a substantial body of knowledge on separation of particulate mixtures using vibrations, but a clear understanding of many of the physical processes involved is still lacking.

It is well known that vibration causes the movement of larger particles to the top of a bed of finer grains, commonly referred to as the "Brazil Nut Effect" (BNE).

However, more recently, it has been found that vibrations can also cause the separation of similar size particles of different density, such as glass and bronze or ilmenite from sand. It has been found that fine particles of less than 300μm will segregate into layers under vibration provided there is enough difference in density of the two materials . To separate particles by density having a size greater than 300 μm requires a more viscous fluid than air. Such larger particles have been separated using water, which has a viscosity approximately fifty times that of air, allowing the particle size range of separation to be increased to 1.2 mm.

An approach for the separation of particles that uses this effect is described in International patent application No: WO 03028877, which is incorporated herein by reference. This document describes the concept of vibrating a particulate mixture in a box to induce separation of the particles into strata and apparatus for removal of the stratified material. A problem with the apparatus and method described in WO 03028877 is

that it is very difficult to utilise practically due to the technical issues associated with getting materials both into and out of the apparatus in a continuous manner, which is key for apparatus to be of commercial value. In particular, the apparatus described in WO 03028877 requires settled and stable strata before any extraction of the material can take place. However, the continuous feed of material into the box can disturb the formation of strata, as can the conduits that extend into the bed of material. Furthermore, the sucking of separated material out of the beds via the conduits is difficult to implement and control and altering the fluid flow through the bed could interfere with the separation mechanism.

It has also been shown that irregular shape particles also separate into two layers under vibration.

Accordingly, it is known that vibrations can be used to separate a particulate mixture based on density, size and/or shape of the particles. However, none of this work provides a practical system for the separation of materials .

According to a first aspect of the invention there is provided apparatus for separating a particulate mixture comprising a support for the particulate mixture, a vibrator for subjecting the support to linear vibration thereby to effect separation of the particulate mixture into strata one above the other, each stratum being rich in one particle type, a barrier for blocking the particles from an upper stratum from flowing past the barrier whilst allowing particles from lower a stratum to flow past the barrier.

The invention therefore provides apparatus that can separate a particulate mixture in a continuous process. In particular, the barrier allows particles in one stratum to flow continuously from the apparatus,

providing means to continuously collect particles of one particle type that have been separated by the vibrations.

The barrier may be arranged such that gravity causes the particles of the lower stratum to flow past the barrier. In particular, the barrier may be arranged to allow the flow of particles from the lower stratum underneath the barrier. In this way, there is no need to recreate artificial forces, such as suction, for the extraction of particles from stratum.

The apparatus may comprise a cell for receiving the particulate mixture. The barrier may define a lower outlet from the cell for particles of the lower stratum. Alternatively, the barrier may divide the cell into chambers, the barrier defining an outlet for particles of the lower stratum to flow from one chamber to another chamber. The barrier may be movable to alter the size of the outlet. In this way, the barrier can be used to accurately control the outflow of particles, which in turn can affect the purity of the separated particles.

The apparatus may be provided with a further outlet for particles of the upper stratum. This further outlet may be provided in a wall of the cell.

According to a second aspect of the invention there is provided apparatus for separating a particulate mixture comprising a support having a planar surface for supporting the particulate mixture, the planar surface being at an angle to the horizontal, a vibrator for subjecting the planar support to linear vibration thereby to effect separation of the particulate mixture into strata, each stratum being rich in one particle type, a barrier for blocking the particles in one stratum from flowing past the barrier whilst allowing the flow of particles in another stratum to flow past the barrier.

The invention therefore provides alternative apparatus that can separate a particulate mixture in a continuous process. In particular, in both apparatus, a barrier allows particles in one stratum to flow continuously from the apparatus, providing means to continuously collect particles of one particle type that have been separated by the vibrations. Therefore, particulate mixture can be continuously deposited on the support to replace the particles that flow past the barrier.

The apparatus may be arranged such that during vibration particles in one stratum flow from the support past the barrier and particles from another stratum leave the support at an upper end of the planar surface. By the particles of each stratum leaving the support at the bottom and top of the planar surface, the apparatus can separate particulate mixtures having particles of a size of any one of a broad range of particle sizes.

The barrier may act as a weir and may be adjustable to alter the height of the weir. In this way, the barrier can be used to accurately control the outflow of particles, which in turn can affect the purity of the separated particles. The weir prevents all of the particulate mixture flowing off of a lower end of the support surface. A further weir or a wall may be provided at the upper end of the support surface. The provision of a further weir can increase the purity of the product (particles) dispensed from the upper end of the slope.

Alternatively, the barrier may be arranged to allow the flow of particles from the lower stratum underneath the barrier.

The apparatus may comprise means for feeding particulate mixture onto the surface of the support at a feed point. The position on the support upon which particulate mixture is fed significantly affects the movement of particles during vibration of the support and consequentially the

separation of the particles into strata and the purity of the separated product. In use, the particulate mixture feed onto the support surface forms a heap having a peak. The location of the peak can vary depending upon a number of factors, including the types of material being separated, however, it is the position of the feed point relative to the peak of the heap that influences the movement of particles during vibration and the subsequent separation.

Accordingly, in one arrangement, the feed point of the particulate mixture is located near a lower end of the support surface. In this arrangement, the particles flowing over the barrier comprise a high proportion of all particle types of the particulate mixture, however, the particles leaving the support at the upper end of the support surface have a high percentage of one particle type.

In a different embodiment, the feed point of the particulate mixture is located away from a lower end of the support surface (i.e. centrally along the support surface or above) such that a peak of the particulate mixture between the feed point and the upper end of the support surface. This arrangement, results in a purer product being dispensed over the barrier, however a greater contamination of the product dispensed at the top of the support surface can occur.

In yet another arrangement, the feed point is located near the upper end of the support surface such that a peak of the particulate mixture is formed between the feed point and a lower end of the support surface.

This arrangement reverses the particle types reporting to the upper and lower ends of the support surface compared with the other arrangements, which may be desirable in order that the particles that make up the higher proportion of the particulate mixture reports to the lower end of the support surface.

The surface of the support may be at an angle to the horizontal of between 0 and 45°. The greater the angle of the support surface, the deeper the heap (bed) of particulate mixture can be. However, it is believed that in most circumstances, the chief separation effects occur at the surface of the bed and a deep bed would not be advantageous. In general, only a slight angle may be required in order to break up the symmetry of the bed and the movement of the particles. Furthermore, a smaller angle for the support surface reduces the energy that is required for particles to travel up the support surface. As the energy increases for particles to travel up the support surface, the purity of the product dispensed at the lower end of the support surface decreases. Accordingly, in a preferred embodiment, the angle of the support surface to the horizontal is between 0 to 25° and preferably, between 10 and 25°. It is believed that these angles provide a satisfactory balance between the energy required for the particles to travel up the support surface, while ensuring that adequate asymmetry in movement of the particles is achieved.

The apparatus may comprise a cell for receiving the particulate mixture.

Preferably, the cell (of either the first aspect or second aspect of the invention) is narrow enough to reduce movement of the particles across the width of the cell to the extent that the level of the formed strata is substantially the same across the width of the cell (even if the level of the strata varies across the cells length) . In one arrangement, the width of the cell is of the order of a 100 millimetres, or less, preferably 50 millimetres or less and may be 10 mm. In this way, the apparatus acts as a 2-dimensional separator with the movement of the particles along the length and height of the cell dominating over movement across the width of the cell.

The vibrator may be arranged to vibrate the support at a frequency and amplitude such that differential damping forces on each particle type causes the particles to separate into strata, each stratum being rich in one particle type. In one embodiment, the frequency may be between 10 and

120Hz and F (which is the ratio of the maximum acceleration of the container to the acceleration due to gravity, given by F = Aω ² /g where A is the amplitude of the vibration, ω is the frequency of vibration and g is the acceleration due to gravity) may be between 2 and 10. It is believed that these values of frequency and gamma produce the desired strata.

The apparatus preferably comprises a fluid in which the particulate mixture is vibrated, the fluid having the required viscosity to produce differential damping forces great enough to achieve separation of the particulate material into strata. For particulate mixture having particle sizes of less than 300μm the fluid can be a gas, preferably air. However for particulate mixtures comprising larger particle sizes, the fluid requires a greater viscosity than air. For example, to separate mixture comprising particles having a size of the order of 1.2mm, the fluid may be water.

The vibrator may be tunable to provide the required frequency and gamma (F) of vibration. The vibrator may comprise a speaker, preferably, a pair of opposed speakers.

According to a third aspect of the invention there is provided apparatus for separating a particulate mixture comprising a support having a single planar surface for supporting particulate mixture, the planar surface being at an angle to the horizontal, a vibrator for subjecting the planar surface to linear vibration thereby to effect separation of the particulate mixture into strata, each stratum being rich in one particle type, a barrier at a

lower end of the surface for blocking the flow of particles in one stratum whilst allowing the flow of particles in another stratum.

According to a fourth aspect of the invention there is provided apparatus for separating a particulate mixture comprising a support having a planar surface for supporting particulate mixture, the surface extending from a first outlet to a second outlet and being at an angle to the horizontal, a vibrator for subjecting the planar surface to linear vibration thereby to effect separation of the particulate mixture into strata, each stratum being rich in one particle type, a barrier at a lower end of the surface for blocking the flow of particles in one stratum whilst allowing the flow of particles in another stratum into one of the outlets.

According to a fifth aspect of the invention there is provided apparatus for separating a particulate mixture comprising a support for the particulate mixture, a vibrator for subjecting the support to linear vibration at a frequency and amplitude such that differential damping forces on each particle type causes the particles to separate into strata, each stratum being rich in one particle type, and a barrier for blocking the flow of particles from one stratum whilst allowing the flow of particles in another stratum.

According to a sixth aspect of the invention there is provided a method for separating a particulate mixture comprising dispensing a particulate mixture onto a support, subjecting the support to linear vibrations to cause the particulate mixture to separate into strata, each stratum rich in at least one particle type, and blocking with a barrier particles from an upper stratum from flowing past the barrier whilst allowing particles in a lower stratum to flow past the barrier.

The method may comprise continuously dispensing particulate mixture onto the support. In this way, particles that are allowed to flow from the support are replaced.

According to a seventh aspect of the invention there is provided a method for separating a particulate mixture comprising dispensing a particulate mixture onto a planar surface of a support, the planar surface being at an angle to the horizontal, subjecting the support to linear vibration to effect separation of the particulate mixture into strata, each stratum being rich in one particle type, and, at a lower end of the planar surface, blocking with a barrier particles in one stratum from flowing past the barrier whilst allowing particles in another stratum flow past the barrier.

The method may comprise allowing particles to leave the support at an upper end of the planar surface. In this way, different particle types can be collected from the lower and upper end of the support surface.

The method may comprise continuously feeding particulate mixture onto the surface of the support at a feed point. In one arrangement, the feed point of the particulate mixture is located near a lower end of the support surface. In a different arrangement, the feed point of the particulate mixture is located away from a lower end of the support surface (i.e. centrally along the support surface or above) with a peak formed by the particulate mixture between the feed point and the upper end of the support surface. In yet another arrangement, the feed point is located near the upper end of the support surface with a peak formed by the particulate mixture between the feed point and a lower end of the support surface.

The method according to the sixth or seventh aspects of the invention may comprise subjecting the support to vibrations at a frequency and

amplitude such that differential damping forces on each particle type causes the particles to separate into strata, each stratum being rich in one particle type. In one embodiment, the frequency may be between 10 and 120Hz and F (which is the ratio of the maximum acceleration of the container to the acceleration due to gravity, given by F = Aω ² /g) may be between 2 and 10. It is believed that these values of frequency and gamma produce the desired strata.

The method may comprise selecting a fluid in which the particulate mixture is vibrated, the fluid having the required viscosity such that the differential damping forces are great enough to achieve separation of the particulate material into strata. For particulate mixture having particle sizes of less than 300μm the fluid may be a gas, preferably air. However for particulate mixtures comprising larger particle sizes, the fluid requires a greater viscosity than air. For example, to particulate mixture comprising particles having a size of the order of 1.2mm, the fluid may be water.

According to a an eighth aspect of the invention there is provided a method of separating particulate mixture using the apparatus of any one of the first to fifth aspects of the invention, the method comprising re- circulating particles of one particle type dispensed from the apparatus back into the apparatus. In this way, the method continuously refines the particulate mixture until the desired purity of particle type is achieved.

According to a ninth aspect of the invention there is provided a method for separating a particulate mixture comprising separating the particulate mixture by sequentially using apparatus of any one of the first to fifth aspects of the invention to progressively refine the particulate mixture.

According to a tenth aspect of the invention there is provided a method of separating materials comprising granulating the material to form a particulate mixture having an average particle size of less than lOOμm and separating the particulate mixture using the method according to the sixth or seventh aspect of the invention.

This method allows valuable materials, such as metals, to be liberated from a combination of materials, even for large items, such as circuit boards or electric wires.

According to a eleventh aspect of the invention there is provided a method of separating particles comprising dispensing a particulate mixture onto a support, subjecting the support to linear vibrations to cause the particulate mixture to separate into strata based on the density of the particles, and blocking the flow of particles of a certain density while allowing the flow of particles of a different density.

Embodiments of the invention will now be described, by example only, with reference to the accompanying drawings, in which :-

FIGURE 1 shows a perspective view of a first embodiment of apparatus according to the invention;

FIGURE 2 shows a schematic view of the apparatus according to the first embodiment of the invention;

FIGURE 2a to 2c are phase diagrams showing the effect of the bed depth on separation of the particulate material into stratum;

FIGURE 3 shows apparatus according to the first embodiment of the invention in use;

FIGURE 4 shows a schematic view of apparatus according to a second embodiment of the invention;

FIGURE 5 shows apparatus according to the second embodiment of the invention in use, wherein the feed point is between the peak of the particulate material and the lower end of the support surface;

FIGURE 6 shows a further view of apparatus according to the second embodiment of the invention in use, wherein the feed point is between the peak of the particulate material and an upper end of the support surface;

FIGURE 7 is a table showing the percentage of bronze dispensed at each end of the support surface for different feed points during the separation of a bronze and glass particulate mixture;

FIGURE 8 is a table showing the ratio of bronze dispensed at each end of the support surface for different percentages of bronze feed;

FIGURE 9 is a table showing the effect of angle of the support slope on the percentage of bronze dispensed at the upper and lower ends of the support surface;

FIGURE 10a shows apparatus according to the invention in which illmenite has been separated from a mixture of sand and illmenite;

FIGURE 11a is a graph showing the composition of a granulated mixture of electric wires before separation, the particles granulated to a size of 106 to 212 μm;

FIGURE lib is a graph showing the composition of the granulated mixture either section of the apparatus after separation;

FIGURE lie is a graph showing the composition of a granulated mixture of electric wires before separation, the particles granulated to a size of 212 to 425μm;

FIGURE Hd is a graph showing the composition if the granulated mixture in each section of the apparatus after separation;

FIGURE 12 is a table detailing the composition of a granulated mixture formed from a circuit board;

FIGURE 13a is a graph showing the composition of the granulated mixture in the apparatus before separation, the particles granulated to a size of 300 to 425μm;

FIGURE 13b is a graph showing the composition of the granulated mixture of Figure 13a in each section of the apparatus after separation;

FIGURE 13c is a graph showing the composition of the granulated mixture in the apparatus before separation, the particles granulated to a size of 212 to 300μm;

FIGURE 13d is a graph showing the composition of the granulated mixture of Figure 13c in each section of the apparatus after separation;

FIGURE 13e is a graph showing the composition of the granulated mixture in the apparatus before separation, the particles granulated to a size of 150 to 212μm;

FIGURE 13f is a graph showing the composition of the granulated mixture of Figure 13e in each section of the apparatus after separation;

FIGURE 14 shows apparatus of the invention after separation of particles by size, a blown up portion of the Figure showing the particles separated;

FIGURE 15 is a graph showing the size distribution of particles in each section of the apparatus;

FIGURES 16a and 16b are graphs illustrating the separation of coal and pyrite using the separation method of the invention;

FIGURE 17a and 17b show further embodiments of apparatus according to the invention; and

FIGURE 18a and 18b are bar graphs showing the effect of cell width on purity of separation.

The first embodiment of the invention shown in Figures 1 and 2 will be referred to hereinafter as the 'partitioned cell apparatus' . This apparatus comprises a rectangular cell (i.e. compartment) 1 having a support surface 2, sidewalls, 10, 11, 12 and 13 and a central partition (barrier) 3 that divides the cell into two chambers 4 and 5. The partition 3 can be fixed relative to the support surface 2 such that it moves with the support surface 2 as vertical vibrations are delivered. However, the partition 3 can be raised and lowered to alter the size of the gap 6 between the end of the barrier 3 and the support surface 2. Altering the size of the gap 6 alters the flow of material between the chambers. Fixing the partition 3 at different positions on the support surface 2 can alter the relative widths of the two chambers 4 and 5.

A first outlet 6 a is provided for the dispensing particles from the left hand chamber 4 and a second outlet 7 provides is for dispensing particles from the right hand chamber 5.

In this embodiment, the width of sidewalls 12 and 13 is 50mm, the length of sidewalls 10, 11 350mm and the cell has a height of 200mm, however it will be understood that other suitable dimensions of the cell could be used.

Means (not shown) are used for feeding particulate mixture into the left hand chamber 4. Normally the bed of feed material would be relatively deep whilst the partition 3 results in the bed of material in the product (right hand) chamber 5 being relatively thin. Feed material bed depth and product extraction can be controlled via the outlets 6a, 7 at each end of the cell 1. The depth of bed chosen will be dependent on, amongst other things, whether the useful/valuable products represent a minor or major component of the particulate mixture being fed into the apparatus.

The partition cell is efficient when the bed depth on the left hand side chamber is sufficiently bigger than the size of the gap below the partition gate so that when materials flow to the next compartment the bed does not spread into a single large bed and behave as in a cell without partition.

The cell 1 is arranged with a tunable vibrator (not shown) , for example a speaker or a pair of opposed speakers, such that the cell 1 can be vibrated at a selected frequency and amplitude. Vibration can be sine waveform, although other waveforms might also be suitable. The frequency and amplitude of the vibrations is dependent on the material to be separated but, in general, the frequency range is between 20 to 200Hz and T is between 2 and 18.

The apparatus described can be used to separate a continuous stream of mixed granular material into multiple products. The particles can be separated on the basis of particle density.

The partitioned cell apparatus is generally operated with the support surface 2 in a horizontal arrangement so that the walls of the cell 1 are vertical. However, separations can also be carried out with the support surface 2 of the container at an angle as shown in Figure 3.

Figure 2 illustrates vertical (linear) vibration being delivered to the cell with the support surface horizontal.

A particulate mixture is fed into the left hand chamber 4 on a continuous or batch basis. During vibration the particulate mixture separates into strata on the basis of density, size and/or shape. Particles forming a stratum in the left hand chamber 5 can flow under the partition 3 into the right hand chamber and out of the cell 1 via outlet 7 where the particles are collected. The level of particulate mixture in the left hand chamber 4 might be regulated using a variable height outlet 6a. In this type of arrangement the particulate mixture and resultant products might be fed into and removed from the cell 1 on a continuous basis.

Now referring to Figures 2a to 2c, Figure 2a is a phase diagram showing the frequency and T of vibration at which a particulate mixture separates when the gap is 3mm and the bed depth is 30mm. A, is a region at which good separation of the particulate mixture occurs, area B for separation and area C no separation. Accordingly, for a bed depth of 30mm separation can be achieved for a reasonable range of T and frequency .

Figure 2b is a similar graph but wherein the bed depth is 20mm. As can be seen the area, A, at which separation occurs is larger than in Figure 2a.

Figure 2c is a graph for a bed depth of 10mm. As can be seen, for this bed depth, no adequate separation is achieved.

It has been concluded that the bed height should be kept at least 3 to 30 times and particularly seven times greater that the size of gap 6.

A second embodiment of the invention will now be described with reference to Figure 4. In this embodiment, the apparatus comprises a support surface 102 driven by a vertical waveform at a selected frequency and amplitude. The support surface 102 may be positioned at an angle, θ, between 0 and 45° . The vibrating bed may be interrupted by a partition barrier, 103, creating a gap near the surface of the support surface 120.

Weirs (barriers) 104 and 105 located at upper and lower ends of the support surface 102 and are adjustable in the vertical direction to regulate flow of particles from the support surface 102. The weirs 104, 105 may be shaped or may be a simple vertical divider feeding into either a container, another separation platform or for conveyance into further processing systems. The heights of the side weirs control the depth of the bed of the particulate mixture on the support surface 102. Particles travel both horizontally and vertically through the bed depending on the convection currents created by the vibration and the characteristics of the particle. The front and back (as drawn) of the apparatus is contained by walls (not shown in Figure 4 but shown in Figure 5 ) that form a cell to contain the contents of the bed.

The apparatus is arranged so that it is mounted onto a vibrating platform (not shown) . This enables precise control over the frequency and amplitude of vibration delivered to the separation cell. Generally the apparatus is set to vibrate prior to any feed material being loaded onto the bed, although it can also be stopped and restarted as required. A particulate mixture can be deposited at any point along the length of the bed.

Separation of a bronze and glass particulate mixture will now be described. The mixed material is fed from above the vibrating surface 102. As it lands it undergoes separation with the bronze forming a layer along the surface 102. This layer remains and the bronze cascades down the slope. The layer has upper surface that is closer to the horizontal than a lower interface between the bronze and glass. This can be seen in Figure 5. The glass flows underneath the wedge shaped bronze layer and down at the end weir 107. As it reaches the vibrating surface 102, it then travels back up the support surface 102 until it reaches an upward convection current underneath the peak of the particulate mixture.

As it travels under the bronze wedge, some bronze can become entrained in the glass, either from the interface or as bronze that did not successfully separate when the feed landed on the bed surface. This bronze quickly moves back up the bed to the bronze layer as it is carried up the along the support surface. The bronze layer convects separately. The free grains on the surface of the bronze layer, travelling down the slope travel over the weir 107. From here they can either be collected. An amount of glass can also report to this exit point. The amount of glass varies depending on the feed point, vibration conditions and weir heights.

The glass travels up to the surface of the peak and then cascades down the slopes. One slope leads to the second weir 106 collection point and the

other back down towards the bronze layer. As it reaches the bronze layer it travels underneath and recirculates .

The feed point can dramatically affect which product streams report to which weir exit and the purity of each product. If the feed is located above the formed bronze layer, it causes interference. The bronze and glass landing on top of the bronze layer disturbs the bronze layer as the glass percolates through. As the grains at the surface of the bed at this feed point are travelling down the slope, the bronze and glass mixture can get entrained on or near the surface and report directly into the product stream, increasing the proportion of glass. In this set up, the bronze rich product reports to the low end collection point and the glass to the high end collection point. The glass fraction recovered is very pure as little to no bronze convects up the slope. However, as the feed is near the low exit point, a larger flow rate at this exit occurs as the glass is carried by the bronze over the weir 107 without spending any time within the bed to achieve separation.

If the feed is located in a middle point along the bed (as shown in Figure 5) , although this is still on the major downward slope and the surface grains still have a horizontal component. However at this point the feed point is before the beginning of the triangular bronze layer. This gives the glass and bronze an opportunity to separate. The bronze continues down the surface of the bronze layer and reports to the exit at weir 107 while the glass passes under the bronze as outlined before.

Feeding the mixture near the top of the slope of the particulate mixture has different results depending on the location of the peak. If the peak is located between the feed point and the upper end of the support surface 102, then separation is similar to feeding midway along the bed. This can lead to purer products as the bronze and glass have a longer journey down

the slope before meeting the edge of the bronze layer allowing for better separation. The glass reports to the exit at the upper end of the support surface 102. Contamination of the glass recovered can occur as feeding near the peak means that some of the mixture immediately becomes part of the bed and is carried upwards to the top of the peak. Any bronze here can end up in either of the product streams as once at the top of the bed, it is unlikely to be reincorporated.

Feeding onto the peak results in bronze and glass reporting to the exits at both ends of the support surface 102. If the feed location is between the exit at the upper end of the support surface 102 and the peak, the separated bronze travels down the minor slope and reports to the exit at the upper end of the support surface 102. The glass meanwhile circulates underneath and reports to the low side. There is a potential benefit to this arrangement as removing the glass at the low side may provide advantageous in terms of flow rate as this is the more damped material in this arrangement (damping being dependant on size and density of the particles) and forms a higher proportion of the mixtures overall volume.

The effect of the feed position an the quality of separation is demonstrated in the table of Figure 7. When the feed material is fed at the high end or close to the middle of the slope then a bronze product is generated at the low end of the slope with an increased concentration. When the feed is fed close to the low end of the slope the material input interrupts the separation system and results in minimal concentration of bronze.

Weir 107 at the lower end of the support surface is necessary otherwise all of the material will flow off the lower end of the support surface and a bed would not be formed over the whole vibration surface 102. The presence of the weir 107 allows the movement downward through the bed

that is required for the glass to travel back up the slope. Conversely a weir 106 does not appear to be necessary for the upper end of the support surface 102. However a potential advantage, in the case where the bronze concentrates at the high side, is identified as the presence of a weir 106 can improve the purity of this concentrate by allowing the glass to recirculate.

Bed depth is dependant on the length and angle of the support surface 102, the location of the weirs 106, 107 and the characteristics (including angle of repose) of the particulate mixture. Longer beds are assumed to provide an advantage as the feed can be located further away from exit points allowing a longer particle journey from feed to exit point, hence the particles are subject to vibration for longer and can achieve a better degree of separation.

The lower angle means shallower bed and lower overall height difference between the tops of the weirs 106, 107.

Currently, it is believed that the most suitable waveforms to use for the vibrations are sinusoidal, however, tapping (non-sinusoidal waveforms) may be used where the material settles before being thrown again. Other studies have also shown changes in intruder behaviour in brazil nut studies by changing the waveform.

The frequency and amplitude of the vibrations have been chosen because it has been observed that on increasing the frequency and gamma the mineral particles begin to display more unusual behaviour. Specifically, the particles begin to form surface waves. Surface waves on the inclined slope separator have a risk of promoting mixing at the exit points and reducing product purity. However, this is not to say that this cannot be overcome or should be ignored as long as a degree of concentration is

achieved. The concentrate (disposed product) can then undergo further passes along other slopes, which may or may not be the same dimension and under the same operating conditions as the first pass.

A narrow cell is desirable in order to reduce the formation of significant convection currents across the width of the cell. It is believed that a width of 100mm or less is sufficient to ensure that unwanted convention currents are avoided.

The separator cells can achieve significant concentration of valuable or useful components within a single process step. However, the separation cells can also be arranged in series or parallel with significant process benefits. For example, banks of cells in parallel permit large throughput volumes or tonnages. Arranging separator cells in series permits the product from one cell to be further concentrated in subsequent units to achieve specified levels of performance. Loads can also be re-circulated back into feed materials as required.

Specific examples of separation of particulate mixture using the apparatus will now be described with reference to Figures 9 to 16.

Example 1: The separation of ilmenite from sand in the partitioned cell.

A mixture comprising 10% ilmenite (4.5g/cm ³ ) and 90% sand (2.7g/cm ³ ) on a weight: weight basis was prepared. In this specific example the feed material has been pre-screened to have particle size range broadly within 90μm to 125μm.

This material was placed into the left hand side of the partitioned cell and appropriate vibration conditions identified through a series of standard

experiments. The experiments were conducted under atmospheric conditions with vibrational frequency ranging from 10-120 Hz and dimensionless vibration acceleration,]? ,in the range of 2-10.

During the operation of the cell the ilmenite concentrate moves rapidly from the left hand (feed) chamber through to the right hand chamber, whilst the sand was retained in the left hand chamber. The ilmenite concentrate extracted from the mixture is shown in 10.

Quantitative analysis of the 'product' reporting to the right hand chamber demonstrates that the higher density mineral can be extracted from the lower density sand. The ilmenite concentration of the right hand side of the cell compared to the original feed material is presented in Figure 10b. The 10% ilmenite grade of the feed was upgraded to 85%.

In this particular example the ilmenite yield is 50%. However it should be noted that the end of the experiment is arbitrary for these batch experiments .

Example 2. Recovery of copper from electrical cables

The recovery of value from wastes such as electrical cables can be achieved using vertical vibration. One useful product that might be extracted from such a waste is copper, however, this is inherently associated with plastic. The example describes some of the process steps that might be used to concentrate copper from the mixed waste.

The electrical cables were first shredded to liberate the copper wiring from the plastic insulation. Once reduced into the granular state they were screened to separate them into different size fractions. The two different size fractions considered here are the 106-212 microns and the

212-425 microns. These size fractions were placed into the left hand side of the partitioned cell and appropriate vibration conditions identified through a series of standard experiments. The experiments were conducted under atmospheric conditions with vibrational frequency ranging from 10-120 Hz and dimensionless vibration acceleration, F, in the range of 2-10.

The copper wiring separated from the mixture within 2 minutes of vibration, entraining very little plastic particles. As soon as the cell was subjected to vibration, a convection current was set up in the bed. The convection current entrained the copper wirings together and tend to move them towards the top of the bed. Once enough copper wirings were grouped together, the copper-rich area and the plastic-rich area formed two distinct convection currents moving in opposite direction. It was observed that the separation remained in equilibrium even after 10 minutes of vibration. To allow for sufficient time for exchange of materials, all experiments with the shredded electrical cable were subjected to 5 minutes of vibration. Figures 11a to Hd illustrate the concentrate of copper wirings formed at the end of vibration (copper is concentrated in the right hand partition) .

Since analysis of the shredded electrical cables consisted of two materials only; copper wiring and plastics insulation, Float-Sink heavy liquid separation analysis was carried out to assess the separation.

The results show very successful separation of copper wiring from the electrical cables. The 106-212 μm mixtures reduced from 30%: 70% plastics: copper to a mixture of 12%:88% plastics: copper. The copper wiring streams in chamber 5 consisted of 95% copper and only 5% plastics insulation particles. The above results are in agreement where a concentrate of denser materials was formed from a mixture of less dense

materials. This also confirms the observation of that finer size materials below 300 μm separate better under vibration as less copper was separated from the 212-425 μm mixture. The composition in Chamber 1 changed from 30%:70% plastics: copper to only 33%:67% plastics: copper. However, although the yield was lower than the smaller size fraction, a 90% concentrate of copper wiring was formed in chamber 2 for the 212-425 μm mixture.

Example 3. - Printed circuit boards

Printed circuit boards are present, to some extent, in most waste electrical and electronic equipment. This example demonstrates the process steps that might be carried out to recover valuable/useful materials from the mixed waste.

The printed circuit board were cut into small pieces and passed through the shredder to reduce them to granular state and thus liberate the metals from non-metals. The resulting granular materials were screened into different size fractions and samples were taken to analyse the composition of each size fraction through the ICP-AES. Figure 12 illustrates the composition of the granulated circuit boards.

The chemical compositions of circuit boards are very complex and they vary from manufacturer to manufacturer. However these results can provide us with guidelines to recover the most concentrated metal from the circuit boards. Therefore this study focuses recovery of copper, lead, tin and aluminium. The rest of the metals are not considered, as they are not present in significant amounts.

Three size fractions (300-425 μm, 212-300 μm and 150-212 μm) of the materials were vibrated in the cell to obtain a metal concentrate. Figures

13(a-f) shows the concentration of copper, lead, tin and aluminium before and after vibration separation in the cell.

The data indicates that denser metallic elements such as copper, lead and tin can be successfully extracted from a mixed granular feed material comprising circuit boards. Aluminium was less well separated.

Example 4 - Potential to use system to promote size separation

To determine if the coarser particles contained within a sand sample could be removed, the application of the new partitioned cell (overall dimensions in this case were 80x40xl0mm) was investigated. In this arrangement a divider splits the cell into two smaller rectangular partitions. In this case the feed material is placed into the left hand cell

(as pictured in Figure 14) . The centre divider does not extend to the base of the cell, a small adjustable gap remains that allows certain particles to pass through into the right hand cell.

When a sand only sample was separated in the partitioned cell, size separation was clearly demonstrated as coarser material moved through from the left hand cell to the right hand cell. This observation was confirmed by simple particle size analysis of the contents of each cell, as shown in Figure 15.

Example 5 - Separation of pyrite from coal

Pyrite in coal contributes to sulphur dioxide formation during combustion. It is therefore beneficial to remove this mineral from coal prior to combustion.

Pyrite can be also be cleaned from coal by the vertical vibration method. A made up mixture coal and pyrite of about 50:50% by mass of coal and pyrite were vibrated in a partition cell. The results are illustrated in Figure 16. During vibration a pyrite concentrate moves through to chamber 5 from the feed cell (chamber 4) . This results in a coal product with reduced pyrite concentration (retained in the feed cell, chamber 4) and a pyrite rich fraction reporting to chamber 5. The particle size range of both the pyrite and coal in this example was 90-125microns.

Now referring to Figures 17a, a further embodiment of apparatus according to the invention is shown. This embodiment is similar to that shown in Figures 4 to 6 and like reference numerals are used to refer to similar parts but in the series 200.

In this embodiment, the apparatus comprised one or more additional partitions 203' that define further gaps 206' , in this embodiment with support surface 202. These additional gaps effectively divide the apparatus into a series of chambers 221, 222, 223 along the support surface 202, with further refinement of the particulate mixture occurring within each chamber 221, 222, 223.

It will be understood that it is not necessary for the partitions 203 203' to define gaps 206 206' with the support surface 202 but may define gaps higher up the partition. For example, in the embodiment of the apparatus shown in Figure 17b, partition 203 has a gap therein such that it blocks particles that are close to the support surface flowing past barrier 103 but allows particles higher in the bed from flowing past the barrier 203. This may be suitable when one wants particles in a stratum that is not the lowest stratum to flow past partition 103 in chamber 222.

Using a partition 203, 203' with a gap near the support surface 202 may obviate the need for a weir 207 at the lower end of the support surface 200 as only a thin stream of separated material may pass under the gap 206.

For all of the embodiments of the apparatus described, the dimension of the apparatus of the apparatus will effect the purity of separation achieved. To achieve good separation of the particulate mixture, currents of particles produced should be confined as much as possible to the vertical planes that are substantially parallel with the direction of flow past the partition(s) 3, 103, 203 (i.e. along the length of the apparatus) . Reducing flow of particles across the width of apparatus is expected to increase the purity of separation.

During experiments on cells (apparatus) having a width of 100mm it has been found that undesirable convention currents occur from the application of imperfect vertical vibrations. Narrowing the width of the cell to 50mm mitigated this effect. This is illustrated by the results of the experiment shown in Figures 18a and 18b. In these graphs it can be seen that for a 75% and a 25% bronze mixture the 100mm width cell produced a bronze grade of 60% compared to a much improved 90% bronze grade in the 50mm cell.

Accordingly, the closer the vibrations produced by the vibrator are to vertical then the more tolerance there is for a wider cell, however for the typical vibrators that can be acquired "off the shelf" it is envisaged that a cell having a width of less than 100mm and preferably 50mm or less is desirable.