Metal or metalloid extraction apparatus

Abstract

Apparatus for leaching a metal or metalloid such as antimony comprises a container 12, a liquid permeable separator 16 located in the container which divides the container into first 18 and second 20

Description

This invention relates to a metal or metalloid extraction apparatus. More particularly, the present invention relates to a continuous leaching system used during extraction of metals or metalloids, such as, antimony. The process of chemical leaching of metals or metalloids is generally known in the art. In the case of chemical leaching of Antimony, as a non-limiting example, reagents such as Sodium Hydroxide and Sodium Sulphide are mixed with hot water and added to a leach vessel containing a metal or metalloid containing ore. The pulped material within the leach vessel is mixed or stirred for a predetermined amount of time (in some cases, about 90 minutes) whilst maintaining a relatively high temperature (around 80°C). Loaded leachate obtained through the above process is filtered to remove residual solid impurities after which the filtered leachate is pumped to a crystallizer where the temperature is maintained whereafter further reagents such as Air, Oxygen, Ozone or Hydrogen Peroxide are added. Addition of the reagents cause the temperature of the mixture to rise due to an exothermic reaction taking place with the dissolved materials. Cooling and flow inside the crystallizer causes crystals to form in an updraft centre section and to be deposited in a lower section of the crystallizer. The crystals are collected, drained and dried, ready to be packaged for shipping while the barren leachate is safely disposed of. It has been found that a single or batched leach process as described above produces relatively low metal or metalloid recovery - in some cases under around 35%. It is believed that improvements in the leaching process could result in significantly improved metal or metalloid recovery, resulting in increased process viability and efficiency. CN104212981A utilises an acidic process with addition of ozone to precipitate the antimony metalloid in the leach vessel. Leaching and precipitation therefore takes place in a single vessel or compartment, which could negatively impact the purity of the final product. EP0191102A1 utilises solid-liquid separation with a spray bar. The spray bar is used to remove solids from a rotating continuous filter cloth before the cloth is returned to the slurry exposure and vacuum. The system comprises alternative wet and dry cycles with intermittent or limited exposure to the suction or vacuum. As such, the system is believed to be ineffective and may result in a reduced purity of the final product and dilution of the leachate and restricted production and recovery efficiency. Continuous leaching processes pose certain known complications, for example, due to difficulties associated with material handling (pumpability of pulped material) and the like. It is accordingly an object of the invention to provide an extraction apparatus used during leaching of metals or metalloids that will, at least partially, address the above disadvantages. It is also an object of the invention to provide an extraction apparatus used during leaching of metals or metalloids which will be a useful alternative to existing extraction apparatuses. SUMMARY OF THE INVENTION In accordance with a first aspect of the invention there is provided an extraction apparatus used during a leaching process of metals or metalloids, the extraction apparatus comprising: a container having an internal volume; a liquid permeable separator located within the internal volume, defining a first and second compartment within the internal volume; a slurry inlet for operatively receiving slurry into the first compartment and a slurry outlet for operatively disposing slurry from the first compartment; a leaching solution feed arrangement for operatively feeding leaching solution into the first compartment; a leachate outlet for operatively extracting leachate from the second compartment; and a pressure regulating arrangement for operatively maintaining a negative pressure differential over the liquid permeable separator and between the first and second compartments. In some cases, the container and liquid permeable separator may be substantially cylindrical and optionally concentric. In other cases, such as a horizontal configuration mentioned below, the container and liquid permeable separator may be non-concentric, such that a liquid holdup is formed below the inner compartment. The first compartment may be an inner compartment and the second compartment may be an outer compartment, surrounding the first or inner compartment. The apparatus according to the first aspect of the invention may further comprise an agitating arrangement within the first compartment which may be provided for operatively agitating slurry within the first compartment to enhance mixing. The agitating arrangement may extend substantially along a length of the first compartment. The agitating arrangement may comprise an auger or screw, an impeller arrangement or a spray arrangement for injecting fluid flows in the form of a gas or a liquid used to suspend solids in the slurry, or a combination of the aforementioned. In an embodiment where the agitating arrangement comprises an auger or screw, same may be mounted or supported centrally by a central shaft or peripherally by an inner surface or structural component of the separator. The impeller arrangement may comprise more than one impeller supported on a central shaft. The more than one impeller may be spaced longitudinally (typically at regular intervals), along a length (or at least substantially along a length) of the first compartment. The central shaft may be driven by a drive motor from either one or both ends of the central shaft. The impeller arrangement may comprise at least one impeller of a first kind and one impeller of a second kind. The impeller of the first kind may have a first, larger diameter and a first pitch direction. The impeller of the second kind may have a second smaller diameter and a second pitch direction. The first pitch direction of the impeller of the first kind is configured operatively to displace slurry in a direction towards the slurry outlet (or upward, when the apparatus is configured substantially vertically). The second pitch direction of the impeller of the second kind is configured operatively to displace slurry in a direction towards the slurry inlet (or downward, when the apparatus is configured substantially vertically). In use, the impellers of the first and second kind cause, at least a local, counter current or non-laminar mixing flow of slurry within the first compartment. Due to the fact that the impeller of the first kind has a relatively larger diameter than the impeller of the second kind and / or the fact that the slurry is operatively fed from the slurry inlet and positively pumped into the first compartment, a net flow of slurry within the first compartment may be in the direction towards the slurry outlet (which may be upward). The container may form an outer, liquid impermeable body. The container may further comprise first and second end caps. The liquid permeable separator may extend from the first to the second end cap. The liquid permeable separator may comprise a base structure comprising a cylinder formed from mesh or expanded metal, linearly spaced hoop members interconnected by longitudinally extending members, the hoop members and longitudinally extending members forming a grid or mesh, optionally formed from wedge wire or plastic or rubber mesh structures. Apertures of the base structure may be at least 1.5 times an average size particle size of particles in the slurry. The liquid permeable separator may further comprise an apertured screen, filter material or perforated sheet supported by the base structure. The apertured screen filter material or perforated sheet may have apertures in the range of 0.1 - 1 times an average particle size of particles in the slurry. Furthermore, the apertures may comprise or make up at least 45% of a -4-surface of the screen. The apertures may be selected and configured to facilitate an effective flow and throughput of the leachate solution. The base structure may comprise of a single support layer to which the apertured screen, filter material or perforated sheet is fastened by means of bands, straps or similar restraining devices. Alternatively, the base structure may comprise a double layer structure between which the apertured screen, filter material or perforated sheet is sandwiched. In use, the slurry inlet may be provided in flow communication with a leach vessel in which the slurry is operatively prepared by combining a metal or metalloid containing ore source with reactants in a chemical leaching process. Furthermore, in use, the leachate outlet may be provided in fluid flow communication with one of another apparatus according to the first aspect of the invention, a secondary leach vessel, a filter and crystallizer plant for downstream processing. The pressure regulating arrangement may be provided in fluid flow communication with an opening in the first or second compartment. The pressure regulating arrangement may be configured operatively to cause a pressure to be maintained in the second compartment which is lower than an operative pressure in the first compartment. The pressure regulating arrangement may achieve this by creating a below-atmospheric pressure in the second compartment (by way of suction) or an above-atmospheric pressure in the first compartment (by way of positive pressure provided to the second compartment). The leaching solution feed arrangement may comprise a duct or tube extending longitudinally within the first compartment, comprising a plurality of openings or nozzles spaced along a length thereof, for operatively distributing leaching solution along a length of the first compartment. The tube or duct may be configured according to one of the following three configurations: 1) A uniform addition of leaching solution along the length of the tube or duct to provide both agitation and replacement of liquid permeated to the second compartment. 2) A reducing flowrate to match the flowrate to either the permeation at each point (in the vertical configuration there will be more permeation at the lower levels due to higher head pressure, which diminishes up the column) or to match the need to reduce the liquid-solids ratio in the inner compartment. 3) An increased flow rate along the length of the tube (during a wash process) where the intention is to retain the loaded leachate in the column and to use the fresh wash liquid to lift the solids out of the top section of the column even to the point of creating some liquid backflow to enhance the retention of the loaded leachate. In some cases, the duct or tube may be formed by the central shaft of the agitating arrangement. The openings or nozzles may be located between the impellers supported by the central shaft. One or both of the container and the liquid permeable separator may be rotated by one or more drive motors such that the container and the liquid permeable separator may operatively rotate relative to each other. In a first embodiment of the first aspect of the invention, the container may be arranged in a substantially vertical orientation. Here the slurry inlet may be located towards a bottom of the container while the slurry outlet may be located towards a top of the container. Typically, dimensions of the container and liquid permeable separator may be such that a volumetric ratio of the second to first compartments are between 0.5:1 and 2:1. The container and liquid permeable separator may have non-exhaustive and non-limiting example dimensions as indicated in the table below: OD-Container (m) OD-Separator (m) Length (m) Vol - 2nd Compartment (m3) Vol - 1st Compartment (m3) 0.25 m 0.2 m 0.5m 0.008836 0.015708 0.3 m 0.2 m 1m 0.03927 0.031416 0.4 m 0.3 m 1.5m 0.082467 0.106029 0.5 m 0.3 m 3m 0.376991 0.212058 In an alternative embodiment of the first aspect of the invention, the container may be arranged in a substantially horizontal orientation. In either the first or second embodiments of the first aspect of the invention, the container may have a substantially symmetrical cross-sectional shape. Axial centre lines of the container and the liquid permeable separator may be coincident. In a variation of the second embodiment of the first aspect of the invention, the first container may be located towards and may extend along an upper portion of the internal volume (now the axial centre lines are no longer coincident). Further in respect of the second embodiment of the first aspect of the invention, dimensions of the container and liquid permeable separator may such that a volumetric ratio of the second to first compartments may be between 0.5:1 and 5:1. In accordance with a second aspect of the invention there is provided an extraction system comprising at least a first and second extraction apparatus arranged in series. Each extraction apparatus may be according to the first aspect of the invention. The slurry outlet of the first -6-extraction apparatus may be provided in direct flow communication with the slurry inlet of the second extraction apparatus. Further according to the second aspect of the invention, a third and optionally further extraction apparatuses may be arranged in series with the first and second extraction apparatuses. Each of the third and optional further extraction apparatuses may be an extraction apparatus according the first aspect of the invention. Operatively, a flow rate of slurry through the first compartment may be a variable that may be controlled to achieve either a) a predetermined leachate or loaded leachate removal to the second chamber, and / or b) a specified residence time of slurry in the first compartment to facilitate interaction between the leaching solution and the solids in the slurry. Flow rates of slurry into or within the apparatus may be variable. The agitating apparatus may be caused to rotate from 15 to 40Hz. The rotational speed of the agitating apparatus may be regulated depending on a size and density of solids within the slurry. The rotational speed of the agitator may be increased when the slurry comprises a relatively higher density or relatively larger particles. A flow rate at which leaching solution may be supplied to the first compartment may be controlled during the following configurations and scenarios: 1) constant liquid to solid control (base configuration) in which the feed additional leachate is adjusted to maintain the solid-liquid ratio in the first compartment at a predetermined or fixed value to maintain suspension and pumpability; 2) a reducing ratio in which a rate of addition of leachate is lower than a rate of permeation of leachate or loaded leachate to the second compartment resulting in a net decrease in the liquid-solid ratio and a thickening of the slurry; and 3) increasing ratio or “wash scenario” in which the flow rate of leachate into the first compartment is increased such that the flow rate exceeds the permeation rate into the second compartment. A flow rate of leachate extracted from the second compartment may be controlled to a) protect pumps and other hardware used to extract it, and b) moderate the permeation rate to the second compartment. Typically, leaching solution is added to the first compartment at a rate at least equal to a rate at which loaded leachate is extracted from the second compartment. Leaching solution flows within the extraction system may be configured to be operated in a counter-current fashion to the slurry flows, such that: fresh leaching solution may be provided to the first chamber of the last apparatus of the system, partially loaded leachate from the second chamber of the last apparatus of the system may be provided to the first chamber of an upstream apparatus of the system, and so on, loaded leachate may be extracted from the second chamber of the first unit where it contacts or after having contacted the slurry. Alternatively, leaching solution flows within the extraction system may be configured to be operated in a co-current fashion to the slurry flows, such that fresh leaching solution may be provided to the first chamber of each apparatus and loaded leachate may be removed from the second chamber of each apparatus and passed for downstream processing. Further alternatively, a combination of the counter-current and co-current flows may be used, in which leachate and fresh addition of leaching solution is supplied to the first chamber of each unit. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a perspective view of a first example embodiment of an extraction apparatus according to the invention; Figure 2 Figure 3 Figure 4 shows an exploded view of the extraction apparatus of Figure 1; shows a front view of the extraction apparatus of Figure 1; shows a sectioned front view of the extraction apparatus of Figure 1 (in which an agitating arrangement is not sectioned for clarity and to show features thereof more clearly); Figure 5 shows a bearing arrangement supporting the agitating arrangement forming part of the extraction apparatus of Figure 1; Figure 6 shows a top view of an end cap forming part of the extraction apparatus of Figure i ■ Figure 7 Figure 8 1 , shows a sectioned top view of the extraction apparatus of Figure 1; shows a perspective view of a second example embodiment of an extraction apparatus according to the invention; Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 shows a side view of the extraction apparatus of Figure 8; shows a sectioned side view of the extraction apparatus of Figure 8; shows a front view of the extraction apparatus of Figure 8; shows a sectioned front view of the extraction apparatus of Figure 8; and shows a diagrammatic representation of a system incorporating a number of extraction apparatuses of Figure 1. DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted", "connected", "engaged" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings and are thus intended to include direct connections between two members without any other members interposed therebetween and indirect connections between members in which one or more other members are interposed therebetween. Further, "connected" and "engaged" are not restricted to physical or mechanical connections or couplings. Additionally, the words "lower", "upper", "upward", "down" and "downward" designate directions in the drawings to which reference is made. The terminology includes the words specifically mentioned above, derivatives thereof, and words or similar import. It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the," and any singular use of any word, include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items. Throughout this disclosure, the term “fresh leaching solution” will be taken to refer to a leaching solution that has not been exposed to metal or metalloid containing material or slurry in a leaching process. Throughout this disclosure, the term “leachate” will be taken to refer to a leaching solution that has been in contact with metal or metalloid containing material or slurry in an ongoing or completed leaching process. Throughout this disclosure, the term “loaded leachate” will be taken to refer to a leachate obtained as a final product after the completion of a leaching process. Throughout this disclosure, the term “recycled leachate” will be taken to refer to leachate or loaded leachate that has been subjected to a further process to reduce the concentration of at least one of the target metals or metalloids in the leachate or loaded leachate to substantially zero, thereby to produce a leaching solution for continued use in a leaching process and / or in the method of the invention. Throughout this disclosure, the term “partially loaded leachate” will be taken to refer to leachate or loaded leachate that has been subjected to a further process to reduce the concentration of at least one of the target metals or metalloids in the leachate or loaded leachate to a concentration less than a concentration of that metal or metalloid in the leachate or loaded leachate, thereby to produce a leaching solution for continued use in a leaching process and / or in the method of the invention. Alternatively, where indicated by the context the term “partially loaded leachate” may refer to a leachate obtained from a first apparatus or run that will be used as leaching solution in a second apparatus in fluid communication with the first apparatus or a second run of the leaching process. Throughout this disclosure, the term “leaching solution” will be understood to encompass fresh leaching solution, leachate, recycled leachate, partially loaded leachate, or mixtures thereof. Throughout this disclosure, the term “leaching process” will be understood to encompass any one of: a single-stage leaching process associated with a single leaching apparatus; a multistage leaching process associated with more than one batched run of the leaching process in a single leaching apparatus; or a multi-stage leaching process associated with more than one leaching apparatus provided in series, parallel, or any combination of the aforementioned. Referring to the drawings, in which like numerals indicate like features, a non-limiting example of an extraction apparatus (or simply “apparatus”), in accordance with the invention, is generally indicated by reference numeral 10. The apparatus 10 operatively forms part of a larger system 100 used in the process of leaching metals or metalloids from ores. Figures 1 to 7 show a first and preferable example of the apparatus 10, while figures 8 to 12 show a second and alternative example embodiment of the apparatus 10. Like features associated with both example embodiments are indicated by like numerals. The apparatus 10 comprises a container 12 defining an internal volume 14 (which is best shown in the exploded view in figure 2). For ease of reference, the container 12 is shown in the figures to be manufactured from a transparent material, such as Perspex, glass or the like. Even though the use of transparent material has some advantages, such as allowing visual inspection of internal components, materials, flows, blockages and the like, the container 12 need not be manufactured from such a transparent material and is not limited as such. The container 12 forms an outer and liquid impermeable body of the apparatus 10. The apparatus further comprises a liquid permeable separator (or simply “separator”). The separator 16 is located within the internal volume 14 and defines therewithin a first compartment 18 and a second compartment 20. The first compartment 18 comprises a volume enclosed by the separator 16 and the second compartment is defined between an outer surface of the separator 16 and an inner surface of the container 12. This is best shown in the sectioned top view in figure 7. The first compartment 18 is therefore an inner compartment while the second compartment 20 is an outer compartment. It will be appreciated that, theoretically though perhaps not optimally, the first and second compartments (18, 20) may be formed in side-by-side fashion with the separator 16 forming a mutual separating barrier or wall between the two. A first end cap 22 and second end cap 24 are located at opposite ends of the container 12 and are provided for enclosing the internal volume 14. The end caps (22, 24) are provided with seating grooves 26 for sealingly receiving end portions of the container 12 and separator 16. The seating grooves 26 may be provided with seal elements (not shown). A slurry inlet 28 is provided into the first compartment 18 and facilitates operative introduction of slurry into the first compartment 18. The slurry inlet 28 may take the form of one, but typically two or more openings through the first end cap 22, which are spaced radially between a centre point of the end cap 22 and the seating groove 26 associated with the separator 16. The openings are furthermore equidistantly spaced about the centre point to provide for a relatively constant flow rate and introduction of slurry into the first compartment 18. In use, the slurry inlet 28 is either provided in fluid flow communication with an upstream process with which the slurry is prepared, with a slurry outlet of another apparatus 10 forming part of the system, or with a slurry outlet of the apparatus 10 in cases where slurry is passed through the apparatus 10 in more than one run. This is expanded on further below. Furthermore, a slurry outlet 30 is provided from the first compartment 18 and facilitates operative disposing of spent (or at least relatively spent) slurry from the first compartment 18. The slurry outlet 30 may take the form of one, but typically two or more openings through the second end cap 24, which are spaced radially between the centre point of the end cap 24 and the seating groove 26 associated with the separator 16. The openings are furthermore equidistantly spaced about the centre point to provide for a relatively constant flow rate of spent slurry from the first compartment 18. In use, the slurry outlet 30 is provided in fluid flow communication with a downstream process with which the spent slurry is handled, or with slurry inlets as aforementioned. This is expanded on further below. The apparatus 10 furthermore comprises a leaching solution feed arrangement 32 with which leaching solution is fed into the first compartment 18 in use. The leaching solution feed arrangement 32 may take various forms and is not limited to the example shown in the figures. For example, in embodiments not shown in the figures, the leaching solution feed arrangement 32 may simply comprise openings into the first compartment 18 through which leaching solution is operatively supplied into the first compartment 18. Alternatively, the leaching solution feed arrangement 32 may comprise spray or header bars which spray leaching solution into the first compartment 18. The leaching solution fed through the feed arrangement 32 may be fresh -11-leaching solution, leachate, leachate recycled in a downstream process, partially loaded leachate, or mixtures of the aforementioned. In the example embodiment shown in the embodiment of figures 1 to 7, the leaching solution feed arrangement 32 is incorporated with an agitating arrangement 34. The leaching solution feed arrangement 32 and agitating arrangement 34 are discussed in more detail below. Suffice to say, incorporation of the leaching solution feed arrangement 32 into the agitating arrangement 34 has certain distinct advantages, such as facilitating feeding of leaching solution substantially along a whole length of the first compartment 18 and allowing the introduction of the leaching solution to enhance the efficiency or contribute to the agitation caused by the agitating arrangement 34. A leachate outlet 36 is provided from the second compartment 20 and facilitates operative disposing or extracting of leachate (this is discussed in more detail below). The leachate outlet 36 may take the form of one, but typically two or more openings through the first end cap 22, which are spaced radially between the seating groove 26 associated with the separator 16 and the seating groove 26 associated with the container 12. In use, the leachate outlet 36 is provided in (direct or indirect) fluid flow communication with a downstream process with which the leachate is treated. Alternatively, the leachate may be fed back to the leaching solution feed arrangement 32 of the apparatus 10 or another apparatus 10 forming part of the system 100. This is expanded on further below. A pressure regulating arrangement (not shown) is provided for operatively maintaining a negative pressure differential over the separator 16 and therefore between the first and second compartments (18, 20). The pressure regulating arrangement may typically comprise a suction pump or the like connected in fluid flow communication with the second compartment and may be arranged in flow communication with the second compartment 20 by means of an opening 38 in the second end cap 24. Alternatively, the pressure regulating arrangement may comprise a pump or compressor with which a positive flow of air or leaching solution and slurry is provided to the first chamber 18, to create an above-atmospheric pressure in the first compartment. In the first embodiment, the container 12 and separator 16 are typically both substantially cylindrical (as best shown in figure 2) and are arranged concentrically (as best shown in figure 7). This is particularly relevant in configurations where the apparatus 10 extends substantially vertically (as is the case in the first embodiment) since relatively constant cross-sectional flow rates are achievable along a perimeter of the separator 16. The agitating arrangement 34 is located axially within the first compartment 18 and along a whole length of the first compartment 18 and is provided for operatively agitating the slurry in the first compartment 18. As shown in figures 1 to 7, the agitating arrangement 34 may comprise an impeller arrangement. However, the agitating arrangement 34 may alternatively comprise an auger or -12-screw arrangement, a spray arrangement in which a fluid (gas or liquid) is injected into the slurry to suspend solids therein, or as shown and discussed, combination of the above. In the horizontal configuration shown in figure 12, for example, the agitating arrangement may also include an auger, screw or helical arrangement mounted to and driven by the rotation of the separator 16. The agitating arrangement 34 as shown, includes a plurality of impellers 40 which are supported on a central drive shaft 42. The impellers are generally spaced axially at regular intervals. The central drive shaft 42 is driven by a single drive motor or more than one drive motors (not shown) coupled to opposite sides of the drive shaft 42. Typically, the plurality of impellers are made up of a number of impellers of a first kind (indicated by reference numeral 40.1) and a number of impellers of a second kind (indicated by reference numeral 40.2). The impellers of the first kind 40.1 have a first, larger size or diameter and a first pitch direction, while the impellers of the second kind 40.2 have a second, smaller size or diameter and a second pitch direction. The first pitch direction of the impeller of the first kind 40.1 (seen in view of the predetermined rotational direction of the central shaft 42) is configured to displace the slurry within the first compartment in a direction towards the slurry outlet 30 or away from the slurry inlet 28 (and in the embodiment shown in the figures, substantially upwards). The second pitch direction of the impeller of the second kind 40.2 (seen in view of the predetermined rotational direction of the central shaft 42) is configured to displace the slurry within the first compartment in a direction towards the slurry inlet 28 or away from the slurry outlet 30 (and in the embodiment shown in the figures, substantially downwards). By having opposite pitch directions, the impellers of the first and second kind (40.1, 40.2) therefore exert forces on the slurry that comes into contact therewith, in substantially opposite directions, when rotated in the same rotational direction. By being mounted to a single central shaft 42 which is operatively rotated in a predetermined rotational direction, the impellers of the first and second kind (40.1, 40.2) create at least a localised counter-current flow or local non-laminar mixing flow in the slurry contained in the first compartment 18. The relevance of this is discussed more fully below. Despite the (at least a localised) counter-current flow or local non-laminar mixing flow of the slurry, a net flow of slurry within the first compartment 18 is created from the slurry inlet 28 to the slurry outlet 30. This is caused or induced by one or more of the following factors: 1) since the impellers of the first kind 40.1 have a larger size or diameter than that of the impellers of the second kind 40.2, a larger net force is exerted by the impellers of the first kind 40.1; and / or 2) the slurry is fed or pumped positively from the inlet and towards the slurry outlet (the pumpability and -13-moisture content, and particularly the management of the moisture content of the slurry is discussed more fully below). As discussed, the leaching solution feed arrangement 32 can be incorporated with the agitating arrangement 34. For this purpose, the central shaft 42 is hollow, forming a duct or tube for conveying the leaching solution. The central shaft 42 comprises a plurality of openings or nozzles (not shown) which are spaced along a length thereof, between the impellers 40, and which allow streams of leaching solution to flow or be projected radially outward from the central shaft 42 into the first compartment, substantially along a length of the first compartment 18. The size of and / or spacings between the openings or nozzles may be configured to facilitate a number of flow regimes or configurations of the leaching solution. The flow regimes or configurations may comprise 1) a substantially uniform distribution along the length of the first compartment 18; 2) a decreasing distribution along the length of the first compartment 18; and 3) an increasing flow distribution along the length of the first compartment 18. This is discussed more fully below. In an alternative arrangement (not shown and one which may not necessarily be optimal) leaching solution may be fed from the first endcap instead of through a hollow shaft 42, and so, the shaft may instead be solid. The central shaft 42 is supported by bearing housings 44. The separator 16 comprises a base structure which takes the form of a cylinder formed from mesh or expanded metal. Alternatively, and as shown, the separator 16 comprises linearly spaced hoop members 46 interconnected by longitudinally extending members 48 which form a mesh (known as a wedge wire structure). Provision is also made for the base structure to be manufactured from plastic or rubber mesh structures. The base structure comprises openings or apertures which are at least 1.5 times the average particle size of the particles in the slurry. An apertured screen, filter material or perforated sheet (not shown) is provided in contact with the base structure, such that the base structure supports the apertured screen, filter material or perforated sheet. In some cases, the base structure comprises a single support layer to which the apertured screen, filter material or perforated sheet is fastened or by which the apertured screen, filter material or perforated sheet is supported. The apertured screen, filter material or perforated sheet may typically be fastened by bands, straps or similar restraining devices. Alternatively, the base structure may comprise a double layer between which the apertured screen, filter material or perforated sheet is sandwiched. The aperture size of the apertured screen, filter material or perforated sheet is selected based on the type of material that will be processed by the apparatus 10. Typically, the aperture size is between 0.1 and 1 times the average particle size of the particles in the slurry. The -14-apertured screen, filter or sheet may have an open to closed extent of at least 45%. This ensures and facilitates effective flow and throughput of leachate through the separator 16. Typically, the container 12 and the separator 16 have symmetrical cross-sectional shapes and axial centre lines thereof are coincident. Dimensions of the container and liquid permeable separator are such that a volumetric ratio of the second to first compartments are between 0.5:1 and 2:1. Example dimensions of the apparatus are shown in the table below. OD-Container (m) OD-Separator (m) Length (m) Vol - 2nd Compartment (m3) Vol - 1st Compartment (m3) 0.25 m 0.2 m 0.5m 0.008836 0.015708 0.3 m 0.2 m 1m 0.03927 0.031416 0.4 m 0.3 m 1.5m 0.082467 0.106029 0.5 m 0.3 m 3m 0.376991 0.212058 Reference is now made to figures 8 to 12 in which a horizontally configured embodiment of the apparatus 10 is shown. The horizontally configured embodiment operates conceptually substantially similarly to the vertical configuration detailed above, and only minor differences will be discussed. Firstly, since the apparatus 10 is now configured horizontally, the internal volume 14 therefore also extends substantially horizontally and the flow of slurry within the apparatus 10 is generally from one side to the other (horizontally) rather than upwards (vertically). The agitating mechanism 34 now takes the form of an auger, spiral or helix of which an outer periphery is fixed to the separator 16. The whole inner compartment therefore rotates relative to the outer compartment, which allows the agitating mechanism 34 to cause the slurry to be displaced towards the slurry outlet 30. Since the auger, spiral or helix is fixed towards an outer periphery thereof, no central shaft is required to support it, and therefore a longitudinal axial opening is defined within which the leaching solution feed arrangement 32 may extend and with which the leachate may be fed into the first compartment 18. The leachate outlet 36 is made up of a number of outlets 36 associated with a number of catchment formations 54 which form part of the second compartment 20 and which are situated below the first compartment 18. In a further alternative embodiment, which represents a variation to the horizontal configuration, and which is not shown in the figures, the inner volume 14 of the apparatus extends at a slight angle (upwards in a travel direction of the slurry). This may be achieved by arranging the whole apparatus 10 at a slight angle, or by arranging the separator 16 and therefore the first -15-compartment 18 at an angle relative to the second compartment 20. The first and second compartments (18, 20) in this configuration, therefore, need not extend parallel. In this way, a “changing depth” along the axial direction of the inner compartment 18 may be created (based on the assumption that the inner compartment 18 is not completely filled with slurry and / or leaching solution, though such a configuration is not impossible). The depth therefore reduces in the travel direction of the slurry, which, together with the interaction of the agitating mechanism 34 on the slurry, results in a relatively “dry cake” exiting the slurry outlet 30. Reference is again made to either embodiment, but particularly the first embodiment of the invention. The apparatus 10 may form part of a larger extraction system 100 (as shown schematically in the system diagram of figure 13). As part of the system 100, the slurry inlet 28 is provided (directly or indirectly) in flow communication with a leach vessel 102 in which the slurry is operatively prepared by combining a metal or metalloid containing ore source with reactants in a chemical leaching process. Furthermore, the leachate outlet 36 is operatively provided (directly or indirectly) in fluid flow communication with one of a filter and crystallizer plant 104 for downstream processing. In some cases, and as shown in figure 13, the system 100 may comprise more than one apparatus 10 provided in series. In such cases, the slurry outlet 30 of the first apparatus 10 is provided in (direct or indirect) flow communication with the slurry inlet 28 of the second or a further extraction apparatus 10, and so on. By providing more than one apparatus 10 in series, extraction of the metal or metalloid from the slurry may be more effectively achieved. In some cases, a washing arrangement 106 may be received between two extractor apparatuses 10. The washing arrangement 106 may comprise an apparatus of similar construction than the apparatus 10, but which is configured and set up for washing, rather than extraction. In systems 100 where more than one apparatus 10 is provided in series, leaching solution or leachate flows within the extraction system 100 may be configured to be operated a countercurrentfashion (as shown in figure 13), a co-currentfashion, ora combination thereof. The system 100 may be adapted to facilitate these flow regimes. For example, in the counter-current configuration the leachate outlet 36 of the final extraction apparatus is provided in fluid flow communication with the leaching solution feed arrangement 32 of an upstream extraction apparatus 10. In such a case, fresh leaching solution is supplied to the first chamber 18 of the final extraction apparatus 10 only. Partially loaded leachate from the second chamber 20 of the final apparatus 10 is then provided to the first chamber 18 of the upstream apparatus 10 of the system 100, and so on. Loaded leachate is finally extracted from the second chamber 20 of the first extraction apparatus 10. A single flow of -16-loaded leachate is therefore extracted from the whole system 100 and provided to the filter and / or crystallizer plant 104. In the co-current configuration, each leaching solution feed arrangement 32 is provided in fluid flow communication with a supply of fresh leaching solution and / or with a leachate outlet of an upstream extraction apparatus. Therefore, a single feed of leaching solution or leachate may flow from the first apparatus, downstream to the last apparatus where loaded leachate is then extracted. Alternatively, fresh leaching solution may be supplied to each apparatus and loaded leachate may be extracted from each apparatus. Further alternatively, (apart from the first apparatus) each apparatus may be supplied with a mixture of partially loaded leachate (being a portion of leachate extracted from an upstream apparatus) and fresh leaching solution. In the combined configuration, the leaching solution feed arrangement 32 of each upstream extraction apparatus is provided in fluid flow communication with both a leachate outlet of a downstream extraction apparatus (from which a portion of extracted partially loaded leachate is supplied to the upstream apparatus) and a supply of fresh leaching solution. In the co-current and combined configurations, more than one feed of loaded leachate may be provided in parallel as a final product for downstream processing. Referring to a single apparatus 10 or each apparatus 10 forming part of a system 100, in use, slurry with an initial moisture content is pumped via the slurry inlet 28 into the first compartment 18. During use, the first compartment 18 is completely filled with slurry. The agitating arrangement 34 continuously rotates and agitates slurry within the first compartment 18 causing the (at least local) counter-current flow or non-laminar mixing flow. At the same time, leaching solution is continuously supplied through the leaching solution feed arrangement 32, which aids in agitating the slurry by suspending solids therein, whilst offsetting the permeation through the separator 16, partially or entirely, thereby controlling the moisture content of the slurry. At the same time, the pressure regulating arrangement creates a pressure differential over the separator 16. The interaction between all or at least some of the above factors causes leachate or loaded leachate to be extracted from the slurry and therefore from the first compartment 18 through the separator 16 and into the second compartment 20, where the leachate or loaded leachate either collects or is immediately drained through the leachate outlet 36. It is not the intention of this disclosure to comment on the chemical reactions that take place in the preparation of the slurry, the extraction of the loaded leachate or the downstream processing of the loaded leachate. That said, from a process point of view, the following parameters may be controlled: Flow rate of slurry through the first compartment: a variable that is controlled through various mechanisms to achieve either: a) a necessary or predetermined leachate removal to the second compartment 20; or b) a specified residence time of slurry in the first compartment 18 to facilitate interaction between the leachate and the solids in the slurry. Balance of flow rates: In some cases, flow rates (of slurry into the first compartment 18 through the slurry inlet 28, slurry from the first compartment 18 through the slurry outlet 30, leaching solution into the first compartment 18 by means of the leaching solution feed arrangement 32 and leachate from the second compartment 20 through the leachate outlet 36) may be balanced to result in a relatively constant moisture content of the slurry before entering and after being expelled from the apparatus 10. In other cases, the flow rates may be unbalanced to result in a moisture content at the slurry outlet 30 which is lower than the moisture content at the slurry inlet 28. In such a case, the volume of leachate extracted from the second compartment 20 exceeds the volume of leaching solution provided via the leaching solution feed arrangement 32. This may produce a relatively dry solid output from the first compartment 20. Rate of rotation of the agitating arrangement 34: Typically, the shaft 42 is driven to rotate at 15 to 40Hz. The rate is a variable which can be regulated depending on the size and density of the solids within the slurry. A higher density or larger particles will require a higher rate of rotation. Feed rate of leaching solution supplied via the leaching solution feed arrangement 32 into the first compartment 18: The feed rate of leaching solution can be controlled for three different configurations as follows: 1) constant liquid-solid control (first configuration) in which the feed is adjusted to maintain the solid-liquid ratio of the slurry within the first compartment 18 at a fixed and predetermined value optimised for extraction and pumpability of the slurry; 2) a reducing ratio (second configuration) in which the feed rate is lower than the rate of permeation or extraction of leachate or loaded leachate through the separator 16 to the second compartment 20, resulting in a net decrease in the liquid-solid ratio and therefore a thickening or drying of the slurry and 3) an increasing ratio (third configuration) in which the moisture content of slurry exiting the first compartment 18 through the slurry outlet 30 exceeds the moisture content of slurry entering the first compartment 18 through the slurry inlet 28 (and therefore, wherein the feed rate of leaching solution through the leaching solution feed arrangement 32 exceeds the rate at which leachate is extracted into the second compartment 20). Typically, the third configuration is useful in a wash configuration -18-wherein fresh leaching solution, water, or an alternative wash solution may be provided through the leaching solution feed arrangement 32. Flow rate of leachate extracted into the second compartment and through the leachate outlet 36: Controlled in the first embodiment to maintain a sufficient level to: a) protect the pumps removing the leachate from the second compartment 20; and b) moderate the permeation rate to the second compartment (higher levels of leachate will create back pressure and reduce the permeation rate). In the second embodiment, only criteria a) is applicable. Ratios of leachate to leaching solution supplied to the slurry: Base case (noting that exceptions in the changes to the solid liquid ratio could apply) would be that the volume of leachate should be at least equal to the liquid fraction in the feed slurry to allow for a total swap-out of leachate within the apparatus 10 up to a ratio of over 6 leachate swop outs in a single slurry pass. Flow distribution / supply rate of leaching solution along the length of the shaft 42: Three operating configurations are provided for: 1) uniform addition of the leaching solution along the length of the shaft 42 to provide both agitation and replacement of permeated leachate to the second compartment 20; 2) a reducing flowrate along the length of the shaft 42 to match a flowrate to either the permeation at each point (in the first embodiment there will be more permeation at the lower levels due to higher head pressure, which diminishes up the column) or to match the need to reduce the liquid solids ratio in the first compartment: 3) an increased flow rate along the length of the shaft 42, which would be particularly relevant in a “wash column” where the intention is to retain the loaded leachate in the column and to use the fresh wash liquid (for example water) or fresh leaching solution to lift the solids out of the top section of the column even to the point of creating some liquid backflow to enhance the retention of the loaded leachate. At least the first two configurations may be particularly relevant in a case where antimony is the target metal or metalloid which is extracted using the apparatus 10. It is believed that the system and apparatus provided for herein provides various improvements over the prior art and may result in producing a final product of relatively high purity and greater extraction of the desired component. Compared to known prior art, the invention provides a recycled counter current flow system, which holds the slurry material for the duration of the run in motion as a continuous process with moving slurry in opposite flow direction. The leach and precipitation steps take place in different vessels to optimise the separation and resulting purity of the product. The spray system provides a leaching solution supply strategy and plays no role in cleaning or clearing a filter. The system operates continuously with a wet face -19-and a partially dry face with continuous suction on all side of the filter at any given time, which again optimises and maximises contact time between the leach solution and the solids. It will be appreciated that the above description only provides example embodiments of the invention and that there may be many variations without departing from the spirit and / or the scope of the invention. For example, with reference to the first embodiment, the container 12 and separator 16 may be rotated relative to each other. Furthermore, even though provision is specifically made for the extraction of antimony using the apparatus 10, provision is made for the extraction of other metals or metalloids, such as (but not limited to): gold; copper; nickel; arsenic; cobalt; and aluminium. Subject to the material to be extracted, the respective reagents and chamber conditions in respect of chemicals used, concentrations thereof, temperature and pressure may be changed from those detailed for example of extraction of antimony. It will be easily understood from the present description that the particular features of the present invention, as generally described and illustrated in the figures, can be arranged and designed according to a wide variety of different configurations. In this way, the description of the present invention and the related figures are not provided to limit the scope of the invention but simply represent selected embodiments. The skilled person will understand that the technical characteristics of a given embodiment can in fact be combined with characteristics of another embodiment, unless otherwise expressed or it is evident that these characteristics are incompatible. Also, the technical characteristics described one embodiment can be isolated from the other characteristics of this embodiment unless otherwise expressed.

Claims

1. An extraction apparatus used during a leaching process of metals or metalloids, the extraction apparatus comprising:a container having an internal volume;a liquid permeable separator located within the internal volume, defining a first and second compartment within the internal volume;a slurry inlet for operatively receiving slurry into the first compartment and a slurry outlet for operatively disposing slurry from the first compartment;a leaching solution feed arrangement for operatively feeding leaching solution into the first compartment;a leachate outlet for operatively extracting leachate from the second compartment; anda pressure regulating arrangement for operatively maintaining a negative pressure differential over the liquid permeable separator and between the first and second compartments.

2. The extraction apparatus according to claim 1, wherein the container and liquid permeable separator are substantially cylindrical and optionally concentric.

3. The extraction apparatus according to claim 1 or 2, wherein the first compartment is an inner compartment, and the second compartment is an outer compartment, surrounding the first or inner compartment.

4. The extraction apparatus according to any one of the preceding claims, further comprising an agitating arrangement within the first compartment, provided for operatively agitating and suspending partially or totally the slurry within the first compartment.

5. The extraction apparatus according to claim 4, wherein the agitating arrangement extends substantially along a length of the first compartment.

6. The extraction apparatus according to claim 4 or claim 5, wherein the agitating arrangement comprises at least one of: i) an auger or screw; ii) an impeller arrangement; and iii) a spray arrangement for injecting fluid flows in the form of a gas or a liquid used to suspend solids in the slurry.

7. The extraction apparatus according to claim 6, wherein the impeller arrangement comprises more than one impeller supported on a central shaft and spaced longitudinally, optionally at regular intervals, along a length of the first compartment, and wherein the central shaft is driven by a drive motor from either one or both ends of the central shaft.

8. The extraction apparatus according to claim 6 or 7, wherein the impeller arrangement comprises at least one impeller of each of a first and a second kind, wherein the impeller ofthe first kind has a first larger diameter and a first pitch direction and wherein the impeller of the second kind has a second smaller diameter and a second pitch direction.

9. The extraction apparatus according to claim 8, wherein the first pitch direction of the impeller of the first kind is configured operatively to displace slurry in a direction towards the slurry outlet and wherein the second pitch direction of the impeller of the second kind is configured operatively to displace slurry in a direction towards the slurry inlet, such that the impellers of the first and second kind operatively cause, at least a local, counter current or non-laminar mixing flow of slurry within the first compartment.

10. The extraction apparatus according to any one of the preceding claims, wherein the container forms an outer, liquid impermeable body.

11. The extraction apparatus according to any one of the preceding claims, wherein the container further comprises first and second end caps and wherein the liquid permeable separator extends from the first to the second end cap.

12. The extraction apparatus according to any one of the preceding claims, wherein the liquid permeable separator comprises a base structure comprising one of: i) a cylinder formed from mesh or expanded metal; ii) linearly spaced hoop members interconnected by longitudinally extending members, the hoop members and longitudinally extending members forming a grid or mesh, optionally formed from wedge wire; and iii) plastic or rubber mesh structures, and wherein the base structure comprises apertures in the range of at least 1.5 times an average particle size of particles in the slurry.

13. The extraction apparatus according to claim 12, wherein the liquid permeable separator further comprises an apertured screen, filter material or perforated sheet, supported by the base structure, wherein the apertured screen, filter material or perforated sheet has apertures in the range of between 0.1 and 1 times an average particle size of particles in the slurry, and further wherein the apertures of the apertured screen, filter material or perforated sheet comprise at least 45% of a surface thereof.

14. The extraction apparatus according to claim 13, wherein the apertured screen, filter material or perforated sheet is fixed relative to the base structure by way external fastening means in the form of one of bands and straps.

15. The extraction apparatus according to claim 13, wherein the base structure is formed by a double-layered structure, and wherein the apertured screen, filter material or perforated sheet is sandwiched between the layers of the double-layered structure.

16. The extraction apparatus according to any one of the preceding claims, wherein the slurry inlet is provided in flow communication with a leach vessel in which the slurry is operatively prepared by combining a metal or metalloid containing ore source with reactants in a chemical leaching process.

17. The extraction apparatus according to any one of the preceding claims, wherein the leachate outlet is operatively provided in fluid flow communication with one of a filter and crystallizer plant for downstream processing.

18. The extraction apparatus according to any one of the preceding claims, wherein the pressure regulating arrangement is provided in fluid flow communication with an opening in the second compartment, and wherein the pressure regulating arrangement is configured operatively to cause a pressure to be maintained in the second compartment which is lower than an operative pressure in the first compartment.

19. The extraction apparatus according to any one of the preceding claims, wherein the leaching solution feed arrangement comprises a duct or tube extending longitudinally within the first compartment, comprising a plurality of openings or nozzles spaced along a length thereof, for operatively distributing leaching solution along a length of the first compartment.

20. The extraction apparatus according to claim 19 when dependent on claim 7, wherein the duct or tube is formed by the central shaft and wherein the openings or nozzles are located between impellers supported by the central shaft.

21. The extraction apparatus according to any one of the preceding claims, wherein one or both of the container and the liquid permeable separator are operatively rotated by one or more drive motors such that the container and the liquid permeable separator operatively rotate relative to each other.

22. The extraction apparatus according to any one of the preceding claims, wherein the container is arranged in substantially vertical orientation and wherein the slurry inlet is located towards a bottom of the container and wherein the slurry outlet is located towards a top of the container.

23. The extraction apparatus according to claim 22, wherein dimensions of the container and liquid permeable separator are such that a volumetric ratio of the second to first compartments are between 0.5:1 and 2:1.

24. The extraction apparatus according to any one of claims 1 to 21, wherein the container is arranged in substantially horizontal orientation.

25. The extraction apparatus according to claim 24, wherein the container has a symmetrical cross-sectional shape and wherein axial centre lines of the container, and the liquid permeable separator are coincident.

26. The extraction apparatus according to claim 24, wherein the first container is located towards and extends along or towards an upper portion of the internal volume.

27. The extraction apparatus according to any one of claims 24 to 26, wherein dimensions of the container and liquid permeable separator are such that a volumetric ratio of the second to first compartments are between 0.5:1 and 5:1.

28. An extraction system comprising at least a first and second extraction apparatus arranged in series, each extraction apparatus according to any one of claims 1 to 27, wherein the slurry outlet of an upstream one of the extraction apparatuses is provided in flow communication with the slurry inlet of a downstream one of the extraction apparatuses.

29. The extraction system according to claim 28, comprising a third and optionally further extraction apparatuses arranged in series with the first and second extraction apparatuses, each of the third and optional further extraction apparatuses according to any one of claims 1 to 27.

30. The extraction system according to claim 28 or 29, wherein the system is configured in one of the following configurations:i) a counter current configuration, in which the leachate outlet of a final one of the extraction apparatuses is provided in fluid flow communication with a leaching solution feed arrangement of an upstream extraction apparatus;ii) a co-current configuration, in which each leaching solution feed arrangement is provided in fluid flow communication with a supply of fresh leaching solution and / or with a leachate outlet of an upstream extraction apparatus; andiii) a combined configuration, in which the leaching solution feed arrangement of each upstream extraction apparatus is provided in fluid flow communication with both a leachate outlet of a downstream extraction apparatus and a supply of fresh leaching solution.

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