Technical Field

The present invention relates to a dewatering system. In particular, although not exclusively, the present invention relates to a dewatering system for use in a hydraulic ore hoisting system (HOHS).

Background

In the minerals processing industry, one problem relates to transporting ore from underground or subsea locations to a surface level. A novel system for such transportation has been described in PCT application number PCT/IB2019/055957, in the name of Weir Minerals Netherlands B.V., and is referred to as an HOHS.

The HOHS comprises a Positive Displacement (PD) pump, which is used to displace a mixture of ore and water, referred to as ore slurry, into a riser via a Pressure Exchange Chamber (PEC) using a driving fluid. A slurry is a two-phase mixture (a liquid with solid particles suspended or otherwise located therein). A specific advantage of the HOHS as described in PCT/IB2019/055957 is the use of a PD pump, which allows the use of a driving fluid containing fine particles (typically smaller than 500 pm).

A typical high-level schematic diagram of the HOHS system is shown in Fig. 1 showing both the equipment used and, to some extent, the process flow. One benefit of the process flow shown in Fig. 1 is that the driving fluid displaced from the Pressure Exchange Chamber (PEC) 1 (via low pressure line 2) is re-used as a carrier fluid in the ore slurry preparation (at location 3). After the ore slurry is pumped through the riser 4 to the surface, the ore slurry is dewatered (at location 5), and the carrier fluid is re-used again by the PD pump 6 as driving fluid in high pressure line 7. As an option, additional re-used fluid can be injected to line 7 via high pressure injection line 8. Reclaimed water from the driving fluid can be returned to the ore slurry preparation stage 3 via a low pressure fluid return line 9.

In Fig. 1 , Cv is the volumetric concentration of solids, and Q_up is the total volumetric flowrate of the mixture of fluid and solids delivered to the surface.

The challenge in the design of the dewatering system in this closed circuit is the potential build-up of fine particles in both the driving and carrier fluids. The typical Run-Of-Mine (ROM) ore that is to be fed into the HOHS can have a wide Particle Size Distribution (PSD), for example, covering the range from 10 micrometres (pm) to 100mm. To prevent a solids build-up in the carrier and driving fluids in the HOHS, the full PSD needs to be separated from the hoisted ore slurry at a rate equal to the feed rate of dry ROM into the HOHS, which presents a challenge.

A conventional approach to removing the full PSD of ore from the slurry is to fully separate all solid particles from the ore slurry before re-using the cleaned carrier fluid again as driving fluid. This would be driven by two requirements.

Firstly, to provide a clean driving fluid with minimum contamination of solid particles to enable the use of a clean water pump as a high-pressure driving fluid pump, for example a multistage centrifugal pump. Secondly, to prevent a gradual build-up of solids in the driving and carrier fluids, which otherwise could lead to blockage and/or transport issues due to too high solids concentration in the HOHS.

A conventional dewatering system consists of one or more screening stages, followed by clarification stages and a filtration stage. One or more screening stages are used to separate the coarse fractions from the ore slurry. The screened fine particle slurry would then be concentrated in a thickener typically using flocculants to assist sedimentation of the solid particles in the thickener. The overflow from the thickener would then be virtually free of solids to enable re-use as driving fluid satisfying the abovementioned criteria. The concentrated thickener underflow then contains all fine particles but is still in slurry form and therefor too wet for sequential transport and/or stacking in dry condition. To remove the majority of the water to create a sufficiently thick slurry, a filtration step would conventionally be used, for example using a filter press.

One drawback of this conventional approach is its complexity, size (footprint) and cost. Complexity is a result of the relatively large number of steps involved in the dewatering process, and the multiple stages in the system where solids (dry product) are separated from the slurry. This requires additional transportation steps to pump the slurry between the multiple stages of the dewatering system and to convey the dry solids from the multiple separation stages to a single point where they are to be combined and finally mixed again.

Even though the PD pumps in the HOHS can handle a high amount of fine particles, the build-up of fine particles must be limited so that a maximum concentration is reached at steady state that is within the solids concentration pumping performance of the PD pumps and still allows for significant addition of dry ROM ore in the slurry preparation step. To enable the fine particle build up to be constrained at steady state operation of the HOHS, the full PSD of the ROM ore feed is to be removed from the system at the same rate as it is fed into the system. Hence, in the steady state, the mass flow and PSD of the solids stream “ore in” should be equal to the mass flow and PSD of the solids stream “ore out”. In other words, both total mass flow as well as the PSD of ore in and ore out need to be very similar to prevent an unlimited build up of any specific portion of the PSD, and in steady state they should be equal.

It is among the objects of an embodiment of the present invention to obviate or mitigate the above disadvantages or other disadvantages of the prior art or to provide a useful alternative to the prior art, or improved operation thereof.

The various aspects detailed hereinafter are independent of each other, except where stated otherwise. Any claim corresponding to one aspect should not be construed as incorporating any element or feature of the other aspects unless explicitly stated in that claim.

Reference in this specification to any prior publication (or information derived from the prior publication), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from the prior publication) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates, or is even citable as prior art against this application.

Summary of Disclosure

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

According to a first aspect, there is provided a dewatering system for dewatering a slurry discharged from a riser in a hydraulic ore hoisting system to provide a driving fluid for use in said hydraulic ore hoisting system, said dewatering system being a substantially closed loop system in combination with the said hydraulic ore hoisting system during steady state operation, and comprising: a primary cyclone for separation of the discharged slurry into a primary cyclone overflow stream and a primary cyclone underflow stream; a dewatering screen for receiving the primary cyclone underflow stream and having at least one upwardly sloping vibrating screen deck to create a lateral flow from the underflow stream over the raised end of the deck and a vertical flow from the underflow stream through the screen deck, wherein the deck (i) forms a bed of particles of mixed particle size thereon so that the bed contains a portion of fine particles smaller than the apertures of the screen deck, (ii) retains a significant portion of the liquid and fine particles from the underflow stream at the lower part of the sloping deck, and (iii) retains the underflow stream on the deck surface for a significant time to ensure that the lateral flow has a low liquid content; and a secondary cyclone for receiving a combination of the primary cyclone overflow and the dewatering screen underflow to concentrate the remaining fine particles into a secondary cyclone underflow stream to be recirculated to the vibrating screen deck of the dewatering screen, and a secondary cyclone overflow stream suitable for use as a driving fluid.

Optionally, the solids mass flow of ore fed into the hydraulic ore hoisting system is substantially equal to the solid mass flow of the output of the dewatering system comprising (i) the significantly dewatered particles and (ii) the produced driving fluid, so as to enable a steady state operation in which the full particle size distribution separated from the discharged slurry by the dewatering system is substantially similar to the particle size distribution fed into the hydraulic ore hoisting system.

Optionally, the dewatering screen comprises a plurality of screen decks, each deck having a different aperture size to the adjacent decks.

Optionally, the discharged slurry undergoes coarse screening before being discharged to the primary cyclone to remove the most coarse particles (for example, at a cut size larger than 1 mm) to reduce the solids loading on the dewatering screen.

Optionally, the dewatering screen upper deck is oriented at an angle between one degree and ten degrees; in some embodiments, the dewatering screen upper deck is oriented at an angle between one degree and five degrees.

Optionally, the driving fluid provided by the dewatering system retains a concentration of fine particles lower than 30% by weight, in some embodiments lower than 20% by weight, in some embodiments, lower than 10% by weight. The solids in the driving fluid optionally comprise very fine particles of less than 200 pm in any dimension.

The driving fluid provided by the dewatering system is preferably used in the hydraulic ore hoisting system by a positive displacement pump to displace an ore slurry into a riser via a Pressure Exchange Chamber (PEC).

The separation point (also called the d50 cut point) of the primary cyclone underflow is optionally in the range of 20 to 200 pm. The separation point is the size at which a particle has a fifty percent chance of being directed to the underflow (and a fifty percent change of being directed to the overflow).

The solids concentration of the primary cyclone underflow is optionally larger than 50% by weight of the underflow.

The dewatering screen optionally has apertures in the range of 100 to 500 pm.

In some embodiments, the percentage of fine particles removed in the dewatering screen overflow is optionally in the range of: 60 to 100% of the solids hoisted in the riser; or 95 to 99.9% of the solids fed into the dewatering system; or 50 to 95% of the solids fed onto the dewatering screen.

The dewatering screen upward sloping deck optionally enables a majority of the underflow stream to be retained at an upstream end (i.e. a lower end) of the screen deck for optimised dewatering thereof.

The primary cyclone overflow and the dewatering screen underflow are optionally collected as a slurry in a sump.

A majority of solid particles in the slurry in the sump are optionally of a particle size smaller than the apertures of the screen deck of the dewatering screen.

The dewatering system may further comprise a screen having relatively large apertures for removing large particles (i.e. coarse screening) from the ore slurry prior to separation by the primary cyclone.

The dewatering system may further comprise a primary driving fluid tank for receiving the secondary cyclone overflow stream and optionally additional fluid to compensate for the fluid loss by the moisture in the dewatering screen overflow.

The dewatering system may further comprise a low capacity clarifier for receiving fluid from the primary driving fluid tank and for diverting fluid having a high fine particle concentration to the vibrating screen deck and for returning fluid having a low fine particle concentration to the primary driving fluid tank, thereby reducing the possibility of an uncontrolled build-up of the fine particles circulating in the dewatering system.

Preferably, all particle sizes of the particle size distribution are removed from the ore slurry at the same rate as they are fed into the system in the slurry preparation stage.

Each positive displacement (PD) pump in the HOHS may be fed by a centrifugal pump to increase its suction pressure thereby reducing the potential for cavitation in the PD pump allowing most efficient and reliable operation of the PD pump, especially at higher stroke rates.

One advantage of having a closed loop fluid system is that all valuable ore is retained in the system; in contrast to open loop systems in which fine particles are typically discarded, even though those fine particles may have valuable ore, and may not need any size reduction before the valuable mineral content can be removed therefrom.

As used herein, a closed loop driving fluid system refers to a system in which a slurry discharged from a riser in a hydraulic ore hoisting system is dewatered and the recovered water provides a driving fluid for use in the hydraulic ore hoisting system such that a significant percentage of the driving fluid used by the hydraulic ore hoisting system is recovered from the discharged slurry. The significant percentage may be above 85%, but is preferably above 90%, and advantageously above 92% or 94%. In some embodiments the significant percentage may even be above 96% or 98%, and possibly above 99%. The reason that the significant percentage may not be 100% is that the dry particles removed from the slurry may have absorbed some amount of moisture from the slurry water.

To implement a hydraulic ore hoisting system that in steady state uses a significant percentage of recovered water as the driving fluid, the full range of particle sizes should be removed from the slurry discharged from the riser. This may require a particle separation device (such as a cyclone, a screen, a combination of one or more of either, or another separation device) to remove a significant proportion of particles that are significantly smaller than the nominal cut point of particle size of that separation device. In some embodiments, this may be implemented using an upwardly sloping vibrating screen deck to form a bed of particles of mixed particle size thereon so that the bed contains a portion of fine particles smaller than the apertures of the screen deck. Such a vibrating screen deck would normally be considered as a poor classification device because it does not have a clear separation point such that all particle sizes smaller than that point pass through and all particle sizes larger than that point do not pass through.

For steady state closed loop operation, the full range of particle sizes may need to be removed at the output of the riser at the same or a very similar rate to the rate at which new particles are added to the input of the riser.

The hydraulic ore hoisting system may be considered as a system that only requires partial removal of particles, such that relatively fine particles may not have to be removed as they can still be present in the driving fluid.

According to a second aspect there is provided a dewatering system for dewatering a slurry discharged from a riser in a hydraulic ore hoisting system to provide a driving fluid for use in said hydraulic ore hoisting system, said dewatering system having a dewatering screen to enable steady state operation of a substantially closed loop system by substantially maintaining an equilibrium in a concentration of fine particles in the dewatering system whereby said dewatering screen comprises: at least one upward sloping vibrating screen deck for receiving a slurry stream and having an aperture size configured to form a bed of particles on the screen deck whereby particles larger than the aperture size and a portion fine particles smaller than the aperture size are retained in the formed bed for removal from the screen deck in a lateral flow containing particles of every size present in the received slurry stream, and a vertical flow of particles is maintained through the formed bed to produce an underflow fluid stream with a portion of the particles smaller than the aperture size, said underflow fluid stream at least in part being suitable for use as a driving fluid.

According to a third aspect there is provided a method of dewatering a slurry discharged from a riser in a hydraulic ore hoisting system to provide a driving fluid for use in said hydraulic ore hoisting system in a substantially closed loop manner during steady state operation of the system, the method comprising: separating the discharged slurry into a primary cyclone overflow stream and a primary cyclone underflow stream; receiving the primary cyclone underflow stream; creating on a screen deck, from the underflow stream, a lateral flow across the screen deck and a vertical flow through the screen deck; forming a bed of particles of mixed particle size so that the bed contains a portion of fine particles smaller than apertures in the screen deck; retaining a significant portion of the liquid and fine particles from the underflow stream at a lower part of the sloping deck; combining the primary cyclone overflow stream and the vertical flow through the screen deck and feeding the combination into a secondary cyclone; and separating the combination into a secondary cyclone underflow stream containing a majority of the fine particles in the combination, and a secondary cyclone overflow stream suitable for use as a driving fluid.

According to a fourth aspect there is provided a hydraulic ore hoisting system including the dewatering system of the first aspect for dewatering a slurry discharged from a riser in the hydraulic ore hoisting system.

It will now be appreciated that a dewatering system can be provided that does not require all fine particles to be removed from fluid recycled from an ore slurry before it can be used as driving fluid but still limits the build-up of fine particles in the essentially closed loop system.

Brief Description of Figures

These and other aspects will be apparent from the following specific description, given by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a simplified schematic diagram of a prior art HOHS;

Fig. 2 is a simplified schematic diagram of a HOHS according to one embodiment of the present invention; Fig. 3 is a schematic diagram illustrating one part (the slurry dewatering system) of the HOHS of Fig. 2;

Fig. 4 is a schematic diagram illustrating an alternative slurry dewatering system that can be used in the HOHS of Fig. 2;

Fig. 5 is a schematic diagram illustrating another part (the slurry preparation system) of the HOHS of Fig. 2;

Fig. 6 is a schematic diagram illustrating a third part (the solids removal system) of the HOHS of Fig. 2;

Fig. 7 is a schematic diagram illustrating a first alternative solids removal system that can be used in the HOHS of Fig. 2; and Fig. 8 is a schematic diagram illustrating a second alternative solids removal system that can be used in the HOHS of Fig. 2.

Detailed Description

Reference is first made to Fig. 2, which is a simplified schematic diagram of a hydraulic ore hoisting system (HOHS) 10 according to a first embodiment of the present invention. The HOHS includes a slurry dewatering system (SDS) 12, a slurry preparation system (SPS) 14, and a solids removal system (SRS) 16.

One embodiment of the slurry dewatering system 12 is shown in Fig. 3. An alternative embodiment of the slurry dewatering system 12 is shown in Fig. 4 and labelled 112. Either of these slurry dewatering systems 12, 112 could be used in the HOHS 10 of Fig. 2.

Reference is now made to Fig. 3, which illustrates the slurry dewatering system 12. The SDS 12 comprises a primary cyclone 20 which receives hoisted ore slurry from riser 4. The primary cyclone 20 is used to perform a dewatering / concentrating function and separates the received hoisted ore slurry into a primary cyclone overflow 22 and a primary cyclone underflow 24. In this embodiment, the d50 cut size (i.e. the size of particle at which there is a fifty percent chance of going to the overflow) of the primary cyclone is typically in the 20 to 200 pm range and the concentration of the underflow is typically larger than 50% (by weight) of the ore slurry input to the primary cyclone 20.

The primary cyclone underflow 24 is conveyed onto a vibrating dewatering screen 26; in particular, onto an upper deck 28 thereof. The dewatering screen 26 has only one deck in this embodiment and has a relatively fine aperture size in the range of 100 pm to 500 pm. The dewatering screen 26 is upwardly sloping in that it is angled such that an exit end 30 of the screen 26 is higher than an entry end 32. The entry end 32 is the end onto which the primary cyclone underflow 24 is conveyed. In this embodiment, the angle is approximately five degrees, but in other embodiments, a different angle may be selected.

The upward sloping deck 28 enables a relatively thick bed 34 of particles to build up on the screen deck 28 so that the bed 34 acts as a filter, ensuring that some particles smaller than the deck aperture size are retained in the bed 34 on the screen deck 28, but liquid (typically water) from the underflow 24 percolates through the bed 34 and passes through the deck 28. The result is that liquid and some fine particles (but no particles larger than the aperture size of the deck 28) flow through the deck 28 as a vertical flow 36.

The upward slope of the deck 28 also retains most of the liquid from the underflow 24 at the entry end 32 (or upstream end) of the screen deck 28, which promotes dewatering through the bed 34. The liquid from the underflow 24 forms a small pool at the entry end 32. There is also a lateral flow 38 of the bed 34 such that particles in the bed 34 drop off the exit end 30 and into an ore pile 40. The ore pile 40 comprises low moisture content particles that can be stacked and conveyed in a more or less granular fashion, rather than a wet flowing slurry, before being processed to obtain the desired minerals or other content.

Although the screen aperture is typically in the 100 to 500 pm range, a significant amount of the finer particles (smaller than 100 pm) are retained in the bed 34 on the screen deck 28 while the liquid is percolating through. This results in particles finer than the screen aperture being discharged with the coarser particles in the screen overflow (the lateral flow 38) at a low moisture level. The low moisture content means that a large amount of the liquid from the ore slurry has been reclaimed for use as driving fluid.

The upward slope of the deck 28 also increases the dwell time of the ore slurry on the deck 28, thereby providing additional time for fuller dewatering compared with screens that are horizontally disposed or have a downward sloping deck.

The primary cyclone overflow 22 is a dilute slurry only containing only fine particles (e.g. smaller than 1000 pm).

The primary cyclone overflow 22 and the underflow (vertical flow) 36 of the dewatering screen 26 is collected in a sump 44.

The slurry in the sump 44 contains solids that, primarily, have a particle size smaller than the dewatering screen aperture size. A cyclone feed pump 46 (which in this embodiment is a slurry centrifugal pump) pumps the dilute fine particle slurry from the sump 44 to a secondary cyclone 50.

The secondary cyclone 50 concentrates the dilute fine particle slurry from the sump 44, and separates the fine particle slurry into a secondary cyclone overflow 52 and a secondary cyclone underflow 54. The concentrated secondary cyclone underflow 54 is discharged back on the dewatering screen 26 to enable partial removal of the fine particles during their percolation through the bed 34 on the screen deck 28. The typical secondary cyclone underflow concentration is larger than 50% by weight of the secondary cyclone underflow 54.

The secondary cyclone overflow 52 contains only a low concentration, typically less than 10% by weight, of very fine particles (less than 200 pm). The secondary cyclone overflow 52 is fed into a relatively small primary driving fluid tank 60, which is used to supply fluid to the PD driving fluid pump 6. An additional water supply 61 is provided so that extra water may be added to ensure the primary driving fluid tank 60 is maintained at a sufficiently full level. The main reason for loss of water from the system is the moisture content in the dewatered ore 40 discharged from the dewatering screen 26 as the lateral flow 38.

Reference is now made to Fig. 4, which illustrates an alternative slurry dewatering system 112. The SDS 112 may be used in the HOHS 10 of Fig. 2 instead of SDS 12. SDS 112 is very similar to SDS 12. The difference is that SDS 112 includes a small clarifier 62. The clarifier 62 drains out a small amount of fluid (on a volumetric flow rate basis) from the primary driving fluid tank 60 compared with the fluid going from the primary driving fluid tank 60 to the PD pump 6. The clarifier 62 separates this into a reduced solids flow 64 comprising a fluid having a very low concentration of particles, and an increased solids flow 66. The reduced solids flow 64 is returned to the primary driving fluid tank 60; whereas, the increased solids flow 66 is pumped back to the screen 26 for further separation thereby. The clarifier 62 only processes a small percentage of the volumetric flow rate being discharged from the primary driving fluid tank 60, but it does assist in preventing any build-up of fine particles in the HOHS 10. It should be appreciated that the clarifier 62 includes a pump, although this is not illustrated in Fig. 4. In some embodiments, the clarifier 62 may not include a pump, but a pump may be provided external to the clarifier 62.

The solids mass flow in this increased solids flow 66 is very low compared to the ROM ore feed into the system. Flowever, in some rare situations where the increased solids flow 66 is pumped back to the screen 26 for further separation, it is possible that this additional input of fine particles onto the screen 26 may increase the fine particle content on the screen deck 28 too much, thereby inhibiting dewatering of the bed 34 resulting in too high a moisture content in the lateral flow 38. To prevent this, one option, not illustrated in Fig. 4, is that instead of discharging the increased solids flow 66 onto the dewatering screen 26, it can be discharged to a different location. For example, it may be transported in slurry form, or in dry form after undergoing additional dewatering (for example by pressure filtration or by centrifugation).

Reference is now made to Fig. 5, which illustrates the slurry preparation system (SPS) 14 of Fig. 2 in more detail. The purpose of the SPS 14 is to take the ore 120 that is created from the mining process and to create an ore slurry mix that can be pumped to the surface by the PD driving fluid pump 6 via the PEC 1. The quantity of ore in the ore slurry mix is regulated by the SPS 14.

The ore particles from the pile of ore 120 are placed onto a belt feeder (or conveyor) 122 that moves the ore particles into an ore bunker (or silo hopper) 124. The ore bunker 124 is located on a weighing belt feeder (or transport belt) 126 that removes ore particles from the ore bunker 124 and provides a fixed mass flow of dry (i.e. not in a slurry) particles onto an upwardly angled belt feeder (or conveyor) 128 that transports these particles into an ore feed hopper 130. The ore feed hopper 130 mixes the ore particles with fluid from the low pressure fluid return line 9 to create the ore slurry that is filled into the PEC 1 and hoisted through the riser 4 to the surface for dewatering by the SDS 12, 112.

The configuration of Fig. 5 is suitable for uses where coarse particles (for example larger than 20 mm in size) have been screened out. In systems that include coarse particles, an additional (coarse) screen may be provided to remove particles larger than an acceptable size (for example 20 mm). These removed particles may be returned for further size reduction elsewhere (for example, an underground crusher), or transported to the surface by another mechanism, such as a skip hoist. The particles 20 mm or smaller may be included in the ROM ore to be hoisted in the riser 4 (Fig. 2).

Reference is now made to Fig. 6, which illustrates a solids removal system (SRS) 16 for use with the HOHS 10. It should be appreciated that two alternative SRS configurations 116, 216 are shown in of Figs. 7 and 8, respectively, which will be described in more detail below. Any one of the SRS configurations 16, 116, 216 may be used in the HOHS 10.

Referring specifically to Fig. 6, the SRS 16 comprises an angled static (i.e. non-vibrating) screen 140 having an aperture size of 0.5 to 5 mm that receives driving fluid from the low pressure line 2. The screen 140 separates this driving fluid into a particle overflow stream 142 that exits the screen 140 and is discharged into a pile of particles 144 and an underflow stream 146 that is discharged into a carrier fluid tank 148. It is anticipated that a relatively small amount of particles are directed to the pile 144 as the displaced driving fluid is not expected to contain many particles larger than the screen aperture. The function of the screen 140 is primarily a safety back-up in case of control errors in the sequencing of the individual chambers in the PEC 1 and the actuated valves therein and furthermore allows low pressure flushing of the PEC 1. The carrier fluid tank 148 feeds the low pressure fluid return line 9.

One problem with the SRS 16 is that the carrier fluid tank 148 overflows because the discharged driving fluid is received at a faster rate than the rate of feed to the low pressure fluid return line 9. To address this problem, the SRS 16 includes a fluid outlet (or overflow) line 150 to direct any overflow of the carrier fluid tank 148 to a desired area. For example, if there is an existing mine dewatering system which is not further integrated into the HOHS 10 in which the surplus water is hoisted separately.

One advantage, however, is that the optional driving fluid injection PD pump (shown between broken arrows in Fig. 2) is not required with this SRS configuration.

Referring specifically to Fig. 7, a second configuration of SRS (that is, SRS 116) comprises, in addition to the components shown in Fig. 6, a secondary driving fluid tank 152 which is fed by the fluid outlet line 150. The secondary driving fluid tank 152 is used to supply the driving fluid injection PD pump that injects driving fluid into the high pressure line 7 via the high pressure injection line 8. This ensures that any surplus water that would overflow carrier fluid tank 148 is re-used to drive out the ore slurry in the PEC 1. This prevents a build-up and overflow of fluid in the carrier fluid tank 148. Flowever, is not essential to have the secondary driving fluid tank 152 to supply the driving fluid injection PD pump. In other embodiments, the driving fluid injection PD pump may take fluid directly from carrier fluid tank 148 via the fluid outlet line 150.

One benefit of staged tanks, for example, secondary driving fluid tank 152 being fed via an overflow (the fluid outlet line 150) from carrier fluid tank 148, is that it prevents coarser particles, smaller than the aperture size of the static screen 140, which may be present in the displaced driving fluid, from passing through the driving fluid injection PD pump.

Referring specifically to Fig. 8, a third configuration of SRS (that is, SRS 216) comprises, in addition to the components shown in Fig. 6, a PD pump 160 (which is the optional driving fluid injection PD pump shown in Fig. 2, but used for a different purpose). The PD pump 160 is connected to the fluid outlet line 150 from the carrier fluid tank 148 and pumps the received fluid up to the surface to the sump 44 in the SDS 12, 112, from where it will be pumped to the sump 44 feeding the secondary cyclone 50, as described with reference to Figs. 3 and 4 above. This provides an alternative way of preventing a build-up and overflow of fluid in the carrier fluid tank 148.

It should now be appreciated that one of the benefits of this HOHS 10 and the SDS 12, 112 is its simplicity, small footprint and low cost. Although it does not remove all solids from the slurry fed into it, it does remove all coarse particles larger than the aperture of the dewatering screen 26 and partially removes the fine particles that can pass the screen aperture during their percolation through the bed 34 of solid particles on the screen deck 28. The fine particles which pass the dewatering system 12, 112 will result in some build-up of fine particles in the HOHS 10 changing the particle size distribution (PSD) of the Run-Of-Mine (ROM) ore feed into the HOHS 10, resulting in an in-situ PSD having a higher fine particles content. This higher fine particles concentration in the HOHS 10 will increase the fine particle removal rate in the dewatering screen 26 resulting in a stable fine particle concentration after some initial increase (i.e. during steady state operation of the HOHS 10).

In other embodiments, the slurry dewatering system 12, 112 may be used on their own or in other systems than an HOHS.

In other embodiments, a coarse screen may be provided between the output of the riser 4 and the input to the SDS 12, 112. The coarse screen may have relatively large apertures for removing large particles (i.e. coarse screening) from the ore slurry prior to separation by the primary cyclone 20.

The steps of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate.

The terms “comprising”, “including”, “incorporating”, and “having” are used herein to recite an open-ended list of one or more elements or steps, not a closed list. When such terms are used, those elements or steps recited in the list are not exclusive of other elements or steps that may be added to the list.

Unless otherwise indicated by the context, the terms “a” and “an” are used herein to denote at least one of the elements, integers, steps, features, operations, or components mentioned thereafter, but do not exclude additional elements, integers, steps, features, operations, or components.

The presence of broadening words and phrases such as "one or more," "at least," "but not limited to" or other similar phrases in some instances does not mean, and should not be construed as meaning, that the narrower case is intended or required in instances where such broadening phrases are not used.

The reference numerals and corresponding parts that are used herein are provided below:

Pressure Exchange Chamber (PEC) 1 Low pressure line 2 Ore slurry preparation 3 riser 4 dewatering location 5

PD pump 6 high pressure line 7 high pressure injection line 8 low pressure fluid return line 9. hydraulic ore hoisting system (HOHS) 10 slurry dewatering system (SDS) 12, 112 slurry preparation system (SPS) 14 solids removal system (SRS) 16, 116, 216 primary cyclone 20 primary cyclone overflow 22 primary cyclone underflow 24 vibrating dewatering screen 26 screen deck 28 exit end 30 entry end 32 bed of particles 34 through screen vertical flow 36 off screen lateral flow 38 ore pile 40 sump 44 cyclone feed pump 46 secondary cyclone 50 secondary cyclone overflow 52 secondary cyclone underflow 54 primary driving fluid tank 60 additional water supply 61 clarifier 62 reduced solids flow 64 increased solids flow 66 pile of ore belt feeder / conveyor 122 ore bunker/ silo hopper 124 weighing belt feeder / transport belt 126 upwardly angled belt feeder / conveyor 128 ore feed hopper 130 static screen 140 particle overflow stream 142 pile of particles 144 underflow stream 146 carrier fluid tank 148 fluid outlet line 150 secondary driving fluid tank 152

PD pump 160