Materials handling

Abstract

An embodiment provides a process of processing a slurry of fluid and solids. The process comprises passing the slurry into a filter (230) to form a filtrate and filter cake, and collecting the filtrate (217). The process may further comprise washing the filter cake with a washing fluid to form a wash stream and a washed filter cake. The washing fluid may be at a temperature above a threshold temperature to at least partially avoid precipitation of liquid-soluble reactive species in the filter cake.

Description

Technical Field The present disclosure relates to processes and systems for separating components of a slurry. Background Many processes related to extracting metal values from an ore often requires separation of slurry components. Depending on the metal values and their extraction method, the extracted metal values may be present as a liquid-soluble species in a slurry. When the liquid-soluble species in the slurry are unstable, such as being prone to prematurely precipitate from solution, it can be helpful to reduce a time required to separate a pregnant liquor with the liquid-soluble species from the solids in the slurry. However, on industrial scales, it can be difficult to reduce such a separation time. Accordingly, new separation methodologies are required. Summary An embodiment provides a process of processing a slurry of fluid and solids, such as in a Bayer plant or Bayer process, the process comprising: passing the slurry into a centrifuge to separate the fluid from the solids, the centrifuge being a pressure centrifuge; collecting the fluid; washing the solids in the pressure centrifuge to form a wash stream and washed solids; and collecting the washed solids. The pressure centrifuge may be a vertical pressure centrifuge. The solids in the pressure centrifuge may be washed a plurality of times. An embodiment provides a process of processing a slurry of fluid and solids, such as in a Bayer plant or Bayer process, the process comprising: passing the slurry into a centrifuge to separate the fluid from the solids; collecting the fluid; washing the solids in the centrifuge a plurality of times to form a wash stream and washed solids; and collecting the washed solids. The centrifuge may be a pressure centrifuge. Washing the solids a plurality of times may include: performing a first wash where the solids are washed to form a first wash stream and washed solids; and performing a second wash where the washed solids are washed to form a second wash stream and further washed solids. The fluid of the slurry and the wash stream may be maintained at a temperature of >100°C, such as >120°C. A pressure in the pressure centrifuge may be > atmospheric pressure. An embodiment may further comprise adding a modifier to the slurry to promote separation of the fluid and solids. The modifier may include a flocculant or coagulant. The modifier may be added to the slurry before the slurry is passed into the centrifuge. The modifier may be added to the slurry after the slurry has been passed into the centrifuge but before the slurry contacts a sidewall of the centrifuge. The process may further comprise filtering the wash stream to remove fines from the wash stream. The process may further comprise washing the fines to form washed fines and a fines wash stream. The process may further comprise recirculating at least a portion of the wash fluid back into the slurry. The process may further comprise decreasing a sand content of the solids in the slurry prior to passing the slurry into the centrifuge. The process may further comprise increasing a solids content of the slurry prior to passing the slurry into the centrifuge. The slurry may include pregnant liquor as the fluid and bauxite residue as the solids. The slurry may include Bayer liquor or water as the fluid and oxalate precipitation products or desilication products or lime precipitation products as the solids. The slurry may include spent liquor or a washing solution as the fluid and aluminium hydrate or aluminium hydroxide as the solid. In an embodiment, when the pregnant liquor is the fluid and bauxite residue is the solid, the separation of the fluid and solids in the centrifuge may have a separation time less than a desilication product precipitation threshold time to prevent precipitation of desilication products in the pregnant liquor. Following separation of the fluid and solids, desilication products may be selectively precipitated from the pregnant liquor whilst retaining aluminium species in their soluble form in the pregnant liquor. The process may further comprise passing the pregnant liquor though a heat exchanger prior to precipitating alumina from the pregnant liquor. An embodiment provides a centrifuge system for separating fluid and solids in a slurry, the centrifuge system comprising: a rotatable bowl having a liquid outlet and conical beach having a solids outlet, and a screw conveyor coaxially arranged within the bowl for moving solids to the solids outlet; a slurry outlet for passing a slurry into the bowl; and a wash water outlet positioned between the slurry outlet and the solids outlet configured to contact the solids that have been moved into the conical beach with a washing solution to wash the solid. The rotatable bowl may be arranged vertically such that an axis of rotation of the bowl extends vertically. The centrifuge may be a pressure centrifuge. The centrifuge system may further comprise a modifier outlet for injecting a modifier into the slurry to help promote separation of the fluid and solids. The modifier outlet may be positioned upstream of the slurry outlet such that, in use, the modifier is mixed with the slurry before the slurry is passed through the slurry outlet. The centrifuge system may further comprise wear liners on an inner surface of the rotatable bowl and / or conical beach. An embodiment provides a process of processing a slurry of fluid and solids, such as in a Bayer plant or Bayer process. The process may comprise: passing the slurry into a filter to form a filtrate and filter cake; collecting the filtrate; and washing the filter cake with a washing fluid to form a wash stream and a washed filter cake, wherein the washing fluid is at a temperature above a threshold temperature to at least partially avoid precipitation of liquid-soluble reactive species in the filter cake. The process may further comprise washing the filter cake a plurality of times with the washing fluid. The filter cake may be washed with the washing fluid from >2 to <4 times. Each washing may form a separate wash stream that is collected separately from one another. The washing fluid may include a neutralising agent that at least partially neutralises the filter cake to form a neutralised filter cake. The neutralising agent may include a buffer species or an acid. The filter cake may be washed with a washing fluid in absence of the neutralising agent prior to washing the filter cake with the neutralising agent. The threshold temperature may be >100°C, such as >120°C. The process may further comprise dewatering the filter cake after washing the filter cake with the washing fluid. Dewatering may be performed with a dewatering fluid. The dewatering fluid may include steam and / or air. The filter cake may be dewatered until the filter cake is dried. The filter may include a first filter and a second filter. The process may comprise passing a residue from the first filter to the secondary filter. The process may comprise washing the residue in the secondary filter to produce a washed residue and a filtrate. The process may further comprise recirculating the filtrate from the secondary filter back to the first filter. The secondary filter may receive a wash input separate from the washing fluid used to wash the filter cake in the first filter. The washed residue from the secondary filter may form the collected washed solids. The process may further comprise passing the filtrate through a flash tank. The process may further comprise passing the filtrate to a polisher to form a polished pregnant liquor stream. The process may further comprise passing a flashed solution from the flash tank to the polisher. The process may further comprise passing the polished pregnant liquor stream to a precipitator. The process may further comprise removing desilication products from the fluid in the polisher. An embodiment provides a Bayer process for treating bauxite to form alumina, comprising: separating pregnant liquor from digested bauxite residue using only a single separation step; wherein the pregnant liquor is maintained at a temperature of >100°C during separation. An embodiment provides a Bayer process for treating bauxite to form alumina, comprising: separating pregnant liquor from digested bauxite residue using a separation step; and performing at most one additional filtering step to remove fines from the separated pregnant liquor; wherein the pregnant liquor is maintained at a temperature of >100°C during separation and the at most one additional filtering step. The pregnant liquor may be maintained at a temperature of >120°C. The separation step may include using a filter or centrifuge. The centrifuge may be operated according to the process as set forth above. The filter may be operated according to the process as set forth above. Separating pregnant liquor from digested bauxite residue may include using one or more displacement washing steps. Separating the pregnant liquor from the digested bauxite residue may be performed using a single bank of separation devices. The digested bauxite residue may have a desilication product content of <0.5%. In an embodiment, the Bayer process may be free from a pre-desilication step prior to separating the pregnant liquor from the digested bauxite residue. The Bayer process may further comprise processing the pregnant liquor after separation from the digested bauxite residue to remove at least some desilication product present in the pregnant liquor to form a desilication product stream and a polished pregnant liquor. The polished pregnant liquor may be free from silica or silica-baring compounds that may be precipitated as desilication products. The desilication product may be removed from the pregnant liquor by precipitation to form the desilication product stream and the polished pregnant liquor stream. The Bayer process may further comprise drying the digested bauxite residue. An embodiment provides a Bayer plant, configured to perform the Bayer process of as set forth above. Brief Description of the Drawings One or more embodiment of the present disclosure will now be described, by way of example only, with reference to the accompanying non-limiting drawings, in which: Figure 1 is a schematic view of an embodiment of separation system that includes a centrifuge. Figure 2 is a schematic view of another embodiment of a separation system that includes a centrifuge. Figure 3 is a schematic view of another embodiment of a separation system that includes a centrifuge. Figure 4 is a schematic view of an embodiment of a separation system that includes a filter. Figure 5 is a schematic view of another embodiment of a separation system that includes a filter. Figure 6 is a schematic view of another embodiment of a separation system that includes a filter. Figure 7 is a schematic view of an embodiment of a separation system that includes a filter. Figure 8 is a process flow of operating the separation system of Figure 7. Figure 9 is an embodiment of a Bayer plant. Figure 10 is an embodiment of a filter arrangement used in a Bayer plant. Figure 11 is another embodiment of a Bayer plant. Figure 12 is another embodiment of a Bayer plant. Figure 13 is another embodiment of a Bayer plant. Detailed Description The following embodiments are described with reference to the Bayer process to extract aluminium species from bauxite. However, the disclosure is not limited to the Bayer process and may be used in other industries that requires separation of slurry components. The disclosure relates to embodiments of system(s), device(s) and processes for separating out components of a slurry, namely a fluid portion and a solids portion. Depending on the slurry and its formation, the slurry may include species that are inherently unstable at the conditions used to separate the fluid from the solids. For example, a slurry of pregnant liquor and digested bauxite residue (i.e. bauxite that has been subjected to digestion at elevated pH and temperature) can have unstable liquid-soluble aluminium-based species that have a tendency to precipitate from solution when the pregnant liquor falls outside a predefined condition. If this precipitation of unstable liquid-soluble aluminium-based species occurs prior to selective aluminium hydroxide precipitation to form spent liquor, such as during separation of the pregnant liquor from the digested bauxite residue, this can result in decreased alumina recovery and decreased Bayer efficiency. Similarly, it may also be desirable to control unstable, liquid-soluble byproducts so that they can be selectively removed from the pregnant liquor by e.g. precipitation and filtration. An issue with existing Bayer plant designs is that the steps required for isolation of pregnant liquor are often multi-stage with various temperature letdowns that have the effect of facilitating premature aluminium hydroxide precipitation. These multi-stage isolation steps and temperature letdowns also determine how desilication products are to be treated. One or more embodiments of the present disclosure relate to devices, systems and / or processes that allow for rapid separation of pregnant liquor from digested bauxite residue thereby reducing a residence time of the pregnant liquor during separation which helps to minimise or prevent premature precipitation of aluminium hydroxide and / or desilication products. Rapid separation of pregnant liquor from digested bauxite residue may also allow a temperature of the pregnant liquor to remain above a threshold temperature or within a predefined condition where aluminium hydroxide and / or desilication products stay solubilised in solution such as the pregnant liquor. Rapid separation may also be useful in one or more embodiments in applications of process chemistry such as controlling lime reaction extents where lime may transform very rapidly from one species to another and incur inefficiencies of application at high or low temperature(s) or pressure(s). The term “liquid soluble species” as used herein means a species that is soluble in a liquid. The liquid may include water or be water-based. For example, in the case of aluminium hydroxide extracted from bauxite, the aluminium hydroxide is soluble in an aqueous caustic solution, for example as a sodium aluminate species. Centrifuge Now referring to Figure 1, an embodiment of a slurry separation system for separating fluid and solids in a slurry will now be described. The system is in the form of centrifuge system 10 having centrifuge 11. The centrifuge 11 has a rotatable bowl 12 having a liquid outlet 18 and a solids outlet 20. The rotatable bowl 12 also has a conical beach 14 where sidewalls of the rotatable bowl 12 are tapered inwards. The solids outlet 20 is in fluid communication with the conical beach 14. The centrifuge 11 is also provided with a screw conveyor 16 coaxially arranged with the rotatable bowl 12. The blades of the screw conveyor 16 are omitted from the Figures for clarity only. In an embodiment, the centrifuge 11 is a vertical centrifuge whereby an axis of rotation of the rotatable bowl 12 extends vertically. However, in another embodiment, the centrifuge 11 can be a horizontal centrifuge. The centrifuge 11 has a slurry outlet 26. In the embodiment shown in Figure 1, the slurry outlet 26 is provided as an opening in the screw conveyor 16. The slurry outlet 26 is connected to a slurry source 22, such as a slurry tank, via slurry line 24. In use of the centrifuge 11, the rotatable bowl 12 is rotated at a predetermined speed depending on the properties of the slurry and the desired level of separation or dewatering of the slurry. Slurry from the slurry source 22 is passed through slurry outlet 26 into the rotatable bowl 12 where it is forced against an inner sidewall of the rotatable bowl 12. The screw conveyor 16 rotates at a differential speed to the rotatable bowl 12 such that the screw conveyor 16 moves the separated solids of the slurry towards the solids outlet 20. This movement separates the solids from the liquid thereby forming a solids component 30 that is passed through solids outlet 20 to form a solids discharge stream 31, and a liquid stream 28 that is passed through liquid outlet 18 to form a liquid discharge stream 29. As the solids move towards the solids outlet 20 they become increasingly more dewatered. The degree of dewatering depends on the initial water (fluid) content of the slurry and the rotation speed of the rotatable bowl 12. To wash this dewatered solid, the centrifuge 11 is also provided with a wash water outlet 32 that is positioned between the slurry outlet 26 and the solids outlet 20. The wash water outlet 32 is connected to a source of washing fluid (not shown) by washing supply line 33. In an embodiment, the wash water outlet 32 is provided in the screw conveyor 16 as an opening. In use, a washing solution is passed through the wash water outlet 32 to define a washing zone 44 where the washing fluid can contact and wash the dewatered solid thereby forming a wash stream and washed solids. In the embodiment shown in Figure 1, the wash stream combines with or forms part of the liquid stream 28. The arrangement of the wash water outlet 32 and washing zone 44 relative the slurry outlet 26 means that the dewatered solids are washed in counter current relative a flow of the slurry through the rotatable bowl 12. In an embodiment, the centrifuge 11 is a pressure centrifuge. Operating the centrifuge 11 under pressure allows the slurry, solids and fluid to be maintained at higher temperatures compared to conditions at atmospheric pressures. This may allow the slurry, solids and fluid to be maintained above a threshold value to help retain unstable liquid-soluble species in solution. For example, in the case where the slurry is formed from pregnant liquor and digested bauxite residue, maintaining a temperature of the pregnant liquor above a threshold value can help retain liquid-soluble aluminium species in solution thereby helping to minimise or prevent premature precipitation of aluminium species. A temperature of the residue and / or filtrate may be maintained above a threshold value to avoid precipitation such as auto-precipitation of reactive species in the filter cake. In an embodiment, the fluid of the slurry and the wash stream are maintained at a temperature of >100°C. The temperature of the slurry and wash stream may be >110°C, >115°C, >120°C, >125°C,>130°C, >135°C, >140°C, >145°C, >150°C, >155°C, >160°C, >165°C, >170°C, >175°C, >180°C, >185°C, >190°C, >195°C, >200°C, >205°C, >210°C, >215°C, >220°C, >225°C, >230°C, >235°C, >240°C, >245°C, >250°C, >255°C, >260°C, >265°C, >270°C, >275°C, or about 280°C. When the centrifuge 11 is a pressure centrifuge, the centrifuge 11 is fitted with valves, pumps and the like to maintain a pressure inside the centrifuge 11 within a predefined condition. In an embodiment, a pressure in the pressure centrifuge is > atmospheric pressure. To promote or assist with separating the fluid from solids in the slurry, a modifier can be added to the slurry. For example, the modifier may be injected into or mixed with the slurry. In an embodiment, the modifier includes a flocculant, a coagulant, or a dewatering aid that helps to dewater the solids. In an embodiment, the slurry line 24 is provided with a modifier inlet 42. The modifier inlet 42 is positioned upstream of the slurry outlet 26 such that the modifier can be passed through the modifier inlet 42 and be mixed with the slurry prior to the slurry passing through the slurry outlet 26. The modifier inlet 42 may be formed with or have associated mixing means to help mix the modifier into the slurry. In an embodiment, the modifier inlet 42 is positioned at or associated with the slurry outlet 26. In an embodiment, the modifier inlet 42 is positioned downstream of the slurry outlet 26 such that the modifier is added to the slurry after the slurry has been passed into the rotatable bowl 12 but before the slurry contacts a sidewall of the rotatable bowl 12. In an embodiment, the liquid discharge stream 29 is filtered to remove fines from the liquid stream 28, including the wash stream formed from the washing fluid passed through the wash water outlet 32. The fines may be washed to form washed fines and a fines wash stream (not shown). In an embodiment, the fines wash stream may be added to the slurry source 22 or the washing fluid. When the fines wash stream is added to the washing fluid, the washing is counter current to the flow of solids. An inner wall or inner surface of the rotatable bowl 12 including the conical beach 14 may be provided with wear liners (not shown). The wear liners may help to protect the rotatable bowl 12 from wear during continual use, especially for slurry that includes abrasive materials such as sand. Another embodiment of a centrifuge system 10a is shown in Figure 2. Centrifuge system 10a is similar to centrifuge system 10 and like references are used to describe like features. Centrifuge system 10a has a centrifuge 11 a. The centrifuge 11 a is similar to centrifuge 11, but centrifuge 11a includes a wash outlet 34 that is connected to the slurry source 22 via a return line 36. The wash outlet 34 is positioned such that the wash stream generated from passing a washing fluid through the wash water outlet 32 can be collected and returned to the slurry source 22. Put another way, at least a portion of the wash stream (or wash fluid) can be recirculated back to the slurry source 22. The rotatable bowl 12 may be provided with weirs or other features that help separate the wash stream from the solids before substantially mixing with the liquid stream 28. For example, a neutralising agent may be provided in the washing fluid to help neutralise the solids component 30. The neutralising agent may include a buffer species or acid or base depending on a pH property of the solids component 30. In the case of digested bauxite residue, the neutralising agent may include an acid, such as an organic acid. It should be appreciated that the wash outlet 34 and return line 36 are optional and not required in all embodiments. Another embodiment of a centrifuge system 10 is shown in Figure 3. Centrifuge system 10 has a centrifuge 11b. Centrifuge 11b is similar to centrifuge 11 and like references are used to describe like features. In centrifuge 11b, an additional wash water outlet 40 that defines a second washing zone 46 is provided downstream of the wash water outlet 32. Similar to wash water outlet 32, additional wash water outlet 40 may be provided as an opening in the screw conveyor 16. In an embodiment, the additional wash water outlet 40 is connected to wash water outlet 32 via auxiliary supply line 38 such that the same washing fluid passes through wash water outlet 32 and additional wash water outlet 40. However, in an embodiment, the additional wash water outlet 40 is connected to its own source of washing fluid. For example, the additional wash water outlet 40 may be connected to a source of washing fluid that has a neutralising agent. The additional wash water outlet 40 and second washing zone 46 allows the solids component 30 to be washed a plurality of times. In centrifuge system 10, the use of centrifuge 11 b allows the solids to be washed twice. The first wash is performed by the wash water outlet 32 to form a first wash stream and washed solids. The second wash is performed by additional wash water outlet 40 where the washed solids from the first wash are washed to form a second wash stream and further washed solids. If a neutralising agent is passed through the additional wash water outlet 40, the further washed solids may be at least partially neutralised. The centrifuge 11b is shown in Figure 3 as having a first and a second wash stations or wash zones. However, in an embodiment, the centrifuge 11b may have a plurality of wash station or wash zones. For example, in an embodiment, the centrifuge 11b may have two, three or four or more wash stations or wash zones. In an embodiment, the centrifuge 11, centrifuge 11 a and / or centrifuge 11 b includes a dewatering zone positioned on a solids outlet 20 side of the last washing step e.g. wash water outlet 32. The dewatering zone helps to reduce a water content of the solids component 30. The centrifuge system 10 and / or centrifuge system 10a may be provided with a de-sanding system that decreases a sand content of the slurry prior to the slurry being passed into the rotatable bowl 12 (not shown). The de-sanding system may be associated with slurry source 22 or may be provided on or associated with the slurry line 24. For example, the de-sanding system may be positioned between the centrifuge 11 and the slurry source 22 on slurry line 24. The centrifuge system 10 may also be provided with a concentrator that increases a solids content of the slurry. For example, the concentrator may be a decanter, such as a pressure decanter, or a screw press. Like the de-sanding system, the concentrator may be associated with slurry source 22 or may be provided on or associated with the slurry line 24. For example, the concentrator may be positioned between the centrifuge 11 and the slurry source 22 on slurry line 24. When the slurry source 22 is a slurry formed from pregnant liquor and digested bauxite residue, a separation time required to separate the and digested bauxite residue (i.e. solids) from the pregnant liquor (i.e. fluid) may be less than an impurity precipitation time. For example, if the impurity precipitation time is one unit at a given separation condition (e.g. temperature and pressure), a time required to separate the digested bauxite residue and pregnant liquor is less than one unit. Impurities can include desilication products, oxalate precipitation products and / or lime precipitation products. In an embodiment, the separation time is the time from which slurry is passed into the rotatable bowl 12 to when the liquid stream 28 passes through the liquid outlet 18. Decreasing a separation time can help to prevent precipitation of impurities in the pregnant liquor. Minimising or preventing premature precipitation of impurities can help to ensure that they can be removed at an appropriate time, such as through a selective desilication product precipitation step, to help retain a higher solubilised aluminium concentration in the pregnant liquor. In an embodiment, following separation of the fluid and solids, desilication products are selectively precipitated from the pregnant liquor whilst retaining aluminium species in their soluble form in the pregnant liquor. In an embodiment, separation of the fluid and solids in the centrifuge 11 / 11a has a separation time less than a desilication product precipitation threshold time to prevent precipitation of desilication products in the pregnant liquor e.g. liquid discharge stream 29. In an embodiment, the centrifuge system 10 is provided with a heat exchanger in fluid communication with the liquid discharge stream 29 such that the liquid discharge stream 29 (e.g. pregnant liquor) can be cooled prior to precipitation of alumina (not shown in Figure 13). In an embodiment, the centrifuge system 10 is provided with a dewatering station or zone to at least partially dewater the solids component 30 (not shown). The dewatering station or zone may be provided within the centrifuge 11 / 11 a / 11b, such as between the last washing, such as washing zone 44 or washing zone 46 and the solids outlet 20. Alternatively, the dewatering station or zone may be associated with the solids outlet 20. Dewatering may be performed with a dewatering fluid which may include steam and / or air. In an embodiment, the solids component 30 is dewatered until it is dry. In an embodiment, solids component 30 has a dry solids component of >68 wt.% solids. In an embodiment, water content of the solids component 30 is < 32 wt.% water. It should be appreciated that the term “water” used throughout to describe a water content includes fresh, not pure water, and other liquids that may be present in the solids. In an embodiment, water content of the solids component 30 is < 30 wt.%. In an embodiment, water content of the solids component 30 is < 25 wt.%. In an embodiment, water content of the solids component 30 is < 20 wt.%. In an embodiment, water content of the solids component 30 is < 15 wt.%. In an embodiment, water content of the solids component 30 is < 10 wt.%. In an embodiment, water content of the solids component 30 is < 5 wt.%. In an embodiment, the centrifuge system 10 and / or 10a (and centrifuges 11, 11a and / or 11 b) may be used to separate specific particles of interest for further processing such as mineral recovery, gangue rejection or other. Filter One or more embodiments of a slurry separation system for separating fluid and solids in a slurry will now be described. The system is in the form of filter system 100 having filter 110. With reference to Figure 4, the filter 110 is a moveable filter such as that used in a rotary, disc, drum or belt filter. Movement of the filter 110 in Figure 4 is shown in the direction of arrow 118. The filter system 100 has a washing zone whereby a filter cake 111 present on the filter 110 can be washed with a washing fluid. The filter cake 111 is formed by passing a slurry onto the filter 110 to form a filtrate. Formation of the filtrate is not shown in Figure 4. In the embodiment shown in Figure 4, the filter system 100 has three washing zones, namely a first washing zone 112, a second washing zone 114, and a third washing zone 116. It should be appreciated that the use of three washing zones is a non-limiting example. In an embodiment, the filter cake 111 is washed with a washing fluid two, three or four times. As the filter 110 moves along the direction of arrow 118, the filter cake 111 enters the first washing zone 112, then exits the first washing zone 112 before moving to the second washing zone 114, then finally exiting second washing zone 114 before moving to the third washing zone 116. The filter system 100 is provided with a washing fluid source 120. The washing fluid source 120 is fluidly connected to the third washing zone 116 such that the third washing zone 116 is washed first. Filtrate from the third washing zone 116 is then used as the washing fluid for the second washing zone 114, and filtrate from the second washing zone 114 is then used as the washing fluid for first washing zone 112. In this way, the washing of the filter cake 111 is counter current. The washing fluid source 120 may be a spent liquor, water, a dewatering additive and / or a neutralising fluid that can neutralise the filter cake 111 thereby forming a neutralised filter cake. In each of the first washing zone 112, second washing zone 114, and third washing zone 116, the washing fluid is at a temperature above a threshold temperature to at least partially avoid precipitation of liquid-soluble reactive species in the filter cake. In an embodiment, the threshold temperature is >100°C, such as >120°C. Washing at such temperatures may also help to reduce or eliminate the use of blow-off tanks and similar devices prior to washing. Having discrete washing zones can also help to decrease a time for washing which has the effect of decreasing a time required to separate fluid from the slurry and wash the filter cake 111. Decreasing this separating and washing time can help to prevent premature precipitation of liquid-soluble reactive species. For example, in the case of bauxite processing, decreasing the separating and washing time can help to prevent premature precipitation of aluminium species including alumina and / or desilication products. In an embodiment, the filter cake, for example solids component 30, may be washed 2< to >4 times. Another embodiment of a filter system 100a is shown in Figure 5. Filter system 100a is similar to filter system 100 and like references are used to describe like features. In filter system 100a, the washing fluid source 120 is fluidly connected to each of the first washing zone 112, the second washing zone 114, and the third washing zone 116, via respective supply lines 112a, 114a and 116a. Accordingly, each of the first washing zone 112, the second washing zone 114, and the third washing zone 116 each receive separately from one another washing fluid from washing fluid source 120. The supply lines 112a, 114a and 116a may each be provided with a flow control system, such as actuated valves, to control flow of fluid from washing fluid source 120 to the respective washing zone (112, 114 and 116). Another embodiment of a filter system 100b is shown in Figure 6. Filter system 100b is similar to filter system 100 and like references are used to describe like features. In filter system 100b, the first washing zone 112, the second washing zone 114, and the third washing zone 116 are connected to respectively first washing fluid source 120a, second washing fluid source 120b and third washing fluid source 120c. Each of the first washing fluid source 120a, second washing fluid source 120b and third washing fluid source 120c are operated and controlled separately to one another. Having different washing fluid sources be connected to different washing zones can allow specific and tailored washing fluid(s) to be used in each washing zone. For example, in an embodiment, first washing fluid source 120a and second washing fluid source 120b may be water used to flush or wash the filter cake 111, and third washing fluid source 120c may include a neutralising agent to help neutralise the filter cake 111. Being able to neutralise the filter cake 111 in situ may help to simplify downstream filter cake processing. In the embodiments described with reference to Figure 1 to Figure 6, the centrifuge system 10 and / or filter system 100 / 100a / 100b may also be provided with a dewatering zone. In an embodiment, the filter system 100 / 100a / 100b is provided with a dewatering station or zone to at least partially dewater the filter cake 111 (not shown). Therefore, the dewatering station or zone serves to remove at least some of the water associated with the filter cake 111. The dewatering station or zone is provided downstream of the last washing zone e.g. the third washing zone 116. However, in an embodiment, the third washing zone 116 also forms or defines a dewatering zone. Dewatering may be performed with a dewatering fluid which may include steam and / or air. In an embodiment, the filter cake 111 is dewatered until it is dry. In an embodiment, the filter cake 111 has a dry solids component of >68 wt.% solids. In an embodiment, water content of the filter cake 111 is < 32 wt.% water. In an embodiment, water content of the filter cake 111 is < 30 wt.% water. In an embodiment, water content of the filter cake 111 is < 25 wt.% water. In an embodiment, water content of the filter cake 111 is < 20 wt.% water. In an embodiment, water content of the filter cake 111 is < 15 wt.% water. In an embodiment, water content of the filter cake 111 is < 10 wt.% water. In an embodiment, water content of the filter cake 111 is < 5 wt.% water. Another embodiment of a filter system 100c is shown in Figure 7. Unlike filter systems 100100b that rely on movement of the filter cake 111 such as in a rotary, disc, drum or belt filter, filter system 100c uses a filter chamber 150. The filter chamber 150 has a tubular filter 110a coaxially arranged with the filter chamber 150 to define a slurry chamber 154 and a filtrate chamber 152. Slurry 158 is introduced into the slurry chamber 154 through slurry inlet 156. In use, a vacuum can be applied to the filtrate chamber 152 to suck or draw filtrate into the filtrate chamber 152. Alternatively, or in addition, the slurry chamber 154 may be under pressure to push filtrate through to the filtrate chamber 152. The filter chamber 150 also has washing fluid inlet 164 where a washing fluid 162 can be introduced into the slurry chamber 154. The tubular filter 110a is shown generally to aid in understanding the function and operation of the filter system 100c and may have any number of shapes and configuration. For example, the tubular filter 110a may be a rounded tube, or could have any shape that assists with filtering, such as one or more rectangular chambers that define the tubular filter 110a. Accordingly, the disclosure is not limited to the tubular filter 110a having a tubular structure. Use of filter system 100c will now be described with reference to process flow 170 in Figure 8. At step 172, slurry is introduced into the slurry chamber 154. Next, at step 174, the fluid component of the slurry can be filtered off by applying pressure and / or vacuum separation across filter 110a. For example, pressure may be applied to slurry chamber 154 and / or vacuum applied to filtrate chamber 152. In the case of bauxite processing, the slurry 158 is digested bauxite residue and pregnant liquor. A filter cake is formed once the fluid of the slurry has been removed. This filter cake can then be washed at step 176 by introduction of the washing fluid 162 through the washing fluid inlet 164 into slurry chamber 154. During washing, the pressure and / or vacuum previously applied to assist with filtration is removed to allow the washing fluid to mix with the filter cake. In some instances, washing may include reslurrying the filter cake in the slurry chamber 154. However, in an embodiment, the pressure and / or vacuum previously applied to assist with filtration is retained and the washing fluid is pushed or sucked immediately through the filter cake. After a predetermined washing time, the washing fluid introduced into the slurry chamber 154 is removed by vacuum and / or pressure as before to form a washed filter cake. This type of washing is displacement washing. The filter cake may be washed a plurality of times. For example, in process flow, additional washing step 178 may be performed a plurality of times. In an embodiment, one of the washing steps in filter system 100c may include a neutralising agent to help at least partially neutralise the filter cake as previously described. If a neutralising agent is used, it is typically done so as the last wash, but may optionally be used with one of the previous washing steps. Following step 176, or additional washing step 178 if performed, a dewatering fluid is passed through the filter cake at step 180 to at least partially de-water the filter cake. Dewatering may be performed with a dewatering fluid which may include steam and / or air. In an embodiment, the filter cake 111 is dewatered until it is dry as described above. Generally, a dewatering fluid is passed through the slurry chamber 154 The above embodiments of the centrifuge and filter have been described with reference to a slurry formed from digested bauxite residue and pregnant liquor. However, the slurry may be formed from Bayer liquor or water as the fluid and oxalate precipitation products or desilication products or lime precipitation products as the solids. Alternatively, the slurry may be formed from spent liquor or a washing solution as the fluid and aluminium hydrate (AI2O3.3H2O, also referred to as “hydrate”) or aluminium hydroxide (AI(OH)3) as the solid. Bayer process and Bayer plant One or more embodiments of a Bayer plant and process will now be described with reference to Figure 9 to Figure 13. Starting with Figure 9, Bayer plant 200 includes a bauxite source 210 that is treated in digestor 212. The bauxite source 210 may be formed into a slurry before treatment in the digestor 212 or may be formed into a slurry by introducing bauxite into the digestor 212. The digestion conditions are dependent on the composition of the bauxite such as its Al and Si content and their form(s). Following digestion in the digestor 212, the slurry of digested bauxite residue and pregnant liquor is passed into filter 214. Filter 214 includes a centrifuge such as system 10 and / or filter such as system 100 / 100a / 100b / 100c. In an embodiment, filter 214 comprises centrifuge system 10. In an embodiment, filter 214 comprises filter system 100, filter system 100a, filter system 100b and / or filter system 100c. In an embodiment, filter 214 comprises centrifuge system 10 and one or more of filter system 100, filter system 100a, filter system 100b and / or filter system 100c. Having only a single separation step that separates the slurry into pregnant liquor and the digested bauxite residue can help to speed up the separation process and allow separation to occur above a threshold temperature to at least partially avoid precipitation of liquid-soluble reactive species in the digested bauxite residue without the need for additional heating systems. During separation using the filter 214, a temperature of the pregnant liquor is maintained at a temperature of>100°C. In an embodiment, the pregnant liquor is maintained at a temperature >110°C, >115°C, >120°C, >125°C, or>130°C, >135°C, >140°C, >145°C, >150°C, >155°C, >160°C, >165°C, >170°C, >175°C, >180°C, >185°C, >190°C, >195°C, >200°C, >205°C, >210°C, >215°C, >220°C, >225°C, >230°C, >235°C, >240°C, >245°C, >250°C, >255°C, >260°C, >265°C, >270°C, >275°C, or about 280°C. The separation step using filter 214 includes one or more washing steps as outlined for centrifuge system 10 and one or more of filter system 100, filter system 100a, filter system 100b and / or filter system 100c. For example, the filter 214 can include using one or more displacement washing steps, dewatering and / or neutralisation. Depending on a volume of slurry outputted from the digestor 212, one or more filters 214 may be required. For example, if the output volume is 10 units, and each filter in the filter 214 has a capacity of 2 units, the filter 214 can include a single bank of five filters. As shown in Figure 10, the filter 214 can include an arrangement that has two or more sub-filter units 215. With reference to Figure 10, in an embodiment the filter 214 is provide with four sub-filter units 215a, 215b, 215c and 215d. The sub-filter units 215 are connected in parallel such that a throughput of each sub-filter units 215 is the same or approximately similar. The number of sub-filter units 215 shown in Figure 10 is exemplary only and there may be more or less than four sub-filter units 215. Connecting the sub-filter units 215 in parallel can help to minimise separation times during separation and reduce the likelihood of premature precipitation of liquid-soluble aluminium species. When two or more sub-filter units 215 are used in the filter 214, they collectively form a single separation step such that the Bayer plant 200 and its associated Bayer process only requires one separation step. In an embodiment, the slurry treated in the digestor 212 is passed directly to the filter 214 such that the Bayer plant 200 is free from pre-desilication systems and steps prior to separating the pregnant liquor from the digested bauxite residue in filter 214. Such an arrangement may help to reduce the number of components required to form the Bayer plant 200, thereby reducing capital and operational expenses. For example, Bayer plant 200 may be free from blow off tanks, flash tanks, and similar devices used to cool a slurry prior to filtration using filter 214. It should be appreciated that depending on the silica content and its form in the bauxite source 210 some steps may be required to treat the slurry formed in the digestor 212 prior to separation in the filter 214, such as pre-desilication steps. In an embodiment, the filter 214 may include various types of filtration devices suitable for separating pregnant liquor from digested bauxite residue. The filter 214 may comprise batch filters or semi-batch or semi-continuous filters such as vertical leaf filters or candle filters, which may provide effective initial separation of the pregnant liquor from the digested bauxite residue. In some embodiments, the filter 214 may include continuous filters such as high-pressure disc filters or high-pressure drum filters. The filter 214 may operate under elevated pressure and temperature conditions. The temperature of the slurry and filtrate in the filter 214 may be maintained at>100°C, and in some instances may range from 150-155°C. In some cases, the operating pressure within the filter 214 may be maintained above atmospheric pressure, such as between 5-15 bar. The output pressure from the filter 214 may be maintained above atmospheric pressure for several reasons. In some cases, maintaining a higher pressure may help prevent flashing or vaporization of the hot pregnant liquor as it exits the filter. This can be important for retaining dissolved species in solution and avoiding premature precipitation. Additionally, a higher output pressure may facilitate downstream processing steps by providing sufficient head pressure for fluid transfer without the need for additional pumping. In some embodiments, maintaining pressure above atmospheric may also help control the release of any dissolved gases in the pregnant liquor. The specific pressure used may depend on factors such as the temperature of the pregnant liquor, its composition, and the requirements of subsequent processing stages in the Bayer process. In certain embodiments, the filter 214 may include multiple filtration stages arranged in series or parallel. For example, the filter 214 may comprise a primary batch filtration stage or primary semi-batch or semi-continuous filtration stage followed by one or more continuous filtration stages. This arrangement may allow for improved liquor recovery and additional washing capability. The batch filters used in filter 214 may operate on cycles of approximately 2-60 minutes, such as up to 60 minutes, up to 30 minutes, up to 15 minutes, up to 10 minutes and / or up to 5 minutes. To provide overall continuous operation, multiple batch filter units may be used in parallel with staggered cycles. In some implementations, 10 or more individual batch filter units may be employed with offset operating cycles. For continuous filters incorporated in filter 214, such as disc or drum filters, these may allow for ongoing filtration without interruption. In some configurations, multiple banks of continuous filters may be used in parallel. As an example, three banks of two disc filters connected in series may be utilized within filter 214. The specific operating parameters and filter configurations for filter 214 may be adjusted based on factors such as the properties of the bauxite being processed, desired throughput, and target separation efficiency. The flexibility in filter types and arrangements within filter 214 may allow for optimization of the separation process for different operating conditions. Following separation of the slurry in the filter 214, a pregnant liquor stream 217 is formed along with digested bauxite residue 220. In an embodiment, by separating the pregnant liquor stream 217 and digested bauxite residue 220 in a quick or rapid manner in the filter 214, the amount or concentration of aluminium-containing species and / or desilication products present in the digested bauxite residue 220 is reduced. Similarly, in an embodiment, separating the pregnant liquor from the digested bauxite residue is performed such that aluminium loss in the pregnant liquor is reduced or eliminated. For example, in an embodiment, the digested bauxite residue 220 may have a desilication product content of <0.5%. Further, if a neutralising agent is used during separation with the filter 214, the digested bauxite residue 220 may be utilised or sent to a storage area without further processing. The digested bauxite residue 220 may, however, be subject to drying processes if no drying or insufficient drying is performed during separation with the filter 214. The pregnant liquor stream 217 contains liquid-soluble aluminium species that can be selectively precipitated in a precipitator 218. Precipitation of liquid-soluble aluminium species can be performed using known methods, such as seeding. The Bayer plant 200 may include blow off tanks, flash tanks, heat exchangers and other devices and / or systems used to cool the pregnant liquor stream 217 prior to precipitation. The pregnant liquor stream 217 may also include other soluble by-products and impurities such as liquid-soluble desilication products in addition to liquid-soluble aluminium species. To remove these other soluble by-products and impurities, the Bayer plant 200 may also include a polisher 216. The polisher 216 is not required in all embodiments and is optional. In an embodiment, the polisher 216 is used to process the pregnant liquor stream 217 to remove at least some desilication product present in the pregnant liquor to form a desilication product stream 222 and a polished pregnant liquor stream 217a. For example, the desilication product (DSP) may be selectively precipitated from the pregnant liquor stream 217 to reduce a silica content of the pregnant liquor stream 217 to form a polished pregnant liquor stream 217a. The pregnant liquor stream 217 may have a silica content ranging from 0 g / L to 15 g / L. If a silica content of the pregnant liquor stream 217 is above a threshold value, the polisher 216 can be used to reduce a silica content of the pregnant liquor stream 217. For example, if the pregnant liquor stream 217 has a silica content of up to 15 g / L due to rapid separation using the filter 214 so that 15g / L of silica stays in solution and doesn't precipitate out as DSP, the polisher 216 can be used to precipitate DSP to reduce the silica content in the pregnant liquor stream 217 down to < 3 g / L. The polisher 216 may reduce a silica content of the polished pregnant liquor stream 217a down to < 2 g / L. The polisher 216 may reduce a silica content of the polished pregnant liquor stream 217a down to < 1 g / L. The polisher 216 may reduce a silica content of the polished pregnant liquor stream 217a down to approximately 0 g / L. A filter or similar may be used to separate the polished pregnant liquor stream 217a from the desilication product stream 222. However, it should be appreciated that such filtration steps are separate and unrelated to the separation of slurry in the filter 214. Another embodiment of a Bayer plant and associate process is shown in Figure 11. Bayer plant 200a is the same as Bayer plant 200 but a secondary filter 224 is positioned immediately downstream of the filter 214 to remove fines that may be present in the pregnant liquor stream 217. Put another way, the secondary filter 224 is positioned upstream of the precipitator 218 and, if used, the polisher 216. Similar to filter 214, the secondary filter 224 may include a single bank of secondary filters 224 depending on a volume throughout requirement. In an embodiment, filter 214 includes centrifuge system 10 and the secondary filter 224 includes filter system 100 / 100a / 100b / 100c. Alternatively, in an embodiment, filter 214 includes filter system 100 / 100a / 100b / 100c and the secondary filter 224 includes centrifuge system 10. If fines are present in the pregnant liquor stream 217, they are typically in small quantities which helps to ensure that the secondary filter 224 can quickly separate these fines from the pregnant liquor in the pregnant liquor stream 217. Accordingly, in an embodiment, the Bayer plant 200a performs at most one additional filtering step to remove fines from the separated pregnant liquor. Figure 12 illustrates another embodiment of a Bayer plant 200b, which shares similarities with the Bayer plant 200a shown in Figure 11. The Bayer plant 200b includes a bauxite source 210, digestor 212, filter 230, polisher 216, and precipitator 218, similar to the arrangement in Figure 11. However, in Bayer plant 200b, the secondary filter 232 is positioned to receive residue separately from the main filter 230, rather than being placed directly in the pregnant liquor stream 217 as in Figure 11. In some embodiments, a flash tank 234 may be positioned downstream of the filter 230 and upstream of the polisher 216, as shown in Figure 12. In some embodiments, a flash tank 234 may be positioned downstream of the polisher 216 (not shown in Figure 12). The flash tank 234 receives, either directly or indirectly, the pregnant liquor stream 217 from the filter 230. The pregnant liquor stream 217 entering the flash tank 234 may be at elevated pressure and temperature conditions. In some cases, the pressure of the pregnant liquor stream 217 may be maintained above atmospheric pressure, such as between 5-15 bar or up to 5 bar. In some cases, the pressure of the pregnant liquor stream 217 may be maintained just above vapour pressure of the pregnant liquor stream 217. The temperature of the pregnant liquor stream 217 may be maintained at>100°C, and in some instances may range from 150155°C or higher. These elevated conditions may help retain dissolved species in solution and prevent premature precipitation prior to entering the flash tank 234. The specific pressure and temperature of the pregnant liquor stream 217 entering the flash tank 234 may vary depending on factors such as the properties of the bauxite being processed, the configuration of the upstream filter 230, and the desired conditions for subsequent processing steps. The flash tank 234 may be configured to rapidly reduce the pressure of the pregnant liquor stream 217, which may cause a portion of the liquid to vaporize. This process may help to cool the pregnant liquor stream 217 and may also assist in removing some dissolved gases or volatile components. In some cases, the flash tank 234 may include multiple stages to achieve a desired temperature reduction. The flash tank 234 may be equipped with various internal components such as baffles or separators to enhance the separation of vapor and liquid phases. The cooled liquid from the flash tank 234 may then be directed to the polisher 216 for further processing. In some embodiments, the steam generated in the flash tank 234 may be directed to a heat recovery system. The recovered heat from the steam may be utilized in various ways within the Bayer process. For example, the steam may be used to preheat the bauxite slurry before it enters the digestor 212. Additionally, the steam may be sent to heat exchangers to warm other process streams or provide heating for other unit operations in the plant. In some cases, the steam may be condensed, and the resulting condensate may be recycled back into the process, such as for use as wash water in the filter 230 or secondary filter 232. Although the flash tank 234 is shown in Figure 12, it is not required in all embodiments. Accordingly, in Bayer plant 200b, the pregnant liquor stream 217 may be sent directly to the polisher 216 and / or the precipitator 218. In embodiments where a flash tank is not used, the temperature and / or pressure of the pregnant liquor stream 217 may be reduced using alternative methods. For example, the Bayer plant may incorporate one or more heat exchangers to gradually cool the pregnant liquor stream 217. These heat exchangers may use spent liquor, cooling water, air, or other heat transfer fluids to remove heat from the pregnant liquor stream 217 in a controlled manner. In some cases, the heat exchangers may be arranged in series or parallel to achieve the desired temperature reduction. The configuration and number of heat exchangers may be adjusted based on factors such as the initial temperature of the pregnant liquor stream 217, the target temperature, and the available cooling media. Pressure reduction may be accomplished using pressure control valves or throttling devices positioned along the pregnant liquor stream 217 flow path. These devices may allow for a more gradual pressure reduction compared to a flash tank, potentially minimizing the risk of sudden precipitation or crystallization of dissolved species. In some embodiments, a combination of heat exchangers may be used to achieve the desired temperature reduction. This approach may allow for finer control over the pregnant liquor stream 217 properties as it moves towards downstream processing steps such as the polisher 216 or precipitator 218. The specific cooling reduction strategy may be tailored to the particular requirements of the Bayer plant, taking into account factors such as energy efficiency, equipment costs, and process optimization goals. Figure 13 illustrates another embodiment of a Bayer plant 200b, which is a variant of the Bayer plant system 200b where components including the bauxite source 210, digestor 212, filter 230, polisher 216, and precipitator 218 are similar. In Bayer plant 200c, the secondary filter 232 is still positioned to receive residue separately from the main filter 230, but a filtrate stream 236 from the secondary filter 232 is directed back to the main filter 230, creating a recirculation loop in the system. The recirculation of the filtrate 236 from the secondary filter 232 back to the main filter 230 may help in recovering additional valuable components and improving overall system efficiency. This recirculation loop may also assist in maintaining optimal concentrations in the main separation process. The secondary filter 232 may provide supplemental or alternative washing to the filter 230, offering several potential benefits. This arrangement may allow for more thorough cleaning through multi-stage washing, targeted removal of impurities, reduced load on the main filter, improved wash water management, and a sequential washing strategy. The secondary filter 232 may use different washing solutions or conditions, potentially improving overall recovery of valuable components and reducing re-contamination risks. By enabling independent adjustment of washing parameters at both filters, the process may be optimized for efficiency and throughput. In some cases, washing at the secondary filter 232 may completely replace washing at the main filter, potentially simplifying the main filtration step and reducing equipment complexity. The filtrate 236 may act as a washing solution for filter 230. In some embodiments, filter 230 may be a batch filter or semi-batch or semi-continuous filter such as a vertical leaf filter or candle filter. These batch filters may provide effective initial separation of the pregnant liquor from the digested bauxite residue. The secondary filter 232 may be a continuous filter such as a high pressure disc filter or high pressure drum filter. In some cases, secondary filter 232 may comprise multiple disc or drum filters arranged in series to allow for additional washing capability and improved liquor recovery. For example, secondary filter 232 may include two or more disc filters connected in series. The batch filter used as filter 230 may operate on cycles of approximately 2-60 minutes, such as up to 60 minutes, up to 30 minutes, up to 15 minutes, up to 10 minutes and / or up to 5 minutes. Multiple batch filter units may be used in parallel and staggered to provide overall continuous operation. For instance, 10 or more individual batch filter units may be used with staggered cycles to achieve continuous filtration. The continuous filters used as the secondary filter 232 may allow for ongoing filtration without interruption. In some embodiments, multiple banks of continuous filters may be used in parallel. For example, three banks of two disc filters in series may be employed. In Bayer plant 200b and / or Bayer plant 200a, the flash tank 234 may be replaced with or supplemented using a heat exchanger to cool the pregnant liquor stream 217 before it enters the polisher 216 and / or the precipitator 218. The heat exchanger may provide controlled cooling of the pregnant liquor stream 217 without the need for sudden pressure reduction typically associated with flash tanks. The heat exchanger may be configured to gradually reduce the temperature of the pregnant liquor stream 217 to a desired level suitable for subsequent processing in the polisher 216 and / or precipitator 218. This gradual cooling process may help maintain the stability of dissolved species in the pregnant liquor, potentially reducing premature precipitation of alumina or other valuable components. The use of a heat exchanger instead of a flash tank may provide more precise control over the cooling process, potentially allowing for optimization of downstream processes such as polishing and precipitation. Filtering using filter 230 and / or 232 at above atmospheric conditions may eliminate the need for flash tanks which may provide refinery optimisation opportunities in terms of equipment capital and operability. Additionally, the heat exchangers are generally operated continuously, which may align with the continuous nature of other components in the Bayer plant. In some implementations, multiple heat exchangers may be used in series or parallel to achieve the desired cooling effect, providing flexibility in system design and operation. Sensors and control systems may be incorporated to monitor and adjust the cooling process as needed, ensuring that the pregnant liquor stream 217 reaches the optimal temperature for subsequent processing steps. In some embodiments, the theoretical remaining liquor in mud as determined by modelling after each filter step in Figures 12 and 13 may be progressively reduced. For the filter 230, the remaining liquor in the mud discharge may be reduced by a factor of about 10. Similarly, for the secondary filter 232, the remaining liquor in the mud discharge may be reduced by a factor of about 10. Put another way, each filter may reduce the liquor in the mud discharge by a factor of about 10. In some implementations, the mud may be reslurried with water between filtering steps, which may affect the liquor content in subsequent stages. These values may provide a guideline for the theoretical performance of the filtering system, though actual results may differ based on the specific operating parameters and conditions of the Bayer plant. In some embodiments, the composition of the digested bauxite residue 220 after filtering in Bayer plant 200 / 200a / 200b / 200c may vary depending on factors such as the initial bauxite composition and processing conditions. The residue 220 may typically contain various metal oxides and other compounds. In some cases, the residue 220 may comprise iron oxides, titanium dioxide, silica, and residual alumina. It should be appreciated that the alumina content in the digested bauxite residue 220 can depend on the properties of the bauxite source 210 and species such as kaolin and desilication products. However, the residual alumina content in the digested bauxite residue 220 due to autoprecipitation during filtering may be lower compared to conventional Bayer processes due to the efficient separation and washing steps employed in the described Bayer plants which can help to reduce autoprecipitation. In some instances, alumina product losses associated with autoprecipitation may be reduced by at least 75%, 80%, 85%, 90% or >95%. The digested bauxite residue 220 may also contain small amounts of other elements such as sodium, calcium, and various trace metals. The soluble sodium content may vary depending on the efficiency of the washing steps, and some cases may be less than 1% by weight. It should be appreciated that the total sodium content of the digested bauxite 220 may be dependent on sodium-containing products such as desilication products including fixed and soluble soda. Water content in the residue 220 may vary based on the effectiveness of the dewatering processes employed. In some embodiments, the water content of the digested bauxite residue 220 may be reduced to less than 35% by weight, and in some cases, may be further reduced to less than 30% or even less than 25% by weight. The particle size distribution of the solids in the residue 220 may vary, but may typically include a mixture of fine and coarse particles. In some aspects, the majority of particles may be less than 100 microns in size, with a significant portion being less than 10 microns. In the claims that follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the disclosure. It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present disclosure.

Claims

1. A process of processing a slurry of fluid and solids, the process comprising: passing the slurry into a centrifuge to separate the fluid from the solids, the centrifuge being a pressure centrifuge;collecting the fluid;washing the solids in the pressure centrifuge to form a wash stream and washed solids; andcollecting the washed solids.

2. A process of claim 1, wherein the pressure centrifuge is a vertical pressure centrifuge.

3. A process of claim 1 or 2, wherein the solids in the pressure centrifuge are washed aplurality of times.

4. A process of processing a slurry of fluid and solids, the process comprising: passing the slurry into a centrifuge to separate the fluid from the solids; collecting the fluid;washing the solids in the centrifuge a plurality of times to form a wash stream and washed solids; andcollecting the washed solids.

5. A process of claim 4, wherein the centrifuge is a pressure centrifuge.

6. A process of any one of claims 3 to 5, wherein washing the solids a plurality of timesincludes:performing a first wash where the solids are washed to form a first wash stream and washed solids; andperforming a second wash where the washed solids are washed to form a second wash stream and further washed solids.

7. A process of any one of claims 1 to 6, wherein the fluid of the slurry and the wash stream are maintained at a temperature of >100°C, such as >120°C.

8. A process of any one of claims 1 to 5, or claims 6 or 7 when dependent on claim 5, wherein a pressure in the pressure centrifuge is > atmospheric pressure.

9. A process of any one of claims 1 to 8, further comprising adding a modifier to the slurry to promote separation of the fluid and solids.

10. A process of claim 9, wherein the modifier includes a flocculant or coagulant.

11. A process of claim 9 or 10, wherein the modifier is added to the slurry before theslurry is passed into the centrifuge.

12. A process of claim 9 or 10, wherein the modifier is added to the slurry after the slurry has been passed into the centrifuge but before the slurry contacts a sidewall of the centrifuge.

13. A process of any one of claims 1 to 12, further comprising filtering the wash stream to remove fines from the wash stream.

14. A process of claim 13, further comprising washing the fines to form washed fines and a fines wash stream.

15. A process of any one of claims 1 to 14, further comprising recirculating at least a portion of the wash fluid back into the slurry.

16. A process of any one of claims 1 to 15, further comprising decreasing a sand content of the solids in the slurry prior to passing the slurry into the centrifuge.

17. A process of any one of claims 1 to 16, further comprising increasing a solids content of the slurry prior to passing the slurry into the centrifuge.

18. A process of any one of claims 1 to 17, wherein the slurry includes: pregnant liquor as the fluid and bauxite residue as the solids; Bayer liquor or water as the fluid and oxalate precipitation products or desilication products or lime precipitation products as the solids; and / or spent liquor or a washing solution as the fluid and aluminium hydrate or aluminium hydroxide as the solid.

19. A process of claim 18, wherein, when the pregnant liquor is the fluid and bauxiteresidue is the solid, the separation of the fluid and solids in the centrifuge has a separation time less than a desilication product precipitation threshold time to prevent precipitation of desilication products in the pregnant liquor.

20. A process of claim 19, wherein, following separation of the fluid and solids, desilication products are selectively precipitated from the pregnant liquor whilst retaining aluminium species in their soluble form in the pregnant liquor.

21. A process of any one of claims 18 to 20, further comprising passing the pregnant liquor though a heat exchanger prior to precipitating alumina from the pregnant liquor.

22. A centrifuge system for separating fluid and solids in a slurry, the centrifuge system comprising:a rotatable bowl having a liquid outlet and conical beach having a solids outlet, and a screw conveyor coaxially arranged within the bowl for moving solids to the solids outlet;a slurry outlet for passing a slurry into the bowl; anda wash water outlet positioned between the slurry outlet and the solids outlet configured to contact the solids that have been moved into the conical beach with a washing solution to wash the solid.

23. A centrifuge system of claim 22, wherein the rotatable bowl is arranged vertically such that an axis of rotation of the bowl extends vertically.

24. A centrifuge system of claim 22 or 23, wherein the centrifuge is a pressure centrifuge.

25. A centrifuge system of any one of claims 22 to 24, further comprising a modifier outletfor injecting a modifier into the slurry to help promote separation of the fluid and solids.

26. A centrifuge system of claim 25, wherein the modifier outlet is positioned upstream of the slurry outlet such that, in use, the modifier is mixed with the slurry before the slurry is passed through the slurry outlet.

27. A centrifuge system of any one of claims 22 to 26, further comprising wear liners on an inner surface of the rotatable bowl and / or conical beach.

28. A process of processing a slurry of fluid and solids, the process comprising:passing the slurry into a filter to form a filtrate and filter cake;collecting the filtrate; andwashing the filter cake with a washing fluid to form a wash stream and a washed filter cake, wherein the washing fluid is at a temperature above a threshold temperature to at least partially avoid precipitation of liquid-soluble reactive species in the filter cake.

29. A process of claim 28, comprising washing the filter cake a plurality of times with the washing fluid.

30. A process of claim 29, wherein the filter cake is washed with the washing fluid from >2 to <4 times.

31. A process of claim 29 or 30, wherein each washing forms a separate wash stream that is collected separately from one another.

32. A process of any one of claims 28 to 31, wherein the washing fluid includes a neutralising agent that at least partially neutralises the filter cake to form a neutralised filter cake.

33. A process of claim 32, wherein the neutralising agent includes a buffer species or an acid.

34. A process of claim 32 or 33 when dependent on claim 28, wherein the filter cake is washed with a washing fluid in absence of the neutralising agent prior to washing the filter cake with the neutralising agent.

35. A process of any one of claims 28 to 34, wherein the threshold temperature is >100°C, such as>120°C.

36. A process of any one of claims 28 to 35, further comprising dewatering the filter cake after washing the filter cake with the washing fluid.

37. A process of claim 36, wherein dewatering is performed with a dewatering fluid.

38. A process of claim 37, wherein the dewatering fluid includes steam and / or air.

39. A process of any one of claims 36 to 38, wherein the filter cake is dewatered until thefilter cake is dried.

40. A process of any one of claims 28 to 39, wherein the filter includes a first filter and a second filter, wherein the process comprises:passing a residue from the first filter to the secondary filter;washing the residue in the secondary filter to produce a washed residue and a filtrate.

41. A process of claim 40, further comprising recirculating the filtrate from the secondary filter back to the first filter.

42. A process of claim 40 or 41, wherein the secondary filter receives a wash input separate from the washing fluid used to wash the filter cake in the first filter.

43. A process of any one of claims 40 to 42, wherein the washed residue from the secondary filter forms the collected washed solids.

44. A process of any one of claims 28 to 43, further comprising passing the filtrate through a flash tank.

45. A process of any one of claims 28 to claim 44, further comprising passing the filtrate to a polisher to form a polished pregnant liquor stream.

46. A process of claim 45, further comprising passing the polished pregnant liquor stream to a precipitator.

47. A process of claim 45 or 46, further comprising removing desilication products from the fluid in the polisher.

48. A Bayer process for treating bauxite to form alumina, comprising: separating pregnant liquor from digested bauxite residue using only a singleseparation step;wherein the pregnant liquor is maintained at a temperature of >100°C during separation.

49. A Bayer process for treating bauxite to form alumina, comprising:separating pregnant liquor from digested bauxite residue using a separation step; andperforming at most one additional filtering step to remove fines from the separated pregnant liquor;wherein the pregnant liquor is maintained at a temperature of >100°C during separation and the at most one additional filtering step.

50. A Bayer process of claim 48 or 49, wherein the pregnant liquor is maintained at a temperature of >120°C.

51. A Bayer process of any one of claims 48 to 50, wherein the separation step includes using a filter or centrifuge.

52. A Bayer process of claim 51, wherein the centrifuge is operated according to the process of any one of claims 1 to 21.

53. A Bayer process of claim 51, wherein the filter is operated according to the process of any one of claims 28 to 47.

54. A Bayer process of any one of claims 48 to 53, wherein separating pregnant liquor from digested bauxite residue includes using one or more displacement washing steps.

55. A Bayer process of any one of claims 48 to 54, wherein separating the pregnant liquor from the digested bauxite residue is performed using a single bank of separation devices.

56. A Bayer process of any one of claims 48 to 55, wherein the digested bauxite residue has a desilication product content of <0.5%.

57. A Bayer process of any one of claims 48 to 56, free from a pre-desilication step priorto separating the pregnant liquor from the digested bauxite residue.

58. A Bayer process of any one of claims 48 to 57, further comprising processing the pregnant liquor after separation from the digested bauxite residue to remove at least 5           some desilication product present in the pregnant liquor to form a desilication productstream and a polished pregnant liquor.

59. A Bayer process of claim 58, wherein the desilication product is removed from the pregnant liquor by precipitation to form the desilication product stream and the 10           polished pregnant liquor stream.

60. A Bayer process of any one of claims 48 to 59, further comprising drying the digested bauxite residue.15   61. A Bayer plant, configured to perform the Bayer process of any one of claims 48 to 60.

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