GB2547899A

GB2547899A - Process for separating materials

Info

Publication number: GB2547899A
Application number: GB1603535.4A
Authority: GB
Inventors: Andrew Burns Steven; Falconer Gregg
Original assignee: IMPACT LABORATORIES Ltd
Current assignee: IMPACT LABORATORIES Ltd
Priority date: 2016-03-01
Filing date: 2016-03-01
Publication date: 2017-09-06
Also published as: GB201603535D0

Abstract

A separation process features the introduction of at least two different materials in a segregation media such as water, into a vessel 18, and linear oscillation of an internal baffle 30, the baffle 30 having a sheath 37. The motion of the baffle 30 may help in the separation of the two materials, which may have similar densities. Typical material for separation may be polyethylene and polypropylene which may be in thin flake form, or mineral from ore. The action of the baffle 30 may be referred to as shuggling. The addition of a sheath 37 may improve separation efficiency.

Description

PROCESS FOR SEPARATING MATERIALS

The present invention relates to a process for separating materials and more particularly, though not exclusively, to a process for separating materials based upon their densities by shuggling the materials in a segregation media under selected conditions. The process finds specific application in the separation of waste plastics and mineral extraction.

Recycling of waste materials has now become a major environmental driver. In this regard the recycling of plastics is placed high on the agenda as these are non-biodegradable. To recycle plastics requires the plastics waste to be capable of being separated into the chemically distinct materials. As a result many techniques have been proposed, primarily based on separating the different plastics by their density. Consequently, the known techniques use either gravity separation in flotation tanks or stirring to create a centrifugal force for separation. These techniques cannot separate lower value (non bottle) 'mixed plastics' which currently can only be separated by expensive IR or optical technology.

The most common plastics in waste are the polyolefins polyethylene (PE) and polypropylene (PP). In recycling they only have a value when the pure materials are recovered. Unfortunately as the density of PE lies between 0.92 and 0.97 g/cm^, and that of PP lies between 0.9 and 0.91 g/cm^, the abovementioned standard techniques cannot provide sufficient segregation to recover PE and PP with sufficient purity for recycling.

Some success has been found in separating PE and PP by using processes employing electrostatic charging; bubbling gas through the mixture; dissolving a part of the mixture; and passing through multiple flotation tanks.

The application of novel and efficient separation techniques to the mineral extraction-processing is of paramount importance due to the constant need of dividing the valuable minerals from the waste minerals upon ores extraction. Ore is a term used to describe an aggregate of minerals from which a valuable constituent, especially a metal, can be profitably mined and extracted. Most rock deposits contain metals or minerals, but when the concentration of valuable minerals or metals is too low to justify mining, it is considered a waste or gangue material. Within an ore body, valuable minerals are surrounded by gangue and it is the primary function of mineral processing, to liberate and concentrate those valuable minerals.

Several techniques have been applied in order to separate the valuable minerals: Sorting, based on appearance, colour, texture, optical properties and radioactivity; Gravity and Dense-Medium Separation, being separation based on specific gravity of the valuable mineral relative to the gangue and the segregation media e.g. water or for dense-medium separation, a mixture of water, magnetite, or ferrosilicon; Magnetic Separation, with separation based upon natural or induced differences in magnetic susceptibility of the minerals within the ore; and Froth Flotation, giving separations based on the surface chemistry properties of a mineral as the natural or modified surface property of the mineral determines its ability to attach to an air bubble and float to the surface.

Dense medium separation relies not only the difference between the specific gravity of the particles but also exploits the variation in the effective of specific gravity (SG) of a fluid medium. Chemicals are often used for lab scale separations while dense medium slurries are used more on an industrial scale. Typical dense mineral separators are: Pinched Sluices, The reichert cone concentrator. Spiral concentrators, jigs and centrifuge gravity concentrators. A known process for separating a mixture of materials is described in GB2522599 to the present Applicants. This process uses a segregation media within a vessel having a central baffle structure which shuggles the mixture by oscillating the baffle structure at a frequency and amplitude to cause separation of at least two materials within the vessel. The present applicants have surprisingly discovered that shuggling the mix using a centrally located oscillating baffle causes separation. This is in contrast to the known stir tank reactors where a mechanically agitated impeller causes mixing of components e.g. for polymerisation and crystallization. Shuggling may be considered as a form of agitation, though it is distinct in that it does not include stirring which is typical of agitation. Shuggling may be considered as shaking.

It is an object of the present invention to provide an improved system for the separation of materials in a mixture of materials of chemically different type and density.

According to a first aspect of the present invention there is provided a baffled oscillation separation system for the separation of materials in a mixture of materials, comprising: a vessel into which is introduced a mixture of at least two materials of chemically different type and a segregation media; a baffle structure centrally located within the vessel, the baffle structure being arranged to oscillate at a first frequency and a first amplitude so as to cause shuggling in the vessel resulting in the separation of the at least two materials within the vessel; characterised in that the baffle structure is sheathed along at least a length thereof providing a top opening and a bottom opening at opposing ends of the sheathed baffle structure.

In this way, the sheathed baffle structure oscillates in the vessel. Advantageously, the mixture and segregation material can enter the baffle structure at an opening, be acted on by the arrangement of baffles, and exit the baffle structure at either end as it is separated. This improves the efficiency of separation as compared to the arrangement described in GB2522599.

Preferably the baffle structure comprises a central shaft upon which are located a plurality of baffle plates, the baffle plates including one or more pathways therethrough for the passage of the mixture and the segregation media. In this way, the baffle plates induce movement to the mixture and the segregation media while still providing a route through which the materials can move to either end of the sheathed baffle structure.

Preferably the baffle structure is sheathed by providing a wall around the baffle plates. Advantageously, the baffle plates are in contact with the wall. In this way, the mixture and the segregation media within the baffle structure must pass through the baffle plates.

Preferably the baffle structure is sheathed along its length from an uppermost baffle plate to a lowermost baffle plate. In this way, the baffle structure is located in a bounded channel with the top opening being at the uppermost baffle plate and the bottom opening being at the bottommost baffle plate. Alternatively, the baffle structure is sheathed along its length from a position above the uppermost baffle plate to a lowermost baffle plate. In this way, a chute is provided at the top opening which may aid the delivery of the mixture into the baffle structure and hold separated material. Optionally, the baffle structure is sheathed along its length from a position above the uppermost baffle plate to a position of a baffle plate before the lowermost baffle plate. In this arrangement the baffle structure protrudes from the bottom opening. This arrangement can assist in evacuating material from the bottom opening.

Preferably, the baffle plates are discs arranged perpendicularly to the central shaft. Preferably also, the baffle structure is cylindrical. In this way, the baffle structure is sheathed by a cylindrical wall. The wall may be metal. Alternatively the wall may be a plastic. The vessel may be a substantially cylindrical tank. In this way, an annulus is provided between the oscillating sheathed baffle structure and the inner wall of the vessel.

More preferably, the discs include apertures therethrough to create the one or more pathways. Alternatively, the discs are star-shaped providing a series of extended portions around a circumference of the disc. The passageways are then created by the spaces between the portions, when the extended portions meet the wall around the baffle structure.

It has been found that varying the number and size of pathways through the discs can be used to assist in separation of the materials. It has also been found that varying the separation between the discs can assist in separation of the materials.

Additionally, it has been found that the first amplitude and first frequency can be selected to assist in separation of the materials. In an embodiment, the first amplitude and/or the first frequency may be varied, in use, to improve separation. In this way, the frequency may be increased as separation begins to increase efficiency.

Preferably, the vessel includes a first inlet and a first outlet for the circulation of the segregation media through the vessel. More preferably, the system includes a pump so that the speed of circulation of the segregation media can be varied. The first inlet and first outlet may be connected via the pump so that the segregation media may be recirculated. In this way, the segregation media can be re-used. The first inlet may be at the top or the bottom of the vessel. The first outlet may be at the top, the bottom or at a side of the vessel. In this way, the direction of circulation of the segregation media can be selected by a user. Preferably, the direction is chosen to apply a counter current of the segregation media.

Preferabiy, the vessei inciudes a second input for the introduction of the mixture. More preferabiy, the second input is arranged at the top of the vessei. Advantageousiy the second input is arranged to direct the mixture towards the top opening of the sheathed baffle structure. Preferably the vessel includes a plurality of second outlets, the second outlets being arranged at positions on the vessei for the separated materials.

Preferably the vessel includes an evacuation system to assist in the exit of separated materiai from the bottom of the baffled structure. More preferably, the evacuation system assists in the exit of separated material from the bottom opening of the sheathed baffle structure into the annuius.

The evacuation system may comprise a skirt arranged at the bottom opening of the sheathed baffie structure. The skirt may be a continuation of the waii of the sheath extending beyond a bottommost baffle plate. Alternatively, the skirt may flare outwardly from the bottom opening.

The evacuation system may comprise a water flow system arranged to supply a cross flow of water perpendicular to the central shaft at the bottom opening. In this way, separated material exiting the bottom opening is swept to the edge of the vessel and into the annulus. This makes space for more separated material to exit from the bottom opening.

The evacuation system may comprise a profiled surface arranged to face the bottom opening. The profiled surface may be on a bottom surface of the vessel. Alternatively, the profiled surface may be on a structure located below the bottom opening. Preferably the profiled surface is a cone, having an apex arranged with the central shaft. In this way, the cone surface directs separated material exiting the bottom opening towards the edge of the vessel and into the annulus.

The baffled oscillation separation system may also include removal means for removing a separated material from the vessel. The means may be arranged to remove the material from the top or bottom of the vessel. The means may be arranged to remove a material from a stack of materials. Such means may include skimmers, vacuum suction, water flows or other techniques which provide for the removal of a layer of material in the vessel.

Preferably, the baffled oscillation separation system also comprises a motor located at an end of the shaft to oscillate the sheathed baffle structure. In this way the shaft is stroked at the amplitude and the frequency to shuggle the vessel contents.

Preferably the segregation media is a fluid. More preferably, the segregation media is a liquid. In an embodiment, the segregation media is water. The segregation media may be selected from a group comprising: solvent blends, isopropyl alcohol or a salt solution.

Preferably, the mixture includes at least a first material having a first density in a first density range and at least a second material having a second density in a second density range. In a first embodiment, the first and second density ranges overlap and the segregation media has a density within the overlap. It has been found that the process provides for separation of materials with overlying density ranges. When the mixture is shuggled, the lighter material will move to the top of the sheathed baffle structure and the heavier material will move to the bottom of the sheathed baffle structure.

In the first embodiment, the materials are polyolefins polyethylene (PE) and polypropylene (PP). In this way, the difficult to separate PE and PP in waste plastic mixtures can be separated. Preferably, the mixture is a shredded mixture. More preferably, the shredded mixture is in the form of flakes. More preferably, the mixture includes 2D flakes which may be considered as thin films i.e. a thickness of < 50 microns. Thus the separation of plastic thin films can be achieved with the present invention. It is believed that by rapidly moving the 2D flakes under oscillation, static friction forces cannot build up between 2D flakes which would otherwise hold them together and prevent separation.

In the first embodiment, the baffle oscillation system may include a preseparation assembly to provide a mixture of materials having overlapping density ranges. For waste plastics, the shredded mixture may initially be separated into high density and low density plastics to provide a mixture with approximately the same density range. Any known process may be used to do the initial separation such as those processes discussed in the prior art. Alternatively, the pre-separation assembly may comprise the same apparatus of the present invention, but with an appropriate segregation media i.e. one who's density lies between the high and low density values of the plastics being separated.

In a second embodiment, the first and second density ranges are distinct and the segregation media has a greater density than the first and second density ranges. It has been found that in shuggling, the first and second materials will float and separate to form a stack at the top of the sheathed baffle structure.

In a third embodiment, the first and second density ranges are distinct and the segregation media has a lower density than the first and second density ranges. It has been found that in shuggling, the first and second materials will sink and separate to form a stack at the bottom of the sheathed baffle structure.

In this way, separation has been found to occur without requiring the separation media to have a density between the materials being separated. This advantageously allows cheaper segregation media, such as water to be used.

The mixture may include minerals. Alternatively or additionally, the mixture may include metals. In an embodiment the mixture is ore. In this way the valuable minerals and metals can be extracted using the present invention.

Preferably, the baffled oscillation separation system further comprises a degasser. In this way the segregation media is degassed prior to introduction into the vessel. This is in contrast to prior art techniques where gas bubbles are introduced to the vessel. Degassing the segregation media has been found to improve the efficiency of separation. More preferably, the vessel is operated at negative pressure. With the degassing this can also improve efficiency of separation.

The baffled oscillation separation system may comprise a plurality of vessels arranged to provide cascaded segregation. The segregation media may be varied between the vessels to improve segregation. The amplitude and frequency may also vary between the vessels.

Alternatively, there may be a plurality of sheathed baffle structures in a single vessel. More preferably, the sheathed baffle structures are spaced apart along a suitably tank-shaped vessel, between an Input and an output at opposite ends. In this embodiment 'centrally located' means away from walls of the vessel. The sheathed baffle structures may be arranged In an array. Preferably, the tank-shaped vessel is on an incline.

This assists in passage of the recirculating segregation media. More preferably there are two outputs, one at a top of the vessel and one at a bottom of the vessel. In this way, the separated materials can be pumped out of the vessel.

Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings of which:

Figures 1(a) and 1(b) are cross-sectional illustrative views, orthogonal to each other, through a baffled oscillation separation system according to an embodiment of the present invention;

Fig ures 2(a) - 2(d) are schematic illustrations of evacuation systems for use in embodiments of a baffled oscillation separation system of the present invention;

Figure 3 is a diagrammatic view illustrating the steps in a process to separate plastics using the system baffled oscillation separation system of the present invention;

Figure 4 is a diagrammatic view illustrating the steps in a process to separate materials according to a further embodiment of the present invention; and

Figure 5 is a schematic illustration of a vessel including a plurality of baffle structures for use in a process for separating materials according to an embodiment of the present invention.

Reference is initially made to Figure 1 of the drawings which illustrates apparatus being a baffled oscillation separation system, generally indicated by reference numeral 10, for the separation of a mixture of at least a first material 12 and at least a second material 14, according of the present invention.

The materials 12,14 are preferably particles of chemically different types with the first material having a first density in a first density range and the second material having a second density in a second density range. The mixture 16 is fed into a vessel 18 along with a segregation media 24. The segregation media is a liquid, preferably water. In a first embodiment, the first and second density ranges overlap and the segregation media has a density within the overlap. In a second embodiment, the first and second density ranges are distinct and the segregation media has a greater density than the first and second density ranges. In a third embodiment, the first and second density ranges are distinct and the segregation media has a lower density than the first and second density ranges. In this way, separation can occur without requiring the separation media to have a density between the materials being separated. This advantageously allows the cheaper segregation media, water to be used.

The vessel 18 is substantially cylindrical having a height greater than its diameter. The capacity of the vessel can be arranged to suit the quantity of materials and can be scaled from a bench-top system of 500 ml to a tank of 10,000 to 20,000 litres easily. There is a first input port 20 through which the mixture 16 and is introduced. A second input port 22 is provided for the segregation media 24. The introduction of the mixture 16 and the segregation media 24 may be referred to as the filler step 46. The mixture 16 and the segregation media 24 may be mixed before being input through a single port, if desired. Separate input 22 for the segregation media 24 allows the segregation media to be removed via an output 23 and pumped 25 back to the input 22 for recirculation. The speed of the pump 25 can be varied.

Referring to Figures 1(a) and 1(b), which illustrate cross sectional views of a baffled oscillation separation system 10, there is shown a baffle structure, generally indicated by reference numeral 30, vertically arranged in the centre of the vessel 18, and extending between the top 32 upon which is located a number of baffle plates in the form of discs 34. For illustrative purposes ten discs 34 are shown. The discs 34 are mounted perpendicularly to the shaft 32 so that they radiate out towards the side wall 36 of the vessel 18. The number and position of the discs 34 may be varied on the shaft 32. Around the discs 34 is arranged a wall 37.Wall 37 is cylindrical and sheaths the baffle structure 30. The wall 37 provides a top opening 39 and a bottom opening 41 at respective ends of the baffle structure 30. Thus the baffle structure 30 is sheathed along its length providing a top opening 39 and a bottom opening 41 at opposing ends of the sheathed baffle structure 45. The wall 37 may be a plastic or metal but is preferably thin-walled to allow the sheathed baffle structure 45 to remain lightweight for easy movement in the vessel 18. The baffle structure 30 is sheathed by the wall 37, akin to wrapping the baffle structure 30, so that the discs make contact with the inner surface 43 of the wall 37. The wall 37 extends from the uppermost disc 34a to the lowermost disc 34b to entirely cover the discs 34 around the circumference of the baffle structure 30. Flowever, in alternative embodiments the baffle structure 30 may be sheathed by the wall 37 along a shorter or longer length. There is an annulus 47 between the wall 37 and the side wall 36 of the vessel 18.

The base 38 of shaft 32 is located at the lowermost disc 34b so that the sheathed baffle structure 45 is free to move longitudinally up and down in the vessel 18, being supported from above the vessel 18. In an alternative embodiment, the base 38 of the shaft 32 is supported on the bottom 28 of the vessel, but is in a sliding hold, which allows the shaft 32 to move longitudinally on its own central axis, vertically with respect to the vessel 18. The discs 34 are attached to the shaft 32 in such a way that they too, move longitudinally when the shaft 32 moves. Similarly, the wall 37 also moves and thus the sheathed baffle structure 45 is moved up and down in the vessel 18 by movement of the shaft 32. Movement of the shaft 32, is achieved by use of an actuator linear movement motor 40 attached to the top end 42 of the shaft 32.

The motor 40 provides a linear movement to the shaft 32 on a central axis. The movement is a stroke, being a backward and forward motion, to extend the shaft 32 into the vessel by a set distance, referred to as the amplitude. The frequency of the strokes can also be set, so that the shaft 32 acts like a piston, continuously moving the sheathed discs 34 up and down within the vessel 18. The movement of the sheathed discs 34 within the vessel 18 shuggles the contents of the vessel 18, these being the mixture 16 and the segregation media 24. This shuggling step 48 can operate over a fixed time, it may be for short repeated pulses or can be stopped and started between checks to determine the degree of separation of the vessel contents. Note that the shaft 32 does not rotate so there is no stirring action.

The shuggling step 48 is controlled by circuitry 52 which operates the motor 40 and determines the amplitude and frequency required to obtain optimum separation. The amplitude and frequency determine the energy introduced to the process 10 and can be selected for particular mixtures. Note that the amplitude and frequency can be adjusted during separation.

The vessel contents, being the mixture 16 and the segregation media 24, are shuggled by repeated contact with the discs 34 contained with the wall 37. The discs 34 are designed to provide sufficient surface area 54 for contact with the vessel contents while still allowing the mixture 16 and the media 24 to move between the discs 34 via passageways 56. Figure 1(b) shows an embodiment for a disc 34. Disc 34 is substantially circumferential with a star shaped configuration. Substantially rectangular long 58 and short 60 strips extend from the shaft 32 and are alternately and equidistantly spread out from the shaft 32. The space 62 between the strips 58,60 and the consequential space between the ends 64 of the short strips 60 and the wall 37 provide the passageway 56 for movement of fluids through the sheathed baffle structure 45. The discs 34 may be of any shape and size, as long as they are proportional to the size of the vessel 18, with passageways for the movement of fluid which are again proportional to the size of the vessel 18.

The discs 34 are comparatively thin compared to the height of the vessel 18 and may be considered as blades, though as said previously, they are not rotated as would occur if the baffle structure 30 was an impeller in a mixing tank. Equally the baffle structure 30 of the present invention is in direct contrast to known baffle structures used in mixing tanks. Prior art baffle structures are typically vertically arranged bars or rods spaced equidistantly around the outer edge of the tank which are fixed in position and do not move during operation of the tank.

In an embodiment the discs 34 are equally spaced along the shaft 32. The spacing is based on the particle size of the materials being separated and is proportional to the size of the vessel 18. In an alternative embodiment the discs 34 are concentrated together at the centre of the vessel 18 and become spaced further apart towards the top 26 and bottom 28.

In the first embodiment, the first material 12 and second material 14 have first and second density ranges which are distinct or may overlap. The segregation media 24 has a density between the first and second density or within the overlap. In shuggling the mixture 48, the first material 12 and the second material 14 will separate with the heavier material 12 moving to the bottom opening 41 and the lighter material 14 moving to top opening 39. A layer of segregation media 24 will be left between the material 12,14 layers. The shuggling facilitates the separation - i.e. it is faster and better separation (more pure) than no shuggiing or just simpie agitation. This separation step 50 aiiows the first materiai 12 to be first drawn off through an outiet 68 at the base 28 of the vessel 18. The segregation media 24 can also be drawn off and filtered for re-use or recirculated via the pump 25. Finally the second material 14 can be drawn off through a port 49 towards the top 26 of the vessel 18. The separated materials 12,14 can then be individually packed and transported to other manufacturing and process sites for new uses.

In the second embodiment, the first materiai 12 and second materiai 14 have first and second density ranges which are distinct and the segregation media 24 has a greater density than the first and second density ranges. In shuggiing the mixture 48, the materiais 12, 14 wiii fioat, rising to the top of the sheathed baffie structure 45. On rising the materiais 12,14 wiii separate to provide a stack of materiais 12,14 in two iayers at the top of the sheathed baffie structure 45. These almost pure materials 12,14 can be drawn off separately from the vessel 18. The segregation media 24 can also be drawn off for re-use.

The corollary also applies. If a lower density of segregation media 24 is used compared to the two materials 12,14, on shuggiing the mixture 48, the materials 12,14 will sink and separate into a stack of individual layers at the base of the sheathed baffle structure 45.

This advantageousiy means that any materials may be separated by water rather than the expensive, and often fiammabie, soivents used as segregation media in prior art separation processes.

In the embodiment iiiustrated in Figure 1(a), it has been found that upon separation the heavier materiai 14 wiii exit the bottom opening 41 and accumuiate at the base 28 of the vessei 18. This prevents efficient separation of materiais in the sheathed baffie structure 45 as the materials mixture just tends to recirculate in the space between the lowermost disc 34b and the base 28 of the vessel 18. An evacuation system, generally indicated by reference numeral 51, is provided at the bottom opening 41 of the sheathed baffle structure 45, to improve this by encouraging circulation up the annulus 47 of the vessel 18. Embodiments of evacuation systems 51a-d are shown in Figures 2(a)-(d), respectively, with like parts being given the same reference numeral to those parts in Figure 1(a) to aid clarity.

In Figure 2(a), the wall 37 extends below the lowermost disc 34b, providing a skirt 53 at the bottom of the sheathed baffle structure 45. The skirt 53 may be parallel with the central shaft 32 to may flare outwards to assist in directing separated material from the bottom opening around to the annulus 47.

In the embodiments shown in Figures 2(a)-(d), the bottom outlet 68 has been repositioned on the side wall 36 of the vessel 18, for the removal of the heavier separated material 14 from the vessel 18, as they are moved into the annulus 47. Note there may be a plurality of outlets 68 to provide faster removal of the separated material 14. Also illustrated in these embodiments is the extension of the wall 37 above the uppermost disc 34a. This raises the top opening 39 and provides a chute 55 into which the mixture 16 can be introduced for immediate shuggling by the sheathed baffle structure 45.

In Figure 2(b), a cross-flow of water or other segregation media 57 is introduced at the base 28 of the vessel 18 to sweep the separated material way from the bottom opening 41 and into the annulus 47 towards the outlet 68. A cone 59 is used as the evacuation system 51c of Figure 2(c). Located centrally on the base 28 of the vessel, the profiled surface 61 of the cone 59 provides a guide for the circulating material to move to the annulus 47. It will be realised that other angled profiled surfaces could be arranged at the base 28, to provide a guide for the separated material to be circulated to the annulus 47.

In Figure 2(d), the lowermost disc 34b protrudes from the bottom opening 41, to provide discs which are not sheathed by the wall 37. The separated material can therefore pass directly into the annulus 47 on exiting the bottom opening, in preference to passing through the exposed discs 34b to travel to the base 28 of the vessel 18.

The baffled oscillation separation system 10 is suitable for the separation of waste plastics and, in particular, for the separation of polypropylene and polyethylene.

It is common for recyclable materials to be collected together and thus an initial sorting stage 44 may be required. This will generally consist of separating paper, metal and plastics. The plastics collected generally represent bottles, canisters, food trays, packaging and films of various thicknesses depending on their initial purpose. Each is made up of one or more plastics which need to be separated for re-use. Currently, many items are provided with identification, in the form of a number within a triangle of chasing arrows, to show the type of plastic of which they comprise. There are seven numbers. Polyethylene Terephthalate (PET) having the number 1; High Density Polyethylene (HOPE) having the number 2; Polyvinyl Chloride (PVC) having the number 3; Low Density Polyethylene (LDPE) and Linear Low Density Polyethylene (LLDPE) both having the number 4; Polypropylene (PP) having the number 5; Polystyrene (PS) having the number 6; with the number 7 being given to other miscellaneous plastics.

While some manual sorting can be done it is typical that an approach is required as described in the prior art. In this way, the risk of contamination is reduced. Plastics are normally shredded or ground to provide flakes of individual material which have dimensions of less than 5mm, but for the films this may be less than 50 microns in thickness. Where the thickness is so small the flakes may be referred to as 2D in contrast to other 3D flakes. The flakes can be washed to remove any residues which adhered to them in use.

Separation of 2D flakes has proved difficult, particularly for processes reliant on the density of the plastic as the differentiator for separation. These 2D flaked films don't segregate very well mostly because the static friction between the flakes is so large it overcomes the natural segregating force arising from the density of the plastics. In the present invention, these 2D flakes can be separated.

The baffled oscillation separation system 10 can include a pre-sorting stage 44 as described above which ultimately produces mixed plastic flakes 16 with densities of approximately the same range. The separating process then continues with inputting mixed plastic flakes 16 into the vessel 18 at the filler stage 46.

In the preferred embodiment the mixed plastics 16 comprise polypropylene 12 and polyethylene 14, which may have been the residue recovered from an earlier stage separation which failed to distinguish these components due to their being approximately in the same range of density. The segregation media 24 is a fluid being isopropyl alcohol whose density may be varied by dilution with water.

The mixed plastics 16 and the segregation media 24 can be input to the vessel in any order as this has negligible effect on the separation process 10. The ratio of mixed plastics 16 to segregation media 24, however, does have an effect. Separation can occur in a much reduced time scaie if the ratio of piastics 16 to media 24 is iow. Separation has been shown to occur at ratios of 40% fiake to 60% media, though the best resuits occur at fiake ioading of no more than 30%.

Referring to Figure 3, the stages in a separation process using a baffied osciilation separation system 10 are presented. Foiiowing the fiiler stage 46 is the shuggiing stage 48. The shuggiing step 48 strokes the shaft 32 at a desired ampiitude and frequency. This ampiitude and frequency can be adjusted during separation. In this way, ioosening of the plastic mixture 16 can be undertaken where the ratio of plastic mix 16 to segregation media 24 is higher, at a first frequency, and then separation can be optimaiiy achieved by increasing the frequency.

In shuggiing the mixture 48, the poiyethyiene 12 and polypropylene 14 will separate with the heavier polyethylene 12 moving to the base 28 of the vessel 18 and the lighter polypropylene 14 moving to top of the sheathed baffle structure 45. Each layer of plastic material will include both the 2D and 3D flakes. A layer of segregation media 24 will be left between the plastic layers. This separation step 50 allows the polyethylene 12 flakes to be first drawn off through an outlet 68 at the base 28 of the vessel 18. The segregation media 24 can also be drawn off and filtered for re-use. Finally the polypropylene 14 can be drawn off. The polypropylene 14 and polyethylene 12 may then be washed, if desired before being batched-up and transported to a suitable plastics site for manufacture into new goods.

While this describes the process for two polymers, the separation process for the present invention can be used on more than two materials. The lightest will go up, the heavier will go down. Therefore, if we have three polymers PP, LLDPE and HDPE, for example, the PP and LLDPE will go up and the HOPE down. We then separate these two streams and then do a separate step to separate PP and LLDPE.

As has been detailed above, the amplitude and frequency of oscillation of the sheathed baffle structure 45 and the design of the discs can be optimised to improve separation. A further feature which can be used is in controlling the flow of the segregation media through the vessel.

If we consider a mixture of polymers in a column of water as an example. When we shuggle the mixture, the polymer stack will rise but still separate with the lighter polymer ending up on top. If, however, we then apply a counter current of water, in this case from top to bottom by putting water in at the top of the vessel and draw it off the bottom of the vessel, then the water flow will drive the heavier particles down. By carefully controlling the flow of water, we can more easily separate the heavy from light polymers. It is the velocity of the water flow through the vessel which is controlled. The separated polymers are taken off in order. In this case the water flow down the vessel can be used to sweep the polymer out of the bottom of the vessel (in the case of light polymers).

The reverse will also work if we have a mixture of polymers with a density greater than water. In this case water if flown up the vessel at a rate needed to get the lightest of the 'heavy' polymers to rise.

The process with water control may also be used to perform three separations in a single vessel. For example, PP & HOPE (lighter than water) and ABS heavier than water. If we shuggle the mixture of three polymers with water as the segregation media and set-up a downward water flow through the vessel, the PP ends up at the top of the vessel. HOPE and ABS are swept down. HOPE can be swept away in the water flow but ABS sits on the bottom and can be withdrawn reasonably pure.

The baffled oscillation separation system 10 is also suitable for the separation of valuable minerals and metals from the waste minerals upon ores extraction. Ore is a term used to describe an aggregate of minerals from which a valuable constituent, especially a metal, can be profitably mined and extracted. Most rock deposits contain metals or minerals, but when the concentration of valuable minerals or metals is too low to justify mining, it is considered a waste or gangue material. Within an ore body, valuable minerals are surrounded by gangue and it is the primary function of mineral processing, to liberate and concentrate those valuable minerals.

The system 10 and process, is as detailed in the previous Figures with the mixture 16 being ore including a first material 12 of at least one valuable mineral and a second material 14 being the undesirable gangue material. The mixture 16 may be pre-sorted 44 visually and then fed through a crushing process to provide fine particles, such as a powder. The materials 12 and 14 will have distinct densities, both being relatively high. The segregation media 24 is water. While this has a lower density than both materials 12,14 the present invention can achieve separation of the materials in contrast to the prior art arrangements. Water also provides a cheaper process.

The process steps are followed as detailed in Figure 3. The shuggling step 48 has a number of variables and the separation 50 is made possible by controlling these variables. The variable are: the disc design; the energy introduced to system i.e. the frequency and the amplitude; the spacing of discs and the speed of water recirculation.

Reference is now made to Figure 4 of the drawings which illustrates a cascaded system, generally indicated by reference numeral 70, according to an embodiment of the present invention. System 70 comprises a number of vessels in a cascaded arrangement to provide separate baffled oscillation separation systems lOa-d which each process a plastics mix 16 and a segregation media 24 to separate out chemically different materials. In this arrangement 70, the density of the segregation media can be selected to lie between those plastics which will be produced and those which will be moved on for further segregation at a later system lOa-d. Thus the segregation media will be varied for each vessel. Each vessel will have a sheathed baffle structure 45 as described herein with reference to Figures 1 and 2 and each system will operate as described herein with reference to Figure 3. The variables for each vessel can be separately controlled to provide the most efficient conditions depending on the mixtures being separated at each stage.

Such cascaded arrangements can also be used to separate a mixture of more than two materials using water as the segregation media and controlling it's flow through the series of vessels as described hereinbefore. Therefore we can separate a complex mixture of materials, for example, a mixture of PP/LLDPE/FIDPE/ABS/FIIPS/PVC.

Shuggling the entire mixture with water in vessel 10a and circulating the water can give: pure PP out of the top of the vessel; LLDPE/ HOPE swept out of the bottom of the vessel in the water flow and directed to vessel 10b; and, ABS/HIPS/PVC withdrawn from the bottom of the vessel and directed to vessel 10c. Using vessel 10b to separate LLDPE/HDPE, shuggling in water produces pure LLDPE out of the top of the vessel and pure HOPE out of the bottom of the vessel. Finally, using vessel 10c, shuggling with controlled water flow gives: ABS out of the top of the vessel; HIPS swept out of the bottom of the vessel; and, PVC withdrawn from the bottom of the vessel.

It will be recognised by those skilled in the art that other variations to separate this complex mix may be applied such as drawing PP/LLPDE from the top of vessel 10a to vessel 10b and having HOPE swept from the bottom of vessel 10a as pure. Then at vessel 10b, separating the PP/LLDPE as pure. The variation selected may be dependent on the materials in the mixture.

Reference is now made to Figure 5 of the drawings which illustrates an alternative apparatus to that of Figure 4, generally indicated by reference numeral 80, according to an embodiment of the present invention. Apparatus 80 comprises a long horizontal tank-like vessel 18 in which is arranged an array of sheathed baffle structures 45 along its full length. They may also be arranged across the vessel 18 width, if desired. Each sheathed baffle structure 45 is as described herein with reference to Figures 1 and 2 and the separation process will operate as described herein with reference to Figure 3. At the input 20, a mixture 16 and a segregation media 24 is introduced in a continuous system, with the output of each baffle structure being the input to the adjacent sheathed baffle structure between the input 20 and the output 68. Each sheathed baffle structure may be identical with identically controlled variables or may vary to as the mixture 16 and segregation media 24 pass from the input 20 to the output 68. At the output 68, separate ports may be arranged at the different heights of the vessel to separately pump-out the materials 12,14 and the segregation media 24.

The separation process can be run continuously, semi-continuously or batch-fed through the baffled oscillation separation system.

The principle advantage of the present invention is that it provides an improved baffled oscillation separation system for the separation of a mixture of materials of chemically different type which have approximately the same density range by shuggling. A further advantage of the present invention is that it provides an improved baffled oscillation separation system for the separation of a mixture of materials of chemically different type using a segregation media which is higher or lower in density than the density of the materials being separated by shuggling. A yet further advantage of at least one embodiment of the present invention is that it provides an improved baffled oscillation separation system for the separation of a mixture of any materials of chemically different type using water as a segregation media by shuggling and controlling the flow of water through the mixture. A yet further advantage of at least one embodiment of the present invention is that it provides an improved baffled oscillation separation system for separating polyethylene and polypropylene. A still further advantage of at least one embodiment of the present invention is that it provides an improved baffled oscillation separation system for separating minerals from ore.

It will be appreciated by those skilled in the art that modifications may be made to the invention herein described without departing from the scope thereof. For example, various other structures can be mounted on the shaft to create the baffle structure as long as it can be sheathed and achieves a surface area for interacting with the vessel contents and leaves a passageway for the plastics to pass through. Additionally, though the vessel is presented in a vertical arrangement, the process will still work where the vessel is tilted or arranged horizontally. Though only examples have been described for the waste plastics and mineral extraction industries, the process may find use in other industries such as pharma and food.

Claims

1. A baffled oscillation separation system for the separation of materials in a mixture of materials, comprising: a vessel into which is introduced a mixture of at least two materials of chemically different type and a segregation media; a baffle structure centrally located within the vessel, the baffle structure being arranged to oscillate at a first frequency and a first amplitude so as to cause shuggling in the vessel resulting in the separation of the at least two materials within the vessel; characterised in that the baffle structure is sheathed along at least a length thereof providing a top opening and a bottom opening at opposing ends of the sheathed baffle structure.

2. A baffled oscillation separation system according to claim 1 wherein the baffle structure comprises a central shaft upon which are located a plurality of baffle plates, the baffle plates including one or more pathways therethrough for the passage of the mixture and the segregation media.

3. A baffled oscillation separation system according to claim 2 wherein the baffle structure is sheathed by providing a wall around the baffle plates.

4. A baffled oscillation separation system according to claim 3 wherein the baffle plates are in contact with the wall.

5. A baffled oscillation separation system according to any one of claims 2 to 4 wherein the baffle structure is sheathed along its length from an uppermost baffle plate to a lowermost baffle plate.

6. A baffled oscillation separation system according to any one of claims 2 to 4 wherein the baffle structure is sheathed along its length from a position above the uppermost baffle plate to a lowermost baffle plate to provide a chute at the top opening.

7. A baffled oscillation separation system according to any one of claims 2 to 4 wherein the baffle structure is sheathed along its length from a position above the uppermost baffle plate to a position of a baffle plate before the lowermost baffle plate so that the baffle structure protrudes from the bottom opening.

8. A baffled oscillation separation system according to any one of claims 2 to 7 wherein the baffle plates are discs arranged perpendicularly to the central shaft.

9. A baffled oscillation separation system according to any preceding claim wherein the baffle structure is sheathed by a cylindrical wall.

10. A baffled oscillation separation system according to claim 9 wherein the vessel is a substantially cylindrical tank to provide an annulus between the oscillating sheathed baffle structure and an inner wall of the vessel.

11. A baffled oscillation separation system according to any one of claims 8 to 10 wherein the discs include apertures therethrough to create the one or more pathways.

12. A baffled oscillation separation system according to any one of claims 2 to 7 wherein the discs are star-shaped providing a series of extended portions around a circumference of the disc.

13. A baffled oscillation separation system according to any preceding claim wherein the vessel includes a first inlet and a first outlet for the circulation of the segregation media through the vessel.

14. A baffled oscillation separation system according to claim 13 wherein the system includes a pump so that the speed of circulation of the segregation media can be varied.

15. A baffled oscillation separation system according to any preceding wherein the vessel includes an evacuation system to assist in the exit of separated material from the bottom of the baffled structure.

16. A baffled oscillation separation system according to claim 15 wherein the evacuation system comprises a skirt arranged at the bottom opening of the sheathed baffle structure.

17. A baffled oscillation separation system according to claim 15 wherein the evacuation system comprises a water flow system arranged to supply a cross flow of water perpendicular to the central shaft at the bottom opening.

18. A baffled oscillation separation system according to claim 15 wherein the evacuation system comprises a profiled surface arranged to face the bottom opening.

19. A baffled oscillation separation system according to claim 18 wherein the profiled surface is on a bottom surface of the vessel.

20. A baffled oscillation separation system according to claim 18 wherein the profiled surface is on a structure located below the bottom opening.

21. A baffled oscillation separation system according to any one of claims 18 to 20 wherein the profiled surface is a cone, having an apex arranged with the central shaft.

22. A baffled oscillation separation system according to any preceding claim wherein the baffled oscillation separation system also comprises a motor located at an end of the shaft to oscillate the sheathed baffle structure.

23. A baffled oscillation separation system according to any preceding claim wherein the baffled oscillation separation system further comprises a degasser.

24. A baffled oscillation separation system according to any preceding claim wherein the baffled oscillation separation system comprises a plurality of vessels arranged to provide cascaded segregation.

25. A baffled oscillation separation system according to any preceding claim wherein there is a plurality of sheathed baffle structures in a single vessel.