Method for the extraction of metals or metalloids from metal and metalloid containing material

Abstract

The invention relates to a continuous method for extracting a metal or metalloid from a metal- or metalloid-containing material. The method comprises contacting the material with a leaching solution to form a slurry, which is provided to a first compartment of an extraction apparatus comprising first and second compartments separated by a liquid-permeable separator. The slurry is contacted under conditions that produce a loaded leachate, which is continuously separated across the liquid-permeable separator into the second compartment by maintaining a negative pressure differential between the compartments. Leaching solution comprising fresh leaching solution, recycled leachate, partially loaded leachate, and mixtures thereof is continuously supplied to the slurry at a rate sufficient to maintain the slurry within a selected solid-liquid ratio range.

Description

[0001] METHOD FOR THE EXTRACTION OF METALS OR METALLOIDS FROM METAL AND METALLOID CONTAINING MATERIAL

[0002] INTRODUCTION

[0003] This invention relates to a metal and metalloid extraction method. More particularly, the present invention relates to a continuous leaching method used during extraction of metals or metalloids, such as, antimony.

[0004] BACKGROUND TO THE INVENTION

[0005] The process of chemical leaching of metals 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 containing ore. The pulped pre-milled material within the leach vessel is mixed or stirred for a predetermined amount of time (in some cases, from 90 minutes to up to 4 hours) whilst maintaining a relatively high temperature (from 60 to 90°C).

[0006] The extracted material is recovered typically either via a chemical precipitation, electrowinning, solvent extraction, or resin absorption process. In one example, loaded leachate obtained through the above process may be filtered to remove residual solid impurities after which the filtered leachate is pumped to a crystallizer where the temperature is maintained while 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 exothermic nature of the reactions taking place. Cooling and flow inside the crystallizer causes crystals to form, 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 metal depleted leachate is safely disposed of.

[0007] It has been found that a single or repeated batched leach process as described above produces relatively low metal recovery. In the case of Antimony, for example, a recovery of about 35% or less of the material in the original feed is generally expected. It is believed that improvements in the leaching process could result in significantly improved metal recovery, resulting in increased process economic viability and efficiency.

[0008] CN104212981A utilises an acidic process with addition of ozone to precipitate the antimony metal 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.

[0009] EP0191102A1 utilises solid-liquid separation with a spray bar. The spray bar is used to remove solids from a rotating 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 for the intended purpose of this invention and may result in a reduced purity of the final product and dilution of the leachate and restricted production and recovery efficiency.

[0010] Continuous leaching processes pose certain known complications, for example, due to difficulties associated with material handling (pumpability and separation of pulped material) and the like. It is accordingly an object of the invention to provide a method for the extraction of metals or metalloids from metal or metalloid containing material that will, at least partially, address the above disadvantages.

[0011] It is also an object of the invention to provide a method for the extraction of metals or metalloids from metal or metalloid containing material that will be a useful alternative to existing extraction processes.

[0012] SUMMARY OF THE INVENTION

[0013] According to a first aspect of the invention there is provided a method for the continuous extraction of a metal or metalloid from a metal or metalloid containing material, the method comprising the steps of: contacting a metal or metalloid containing material with a leaching solution to form a slurry, providing the slurry of the metal or metalloid containing material and leaching solution in a first compartment of an extraction apparatus comprising first and second compartments separated by a liquid permeable separator, contacting the slurry in the first compartment to produce a loaded leachate and continuously separating the loaded leachate from the slurry to the second compartment by maintaining a negative pressure differential over the liquid permeable separator and between the first and second compartments, continuously providing leaching solution comprising fresh leaching solution, recycled leachate, partially loaded leachate, and mixtures thereof to the slurry in the first compartment at a rate such that the solid-liquid ratio of the slurry in the first compartment remains within a selected solid-liquid ratio range, wherein loaded leachate is removed from the second compartment for further processing, and wherein the solid-liquid ratio range is selected from: a first configuration optimized for metal or metalloid extraction or pumpability of the slurry, wherein the rate of addition of leaching solution to the slurry is substantially equal to rate of removal of loaded leachate from the second compartment thereby to maintain a constant solid-liquid ratio, a second configuration wherein the rate of addition of leaching solution to the slurry is reduced relative to the rate of removal of the loaded leachate from the second compartment thereby to increase the solid-liquid ratio, or or a third slurry wash configuration wherein the rate of addition of leaching solution or wash solution to the slurry is increased relative to the rate of removal of the loaded leachate from the second compartment thereby to decrease the solid-liquid ratio.

[0014] In one embodiment, leaching solution is introduced to the first compartment through a feed arrangement comprising 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.

[0015] In one embodiment, leaching solution is continuously provided to the slurry substantially along the whole length of the first compartment.

[0016] In one embodiment, the slurry is provided to the first compartment from a leach vessel in which the slurry is operatively prepared by combining the metal or metalloid containing material with a leaching solution in a chemical leaching process. In one embodiment, the liquid permeable separator defines an operative flow path for slurry within the first compartment and between a slurry inlet and a slurry outlet.

[0017] In one embodiment, the slurry is removed from the first compartment and returned to the leach vessel for further extraction.

[0018] In one embodiment, the method proceeds in the presence of a reduced oxygen atmosphere or an inert gas atmosphere, for example a nitrogen atmosphere.

[0019] Preferably, the metal or metalloid to be recovered is selected from the group of metals consisting of antimony, gold, copper, arsenic, mercury, tin, zinc, cobalt, and nickel.

[0020] In the first configuration, the solid-liquid ratio may be in the range of about 20 wt.% to about 65 wt.% solids.

[0021] Preferably, in the first configuration the solid-liquid ratio is in the range of about 30 wt.% to about 60 wt.% solids.

[0022] Preferably, in the first configuration the solid-liquid ratio is in the range of about 40 wt.% solids.

[0023] In particular embodiments, the metal or metalloid containing material is selected from run-of-mine (ROM) material, ore, tailing concentrates, tailings, calcined material, or alternative preprocessed mineral material, and mixtures thereof.

[0024] Preferably the metal or metalloid containing material present in the slurry has an average particle size of less than about 3 mm, less than about 1 mm, less than about 500 pm, less than about 250 pm, less than about 100 pm, less than about 50 pm, or about 35 pm. Optional further processing of the loaded leachate may include subjecting the loaded leachate to a filtration step, an ion exchange process, an electrowinning process, a precipitation or crystallization step, or a combination thereof.

[0025] In one embodiment, the metalloid extracted by the method is antimony from an antimony containing material.

[0026] In one embodiment, the leaching solution for antimony extraction comprises a mixture of water, a suitable base, and a sulphide containing compound.

[0027] In one embodiment, the leaching solution for antimony extraction comprises a mixture of water, a hydroxide containing base, and sodium sulphide.

[0028] In one embodiment, the hydroxide containing base is selected from sodium hydroxide and potassium hydroxide.

[0029] In one embodiment, the hydroxide containing base and sodium sulphide are independently present in the leaching solution at about 0.25 wt.% to about 12 wt.%.

[0030] The slurry may be kept at a temperature from about 45 °C to about 98 °C.

[0031] Preferably, the slurry may be kept at a temperature from about 70 °C to about 85 °C.

[0032] In one embodiment, the method is employed to extract antimony from antimony containing material in a pre or post gold processing step.

[0033] In a preferred embodiment, the antimony is extracted from the loaded leachate as NaSb(OH)e, Na4O?Sb2, NasC Sb, Sb20s, and mixtures thereof, or electrowon as antimony metal. In one embodiment, the method is implemented through at least a first and second extraction apparatus being arranged in series, wherein a slurry outlet of the first extraction apparatus is provided in direct flow communication with a slurry input of the second extraction apparatus.

[0034] In one embodiment, the method is implemented through at least a first and second extraction apparatus being arranged in series, wherein a slurry outlet of the first extraction apparatus is provided in direct flow communication with an intermediate leach tank where the slurry is held for a predetermined time prior to being pumped to a slurry input of the second extraction apparatus.

[0035] In another embodiment, a third and optionally further extraction apparatuses may be arranged in series with the first and second extraction apparatuses.

[0036] In one embodiment, following the filtration of the slurry from the extraction apparatus, the solids from the filtration with some residual loaded leachate solution wetness are reslurried with a hot water solution and pumped in an extraction apparatus. In place of the leaching solution, further warm water is introduced to remove and recover the loaded leachate and reduce the chemical load on the final tailings. The extracted loaded leachate is recycled to the feed of the process to retain the extracted metal or metalloids and ultimately pass them to the recovery section.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

[0039] Figure 1 shows a perspective view of a first example embodiment of an extraction apparatus according to the invention;

[0040] Figure 2 shows an exploded view of the extraction apparatus of Figure 1 ; Figure 3 shows a front view of the extraction apparatus of Figure 1 ;

[0041] Figure 4 shows a sectioned front view of the extraction apparatus of

[0042] Figure 1 (in which an agitating arrangement is not sectioned for clarity and to show features thereof more clearly);

[0043] Figure 5 shows a bearing arrangement supporting the agitating arrangement forming part of the extraction apparatus of Figure 1 ;

[0044] Figure 6 shows a top view of an end cap forming part of the extraction apparatus of Figure 1 ;

[0045] Figure 7 shows a sectioned top view of the extraction apparatus of Figure 1 ;

[0046] Figure 8 shows a diagrammatic representation of a system incorporating a number of extraction apparatuses of Figure 1 ;

[0047] Figure 9 shows results for leach efficiency, Sb content in precipitate and the relative mass of Sb in leachate after H2O2 oxidation at different temperatures;

[0048] Figure 10 shows results for leach efficiency over time;

[0049] Figure 11 shows results for leach efficiency at different slurry solid-liquid ratios;

[0050] Figure 12 shows results for leach efficiency of Sb and As using a single leach and a double leach;

[0051] Figure 13 shows results for different leaching solution recycling approaches; Figure 14 shows results for experiments conducted to investigate the impact of an inert nitrogen gas atmosphere;

[0052] Figure 15 shows filter cake test results for Sb extraction in air and nitrogen as analysed by XRF;

[0053] Figure 16 shows a summary of the test results from the processing of TSF1 tailings using the apparatus 10; and

[0054] Figure 17 shows a summary of the test results from the processing of calcined TSF1 tailings using the apparatus 10.

[0055] DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0056] The present invention will now be described more fully hereinafter with reference to the accompanying figures, in which some of the non-limiting embodiments of the invention are shown.

[0057] The invention as described hereinafter should not be construed to be limited to the specific embodiments disclosed, with slight modifications and other embodiments intended to be included within the scope of the invention.

[0058] Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0059] As used herein, throughout this specification and in the claims which follow, the singular forms “a”, “an” and “the” include the plural form, unless the context clearly indicates otherwise.

[0060] 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.

[0061] Throughout this disclosure, the term “fresh leaching solution” will be taken to refer to a leaching solution that has not been exposed to metal containing material or slurry in a leaching process.

[0062] Throughout this disclosure, the term “leachate” will be taken to refer to a leaching solution that has been in contact with metal containing material or slurry in an ongoing or completed leaching process.

[0063] 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.

[0064] 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 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.

[0065] 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 in the leachate or loaded leachate to a concentration less than a concentration of that metal 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.

[0066] Throughout this disclosure, the term “leaching solution” will be understood to encompass fresh leaching solution, leachate or recycled leachate, partially loaded leachate, or mixtures thereof.

[0067] 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 multi-stage 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.

[0068] Throughout this disclosure, the term “average or typical particle size” when referring to the dimensions of the particles in the processed slurry, will be taken to refer to a median diameter (D50), which represents a particle size where 50% of the slurry's particles are smaller and 50% are larger.

[0069] Referring to the drawings, in which like numerals indicate like features, a nonlimiting example of an extraction apparatus (or simply “apparatus”) used in the implementation of the method of the invention is generally indicated by reference numeral 10.

[0070] The apparatus 10 operatively forms part of a larger system 100 used in the process of leaching metals or metalloids from ores.

[0071] Figures 1 to 7 show a first and preferable example of the apparatus 10. 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.

[0072] 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.

[0073] 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).

[0074] A slurry inlet 28 is provided into the first compartment 18 and facilitates operative introduction of fresh 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 provided in fluid flow communication with an upstream process with which the slurry is prepared. This is expanded on further below.

[0075] Furthermore, a slurry outlet 30 is provided from the first compartment 18 and facilitates operative disposing of spent (or at least relatively or partially 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.

[0076] In use, the slurry outlet 30 is provided in fluid flow communication with a downstream process with which the spent slurry is handled. This is expanded on further below.

[0077] 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 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 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 leaching solution, recycled leachate recycled in a downstream process, partially loaded leachate, or mixtures of the aforementioned.

[0078] In the example embodiment shown in figures 1 to 7, the leaching solution feed arrangement 32 is incorporated with an agitating arrangement 34. The feed arrangement 32 and agitating arrangement 34 are discussed in more detail below. Suffice to say, incorporation of the 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.

[0079] Irrespective of the form that the leaching solution feed arrangement 32 takes, the arrangement may be configured operatively to provide leaching solution to the first compartment 18 at a rate and / or distribution such that a solid-liquid ratio of the slurry in the first compartment 18, between the slurry inlet 28 and slurry outlet 30, and / or along the operative flow path for slurry, remains within a predetermined or selected solid-liquid ratio range.

[0080] For example, in a first configuration optimized for metal or metalloid extraction or pumpability of the slurry, the rate of addition of leaching solution to the slurry is substantially equal to a rate of removal of loaded leachate to the second compartment thereby operatively maintaining a relatively constant solid-liquid ratio along the operative flow path for slurry in the first compartment. In a second configuration, the rate of addition of leaching solution to the slurry may be less than the rate of removal of the loaded leachate from the second compartment thereby operatively increasing the solid-liquid ratio along the operative flow path for slurry. In a third slurry wash configuration, the rate of addition of leaching solution or wash solution to the slurry may be increased relative to the rate of removal of the loaded leachate to the second compartment thereby operatively decreasing the solid-liquid ratio along the operative flow path for slurry in the first compartment.

[0081] The above may be achieved by controlling the overall flow rate of leaching solution via the leaching solution feed arrangement 32, and / or by controlling the flow distribution of leaching solution along a length of the operative flow path for slurry, which is possible, for example, when the leaching solution feed arrangement 32 is incorporated with the agitating arrangement 34. A loaded leachate outlet 36 is provided from the second compartment 20 and facilitates operative disposing or extracting of loaded leachate (this is discussed in more detail below). The loaded 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.

[0082] In use, the loaded leachate outlet 36 is provided in fluid flow communication with a downstream process with which the loaded leachate is treated. This is expanded on further below.

[0083] 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 eluent and slurry is provided to the first chamber 18, to create an above-atmospheric pressure in the first compartment.

[0084] 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 since relatively constant cross-sectional flow rates are achievable along a perimeter of the separator 16.

[0085] The agitating arrangement 34 is located axially within the first compartment 18 and extends substantially 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 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.

[0086] 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.

[0087] 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).

[0088] 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.

[0089] 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).

[0090] 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).

[0091] 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 countercurrent 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.

[0092] 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 moisture content, and particularly the management of the moisture content of the slurry is discussed more fully below). Therefore, an operative flow path for slurry is defined within the first compartment. The flow path extends between slurry inlet 28 and the slurry outlet 30 and is defined and / or encapsulated by the liquid permeable separator.

[0093] 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.

[0094] 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.

[0095] The central shaft 42 is supported by bearing housings 44.

[0096] 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 or typical particle size of the particles in the slurry. The base structure and the size of its apertures may be selected based on the type of slurry and the average or typical particle size thereof.

[0097] 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.

[0098] 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.

[0099] 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 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 loaded leachate through the separator 16. The apertured screen, filter material or perforated sheet may be selected based on the type of slurry and the average or typical particle size thereof.

[0100] Typically, the container 12 and the separator 16 have symmetrical cross- sectional shapes and axial centre lines thereof are coincident.

[0101] 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.

[0102] The apparatus 10 may form part of a larger extraction system 100 (as shown schematically in the system diagram of figure 8). 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 loaded 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.

[0103] In some cases, and as shown in figure 8, 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, 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.

[0104] 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.

[0105] In systems 100 where more than one apparatus 10 is provided in series, leachate flows within the extraction system 100 may be configured to be operated a counter-current fashion (as shown in figure 8), a co-current fashion, or a combination thereof. The system 100 may be adapted to facilitate these flow regimes.

[0106] For example, in the counter-current configuration the loaded 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. Final loaded leachate is finally extracted from the second chamber 20 of the first extraction apparatus 10. A single flow of loaded leachate is therefore extracted from the whole system 100 and provided to the filter and / or crystallizer plant 104.

[0107] In the co-current configuration, each leaching solution feed arrangement is provided in fluid flow communication with a supply of fresh leaching solution and / or with a partially loaded leachate outlet of an upstream extraction apparatus. Therefore, a single feed of leachate may flow from the first apparatus, downstream to the last apparatus where final 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.

[0108] In the combined configuration, the leaching solution feed arrangement of each upstream extraction apparatus is provided in fluid flow communication with both a loaded 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] At the same time, the pressure regulating arrangement creates a pressure differential over the separator 16.

[0113] The interaction between all or at least some of the above factors causes 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 loaded leachate either collects or is immediately drained through the loaded leachate outlet 36.

[0114] It will be appreciated by the skilled person that the apparatus 10 is specifically configured for use in continuous leaching and / or extraction processes. This immediately differentiates the processes facilitated by apparatus 10 from batch leach processes. For example, the slurry inlet is configured to supply a continuous feed of slurry into the first compartment during use, whilst simultaneously, the slurry outlet is configured to dispose slurry continuously from the first compartment during use. As a result, the slurry is not allowed to become stationary or to settle towards the bottom of the first compartment, to accumulate on the liquid permeable separator, or to form a filter cake. The agitator continuously agitates slurry during use, not just after a filter cake was formed or during discrete times during a batched process. The agitator furthermore continuously suspends and transports the slurry in use. A leaching solution feed arrangement is provided for continuously feeding leaching solution into the dynamically flowing slurry.

[0115] Several of the physical features of the apparatus are specifically configured to facilitate the continuous process. The relative positions of the slurry inlet and outlets to the liquid permeable separator are such that slurry operatively flows along the whole length, of the liquid permeable separator which results in substantial dynamic interaction between the slurry and the separator. In addition, continuous feeding of leaching solution into the first compartment dynamically participates in the leaching process and aids in driving leaching and removal of leachate over the separator. The configuration of the leaching solution feed arrangement, extending substantially along a length of the separator, facilitates this participation and interaction. Furthermore, a continuous pressure differential between the first and second compartments further drives the removal of leachate over the separator. The specific configuration of the agitator is such that agitation again takes place along substantially the whole length of the separator. The features allow for the implementation of a continuous process that significantly enhances the extraction of metal or metalloid from a metal or metalloid containing material. The following parameters may be controlled:

[0116] 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 leaching solution and the solids in the slurry.

[0117] Balance of flow rates:

[0118] 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 loaded leachate from the second compartment 20 through the loaded 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 loaded 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.

[0119] Rate of rotation of the agitating arrangement 34:

[0120] 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.

[0121] Feed rate of leaching solution supplied via the leaching solution feed arrangement 34 into the first compartment 18: The feed rate of leaching solution can be controlled for three different configurations as follows:

[0122] 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;

[0123] 2) a reducing ratio (second configuration) in which the feed rate is lower than the rate of permeation or extraction of 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

[0124] 3) and 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 loaded leachate is extracted into the second compartment 20. Typically, the third configuration is useful in a wash configuration wherein fresh leaching solution, water, or an alternative wash solution may be provided through the leaching solution feed arrangement 32.

[0125] Flow rate of loaded leachate extracted into the second compartment and through the loaded leachate outlet 36:

[0126] Controlled to maintain a sufficient level to: a) protect the pumps removing the loaded leachate from the second compartment 20; and b) moderate the permeation rate to the second compartment (higher levels of loaded leachate will create back pressure and reduce the permeation rate).

[0127] Ratios of loaded leachate to leaching solution supplied to the slurry:

[0128] Base case (noting that exceptions in the changes to the solid-liquid ratio could apply) would be that the volume of loaded leachate should be at least equal 50% of to the liquid fraction in the feed slurry to allow for a swap-out of leachate within the apparatus 10 up to a ratio of over 6 leachate swop outs in a single slurry pass.

[0129] Flow distribution / supply rate of leaching solution along the length of the shaft 42:

[0130] Three operating configurations are provided for:

[0131] 1) uniform addition of leaching solution along the length of the shaft 42 to provide both agitation and replacement of permeated leachate to the second compartment 20;

[0132] 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; and

[0133] 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 which is extracted using the apparatus 10.

[0134] Experiment 1 (Comparative): Batch Extraction of Antimony from TSF1 Tailings

[0135] Small scale batch experiments were conducted to investigate the efficiency of a standard alkaline antimony leaching process on TSF1 tailings obtained from the Stibium Mopani Mine, Gravelotte, Limpopo, South Africa. TSF1 is tailings material that has undergone a previous gold extraction process, and is a metal and metalloid containing material.

[0136] The TSF1 material typically has a composition of about: Sb 0.65-1.5%, Au 0.2-0.8 ppm, Si 6.5-8%, Fe 5-5.5%, Mg 2.4-3.8%, Ca 2.3-2.7%, Al 1-1.4%, Cr 1000-1400 ppm, S 400-1000 ppm, lower elements 78-82%, and As 400- 700 ppm.

[0137] The standard process makes use of sodium hydroxide (NaOH) and sodium sulphide (Na2S) in an aqueous solution to leach tailings material in an agitated vessel. The tailings material is separated using a filter and the resultant liquid oxidised by adding hydrogen peroxide (H2O2) to the filtrate which results in the precipitation of a white sodium pyro-antimonate [NaSb5+(OH)e] precipitate. The white precipitate is filtered out from the liquid and dried.

[0138] These experiments were conducted using a 500 ml glass beaker for the leach container, a magnetic stirrer bar and a stirrer heating plate (as required), a Buchner funnel and vacuum pump for filtration, and 40 pm filtration paper. The leach experiments were performed with 200 ml deionised water, milled TSF1 , 4 g NaOH (98 wt.%), and 4 g Na2S (60 wt.%). Precipitation was done with 40 ml H2O2 (12 wt. %).

[0139] The required quantity of deionized water was placed in the beaker. The stirrer bar was activated and, if required for the run, the heating plate was activated, and the temperature monitored and controlled once the required setpoint was achieved. Once the temperature was attained, the reagents (NaOH and Na2S) were added. The temperature was allowed to stabilise and once at the setpoint, TSF1 was added over a period of 2 minutes. The leach was held at the setpoint conditions for 90 min. Thereafter, the tailings were filtered via vacuum filtration. The mass of filter cake and filtrate were recorded and logged. The filtrate solution (loaded leachate) was returned to the beaker and placed on the heater stirrer. The stirrer was activated, and the solution was heated to 70°C for the precipitation phase, driven by an oxidation reaction. Once the solution was stable at 70°C, 40 ml of 12 wt.% H2O2 was added to the beaker. The beaker was left for 1 hour to cool to ambient conditions and the precipitate resulting from the reaction and cooling was filtered from the solution. Sb leach efficiency for each of these preliminary small scale batch experiments were in the region of about 15% to about 25%. Leach efficiency being defined as: 100

[0140] Experiment 2 (Comparative): Recycling and Regeneration of Leaching Solution

[0141] Given the undesirable Sb leaching efficiency of a single batch approach leach, various leaching solution reuse approaches were investigated to consider the impact on the extraction and recovery of Sb from TSF1. Although leaching solution is reused, this is still a batch experiment.

[0142] These experiments were conducted with the following equipment: a 500 ml glass beaker for the leach vessel, a magnetic stirrer bar and a stirrer heating plate (as required), a Bucher funnel and vacuum pump for filtration, and 40 pm filtration paper. The experiments were performed with 300 g of unmilled and unsized TSF1 an average Sb grade of 0.7%. The leaching solution was made up with 450 ml tap water, 6 g NaOH (98 wt.%), 9 g Na2S (60 wt.%), while precipitation was performed with 12 ml H2O2 (50 wt. %). Post precipitation, leaching solution regeneration test were performed using 2 g Ca(OH)2.

[0143] The required quantity of water was placed in the beaker. The stirrer bar was activated, and the heating plate was turned on, and the temperature monitored and controlled manually once the required setpoint of 80°C was achieved. Once the targeted temperature was attained, the specified quantities of NaOH and Na2S were added. The temperature was allowed to stabilise and once at the run setpoint, TSF1 was added over a period of 2 minutes. The leach was held at the setpoint conditions of agitation and temperature for 30 min. After this time, the tailings were filtered via vacuum filtration. The mass of filter cake and filtrate were recorded and logged. The filter cake was dried to determine residual cake wetness. The balance of the method was performed using different variations of reworked partially loaded leachate, recycled leachate, and regenerated leachate. Recycled leachate was partially loaded leachate (or loaded leachate) that has undergone an oxidation process to precipitate (and filter) solubilised antimony contained in the leachate.

[0144] 1. Partially loaded leachate without leaching reagent addition: water was added to the partially leach solution from the first leach to make up a total mass of 300 g. No further reagents added.

[0145] 2. Recycled leachate with leach reagent make-up: filtered partially loaded leachate (or loaded leachate) was heated to 70°C and H2O2 was added to oxidise the dissolved Sb. The resulting Sb precipitate was filtered out of the solution. The resulting recycled leachate was topped up with the necessary amount of fresh leaching solution. The fresh leaching solution contained 6g NaOH, 9 g Na2S per 300 g water which was used to make up the leaching solution to 300 g. This reworked recycled leachate was used for a second leach with fresh tailings.

[0146] 3. Partially loaded leachate with leach reagent make-up and added NaOH: The partially loaded leachate (“PLL” in Table 1 below) was topped up to 300 g using fresh leaching solution. A further 6 g NaOH was added to the mixture before to produce a reworked partially loaded leachate. This reworked partially loaded leachate was used to leach a fresh sample of tailings.

[0147] 4. Recycled leachate with leach reagent make-up and added NaOH: Recycled leachate (as described above) was topped up to 300 g with fresh leaching solution and 6 g NaOH was added before leaching a second fresh tailings sample.

[0148] 5. Recycled leachate with leach reagent make-up and added Nd2S: Recycled leachate (as described above) was topped up to 300 g with fresh leaching solution and 9 g fresh Na2S was added to the solution before leaching a second sample of tailings.

[0149] 6. Recycled leachate with NaOH regeneration with Ca(OH)2 and added Nd2S: Recycled leachate (as described above) was treated with 2 g of Ca(OH)2 and heated to 80°C for 30 min to allow for NaOH regeneration. After NaOH regeneration, 9 g fresh Na2S was added and allowed to dissolve before leaching a second fresh tailings sample.

[0150] As was expected, the primary leach experiments showed reproducible leach performance within the range of accuracy of the analysis. The Sb concentrations of each of the leach experiments (primary and secondary) are provided in Table 1 below.

[0151] Table 1 : Summary of results for secondary leach with partially loaded leachate and recycled leachate solutions.

[0152] Experiments 1 and 3 utilised partially loaded leachate that resulted from the primary leach as the solution to perform the secondary leach runs. Experiments 2, 4, 5, and 6 utilised recycled leachate to perform the secondary leach. As can be seen from the results in Table 1 , the results for experiments 1 and 3 shows that the addition of the fresh leaching solution and added NaOH (experiment s) improved leaching efficiency by about 20%.

[0153] The results for experiment 2 shows that oxidation has a material effect on the leach efficiency of recycled leachate with reagent addition, diminishing the leach effectiveness by over 20% compared to the primary leach. The results for experiment 4 showed similar leach effectiveness to the primary leach, while the results for experiment 5 indicates that additional Na2S levels improved the leach performance above that in the primary leach. The results for experiment 6 indicated that restoring both NaOH and Na2S concentrations in the leaching solution provided significantly improved leach efficiency.

[0154] It is clear from the experiments conducted that the use of partially loaded leachate and recycled leachate in further leaching of the metal or metalloid containing material would be beneficial. The partially loaded leachate and recycled leachate may be combined with fresh leaching solution, and may further be supplemented with additional leaching reagents in order to optimise the leaching efficiency of the process, while balancing the cost associated with the increased use of leaching reagents.

[0155] Experiment 3 (Comparative): Optimisation of Leaching Process Parameters in Batch

[0156] Optimisation experiments utilised a fixed mass of tailings material (10 kg) to ensure that sufficient precipitate masses were derived to be used as confirmation of Sb recovery. During these experiments, the following variables were altered: temperature from 25 - 90°C, leach time from 10 - 240 min, slurry solid-liquid ratio from 30 - 60 wt.% solids, NaOH addition from 0.5 - 8 wt.% relative to tailings mass, Na2S addition from 0.5 - 8% wt.% relative to tailings mass, double leaching of the same material, and the effect of conducting the leach in the presence of an oxygen deprived or inert gas atmosphere.

[0157] Leach Temperature

[0158] For the experiments where temperature was varied, all other conditions were fixed at 10 kg tailings, 90 min leach time, 50 wt.% solids-liquid ratio, 2 wt% NaOH and 2 wt% Na2S, based on the total weight of the tailings. Figure 9 shows the results for leach efficiency, Sb content in precipitate and the relative mass of Sb in leachate after H2O2 oxidation when compared with the starting mass in the loaded leachate. As can be seen from Figure 9, higher leach temperatures produce higher Sb extraction. This trend is confirmed with the precipitate reporting a higher mass of Sb. While the curve plotting Sb leach efficiency does not appear to increase substantially past 50°C, the increase in Sb precipitate mass confirms that there are gains in extraction past 50°C.

[0159] Leach Time

[0160] Leach times at elevated temperatures were investigated. As can be seen from Figure 10, Sb leach efficiency decreased with increasing leach time. This is supported by a slight drop in Sb mass reported in the precipitate. The decreasing leach efficiency over longer leaches suggests that either preg- robbing or Sb oxidation and precipitation to the residue mass occurs during the leach. Without thereby wishing to be bound by any particular theory, it is believed that Sb oxidation likely the cause, as the experimental setup allowed for increased oxygen exposure over time, and oxidation of dissolved Sb result in sparingly soluble sodium pyro-antimonate, which is likely to filter out with the remaining tailings. This led to further work to investigate a reduced oxygen atmosphere or inert atmosphere (discussed below).

[0161] Slurry solid-liquid ratio

[0162] Leach efficiency showed a decreasing trend with higher pulp thicknesses, in other words higher slurry solid-liquid ratios (see Figure 11), which is likely a result of solubility limits preventing further Sb uptake into solution. For these experiments, the highest leach efficiency was reported at 40 wt.% solids, with a drop in leach efficiency at 30 wt.% solids. This is likely due to kinetic limitations that start to effect extraction as reagents were diluted substantially when compared to the base case.

[0163] Reagent addition rates

[0164] Varying Na2S from 0.5 wt.% to 8 wt.% showed an increase in Sb leach efficiency with diminishing returns after 1 wt.% (relative to tailings mass). Sb mass in precipitate mirrored the leach efficiency trend up to a 3 wt.% Na2S addition. Beyond this point, recovered Sb in precipitate dropped to near zero as most of the Sb remained in solution even after H2O2 addition. This is suspected to be a result of the sulphides reacting with H2O2, leaving less or no H2O2 to precipitate out Sb. The divergence between leach efficiency and precipitation mass highlights the implications of very high Na2S addition on H2O2 consumption. High Na2S addition has marginal leach efficiency benefit past 1 wt.% relative to tailings mass and increases reagent cost for both Na2S and H2O2. At the method parameters used, optimum Na2S concentration for Sb extraction (based on specific tailing material) is approximately 1 wt.% relative to tailings mass. Similarly to Na2S, increased additions of NaOH saw increased Sb leach efficiency. However, the trend continued beyond 3 wt.% addition to 8 wt.%. Higher leach efficiencies were also confirmed with higher Sb precipitate masses.

[0165] Double leaching

[0166] Following washing of the filter, overall Sb recovery was still relatively low (under 30 %). Since the filter cake produced still had an Sb grade of approximately 0.45 %, further leaching on the filter cake was attempted with fresh leaching solution. Figure 12 compares the leach efficiency of Sb and As. The second leach used an additional 10 kg water, 2 wt.% NaOH, 2 wt.% Na2S and was leached at 75°C for 90 min. The moist filter cake was added to the second leach solution after taking a 2 kg sample, so approximately 8 kg of tailings was leached in the second leach. Figure 12 shows an increase in Sb leach efficiency from 15% to 21 %, and an increase in As leach efficiency from 34.7% to 41.3%. This suggests possible viability of double leaching material, however, at additional reagent cost. The additional recovery was not in proportion to the increase in reagent use, the filter cake leaving the second leach contained approximately 0.5% Sb (from a start of 0.685% before any leaching).

[0167] Leach results of experiments conducted up to this point produced Sb extractions up to 30%, which is consistent with the performance of known batch processes. Partially loaded leachate & Recycled leachate recycling

[0168] Different leaching solution recycling approaches were tested on milled and unmilled TSF1 tailings material, with the results shown in Figure 13. The method using 40 wt.% solids, 80°C, 2% NaOH, 3 wt.% Na2S in the leach for 60 min. Recycled leachate recycling involved using oxidized solution after precipitate filtration. The recycled leachate from a previous leach was reused with reagents added only to make up for the loss in water between recycled leachate and fresh leaching solution. The mixture of recycled leachate and make-up water (with relative concentration of reagents) was used to leach fresh tailings material. Recycled leachate for first and second leaches were used from the first and second leaches of a previous run respectively. While reuse of recycled leachate without reagent addition has the potential to reduce input costs, Sb extraction of each run was undesirable and more in line with the amount of reagent added along with the make-up water - suggesting that any unreacted reagents are consumed or deactivated by H2O2 in the precipitation phase. The marginal drop in leach efficiency with partially loaded leachate was a surprising and unexpected result. Very little make-up reagent (fresh leaching solution) was added in the partially loaded leachate leach test, yet comparable Sb extraction to fresh reagents was achieved.

[0169] Inert atmosphere (nitrogen)

[0170] The effect of a reduced oxygen atmosphere, in particular an inert nitrogen gas atmosphere was investigated at 30 min, 60 min and 180 min leach times. In addition, lower reagent additions were also investigated under nitrogen atmosphere. Additions of 1 wt.% NaOH and 1 wt.% Na2S were tested for both single leach and partially loaded leachate recycling under nitrogen to assess the potential of a continuous leach circuit with a reagent recycle. Results are displayed in Figure 14.

[0171] Nitrogen atmosphere showed clear benefit across all experiments, with 1 wt.% NaOH and 1 wt.% Na2S reagent addition under nitrogen outperforming 2 wt.% NaOH 3 wt.% Na2S in air. It is envisaged that similar results will be seen for extraction in any oxygen deprived atmosphere. Surprisingly, Sb recovery vs time trend is reversed under nitrogen atmosphere, longer leach times produced higher Sb leach efficiencies. This supports the theory advanced in respect of oxidative losses from the leach solution. It will be appreciated that this approach has the potential to lead to a significant saving in reagent costs.

[0172] Experiment 4: Continuous Leaching of Sb from Sb Containing Material with Apparatus 10

[0173] Experiments were conducted to investigate continuous leaching in which partially loaded leachate is recycled, with reagent top-up, and used for the continuous leaching of tailings material.

[0174] Each leach run was started with both the reagent top-up and the leaching solution / partially loaded leachate feed tanks filled with 15kg of heated water in each, NaOH and Na2S at 6.7 g / kg H2O (equivalent concentration to 1 wt.% relative to tailings mass in previous batch runs). In a separate vessel, 6 kg tailings was added into 9kg heated reagent solution at 80°C and allowed to mix to prepare a slurry. The slurry mixture containing tailings was transferred to the leaching and filtration vessel and agitation started. Positive nitrogen flow was started. Valves on both the reagent top-up and leaching solution / partially loaded leachate were opened to allow solution to flow into the leaching and filtration vessel. Two vacuum filtration pots were used in tandem. The suction was diverted into one or the other every 15 min. While filtrate collected in one filter pot, the other was sampled and drained to be ready for the next switch. The valve at the bottom of the reagent top-up tank was closed to stop flow into the next tank. The drained partially loaded leachate was poured back into the leaching solution / partially loaded leachate feed tank and the valve on the leaching solution / partially loaded leachate tank was controlled to keep a steady level in the leach / filtration vessel. After 2 hr of recycling partially loaded leachate, hot wash water was added into the reagent top-up tank and allowed to flow down into the rest of the system. Partially loaded leachate was no longer recycled back during the wash phase. Approximately 20 kg of hot wash water was allowed to pass through the system before the run was ended. At the end of the run, the feed to the leach / filtration vessel was shut and the level in the vessel was allowed to drop to dry out the filter cake. A filter cake sample was taken. A continuous leaching experiment was also run in air.

[0175] The filter cake from both air and nitrogen runs was analysed by XRF to determine the Sb extraction (Figure 15). As can be seen from figure 15, both the continuous leaches produced significantly higher Sb extraction from tailings than the batch runs. A 2 hr continuous leach in air extracted 50% of the Sb in the tailings, and a 2.5 hr extraction under nitrogen extracted 58% of the Sb in the tailings to leach according to XRF filter cake data. The extraction achieved by air was surprisingly higher than expected and is likely as a result of the specific experimental setup which led to a reduced oxygen exposure of the leach solution when compared with the equivalent open leach vessel runs (leach vessel fitted with plexiglass lid).

[0176] Experiment 5: Leaching of TSF1 with Apparatus 10

[0177] Sb leaching experiments were conducted using the extraction apparatus 10 and TSF1 material. Based on the run requirements, a slurry make-up tank was loaded with TSF1 fines. The slurry was made up to a specific gravity of 1.2 (about 40 wt.% solids). Continuous circulation of the slurry was maintained to minimize settling until the run was initiated.

[0178] For the duration of these runs, the sulphide and hydroxide content were each held at 2 wt. % of the mass of the TSF1 solids, with run at a temperature between 65°C and 85°C, with a wash water temperature of 65 °C to 75°C. The reagent solution made up in the pre-leach step were matched by the total volume of the leaching solution used in the apparatus 10.

[0179] In the testing of TSF1 tailings material, there were 10 demonstration scale production runs carried out. Each run processed approximately 0.5 ton of tailings material per run. The runs were numbered sequentially in the time order of process runs. The table in Figure 16 provides a summary of the results from the processing of TSF1 tailings using the apparatus 10. The results shown in the table in Figure 16 indicate how much antimony was recovered during processing of the TSF1 material. These runs or experiments represent several variations within the method of the invention, including the use of fresh leaching solution, partially loaded leaching solution, recycled leaching solution, and mixtures thereof in the continuous extraction of the samples. The numbers in the "Mark IV shell" column show what was expected to be recovered from the TSF1 tailings from the second compartment 20. On the other hand, the "Mark IV tube" column shows what remained in the first compartment 18. Significantly, the best extraction of Sb happened in test run marked “T-005”, where 64% of Sb was extracted from the starting material. Following that, the next most effective extractions were seen in tests marked “T-006”, “T-002”, and “T-009”. Excluding data from test T-004, the average extraction across all 9 tests is 48%, which is a significant improvement on standard batch methodology. The difference in run T-004 is a result of a different eluent addition policy that reduced the leach solution into the first chamber.

[0180] Experiment 6: Leaching of Calcined Material with Apparatus 10

[0181] Sb leaching experiments were conducted using the extraction apparatus 10 and calcined TSF1 material. The slurry was made up to a specific gravity of 1.4 (40 wt.% solids). Continuous circulation of the slurry was maintained to minimize settling until the run was initiated.

[0182] The calcined tailings comprised a mixture of tailings and roasting plant residue which was crushed and rolled together. This material was pressure leached through a pipe reactor with O2 injection and cyanidation, after which it was deposited, reclaimed, repulped, polished (milled) and processed through a carbon-in-leach circuit. The calcined material typically has a composition of about: Sb 9.16%, Si 3.44%, Fe 10.5%, Mg 1.69%, Ca 3.34%, Al 1.48%, Cr 0.75%, S 0.28%, lower elements 68.6%, and As 0.54%.

[0183] For the duration of these runs, the sulphide and hydroxide content were each held at between 5 wt.% and 10 wt. % of the contained mass of calcined tailings, and run at a temperature between 65°C and 85°C, with a wash water temperature of 65 °C to 75°C. The reagent solution made up in the pre-leach step were matched by the total volume of the leaching solution used in the apparatus 10.

[0184] The results shown in the table in Figure 17 indicate how much antimony was recovered during processing of the calcined TSF1 material utilising the method of the invention with different configurations including the ratio of solid-liquid in the slurry (pulp thickness), reagent dosage, operating temperatures. Each of the calcined material extraction experiments, utilising the method of the invention, produced theoretical Sb recovery in excess of 46%. The average extraction across the 10 tests is 49% which is, again, a significant and surprising improvement on standard batch methodology.

[0185] 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 gold, copper, nickel, arsenic, cobalt, and aluminium.

[0186] 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.

[0187] This above description of some of the illustrative embodiments of the invention is to indicate how the method of the invention can be carried out. Those of ordinary skill in the art will know that various details or parameters may be modified thereby arriving at further embodiments, but that many of these embodiments will remain within the scope of the invention, as defined by the claims which follow.

Claims

1. CLAIMS1 . A continuous method for the extraction of a metal or metalloid from a metal or metalloid containing material, the method comprising the steps of: contacting a metal or metalloid containing material with a leaching solution to form a slurry, providing the slurry of the metal or metalloid containing material and leaching solution in a first compartment of an extraction apparatus comprising first and second compartments separated by a liquid permeable separator, contacting the slurry in the first compartment to produce a loaded leachate and continuously separating the loaded leachate from the slurry to the second compartment by maintaining a negative pressure differential over the liquid permeable separator and between the first and second compartments, continuously providing leaching solution comprising fresh leaching solution, recycled leachate, partially loaded leachate, and mixtures thereof to the slurry in the first compartment at a rate such that the solid-liquid ratio of the slurry in the first compartment remains within a selected solid-liquid ratio range, wherein loaded leachate is removed from the second compartment for further processing, and wherein the solid-liquid ratio range is selected from: a first configuration optimized for metal or metalloid extraction or pumpability of the slurry, wherein the rate of addition of leaching solution to the slurry is substantially equal to rate of removal of loaded leachate from the second compartment thereby to maintain a constant solid-liquid ratio,a second configuration wherein the rate of addition of leaching solution leachate to the slurry is reduced relative to the rate of removal of the loaded leachate from the second compartment thereby to increase the solid-liquid ratio, or a third slurry wash configuration wherein the rate of addition of leaching solution or wash solution to the slurry is increased relative to the rate of removal of the loaded leachate from the second compartment thereby to decrease the solid-liquid ratio.

2. The method according to claim 1 , wherein the leaching solution is introduced to the first compartment through a feed arrangement comprising 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.

3. The method according to claim 1 or claim 2, wherein the slurry is provided to the first compartment from a leach vessel in which the slurry is operatively prepared by combining the metal or metalloid containing material with the leaching solution in a chemical leaching process.

4. The method according to any one of the preceding claims, wherein the slurry is removed from the first compartment and returned to the leach vessel for further processing.

5. The method according to any one of the preceding claims, wherein the method is performed in the presence of a reduced oxygen atmosphere, or an inert gas atmosphere.

6. The method according to claim 5, wherein the inert gas atmosphere is a nitrogen atmosphere.

7. The method according to any one of the preceding claims, wherein the metal or metalloid to be recovered is selected from the group of metals consisting of antimony, gold, copper, arsenic, mercury, tin, zinc, cobalt, and nickel.

8. The method according to any one of the preceding claims, wherein in the first configuration the solid-liquid ratio is in the range of about 20 wt.% to about 65 wt.% solids.

9. The method according to claim 8, wherein in the first configuration the solid-liquid ratio is in the range of about 30 wt.% to about 60 wt.% solids.

10. The method according to claim 8, wherein in the first configuration the solid-liquid ratio is in the range of about 40 wt.% solids.

11. The method according to any one of the preceding claims, wherein the metal or metalloid containing material is selected from run of mine material, ore, tailing concentrates, tailings, calcined material, or alternative preprocessed mineral material, and mixtures thereof.

12. The method according to any one of the preceding claims, wherein the metal or metalloid containing material present in the slurry has an average particle size of less than about 3 mm, less than about 1 mm, less than about 500 pm, less than about 250 pm, less than about 100 pm, less than about 50 pm, or about 35 pm.

13. The method according to any one of the preceding claims, wherein the optional further processing of the loaded leachate comprises subjecting the loaded leachate to a filtration step, an ion exchange process, an electrowinning process, a precipitation or crystallization step, or a combination thereof.

14. The method according to any one of the preceding claims, wherein the metalloid extracted by the method is antimony from an antimony containing material.

15. The method according to claim 14, wherein the leaching solution comprises a mixture of water, a suitable base, and a sulphide containing compound.

16. The method according to claim 15, wherein the leaching solution comprises a mixture of water, a hydroxide containing base, and sodium sulphide.

17. The method according to claim 16, wherein the hydroxide containing base is selected from sodium hydroxide and potassium hydroxide.

18. The method according to claim 16, wherein the hydroxide containing base and sodium sulphide are independently present in the leachate at about 0.25 wt.% to about 12 wt.%.

19. The method according to any one of claims 14 to 18, wherein the slurry is kept at a temperature from about 45 °C to about 98 °C, preferably from about 70 °C to about 85 °C.

20. The method according to any one of claim 14 to 19, wherein the method is employed to extract antimony from antimony containing material in a pre or post gold processing step.

21. The method according to any one of claims 14 to 20, wherein the antimony is extracted from the loaded leachate as NaSb(OH)e, Na4O?Sb2, NasC Sb, Sb2O3, or mixtures thereof, or electrowon as antimony.

22. The method according to any one of the preceding claims, wherein at least a first and second extraction apparatus are arranged in series,wherein a slurry outlet of the first extraction apparatus is provided in direct flow communication with a slurry input of the second extraction apparatus.

23. The method according to claim 22, comprising a third and optionally further extraction apparatuses arranged in series with the first and second extraction apparatuses.

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