Comminution device

Abstract

The present invention provides a comminution device for reducing size of particles of material in a fluid, the comminution device comprising: a chamber having an inlet for providing a feed of fluid containing particles of material of a size into the chamber and an outlet for allowing particles of material of a reduced size to exit the chamber; a pair of opposing surfaces within the chamber, the surfaces being separated from each other by a distance and being movable relative to each other in a direction transverse to at least one of the surfaces; and an electromagnetic field generator for generating an electromagnetic field between the surfaces, wherein said device is configured so that particles of material of a reduced size are obtained after subjecting the fluid to the relative movement of the surfaces and the electromagnetic field therebetween.

Description

[0001] COMMINUTION DEVICE

[0002] Cross-Reference to Related Application

[0003] The present application claims priority from Australian Provisional Patent Application No. 2024900378, the entire contents of which is incorporated herein by reference.

[0004] Field

[0005] The invention relates to a comminution device for reducing size of particles of material in a fluid. The invention also relates to a method for reducing size of particles of material in a fluid.

[0006] Background

[0007] In hard rock mining / mineral processing, comminution of ore, i.e. crushing and grinding, is a significant cost to the overall operation.

[0008] Grinding mills typically comprise a rotating drum through which hard rock is fed through. The hard rock may be fed into the drum as dry material or in a slurry. The drum may also comprise grinding media, such as balls or rods, which assist the mechanical crushing and grinding by compressing the rock. Grinding mills include ball mills; autogenous (AG) mills; and semi-autogenous (SAG) mills. All of these grinding mills require a large amount of energy to operate they also require constant servicing to replace grinding media and wear components, such as mill liners.

[0009] The IsaMill is a low energy mill developed by Mount Isa Mines Limited and Netzsch Feinmahltechnik. The IsaMill is a stirred mill that uses a number of large diameter disks inside a drum which rotate inside the mill stirring up the grinding media as well as the target ore. However, the wear on the disks is rapid and as a result the disks need to be frequently replaced.

[0010] It is desirable to ameliorate at least one of the above disadvantages or to at least provide a useful alternative.

[0011] Summary

[0012] In a first aspect, the present invention provides a comminution device for reducing size of particles of material in a fluid, the comminution device comprising: a chamber having an inlet for providing a feed of fluid containing particles of material of a size into the chamber and an outlet for allowing particles of material of a reduced size to exit the chamber; a pair of opposing surfaces within the chamber, the surfaces being separated from each other by a distance and being movable relative to each other in a direction transverse to at least one of the surfaces; and an electromagnetic field generator for generating an electromagnetic field between the surfaces, wherein said device is configured so that particles of material of a reduced size are obtained after subjecting the fluid to the relative movement of the surfaces and the electromagnetic field therebetween.

[0013] The present invention is directed to a device for reducing the size of solid particles in a fluid. The device has applications in grinding fragments of rock to liberate or partially expose mineral ore therefrom. The particles of material as described herein may include metalliferous or non-metalliferous or metalloid material. Gold, iron-containing ores, and copper-containing ores are all examples of metalliferous materials. Coal is an example of non-metalliferous material. Boron, silicon, germanium and arsenic are examples of metalloid materials.

[0014] The present invention uses electromechanical fracturing of particles to reduce their size. The present invention may also liberate or partially expose mineral ore from the particles. The partially exposed mineral ore may be more susceptible to downstream chemical processing than would otherwise be the case.

[0015] In the context of this specification, the term “fluid” refers to any material that acts as a fluid, for example exhibiting fluid dynamic properties such as viscosity, viscous shear forces, and a boundary layer. The term “fluid” includes liquid mixtures such as slurries (i.e. water and solid particle mixtures) and fluidized streams (i.e. gas and solid particle mixtures).

[0016] In the context of this specification, the term “particle” refers to a small portion of matter. Particles may be or include macroscopic, microscopic or nanoscopic fragments of rock and mineral ore.

[0017] In the device of the present invention, the surfaces are separated from each other to define a comminution region therebetween. It will be appreciated that distance between the surfaces, and therefore the size of the comminution region, dictates the maximum size of the particles which may be received therebetween. It will also be appreciated that adjusting this distance will also adjust the maximum size of particle that the device can receive.

[0018] The term “electromagnetic field”, as used herein, refers to a classical (i.e. non-quantum) field produced by accelerating electric charges.

[0019] In general, the electromagnetic field is generated as a result of a difference in electrical potential between the surfaces. The electrical potential difference may exist independent of the flow of electrical current through the fluid or the induction of charge on the particles in the fluid. A voltage can be applied across the surfaces in order to generate the electromagnetic field. Subjecting the fluid to the electromagnetic field may result in particles being subjected to electrophoretic conditions. Subjecting the fluid to an electromagnetic field can result in the particles within the fluid acquiring either a temporary or a permanent electrostatic charge, which can be used in downstream processing of particles outputted from the device.

[0020] Use of the device according to the invention may improve the efficiency of comminution when compared with typical grinding mills. It is believed that the combined effect of moving the surfaces relative to one another whilst generating an electromagnetic field may result in the overall improvement in efficiency.

[0021] Without being bound by theory, it is believed that this improvement in efficiency is, in part, due to tension being the dominant force responsible for the fracture of the particles. The energy required to break a particle in tension may be significantly less than (e.g. only about 10% of) the energy required to effect breakage in compression. As such, a comminution device that works predominantly by applying tension loads to particles can provide significant energy savings.

[0022] Comminution processes may be performed on ore-containing materials in order to liberate valuable mineral from the material or reduce the particle size of the particles in order to facilitate downstream processing in order to recover the valuable mineral.

[0023] In many instances, relative movement of the surfaces generates viscous shear forces in the fluid. Typically, the viscous shear forces in the fluid result in tensile forces that act to pull the particles apart.

[0024] The relative movement of the surfaces may generate a standing wave instability. In other words, there may be unexpectedly very high pressure and / or temperature variations within the fluid due to the relative movement of the surfaces. These high pressure and / or temperature variations may result in tensile forces that act to pull the particles apart. This phenomenon can be, in part, described and solved for by applying nonlinear Schrodinger equations with supercritical nonlinearity.

[0025] High pressure and / or temperature variations within the fluid may be further amplified by the electromagnetic field between the surfaces. The electromagnetic field may accelerate the flow of charged particles through the particles in the fluid. For particles made from ionically bonded material, the electrical resistivity may be significantly reduced across the line of maximum tension. The electrical resistivity may depend on the composition of material(s) that form each particle. In some embodiments, the electrical resistivity may be reduced along a line passing through the part of the particle containing a valuable mineral or valuable species. For example, in a particle containing a valuable mineral (e.g. a metal such as gold), the path of least resistance for an electrical current through the material of the particle (e.g. valuable mineral bearing rock) will be through the centre of the valuable mineral.

[0026] Without being bound by theory, subjecting the particles to an electromagnetic field while also subjecting the particles to mechanical loads induced by the relative movement of the surfaces may generate a piezoelectric effect that can result in the maximum line of tension passing through a part of the particle containing the valuable mineral. This phenomenon may be manifested as a reduction in resistivity across the line of maximum tension, the result of which is a tensile force that acts to fracture the rock to expose the valuable mineral contained therein. This effect is referred to as “electromechanical fracturing” and “electromechanical fragmentation” throughout the specification. Accordingly, comminution in accordance with the present invention may enhance exposure of valuable minerals from within a particle as a result of particle fracture and breakage. Furthermore, breakage of a particle under tension through a region of valuable mineral may enhance liberation of valuable mineral into the fluid.

[0027] The flow of electrons within the fluid may alter the electrostatic charge distribution on the particles in the fluid which can aid in the separation of types of particles when processed.

[0028] In some embodiments, subjecting particles of material to comminution in accordance with the present invention may result in the liberation of valuable mineral into the fluid. The valuable mineral may be liberated as smaller particles composed of or comprising the valuable mineral. In some embodiments, as the smaller particles of, or comprising, valuable mineral (also referred to herein as “valuable mineral-containing particles”) pass through the comminution process, one or more valuable mineral-containing particles may contact one or more other valuable mineral-containing particles of the same or similar composition. After contacting, these valuable mineral-containing particles may agglomerate into a larger particle. These larger particles may be substantially valuable mineral. That is, they may have a significantly higher proportion of valuable mineral than the average particle in the fluid. Accordingly, during the comminution process, particles with a concentrated content of valuable mineral may be formed.

[0029] Subjecting particles of material to comminution in accordance with the present invention may result in chemical dissociation of compounds in the particles. In some embodiments, subjecting particles of material to comminution in accordance with the present invention may result in the breakage of bonds within (valuable) minerals. The breakage of bonds may lead to the liberation of metal values from the mineral and / or formation of other chemical species within the fluid.

[0030] Without being bound by theory, the agglomeration of valuable mineral-containing particles may be mechanically induced by valuable mineral-containing particles colliding within the fluid flow. Alternatively or additionally, without being bound by theory, the agglomeration may occurs as a result of the electrostatic charge on the particles causing the particles to fuse or weld together when in close proximity.

[0031] A similar phenomenon may be observed for particles that are “valuable material depleted”, i.e. smaller particles of valuable material in the bulk less valuable material, also agglomerate with each other due to this electrostatic effect.

[0032] In some embodiments, valuable mineral-containing particles may agglomerate into flakes.

[0033] Although there may be some agglomeration of particles during comminution in accordance with the present invention, particles of material of a reduced size are obtained. Thus, the average particle size of the comminution output (e.g. an output from the device of the first aspect) will have a smaller (finer) average particle size than an original input. In some embodiments, comminution may reduce the average particle cut size (d50%). In some embodiments, the output may have particle distributions such that the output may have a dlOO of < 10 microns and a d50 of <5 microns. The output particle size may range between 1 micron and 10 microns.

[0034] The growth of the agglomerations (e.g. flakes) may be limited by the distance between the surfaces. Without being bound by theory, it is believed that the growth of the agglomerations is inhibited by the shearing effect (i.e. viscous shear forces) of the boundary layers on the surfaces - which increases as the surfaces are drawn closer together.

[0035] The surfaces may be substantially flat. However, one or each surface may have a change in profile. Examples of which include curved profiles and undulating profiles.

[0036] A change in profile in one or each surface may provide a variation in distance between the surfaces. It is believed that increasing the distance between the surfaces across the comminution region, towards the output of the region, may enhance the growth of the agglomerations and / or the degree of agglomeration of valuable mineral-containing particles.

[0037] One challenge in implementing a predominantly tensile failure is that particles have different sizes and shapes and it is therefore difficult to apply tension loads to such that they can be pulled apart.

[0038] In some embodiments, a boundary layer of fluid may be produced at one or more of the surfaces. A boundary layer is where the interaction with the surface induces a no-slip boundary condition (i.e. the velocity of fluid at the surface is at zero) and the velocity of the fluid transitions to the free stream value away from the surface. Without being bound by theory, a boundary layer of fluid may be sufficient to apply a tension load to one or more particles between the surfaces. This may be due to the profile of the transition in velocity across the boundary layer. In some embodiments, there may be a separate boundary layer of fluid extending from each of the opposing surfaces. The boundary layers may be separated by a free stream flow of fluid.

[0039] In some embodiments, there is a single boundary layer of fluid that extends from one surface to the other surface of the opposed surfaces.

[0040] Unlike conventional grinding mills, such as the IsaMill, where the minimum output particle size is determined by the spacing of the disks, in the comminution device according to some embodiments of the invention the minimum particle size is not solely determined by the spacing between the surfaces. In these embodiments, the boundary layer together with the electromagnetic field contribute to providing a minimum output particle size that can be significantly reduced when compared with a minimum output particle size of a conventional grinding mill.

[0041] For example, the distance between the surfaces may be 3mm and the average size of the output particles may be less than 3 microns.

[0042] The boundary layer thickness may be altered by adjusting the distance between the surfaces and the relative speed of the surfaces. In addition, the viscous shear forces in the boundary layer(s) may be altered by adjusting the distance between the surfaces and the relative speed of the surfaces.

[0043] It is desirable that the boundary layers of the respective surfaces are close enough to interact.

[0044] It is even more desirable that a single boundary layer is formed between the respective surfaces. Viscous shear forces are more effectively transferred to the fluid via a single boundary layer as opposed to a pair of boundary layers (on respective surfaces) that are separated by a free stream flow. In the latter case, the free stream flow reduces the transfer of viscous shear forces between the boundary layers.

[0045] Boundary layer thickness will be determined by the physical characteristics and operating parameters of the device (such as the relative speed of the surfaces, the distance between the surfaces and roughness of the surfaces), the characteristics of the fluid (such as rheological properties of the fluid, the fluid velocity, density, viscosity, pressure and flowrate) and physical characteristics of the particulate material in the fluid (such as particle density and the particle effective diameter).

[0046] Surface Speed

[0047] Generally, the speed of a surface directly affects the thickness of the boundary layer formed around it. The faster the speed of the surfaces, the thinner the boundary layer will be. This is because a higher speed results in less time for the fluid particles near the surface to slow down, leading to a smaller region where the velocity significantly changes compared to the free stream velocity. In other words, the surface speed closely matches the free stream velocity. Whilst the thickness of the boundary layer is reduced with greater surface speeds, the shear effect is increased with greater relative surface speeds - both factors should be considered when determining an optimal relative speed of the surfaces.

[0048] Surface Distance

[0049] If the surfaces are close enough together, boundary layers formed on each surface will merge to produce a single boundary layer that has a thickness that is equal to or greater than the combined thickness of two boundary layers. Beyond a certain point, increasing the distance between the surfaces causes the single boundary layer to separate into two boundary layers. The maximum distance between the surfaces needed to produce a single boundary layer is determined by the fluid velocity and the viscosity of the fluid.

[0050] Surface Roughness

[0051] Generally, an increase in surface roughness results in a thicker boundary layer and vice versa. This is because a rough surface will lead to increased turbulent mixing and disruption of the laminar flow near the surface.

[0052] Fluid Velocity

[0053] An increase in fluid velocity (free stream fluid velocity) for a constant surface speed generally results in a thinner boundary layer and vice versa.

[0054] Fluid Viscosity

[0055] For Newtonian fluids, an increase in viscosity generally results in a thicker boundary layer and vice versa. For non-Newtonian fluids, the effect of viscosity on the thickness of the boundary layer depends on whether the fluid is shear thickening or shear thinning. Generally, when shear stress is applied (e.g. as a result of relative movement between the surfaces) to shear thickening fluid, the viscosity of the shear thickening fluid increases, which in turn increases the thickness of the boundary layer. Generally, when shear stress is applied (e.g. as a result of relative movement between the surfaces) to a shear thinning fluid, the viscosity of the shear thinning fluid reduces, which in turn reduces the thickness of the boundary layer.

[0056] Fluid temperature

[0057] Fluid temperature is inversely proportionate to fluid viscosity. As such, a decrease in fluid temperature will results in an increase in fluid viscosity and therefore an increase in boundary layer thickness. Conversely, an increase in fluid temperature will result in a decrease in fluid viscosity and therefore a decrease in boundary layer thickness.

[0058] Reynold’s Number

[0059] A Reynold’s number can be used to describe a flow regime that the fluid is operating under. Reynold’s number is proportional to fluid density, fluid speed, length of the flow path and inversely proportional to dynamic viscosity of the fluid. Generally, for Reynold’s numbers less than 2,000, the flow regime is said to be laminar and for Reynold’s numbers greater than 2,000, the flow regime is said to be turbulent. Laminar flow results in a thicker but smoother (i.e. less energetic) boundary layer. Turbulent flow results in a thinner but more energetic boundary layer.

[0060] Fluid Pressure Gradient

[0061] Adverse pressure gradient effects the boundary layer thickness. An adverse pressure gradient is a pressure gradient that increases in the direction of fluid flow. An increase in adverse pressure gradient results in a thicker boundary layer, and vice versa, up to a certain point, beyond this point boundary layer separation occurs. An adverse pressure gradient can be produced by wall blowing, wall sucking or any other means known in the art.

[0062] Particle Shape, Density, Concentration and Size

[0063] The flow behaviour of fluids containing particles (slurries) can depend on particle size, size distribution, shape, density, and concentration. Particle shape, size, density, and concentration can each influence particle interactions and, accordingly, the rheological behaviour of the fluid. The particles in the fluid to be processed may be characterised in terms of the effective or nominal diameter of the particles. That is, the diameter of the sphere of the same volume as the particle. As used herein, references to the particle diameter refer to this nominal diameter. Higher concentrations of fine particles can cause the flow behaviour of a fluid to change from Newtonian to non-Newtonian. Furthermore, the flow characteristics of a fluid can vary depending on whether there is a narrow distribution of particle sizes or a broad distribution of particle sizes. Generally, higher concentrations of finer particles result in a thicker the boundary layer. This is due to a relative increase in intermolecular forces between particles, also known of Van der Waals forces which include Debye force and London dispersion force.

[0064] Particle density (for a given diameter) of the particle affects particle momentum. Differences in particle momentum can affect collision kinetics and, in turn, fracturing or agglomeration behaviour. In accordance with Stokes law, finer particles are inhibited from falling out of the boundary layer which may also contribute to providing a thicker boundary layer.

[0065] It will be appreciated that, due to the comminution effected by the device, the average particle size and distribution of particle sizes will change during the course of processing. Furthermore, the shape(s) of the particles will also change in the course of processing. In some instances, the particle size distribution, in addition to the average particle size, may reduce during comminution effected by the device.

[0066] As the concentration of particles increases, in general, so does the viscosity of the fluid. It will be appreciated that if the concentration of particles becomes too high, the fluid will not be able to effectively flow through the device. Conversely, if the concentration of particles becomes too low, production (i.e. tonnage) of particles of reduced sizes will suffer. The skilled person will appreciate that the concentration can be adjusted and the flowability of resulting slurry assess via know methods in order to select a suitable concentration of particles that provides sufficient flowability for processing. Generally, the flowability will be balanced against the fluid having a high enough particle concentration to attain production levels within an acceptable range.

[0067] It may be possible to alter the boundary layer by changing one or more of the above factors. One or more additive may be added to the fluid to enhance the performance of the comminution device.

[0068] The additive may comprise a rheology modifier. For example, the additive may alter the shear rate dependent viscosity of the fluid. The additive may comprise a viscosity modifier. In other words, the additive may alter the viscosity of the fluid. The viscosity modifier may be of the type employed in wet grinding applications to enhance breakage kinetics.

[0069] The additive may comprise a density modifier. In other words, the additive may alter the density of the fluid.

[0070] The additive may comprise a pH modifier. In other words, the additive may alter the acidity or alkalinity of the fluid.

[0071] The additive may comprise a surfactant. In other words, the additive may alter the surface tension of the fluid. The additive may induce the Rehbinder Effect within the fluid. The Rehbinder Effect is the reduction in the hardness and ductility of a material, particularly metals, by a surfactant film. The Rehbinder Effect may enhance comminution efficiency by reducing the hardness and ductility of the particles within the fluid making them easier to comminute.

[0072] In some embodiments, the additive may comprise one or more commercial available additives that are used to induce the Rehbinder Effect in cutting, drilling or grinding applications, such as cutting, drilling or grinding applications using diamond coated tools.

[0073] The following additives by CHEMFORCE ® are examples of commercially available additives that may be useful in one or more embodiments of the comminution device according to the present invention:

[0074] • Complex42®

[0075] • Complex44®

[0076] • Complex8®

[0077] • The Juice® Rehbinder Effect

[0078] The Rehbinder effect refers to the phenomenon where the presence of surface-active agents (such as liquids, surfactants, or certain chemical environments) significantly reduces the mechanical strength of a solid material.

[0079] The Rehbinder effect is primarily attributed to the interaction of a liquid or surfactant with a solid surface, leading to a reduction in cohesion and an increase in plasticity or embrittlement. The key mechanisms include:

[0080] 1. Adsorption-Induced Weakening: Surface-active agents (e.g., water, oils, surfactants) adsorb onto the solid surface, altering the interatomic or intermolecular forces at the interface. This adsorption weakens atomic bonds, making dislocation motion easier and reducing the stress required for fracture or plastic deformation.

[0081] 2. Capillary-Induced Softening: When a liquid is present in microcracks or grain boundaries, capillary forces can induce local stress fields that modify the energy required for crack propagation. This is particularly relevant to brittle materials like ceramics, glasses, and rocks, where small amounts of moisture can significantly alter mechanical properties.

[0082] 3. Reduction of Dislocation Pinning: The presence of a liquid film on the surface or in grain boundaries can reduce friction between dislocations, facilitating easier slip.

[0083] This effect is particularly relevant in metals and alloys where the adsorption of hydrogen, sulfur, or other elements at the dislocation core can enhance plasticity or embrittlement.

[0084] 4. Stress Corrosion Cracking (SCC) Relationship: The Rehbinder effect is closely related to stress corrosion cracking (SCC), where environmental agents weaken a material under applied stress.

[0085] The fluid may comprise one or more additives that give rise to a number of synergistic effects on the fluid. In one specific example, an alkali hydroxide such as sodium hydroxide or calcium hydroxide may be added to the fluid as an additive. Hydroxide gels may be formed which can affect the rheology of the fluid. This change in rheology may increase the depth of the boundary layer which in turn increases the shear forces on the particles in the fluid. As alkali hydroxides (e.g. sodium hydroxide and calcium hydroxide) alter the pH of the fluid, the bulk conductivity of the fluid can be increased which may also increase the electrical conductivity of the fluid. An increase in conductivity may also result in an increase in gas evolution which may fracture the particles as a result of cavitation. Furthermore, the hydroxide-containing fluid may dissolve or extract material from the particles. In some embodiments, the hydroxide-containing fluid may be used to effect chemical comminution of the particles.

[0086] For some embodiments, it has been observed that the output particles may be electrostatically charged. The electrostatic charge on the particles may be directly proportional to its surface area when exposed to the electric field. Generally speaking, larger particles experience a higher voltage on their surface than smaller particles.

[0087] For some embodiments, it has been observed that the output particles from embodiments of the invention can settle into distinct layers. Without being bound by theory, it is believed that this behaviour is in part due to the electrostatic charges on the particles. The electrostatic charge may vary depending on the composition of the individual particles. Variations in the charge of particles produced using embodiments of the invention may facilitate or promote electrostatic self-assembly of one or more layers of different compositions. For example, the particles outputted from the device may settle in a tank to form bands containing mostly particles of a given composition.

[0088] For some embodiments, it has been observed that the electrostatic charge is temporary. The electrostatic charge may decay over time at different rates depending on the composition of the individual particles. For example, the electrostatic charge may decay over period of less than an hour, such as over about 20 minutes, once the fluid is no longer subjected to the electromagnetic field of the comminution process. Once the electrostatic charge on the particles has dissipated, the output may no longer separate into bands. That is, agitating particles that have separated into bands, after this time, may result in the bands being disrupted. Before any charge has dissipated below a threshold value, the particles may reorder into discrete bands after agitation.

[0089] In the first aspect of the invention, the moveable surfaces may be rotatable relative to each other. In some embodiments, the moveable surfaces may be linearly slidable relative to each other. For example, one surface may reciprocate relative to the other. The device may comprise a disk. At least one moveable surface may be located on the disk.

[0090] The moveable surfaces may be located on a pair of opposing disks. In some embodiments, the moveable surfaces may be located on a pair of opposing plates.

[0091] The disks may be coaxially arranged.

[0092] In some embodiments, the device may comprise a shaft that rotatably supports at least one of the disks.

[0093] In some embodiments, the disks may each have a shaft that are offset from each other.

[0094] The shaft may be upright. However, it is envisaged that the shaft may be arranged in any orientation. For example, it is envisaged that the shaft may be horizontally arranged when height restrictions are a consideration.

[0095] The device may comprise an adjustment mechanism that is configured to adjust the distance between the surfaces. The adjustment mechanism can be used to adjust the distance between the surfaces to optimise performance of the boundary layer. The distance between the surfaces may be adjusted to control the boundary layer(s) on the surfaces and therefore the viscous shear forces applied in the boundary layer(s).

[0096] Generally, the closer the surfaces are together the more viscous shear forces are applied in the boundary layer(s). The distance between the surfaces may be adjusted to control growth of the agglomerations. Ideally, the surfaces should be distanced enough to avoid electrical arcing between the surfaces, as will be discussed later in the specification.

[0097] The adjustment mechanism may apply a preload to the disks. The preload may be directed inwardly, i.e. towards the surfaces. The preload may resist a hydrodynamic load, directed outwardly, i.e. away from the surfaces, that results from fluid pressure of the fluid between the disks. The hydrodynamic load is a function of the fluid properties (density and viscosity) and the surface area of the disks. When the fluid is water and the disks that are two metres in diameter, a hydrodynamic load greater than 300 tons forces the disks apart.

[0098] The device may comprise a housing that defines the chamber. The housing may comprise a base and a side wall extending therefrom to form the chamber.

[0099] When assembled, both disks may be positioned within the chamber of the housing. The disks may be positioned at a spacing above the base of the housing. It can be appreciated that the spacing should be sufficient to allow movement of the disks.

[0100] The disks can be separated from each other to define a distance between the respective surfaces of the disks. In some embodiments, the distance between the surfaces dictates the maximum size of the particles that can be received by the device.

[0101] The disks may be positioned such that there is a gap between an edge of the disks and the side wall of the housing. In some embodiments, the size of the gap dictates the size of particles that can be outputted by the device.

[0102] The distance between the surfaces may be adjustable within the range of between 0.1mm and 100mm. The distance may be between 0.1mm and 10mm, optionally between 0.5mm and 3mm, optionally about 1mm or about 3mm.

[0103] In some examples, the comminution device may be used to process a slurry made from a stockpile of coarsely ground mineral ore. In these examples, it may be desirable to set the distance between 10mm and 100mm.

[0104] In some examples, the comminution device may be used to process a slurry made from a stockpile of mineral tailings or finely ground mineral ore. In these examples, it may be desirable to set the distance less than 10mm.

[0105] As described above, in some embodiments, one or each surface may have a profile that changes between the input and output from the comminution region. The change in profile may be such that the distance between the surfaces increases or varies towards the output. The profile may change so that the distance between the surfaces is: in the region at or near the input of between 10mm and 30mm, preferably 20mm; and in the region at or near the output of between 1mm and 5mm, preferably 1mm.

[0106] The adjustment mechanism may comprise a static frame and a movable frame that is configured to move relative to the static frame. An actuator may be disposed between the static frame and the moveable frame. The actuator may comprise any one or more of the following: a hydraulic piston; a pneumatic piston; Acme thread screws; cams; levers, electrically driven solenoids; a gear arrangement; a rack and pinion arrangement; and an electric motor.

[0107] The movable frame may be positioned above the static frame. In some embodiments, the moveable frame may be positioned beneath the static frame.

[0108] In some embodiments, the moveable frame and static frame are positioned in a side-by- side arrangement relative to a ground surface of an installation site.

[0109] The movable frame may be movable in a direction defined by the longitudinal axis of the shaft. For example, for an upright shaft the moveable frame is movable in a substantially vertical direction.

[0110] One of the disks may be attached to the static frame.

[0111] One of the disks may be attached to the moveable frame.

[0112] It is envisaged that the device may comprise more than two disks, for example four or six disks. For example, in a four-disk arrangement, two of the disks may be attached to the static frame and two may be attached to the moveable frame. The pairs of disks may be configured for the input of material in parallel, in series (i.e. the output of one pair acts as the input for a downstream pair), or a combination thereof.

[0113] The pair of opposing disks may comprise a stationary disk and a moveable disk that rotates relative to the stationary disk. It is also envisaged that both disks may be moveable.

[0114] At least one of the surfaces may comprise a wear resistant material. Suitably, both surfaces may comprise a wear resistant material. In some embodiments, the surfaces are provided by disks. Accordingly, in some embodiments, at least one of the disks may comprise a wear resistant material. Suitably, both disks may comprise a wear resistant material. In general, the device of the first aspect comprises an electrically conductive material so that the fluid can be subjected to an electromagnetic field. Each surface may comprise an electrically conductive material.

[0115] The wear resistant material may comprise a cermet. A “cermet” is a combination of metal and ceramic. Suitably, the cermet comprises one or more of the following: carbon nanotubes; partially stabilised zirconia; aluminium; magnesium; silicon carbide; and silicon nitride.

[0116] An advantage cermet material is that it is electrically conductive and has a high hardness.

[0117] The wear resistant material may be a composite material as will be described below.

[0118] The composite material may comprise a ceramic material. Ceramic compositions, which are not normally electrically conductive can be rendered conductive with the addition of carbon nanotubes. Carbon nanotubes may also increase the tensile strength of the ceramic. Ceramics typically have a low tensile strength.

[0119] The composite material may comprise partially stabilised zirconia. Partially stabilised zirconia is one example of a wear resistant ceramic which is typically non-conductive but can be rendered adequately conductive with the addition of carbon nanotubes. Suitably, the composite material comprises between 0.5% and 20% in weight of carbon nanotubes. Optionally, the composite material comprises between 4% and 6% in weight of carbon nanotubes.

[0120] The composite material may comprise magnesium oxide. Magnesium oxide may contribute to increase the hardness and / or Young’s Modulus of the composite material. Suitably, the composite material comprises between 0.5% and 10% in weight of magnesium oxide. Optionally, the composite material comprises 4% by weight magnesium oxide.

[0121] The composite may comprise reaction bonded aluminium nitride.

[0122] The composite may comprise fused aluminium oxide grains. The relative movement of the surfaces may be at a speed that is between 0.1 meters per second and 250 meters per second, optionally between 20 meters per second and 100 meters per second, optionally about 50 meters per second.

[0123] Generally, higher surface speeds are desirable as this will increase the shear force applied to the fluid. It should be noted that there is a mechanical limit to how fast a disk can be rotated before it fails, also known as its "burst strength". The burst strength can be estimated based on the square root of the ultimate tensile strength of the material divided by the product of the material density and the radius of the disk. A two meter diameter steel disk has a “burst speed” (i.e. a speed that the disk reaches its burst strength) of 3764 rpm, which translates to a surface speed of 599 meters per second. At this speed, the disk has 136 Megajoules of energy. Beyond the maximum surface speed, the disk is likely to fail.

[0124] The electrical potential difference between the surfaces may be between 1 volt and 30,000 volts, optionally between 10,000 volts and 30,000 volts, optionally between 20,000 volts and 30,000 volts.

[0125] The electrical potential difference between the surfaces may be less than 100 volts. Optionally, the electrical potential difference is between 10 volts and 30 volts. Optionally, the electrical potential difference is 25 volts.

[0126] The electromagnetic field generator may induce an electrical current through the fluid. The electrical current may be at an amperage of between 1 milliamp and 70,000 amps, optionally between 100 amps and 1,000 amps, optionally between 500 amps and 1,000 amps.

[0127] The electrical current may be such that the electrical current density is between 1 milliamp / cm2and 50 amps / cm2. Optionally, the electrical current density is between 1 milliamp / cm2and 1 amp / cm2. Optionally, the electrical current density is 0.5 amps / cm2. The current may be adjusted to provide the desired current density.

[0128] It should be noted that the electrical current density is inversely proportional to size (i.e. surface area) of the surfaces. That is, increasing the size of the surfaces will reduce the current density for the same electrical current. The electrical current may be provided by a power source that provides direct current or an alternating current or a combination of direct and alternating current configured for current superposition. The alternating current may be three-phase current. The power source may a mains power source or an electricity generator. Examples of electricity generators include diesel generators, gas turbine generators, dynamos and alternators.

[0129] The electromagnetic field generator may produce an electrical frequency of between 1 hertz to 500 hertz, optionally between 10 hertz and 30 hertz, optionally between 20 hertz and 30 hertz. The electrical frequency may be experimentally optimised to enhance comminution based on a particular ore that is being processed.

[0130] The electrical frequency may be single phase or three phase.

[0131] It has been found that the efficiency of particle size reduction can be enhanced by matching the electrical frequency to the resonant frequency of the particles.

[0132] In some embodiments, the inlet may be configured to direct fluid between the pair of opposing disks. The outlet may be configured to offtake fluid from between the pair of opposing disks. The outlet may be radially offset from the inlet. The inlet may direct fluid in an axial direction relative to the disks. The outlet may direct fluid in a radial direction relative to the disks. The outlet may direct fluid in a tangential direction relative to the disks. The inlet may be located at a centre of at least one of the disks.

[0133] In some embodiments, the feed of fluid may be gravity fed into the inlet, for example, via a tank or vessel. However, it is also envisaged that the feed of fluid may be pressure fed into the inlet, for example via a pump.

[0134] The outlet may be located at a periphery of at least one of the disks. The above arrangement maximises the residence time of the fluid in the comminution region (i.e. space between the disks) by enabling the fluid to flow radially from the inlet to the outlet across the surfaces of the disks.

[0135] The inlet may be configured to direct the feed of fluid in a direction that is transverse to the direction of movement of the surfaces. The inlet may have a tapered portion that tapers over a length, from a first diameter to a second diameter that is smaller than the first diameter. The first diameter may be between 10mm to 200mm, optionally, between 20mm and 70mm, optionally around 50mm. The second diameter may be between 0.1mm and 10mm, optionally between 0.5mm and 3mm, optionally about 1mm or about 3mm. The length may be between 10mm to 200mm, optionally, between 20mm and 70mm, optionally around 50mm.

[0136] The electromagnetic field generator may be configured to produce a three-phase power supply. A three-phase power supply is a power supply that can deliver a three-phase alternating current. Alternatively, the electromagnetic field generator may be configured to produce a single-phase alternating current or direct current.

[0137] In some embodiments, the electromagnetic field generator may comprise a power source, a transformer and a pair of opposing electrode assemblies. The power source may be a generator or alternator.

[0138] The pair of opposing electrode assemblies may comprise a positive electrode assembly and a negative electrode assembly, wherein the positive electrode assembly comprises a positive electrode and the negative electrode assembly comprises a plurality of electrically isolated negative electrodes, each of the plurality of electrically isolated negative electrodes being configured to deliver a single phase of a three-phase alternating current to the positive electrode.

[0139] In some embodiments, the electromagnetic field generator comprises a controller that is configured to allow adjustment of a strength of the electromagnetic field between the surfaces. Examples of suitable controllers may include variable speed drives, field controllers and the like.

[0140] The strength of the electromagnetic field can be adjusted to result in more electromechanical fracture of particles.

[0141] In some embodiments, the frequency of the current through the fluid between the disk may be adjusted so that the electrical current is close to or matches the resonant frequency of the particles. The strength of the electromagnetic field may be adjusted to reduce the current between the negative and positive electrodes. For example, the electromagnetic field can be adjusted to reduce the electrical current to a level that is suitable to be turned off using relatively inexpensive switchgear.

[0142] In some embodiments, at least one of the surfaces may produce a magnetic field. The magnetic field produced by one of the surfaces may be separate from the electromagnetic field produced by the electromagnetic field generator.

[0143] The magnetic field may enhance electromechanical fracture of particles. The magnetic field may induce an impressed current which interacts with the electrical current generated by the electromagnetic field generator. This may result in fluctuations in the electrical current through the fluid between the disks. The frequency of the electrical current generated by the electromagnetic field generator can be adjusted to constructively interfere with the impressed current to amplify the electrical current through the fluid between the disks, thereby resulting in more electromechanical fracturing of particles.

[0144] A further advantage of the magnetic field is that it tends to separate particles of material that have high magnetic susceptibility from particles of materials that have low magnetic susceptibility. Examples of materials that have a high magnetic susceptibility, include iron, nickel, cobalt, magnetite, maghemite, pyrrhotite, and pentlandite. Examples of materials that have a low magnetic susceptibility include copper, silver, and gold.

[0145] In atoms, electrons have an intrinsic angular momentum (spin) and an associated magnetic moment. The way in which these moments interact with each other and with external fields determines the magnetic susceptibility of a material.

[0146] Suitably, the surface that produces the magnetic field is movable. In some embodiments, moving the surface may result in movement of the magnetic field which can induce current through the fluid between the surfaces, due to Flemming’s Right Hand Rule. The induced current may contribute to electromechanical fracture of particles.

[0147] Suitably, at least one of the surfaces is magnetic. At least one of the surfaces may be magnetised, for example, using a magnetising discharge capacitor. At least one of the surfaces may comprise a permanent magnet. The permanent magnet may be a a ferrite magnet or a rare earth magnet, such as a rare earth magnet containing neodymium or samarium. At least one of the surfaces may be magnetised and may comprise a permanent magnet. Suitably, a plurality of permanent magnets may be arranged around the disk. The plurality of permanent magnets may alternate between North and South polarity. In one example, permanent magnets are positioned at 100mm centre spacing around the disk, that is a centre of each permanent magnet is separated by 100mm from a centre of an adjacent permanent magnet. The spacing and magnetic strength of the magnetic surface may be experimentally optimised to enhance comminution based on a particular ore that is being processed.

[0148] The magnetic surface may produce a magnetic field that is between 0.5 Tesla and 1.5 Tesla, such as around 1 Tesla, when the electromagnetic field generator is not generating the electromagnetic field between the surfaces. In some cases, the magnetic field may be up to 2 Tesla.

[0149] When the electromagnetic field generator is generating the electromagnetic field between the surfaces, the magnetic field between the surfaces may be between 5 Tesla and 20 Tesla. The magnetic field between the surfaces may vary across the surfaces. For example, isolated regions of the magnetic surface have a magnetic field of up to 20 Tesla, with the distributed magnetic field being about 10 Tesla. Variations in the magnetic field and, accordingly, variations in the magnetically induced loads to which the particles are subjected may be advantageous in some embodiments. The variations may facilitate the comminution process.

[0150] In a second aspect, the invention also provides a process for reducing size of particles of material in a fluid, the process including: feeding a fluid containing particles of material of a size between a pair of opposing surfaces that are separated by a distance; moving one of the surfaces relative to the other surface in a direction transverse to at least one of the surfaces; during said moving, generating an electromagnetic field between the surfaces, wherein particles of material of a reduced size are obtained through subjecting the fluid to the movement of the surfaces and the electromagnetic field therebetween; and removing particles of material of a reduced size from between the surfaces.

[0151] Some embodiments of the second aspect may be performed using a device in accordance with the first aspect of the present invention. In some embodiments, the comminution process may include processing the fluid between the pair of opposing surfaces for plural passes (recirculating) in order to achieve the desired reduction in particle size. Alternatively or additionally, the comminution processes may include processing the fluid through plural devices in accordance with the first aspect to achieve the desired reduction in particle size. One or more of the plurality of devices may have a configuration and / or operating parameters differing from the other(s) of the plurality of devices. For example, the configuration and / or operating parameters may be selected for processing the output of the preceding device, which will have a reduced particle size. That is, the configuration and / or operating parameters may be tailored to the progressively reduced particle sizes in the fluid as it is fed to the next device of the plurality so as to provide a final output with the desired reduction is particle size.

[0152] As described above, some embodiments of the device of the first aspect include at least one pair of opposing disks. In some embodiments of the second aspect, the process may involve oscillating one or both disks of the (or each) pair about a second axis that is transverse to the longitudinal extent of the axis.

[0153] It may be appreciated that the oscillatory movement may be about multiple axes.

[0154] The disks may be oscillated at an angle between 5° and 180° (i.e. a sweeping action) or between 1° and 5° (i.e. a small rotation of the axis).

[0155] Wear on the surface of the disks (also known as “tracking”) may be reduced by moving the disks about the second axis.

[0156] In a third aspect, the invention also provides a slurry containing particles of material of a reduced size obtained using a process in accordance with the second aspect of the present invention.

[0157] A fourth aspect of the invention provides a process of recovering a valuable mineral from a slurry containing particles of material of a reduced size, wherein the slurry is in accordance with the third aspect and comprises a valuable mineral and the process comprises: subjecting the slurry to a recovery process to yield a valuable mineral.

[0158] The invention also provides a valuable mineral obtained according to the process of the fourth aspect.

[0159] Brief Description of the Drawings

[0160] The invention is described further by way of example with reference to the accompanying drawings of which:

[0161] Figure l is a perspective schematic view of a comminution device according to an embodiment of the present invention;

[0162] Figure 2 is a perspective schematic view of a comminution device according to another embodiment of the present invention that comprises a movable frame and a fixed frame;

[0163] Figure 3 A is a side schematic view of the comminution device shown in Figure 2 with the movable frame in a lowered position;

[0164] Figure 3B is a side schematic view of the comminution device shown in Figure 3 A with the movable frame in a raised position;

[0165] Figure 4 is a perspective schematic view of an electromagnetic field generator of the comminution device according to an embodiment of the present invention;

[0166] Figure 4A is a cross-sectional view of upper and lower disks of the comminution device shown in Figure 4 through plane A;

[0167] Figure 5 is a perspective view of an underside of an upper disk of the comminution device shown in Figure 4;

[0168] Figure 5A is a cross-sectional view of the upper disk through plane A in Figure 5;

[0169] Figure 6 is a schematic view of circuit comprising a variable frequency drive that is configured to allow adjustment of a strength of the electromagnetic field between the surfaces and to thereby amplify electrical current in the comminution device;

[0170] Figure 7 is a schematic view of an electrical safety system for use in the comminution device according to an embodiment of the present invention; and Figure 8 is a schematic view of a hydraulic safety system for use in the comminution device according to an embodiment of the present invention.

[0171] Detailed Description

[0172] In the following detailed description, reference is made to accompanying drawings which form a part of the detailed description. The illustrative embodiments described in the detailed description, depicted in the drawings and defined in the claims, are not intended to be limiting. Other embodiments may be utilised, and other changes may be made, without departing from the spirit or scope of the subject matter presented. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings can be arranged, substituted, combined, separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure.

[0173] Figure 1 shows a comminution device 10 according to an embodiment of the invention.

[0174] The device 10 comprises a housing 12. The housing 12 may be a shell including a base 11 with a cylindrical side wall 13 extending therefrom to define a chamber 17.

[0175] In the illustrated embodiments, the chamber 17 comprises two volumes: a main volume within which a pair of disks (an upper disk 14a and a lower disk 14b) are disposed; and a collecting volume that is located below the lower disk 14b.

[0176] The main volume is cylindrical whereas the collecting volume has a ring-shaped profile when viewed in plan with a semi-circular cross-sectional area.

[0177] The disks 14a, 14b have opposing working surfaces 15a, 15b, respectively.

[0178] When assembled, both disks 14a, 14b are positioned within the chamber of the housing 12. The lower disk 14b is positioned above the base 11 of the housing 12. For example, a bottom surface of the lower disk 14b may be positioned at a spacing of 50mm and 200mm from an inner surface of the base of the housing. The gap should be sufficient to allow the fluid to effectively exit from the device. The upper disk 14a is positioned above the lower disk 14b, such that the surfaces 15a, 15b are separated from each other by a distance to define a comminution region therebetween. For example, this distance may be between 1mm and 20mm. In some embodiments, a distance of about 3mm may be used.

[0179] The disks 14a, 14b and housing 12 are configured such that there is a gap between an edge of the disks and the side wall of the housing 12. For example, this gap may be between 50mm and 200mm. The gap should be sufficient to allow the fluid to effectively exit from the comminution region.

[0180] The device 10 also comprises a frame 16 that supports the housing 12 and the upper disk 14a on the ground. The frame 16 comprises a platform and a pair of upright supports. The platform comprises a rectangular plate and four structural members that frame the parameter of the plate. Each upright support comprises a pair of vertical structural members and a horizontal structural member. The vertical structural members are attached (in this illustrated embodiment welded) to the members of the platform at a first end and are attached (in this illustrated embodiment welded) to the horizontal member at a second end.

[0181] The device 10 also comprises a motor 18 that is coupled to a lower disk 14b via an upright shaft 20. The motor 18 is operable to rotate the lower disk 14b relative to the upper disk 14a in a direction transverse to the surfaces 15a, 15b. The motor 18 is supported on the platform of the frame 16.

[0182] In one example, the motor 18 has the following specifications:

[0183] Power 150 kW

[0184] Speed 1,440 rpm*

[0185] Torque 5,200 Nm

[0186] Efficiency 95 %

[0187] *The electric motor speed is l,440rpm with a 3.5:1 reduction to give a rotational speed of 411 rpm at the shaft 20. The reduction may be a mechanical speed reduction via a gearbox or for example, by increasing the number of poles on the electric motor.

[0188] For a two meter diameter lower disk 14b rotating at a rotational speed of 411 rpm, this gives a surface velocity of 21.5 m / s which is within the acceptable limits of steel. For the same disk spinning at a speed of 3,764 rpm will produce a surface velocity of 599 m / s which is at the burst limit of steel.

[0189] It can be appreciated that the rotational speed may be selected based on the type of material that is being processed.

[0190] Increasing the rotational speed reduces the boundary layer thickness and increases throughput of the device. Conversely, reducing the rotational speed increases the boundary layer thickness and reduces the throughput of the device.

[0191] The shear effect may be increased with an increased rotational speed, depending on other factors that are described herein, such as the type of fluid and the boundary layer thickness.

[0192] Wear of the surfaces may be affected by a change in rotational speed, depending on the type of fluid.

[0193] As the rotational speed of the lower disk 14b increases the flow path of the fluid in the comminution region transitions from a linear or curved flow path to a spiral flow path. The transition in flow path may increase residence time of the fluid within the comminution region.

[0194] In general, the rotational speed of the surfaces will be selected bearing in mind the rheological characteristics of the fluid to be processed. If the speed is too low, inadequate comminution will occur. In some cases, the present invention may be uses to process fluids derived from mined material, such as tailings or a slurry made from “fresh” material. The fluid may be an aqueous slurry comprising particulate mineral material, for instance clay, shale, sand, grit, metal oxides etc. admixed with water. The fluid may be a non-cohesive slurry (e.g. a slurry rich in gravel or sand) or a cohesive slurry (e.g. slurry rich in loam, clay or silt). It may be that a relatively higher rotational speed will be used to process a non-cohesive slurry, while a cohesive slurry may be processed at a relatively lower rotational speed in order to impart the desired shear loadings on to the particles. Typically, there can be observed a point at which increasing the rotational speed further does not result in improved comminution performance. A rotational speed of between 300 rpm and 1,000 rpm performs well under most conditions. However, speeds as low as around 150 to 200 rpm may be used, such as with relatively viscous cohesive slurries.

[0195] The device 10 also comprises an electromagnetic field generator 22 for generating an electromagnetic field between the surfaces 15a, 15b.

[0196] The electromagnetic field generator 22 comprises an electrical transformer. An electrical transformer transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. The electrical transformer comprises a pair of coils wrapped around a core. Each coil has a different number of turns. A varying electrical current in any coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force across any other coils wound around the same core. The transformer can be used to step-up or step-down the voltage from the mains supply. The electrical output from the transformer is used to electrically charge one of the disks (the lower disk 14b shown in Figure 1). The upper disk 14a is connected to a ground. In this arrangement, there is an electrical potential difference between the upper disk 14a and the lower disk 14b which generates an electric field between the surfaces 15a, 15b.

[0197] In one example, the electromagnetic field generator 22 has the following specifications: Power 2 MW

[0198] Voltage 26 V

[0199] Current 66,000 Amps

[0200] Frequency 50 Hertz

[0201] Phase 3

[0202] It has been found that for a distance between the disks of less than 3mm, the voltage must be below 50 V to avoid electrical arcing between the surfaces. Electrical arcing results in rapid destruction of the disks and, in some cases, may result in welding the disks together.

[0203] An electrical current greater than 200 Amps at 26V is necessary to result in any appreciable electromechanical fragmentation of particles. It can be appreciated that the greater the electrical current, the greater the fragmentation of particles.

[0204] An inlet conduit 24 extends through a centre of the upper disk 14a and fluidly communicates with the comminution region. In this embodiment, the inlet conduit 24 has a constant circular cross-section and comprises a straight part and a curved part. An outlet conduit 26 extends radially from the collecting region of housing 12. The outlet conduit 26 offtakes fluid away from a periphery of the disks 14a, 14b.

[0205] In use, fluid containing particles of material of a size are fed into the chamber 12 via the inlet conduit 24. The feed of fluid enters the comminution region. In the comminution region, the particles in the fluid are fragmented due to the combined effect of relative movement of the surfaces 15a, 15b and the electromagnetic field between the surfaces 15a, 15b. The particles of material of a reduced size are able to exit from comminution region via the gap between sides of the disks and the side wall of the housing 12. The reduced size particles enter the collecting region of the housing 12. The reduced size particles exit the collecting region via the outlet conduit 26.

[0206] It can be appreciated that the distance between the disks 14a, 14b dictates the maximum size of the particles that can be received by the device 10. It can also be appreciated that the principal limiting factors governing the throughput of the device 10 are governed by the internal diameter of the input feed (inlet conduit 24 in Figure 1) and by the distance between the disks 14a, 14b. By increasing the inlet feed diameter, the volume that can be fed into the region between the disks 14a, 14b for a given gap is increased at the expense of a reduced surface area of the upper disk 14a. For a given disk spacing and a given inlet diameter, the throughput can be increased by increasing the rotational speed of the lower disk 14b or by increasing the head pressure on the inlet conduit 24.

[0207] Figures 2, 3 A and 3B show a comminution device 10 according to another embodiment of the invention.

[0208] The comminution device 10’ of Figures 2, 3 A and 3B operates in the same way as the comminution device 10 of Figure 1 with the following exceptions.

[0209] The comminution device 10’ comprises a gearbox 28 which converts rotation about an input shaft (not shown) to rotation about an output shaft 20 that is arranged perpendicular to the input shaft (not shown). The output shaft 20 is operably coupled to the lower disk 14b. An advantage of this arrangement is that the motor can be positioned at a distance offset from the device 10’. For example, unlike device 10, the motor does not need to be positioned directly underneath the housing 12. This is particularly useful if the device 10’ is to be used in areas with height restrictions.

[0210] The frame 16 comprises a fixed part 16a and a movable part 16b. The movable part 16b can be raised and lowered relative to the fixed part 16a so as to adjust the distance between the surfaces 15a, 15b of the disks 14a, 14b.

[0211] The fixed part 16a comprises a pair of upright sections. The upright sections support the housing 12 and the upper disk 14a.

[0212] Each upright section comprises a pair of vertical structural members and a horizontal structural member. The vertical steel members are attached to the ground (in this illustrated embodiment bolted) at a first end and are attached (in this illustrated embodiment welded) to the horizontal member at a second end.

[0213] The movable part 16b comprises a platform and a plurality of adjustable leg members.

[0214] The platform supports the gearbox 28 and the lower disk 14b and can be raised and lowered via the adjustable leg members to adjust the distance between the surfaces 15a, 15b of the disks 14a, 14b.

[0215] Each adjustable leg member comprises a pneumatic bag 30 that can inflated / deflated to raise and lower the movable part 16b relative to the fixed part 16a.

[0216] Figure 3A shows the pneumatic bag 30 deflated and the movable part 16b in a lowered position.

[0217] Figure 3B shows the pneumatic bag 30 inflated and the movable part 16b in a raised position.

[0218] The platform is formed from a rectangular plate with four structural members that frame the parameter of the plate.

[0219] Electromagnetic Field Generator

[0220] Figure 4 shows an electromagnetic field generator 22 according to one embodiment. The electromagnetic field generator comprises a power source (not shown) such as a diesel generator / alternator, a transformer 32, a negative electrode assembly 34 and a positive electrode assembly 36.

[0221] The negative electrode assembly 34 is located on the upper (stationary) disk 14a.

[0222] The positive electrode assembly 36 is located on the lower (movable) disk 14b.

[0223] The transformer 32 is connected on an input side 29 to the power source.

[0224] The transformer 32 is connected on an output side 33 to the negative electrode assembly 34 via three phase connection (i.e. wires), as indicated by bus bars 31 and electrical terminals 37 on the stationary disk 14a.

[0225] The positive electrode assembly 36 is connected to neutral via a neutral connection (i.e. wire) 38.

[0226] The negative electrode assembly 34 comprises a composite layered structure 39, which will be discussed in more detail with reference to Figure 5.

[0227] The stationary disk 14a comprises an inlet opening 35 that feeds slurry from the inlet conduit 24 (as shown in Figures 1-3B) into the space between the disks 14a, 14b.

[0228] Figure 4A shows the inlet opening 35 in more detail. The inlet opening 35 is an orifice located at a centre of the stationary disk 14a. The inlet opening 35 has a first section 35a that has a constant first diameter DI of around 50mm and a second, tapered, section, that tapers from the first diameter DI to a second diameter D2 of around 3mm over a length L of 50mm to 200mm. The second, tapered, section is therefore an inverted cone shaped profile. Particles entering the inlet opening 35 are ground down to 3 mm due to physical movement between the particles as well as an electrical force being exerted on them by the electromagnetic field generator 22. That is, in some embodiments, the fluid may be subjected to some degree of electromagnetic field before it enters the comminution region. This, together with particle-to-particle interactions, may be sufficient to facilitate preliminary comminution so as to bring oversized particles down to a size suitable for processing in the comminution region. Turning back to Figure 4, the positive electrode assembly 36 comprises a positive electrode 40 and a bush box 42. A bush box 42 allows electrical connection between stationary and rotating parts. The bush box 42 is configured to electrically connect the positive electrode 40 to the neutral connection 38 via the shaft 20 that drives rotation of the rotatable disk 14b.

[0229] The power source supplies three phase power to the transformer 32 which steps down the voltage and increases the electrical current on the output side of the transformer 32.

[0230] In one example, the transformer 32 has the following specification:

[0231] • Input: 415 V, 3,600 Amps, which equates to around 1.49 MW

[0232] • Output: 26 V, 57,000 Amps, which equates to around 1.48 MW

[0233] There is an Ohmic loss of 0.01 MW from the transformer 32. A radiator, such as a triple radiator, may be used to minimise Ohmic losses from the transformer 32.

[0234] The transformer 32 allows the output voltage to be reduced to an amount that is low enough to avoid electrical arcing across the space between the disks. For example, as previously discussed, a voltage of less than 50 V is required to avoid arcing across a 3mm gap. By virtue of conservation of energy, an output electrical current from the transformer 32 is significantly increased. The increased output electrical current enhances the piezoelectric effect and therefore tensile fracturing of particles.

[0235] Figure 5 shows an underside of the stationary disk 14a and negative electrode assembly 36, which as previously mentioned has a composite layered structure 39. The composite layered structure 39 comprises a top layer 46, a lower layer 47, and a middle layer 48.

[0236] The top layer 46 is made of conductive material (i.e. steel, copper, graphite, cermet and the like) and supports the electrical terminals 37 (not shown in Figure 5 - see Figure 4).

[0237] The lower layer 47 comprises three electrode segments 49a, 49b, 49c made of conductive material (i.e. steel, copper, graphite, cermet and the like). The electrode segments 49a, 49b, 49c are separated from each other via a layer of insulating material M (i.e. ceramic material). The insulating material electrically isolates the three segments from each other. The middle layer 48 is made of insulating material (i.e. ceramic material). The middle layer 48 electrically isolates the top layer 46 from the lower layer 47. The middle layer 48 can be made from the same or different insulating material to the insulating material that separates the electrode segments 49a, 49b, 49c.

[0238] As shown in Figure 5A, each electrical terminal 37, extend through the top layer 46 and the middle layer 48 to contact the lower layer 47.

[0239] An insulating material (i.e. ceramic material) extends around each electrical terminal 37. This insulating material may be the same or different insulating material to the insulating material that separates the electrode segments 49a, 49b, 49c and / or that forms the middle layer 48. As such, each electrical terminal 37 provides an electrically isolated electrical connection to one of the electrode segments 49.

[0240] Each electrical terminal 37 is connected to one of the phases in the three-phase power from the transformer 32. In use, electrical current will flow across the space between the disks from each electrical terminal 37 to the electrode segments 49a, 49b, 49c in the respective phases to the positive electrode 40. As such, the relationship between the electrode segments 49a, 49b, 49c and the positive electrode 40 can be described as a “star” electrical connection. The electrode segments 49a, 49b, 49c provide an even distribution of electrical current between the surfaces 15a, 15b of the disks 14a, 14b.

[0241] For an electrical current of 57,000 Amps generated by the transformer 32, an electrical current of between 500 Amps and 1,000 Amps will be produced through the fluid between the disks. The electrical current between the disks is sufficient to fracture particles in the fluid that are acted on by tensile forces resulting from the piezoelectric effect.

[0242] It is possible to achieve the required electrical current through the fluid using only two electrodes: a positive electrode; and a negative electrode. However, this arrangement has limitations.

[0243] Firstly, it can be inefficient to deliver the electrical current between the two electrodes at the above-described power requirements via single phase current or direct current, as it will result in high energy losses. To minimise energy losses, three phase power can be used but this would need to be converted to single phase or rectified to direct current to be delivered between the two electrodes. This introduces significant practical difficulties in implementing an arrangement involving only two electrodes.

[0244] Secondly, if direct current is used then there can be significant consumption of one of the electrodes.

[0245] Thirdly, if direct current is used then corrosion of the disks may occur if there is a difference in the metallurgy of one of the disks.

[0246] The above-described three-phase electrical connection arrangement avoids the practical issues associated with using only two electrodes.

[0247] The electrical current between the disks can be adjusted using a magnetic field. The magnetic field can be via magnetising the rotating disk 14b or by positioning permanent magnets (i.e. rare earth magnets) in the rotating disk 14b.

[0248] The magnetic field may be up to 20 Tesla. When the electromagnetic field generator 22 is not delivering electrical current, the magnetic field may be between 0.5 and 1.5 Tesla. When the electromagnetic field generator 22 is delivering electrical current, the magnetic field may be between 5 Tesla and 20 Tesla. Isolated regions of the magnetic surface may produce a magnetic field of 20 Tesla which may correspond to a distributed magnetic field of 10 Tesla.

[0249] It has been found that, due to Flemming’s Right Hand Rule, movement of the magnetised disk 14b (and therefore the magnetic field) induces an impressed current. An impressed current may also be produced by changing the strength of the magnetic field. The impressed current interacts with the current from the transformer 32 resulting in fluctuations in the electrical current through the fluid between the disks. It is understood that the fluctuations are a result of constructive and deconstructive interference between the impressed current and the electrical current from the transformer 32.

[0250] A Variable Frequency Drive (VDF) can be used to control the electrical current going into / or out of the transformer 32 to be in-phase with the impressed current. This results in constructive interference which amplifies the electrical current through the fluid between the disks. A VFD converts an input alternating electrical current (AC) to a rectified direct current (DC) via a rectifier and then modulates the rectified DC using pulse width modulation via an Insulated Gate Bipolar Transistor (IGBT) to an output AC of a different frequency. The VFD can be controlled to adjust the frequency of the output AC.

[0251] Figure 6 shows a VFD 50 connected to transformer 32. The VFD 50 monitors the electrical current through the fluid between the disks via a current meter 52 and modulates the frequency of current (in each phase) going into the transformer 32 to amplify the electrical current through the fluid between the disks.

[0252] It can be appreciated that interrupting a 1.5 MW power supply (i.e. 26 V at 57,000 Amps) power supply can be dangerous. Large and expensive switchgear and protective circuits are generally required to interrupt power supplies of this magnitude.

[0253] For example, if the transformer 32 is suddenly turned off, either intentionally or unintentionally, a very high back electromagnetic field (EMF) can be generated. The EMF can generate an electrical current three times the electrical current generated under steady state conditions, i.e. 170,000 Amps. If contactors are opened at this electrical current, they will be rapidly eroded or even welded closed.

[0254] Safety Systems

[0255] In some embodiments, by tripping a field controller in a generator (i.e. the power source), the electrical current outputted from the transformer 32 can be reduced to a level that can be safely turned off using small inexpensive switchgear.

[0256] An electrical safety system 60 is shown in Figure 7. The electrical safety system 60 comprises a plurality (three) first circuit 62 and a second circuit 72 in parallel.

[0257] Each first circuit 62 comprises a current transformer 64 that converts an electrical current across one of the bus bars 31 to a reduced (metered) current that is proportional to the electrical current across one of the bus bars 31. The metered current is circuited, in series, through a variable resistor 66 and a fast response overload contactor, also referred to as a “shunt” 68. The variable resistor 66 is set to a nominal load and amperage. The variable resistor 66 allows the shunt 68, which is a commercially available product, to be repurposed for this application. The shunt 68 is set to a predetermined current value that is proportionate to a maximum allowable electrical current across one of the bus bars 31. If electrical current in any of the three phases exceeds the maximum allowable electrical current, as set by the predetermined current value, the shunt 68 will trip. The electrical current may exceed the maximum allowable electrical current in the event of a short circuit, for example if the surfaces of the disks directly contact.

[0258] The second circuit 72 comprises a control switch 74 connected in series with a field controller 76 of the generator 78. The control switch 74 is configured to trip in response to the shunt 68 tripping.

[0259] The generator 78 has a separately excited field which is typically 40 to 300 volts and about 10 Amps. The strength of the rotating magnetic field inside the generator 78 can be varied by adjusting the exited field using the field controller 76. This works on a similar principle to “Doubly Fed Field” control.

[0260] The control switch 74 can be used to interrupt an excited field current in the generator 78. Interrupting the excited field current reduces an output current of the generator 78 to a level that can be safely turned off using small inexpensive switchgear.

[0261] If electrical current in any of the three phases across bus bars 31 exceeds the maximum allowable electrical current, as set by the predetermined current value, the shunt 68 will trip. Simultaneously, the control switch 74 on the second circuit 72 will also trip which interrupts power to the field controller 76, thereby reducing output current from the generator 78. Typically, within milliseconds the electrical current produced by the generator 78 is reduced to around 100-150 Amps, as opposed to 57,000 Amps, which is a suitable current to be safely turned off using small inexpensive switchgear.

[0262] Two or more of the above-described electrical safety system 60 may be used in parallel for redundancy purposes. The above-described electrical safety system 60 may be used in conjunction with fast acting fuses as an additional safety measure in the event that the electrical safety system 60 fails or is insufficient to shut down the electromagnetic field generator 22.

[0263] Fluid introduced into the comminution device 10 acts as a self-limiting lubricant and forces the opposing disks apart. This is in effect a hydrodynamic bearing, limited by the boundary layer between the opposing disks. For disks that are two metres in diameter, a hydrodynamic load greater than 300 tons forces the disks apart. A preload is applied to the disks to resist the hydrodynamic load. If fluid flow ceases, the disks under the influence of the preload are forced together which can result in the disks becoming sufficiently close enough to result in electrical arcing or even contacting. As can be appreciated, electrical arcing between the disks and contacting of disks should be avoided.

[0264] In addition to the electrical safety system 60, a hydraulic safety system may be utilised with the comminution device 10.

[0265] Figure 8 shows a hydraulic safety system 80 that comprises a separate fluid supply 82 (such as a tank or pressure vessel) that can be used to dump fluid into the feed, e.g. via the inlet conduit 24, of the comminution device 10 / 10’. The fluid supply 82 prolongs a period in which a hydrodynamic load is acted on the disks and thereby provides more time to shut down the generator before the disks become sufficiently close enough to result in electrical arcing.

[0266] Boundary Layer Effect

[0267] In some embodiments, a boundary layer of fluid may be produced at one or more of the surfaces.

[0268] In some embodiments, there may be a separate boundary layer of fluid extending from each of the opposing surfaces 15a, 15b. The boundary layers may be separated by a free stream flow of fluid.

[0269] In some embodiments, it may be desirable to have a single boundary layer of fluid that extends from one surface to the other surface of the opposed surfaces. Viscous shear forces are more effectively transferred to the fluid via a single boundary layer as opposed to a pair of boundary layers (on respective surfaces) that are separated by a free stream flow. In the latter case, the free stream flow reduces the transfer of viscous shear forces between the boundary layers. In these embodiments, it may be desirable to position the surfaces 15a, 15b of the disks 14a, 14b close enough to produce the single boundary layer but distanced enough to avoid electrical arcing between the surfaces 15a, 15b. In the boundary layer, viscous forces act on the fluid due to the no-slip condition at the surfaces 15a, 15b of the disks 14a, 14b. As the rotating disk 14b rotates, viscous shear forces are acted on the fluid which imparts tensile forces on the particles of material in the fluid. The tensile force generates mechanical stress in the particles of material.

[0270] Mechanical stress in the particles of material is increased using the electromagnetic field generator 22. The electromagnetic field generator 22 passes an electrical current through the fluid which is converted to mechanical stress in the particles of material via the piezoelectric effect. The combined mechanical stress is sufficient to fracture the particles.

[0271] It can be appreciated that the boundary layer(s) should be sufficiently developed, i.e. thick enough to exert enough viscous shear forces on the particles of material to result in sufficient size reduction of the particles of material.

[0272] In general terms, the boundary layer(s) are sufficiently developed if an average size of the particles output from the comminution device is around 1,000thof the size of the gap between the surfaces 15a, 15b of the disks 14a, 14b.

[0273] For example, if the average size of the particles are less than 3 micron and the gap between the disks is 3mm then the boundary layer(s) are sufficiently developed.

[0274] For distances between the surfaces 15a, 15b greater than 6 mm, the boundary layer adhesion or shear effect is greatly diminished. Additives may be used to increase the boundary layer adhesion or shear effect above distances greater than 6mm.

[0275] Example

[0276] Experimental tests have been performed using a comminution device in accordance with the present invention.

[0277] Tailings were taken from a mine in Newbridge, Victoria. A slurry for the tailings was formed comprising a 3 : 1 ratio of water to solids. The slurry was input into the comminution device, under the following conditions:

[0278] • Gap between disks: 3mm

[0279] • rotational speed of the rotating disk 14b: 300rpm • Temperature of the slurry: 21 °C

[0280] • Slurry PH: 9-10

[0281] • Voltage: 26 V

[0282] • Current from transformer 32: 57,000 Amps

[0283] • Average current through fluid: 450-480 Amps (150-160 Amps from each of the three phases)*

[0284] *The current fluctuates throughout the test due to material flow, conductivity and the impressed current.

[0285] After processing in the comminution device, the slurry was drained into 20 litre buckets (a small amount of wash-out water was added) and the sample left to settle for 24-48hrs to form a sediment.

[0286] Sediment samples were taken and tested using a standard fire assay test to assess the concentration of gold in parts per million (PPM) in the sediment samples.

[0287] Control samples (prior to being processed by the comminution device) were also tested using the same standard fire assay test to assess the concentration of gold in parts per million (PPM) in the control samples.

[0288] Each sample (sediment and control) was 2kg.

[0289] Table 1 below provides results of material from a palecon at the Newbridge mine before and after being processed in the comminution device according to the above-described conditions.

[0290] Table 1

[0291]

[0292] Table 2 below provides results of material from a sand pile at the Newbridge mine before and after being processed in the comminution device according to the above-described conditions.

[0293] Table 2 Table 3 below provides results of processed material (via a standard industry ball mill) from the Newbridge mine and then processed in the comminution device. The table provides concentrations before and after being processed in the comminution device according to the above-described conditions.

[0294] Table 3

[0295] As can be seen from the above result, the concentration of gold detected can be significantly increased by being processed using the comminution device according to the present invention.

[0296] Without being bound by theory, it is believed that the increase in detected concentration is due to the comminution liberating gold from forms that may be under-detected using standard fire assay. For example, it has been reported the fire assay method for precious metal determination underestimates gold concentration when gold telluride is present (see P.C. Santos-Munguia, F. Nava-Alonso, V.M. Rodriguez-Chavez, O. Alonso-Gonzalez, Hidden gold in fire assay of gold telluride ores, Minerals Engineering, Volume 141, 2019, 105844, ISSN 0892-6875, https: / / doi.Org / 10.1016 / j.mineng.2019.105844). Gold- containing tellurides include calaverite (AuTe2), petzite (AgsAuTe2), sylvanite ((Au,Ag)2Te4), krennerite (Aui-xAgxTe2), muthmannite (AuAgTe2), montbrayite ((AuSb)2Te3), and kostovite (CuAuTe4). Recovery of gold, using cyanide leaching, from telluride ores can be difficult. It may be that in unprocessed ore, as well as in cyanidation tailings, there is more gold than indicated by standard fire assays. Similar issues may arise in processing gold-bearing material containing iridium.

[0297] Where gold tellurides are present, without being bound by theory, it is believed that the comminution process may break the gold tellurium bond. This may lead to the in situ generation of tellurium dioxide and gold metal. Breakage of the gold tellurium bond may result in gold being present in a processed sample in a form that may be detected using fire assay techniques.

[0298] For completeness, various embodiments, of a comminution device, a process, a slurry and a valuable mineral disclosed herein are set out in the following numbered statements:

[0299] Statement 1 : A comminution device for reducing size of particles of material in a fluid, the comminution device comprising: a chamber having an inlet for providing a feed of fluid containing particles of material of a size into the chamber and an outlet for allowing particles of material of a reduced size to exit the chamber; a pair of opposing surfaces within the chamber, the surfaces being separated from each other by a distance and being movable relative to each other in a direction transverse to at least one of the surfaces; and an electromagnetic field generator for generating an electromagnetic field between the surfaces, wherein said device is configured so that particles of material of a reduced size are obtained after subjecting the fluid to the relative movement of the surfaces and the electromagnetic field therebetween.

[0300] Statement 2: The comminution device of Statement 1, further comprising an adjustment mechanism that is configured to adjust the distance between the surfaces.

[0301] Statement 3: The comminution device of Statement 1 or Statement 2, wherein the distance between the surfaces is adjustable within the range of between 0.1mm and 100mm.

[0302] Statement 4: The comminution device of any one of the preceding Statements, wherein the moveable surfaces are rotatable relative to each other.

[0303] Statement 5: The comminution device of any one of the preceding Statements, wherein the moveable surfaces are located on a pair of opposing disks.

[0304] Statement 6: The comminution device of Statement 5, wherein the disks are coaxially arranged.

[0305] Statement 7: The comminution device of Statement 6, further comprising a shaft that rotatably supports at least one of the disks.

[0306] Statement 8: The comminution device of Statement 7, further comprising an adjustment mechanism that is configured to adjust the distance between the surfaces.

[0307] Statement 9: The comminution device of Statement 8, wherein the distance between the surfaces is adjustable within the range of between 0.1mm and 100mm.

[0308] Statement 10: The comminution device of Statement 8 or Statement 9, wherein the adjustment mechanism comprises a static frame and a movable frame that is configured to move relative to the static frame.

[0309] Statement 11 : The comminution device of Statement 10, wherein the movable frame is positioned above the static frame.

[0310] Statement 12: The comminution device of Statement 10 or 11, wherein the movable frame is movable in a direction defined by the longitudinal axis of the shaft.

[0311] Statement 13: The comminution device of any one of Statements 10-12, wherein one of the disks is attached to the static frame.

[0312] Statement 14: The comminution device of any one of Statements 10-13, wherein one of the disks is attached to the moveable frame.

[0313] Statement 15: The comminution device of any one of Statements 10-14, wherein the pair of opposing disks comprises a stationary disk and a moveable disk that rotates relative to the stationary disk.

[0314] Statement 16: The comminution device of any one of Statements 5-15, wherein at least one of the disks comprises a wear resistant material.

[0315] Statement 17: The comminution device of Statement 16, wherein the wear resistant material is a cermet.

[0316] Statement 18: The comminution device of Statement 17, wherein the cermet comprises one or more of the following: carbon nanotubes; partially stabilised zirconia; aluminium; magnesium; silicon carbide; and silicon nitride. Statement 19: The comminution device of any one of the preceding Statements, wherein the distance is between 0.1mm and 10mm, optionally between 0.5mm and 3mm, optionally about 1mm or about 3mm.

[0317] Statement 20: The comminution device of any one of the preceding Statements, wherein the relative movement of the surfaces is at a speed that is between 0.1 meters per second and 250 meters per second, optionally between 20 meters per second and 100 meters per second, optionally about 50 meters per second.

[0318] Statement 21 : The comminution device of any one of the preceding Statements, wherein the electromagnetic field generator produces an electrical potential difference between the surfaces of less than 100 volts, optionally, between 10 volts and 30 volts, optionally, 25 volts.

[0319] Statement 22: The comminution device of any one of the preceding Statements, wherein the electromagnetic field generator induces an electrical current through the fluid.

[0320] Statement 23 : The comminution device of Statement 22, wherein the electrical current through the fluid is between 1 milliamp and 70,000 amps, optionally between 100 amps and 1,000 amps, optionally between 500 amps and 1,000 amps.

[0321] Statement 24: The comminution device of Statement 22 or Statement 23, wherein the electrical current through the fluid is such that the electrical current density is between 1 milliamp / cm2and 50 amps / cm2, optionally, between 1 milliamp / cm2and 1 amp / cm2, optionally, 0.5 amps / cm2.

[0322] Statement 25: The comminution device of any one of the preceding Statements, wherein the electromagnetic field generator produces an electrical frequency of between 1 hertz to 500 hertz, optionally between 10 hertz and 30 hertz, optionally between 20 hertz and 30 hertz.

[0323] Statement 26: The comminution device of any one of Statements 5 to 15, wherein the inlet is configured to direct fluid between the pair of opposing disks and the outlet is configured to offtake fluid from between the pair of opposing disks, and the outlet is radially offset from the inlet. Statement 27: The comminution device of any one of the preceding Statements, wherein the inlet has a tapered portion that tapers over a length, from a first diameter to a second diameter that is smaller than the first diameter.

[0324] Statement 28: The comminution device of Statement 27, wherein the first diameter is between 10mm to 200mm, optionally, between 20mm and 70mm, optionally around 50mm.

[0325] Statement 29: The comminution device of Statement 27, wherein the second diameter is between 0.1mm and 10mm, optionally between 0.5mm and 3mm, optionally about 1mm or about 3mm.

[0326] Statement 30: The comminution device of Statement 27, wherein the length is between 10mm to 200mm, optionally, between 20mm and 70mm, optionally around 50mm.

[0327] Statement 31 : The comminution device of any one of the preceding Statements, wherein the electromagnetic field generator is configured to produce a three-phase power supply.

[0328] Statement 32: The comminution device of any one of the preceding Statements, wherein the electromagnetic field generator comprises a power source, such as a generator, a transformer and a pair of opposing electrode assemblies.

[0329] Statement 33: The comminution device of Statement 32, wherein the pair of opposing electrode assemblies comprises a positive electrode assembly and a negative electrode assembly, wherein the positive electrode assembly comprises a positive electrode and the negative electrode assembly comprises a plurality of electrically isolated negative electrodes, each of the plurality of electrically isolated negative electrodes being configured to deliver a phase of a three-phase alternating current to the positive electrode. Each electrode may be configured to deliver a single phase of the three-phase alternating current that differs from the phase delivered by the other of the negative electrode(s).

[0330] Statement 34: The comminution device of any one of the preceding Statements, wherein the electromagnetic field generator comprises a controller that is configured to allow adjustment of a strength of the electromagnetic field between the surfaces. Statement 35: The comminution device of Statement 34, wherein the controller is a variable speed drive or a field controller.

[0331] Statement 36: The comminution device of any one of the preceding Statements, wherein at least one of the surfaces is magnetic.

[0332] Statement 37: The comminution device of Statement 36, wherein at least one of the surfaces is magnetised, or comprises a permanent magnet, or is both magnetised and comprises a permanent magnet.

[0333] Statement 38: The comminution device of Statement 36 or 37, wherein the magnetic surface produces a magnetic field that is between 0.5 Tesla and 1.5 Tesla when the electromagnetic field generator is not generating the electromagnetic field between the surfaces; or the devices is configured to provide a magnetic field between 5 Tesla and 20 Tesla when the electromagnetic field generator is generating the electromagnetic field between the surfaces.

[0334] Statement 39: A process for reducing size of particles of material in a fluid, the process including: feeding a fluid containing particles of material of a size between a pair of opposing surfaces that are separated by a distance; moving one of the surfaces relative to the other surface in a direction transverse to at least one of the surfaces; during said moving, generating an electromagnetic field between the surfaces, wherein particles of material of a reduced size are obtained through subjecting the fluid to the movement of the surfaces and the electromagnetic field therebetween; and removing particles of material of a reduced size from between the surfaces.

[0335] Statement 40: The process of Statement 39, wherein the distance is between 0.1mm and 10mm, optionally between 0.5mm and 3mm, optionally about 1mm or about 3mm.

[0336] Statement 41 : The process of Statement 39 or Statement 40, comprising moving one or both surfaces at a speed that is between 0.1 meters per second and 250 meters per second, optionally between 20 meters per second and 100 meters per second, optionally about 50 meters per second.

[0337] Statement 42: The process of any one of Statements 39-41, comprising producing an electrical potential difference between the surfaces of less than 100 volts, optionally, between 10 volts and 30 volts, optionally, 25 volts.

[0338] Statement 43: The process of any one of Statements 39-42, comprising producing an electrical current through the fluid.

[0339] Statement 44: The comminution device of Statement 43, wherein the electrical current through the fluid is between 1 milliamp and 70,000 amps, optionally between 100 amps and 1,000 amps, optionally between 500 amps and 1,000 amps.

[0340] Statement 45: The process of Statement 43 or Statement 44, wherein the electrical current is such that the electrical current density is between 1 milliamp / cm2and 50 amps / cm2, optionally, between 1 milliamp / cm2and 1 amp / cm2, optionally 0.5 amps / cm2.

[0341] Statement 46: The process of any one of Statements 43-45, wherein the electrical current is at an electrical frequency of between 1 hertz to 500 hertz, optionally between 10 hertz and 30 hertz, optionally between 20 hertz and 30 hertz.

[0342] Statement 47: The process according to any one of Statements 39-46 using the comminution device according to any one of Statements 5-15.

[0343] Statement 48: The process according to any one of Statements 39 to 47, further involving oscillating one or both disks about a second axis that is transverse to the longitudinal extent of the axis.

[0344] Statement 49: A slurry containing particles of material of a reduced size obtained using the process according to any one of Statements 39-48.

[0345] Statement 50: A process of recovering a valuable mineral from a slurry containing particles of material of a reduced size, wherein the slurry according to Statement 49 comprises a valuable mineral and the process comprises: subjecting the slurry to a recovery process to yield a valuable mineral.

[0346] Statement 51 : A valuable mineral obtained according to the process of Statement 50. The term “about” and the use of ranges in general, whether or not qualified by the term about, means that the number comprehended is not limited to the exact number set forth herein, and is intended to refer to ranges substantially within the quoted range while not departing from the scope of the invention. As used herein, “about” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which it is used. If there are uses of the term which are not clear to persons of ordinary skill in the art given the context in which it is used, “about” will mean up to plus or minus 10% of the particular term.

[0347] In addition, where dimensions are described herein, it will be appreciated that plus or minus (±) typical manufacturing tolerances are applicable to those values. As appreciated by those in the art, manufacturing tolerances may be determined to achieve a desired mean and standard deviation of manufactured components in relation to the ideal component profile.

[0348] Numerical ranges disclosed herein should be understood to refer to a continuous span of values including the upper and lower limits. For example, a range of 1 to 10 includes 1, 10, and all values in between.

[0349] The reference in this specification to any prior publication (or information derived from it), 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 prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0350] Embodiments have been described herein with reference to the accompanying drawings. However, some modifications to the described embodiments may be made without departing from the spirit and scope of the described embodiments, as described in the appended claims.

[0351] In the claims which follow and in the preceding description of the invention, 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 invention.

Claims

CLAIMS1. A comminution device for reducing size of particles of material in a fluid, the comminution device comprising: a chamber having an inlet for providing a feed of fluid containing particles of material of a size into the chamber and an outlet for allowing particles of material of a reduced size to exit the chamber; a pair of opposing surfaces within the chamber, the surfaces being separated from each other by a distance and being movable relative to each other in a direction transverse to at least one of the surfaces; and an electromagnetic field generator for generating an electromagnetic field between the surfaces, wherein said device is configured so that particles of material of a reduced size are obtained after subjecting the fluid to the relative movement of the surfaces and the electromagnetic field therebetween.

2. The comminution device of claim 1, further comprising an adjustment mechanism that is configured to adjust the distance between the surfaces.

3. The comminution device of claim 1 or claim 2, wherein the distance between the surfaces is adjustable within the range of between 0.1mm and 100mm.

4. The comminution device of any one of the preceding claims, wherein the moveable surfaces are rotatable relative to each other.

5. The comminution device of any one of the preceding claims, wherein the moveable surfaces are located on a pair of opposing disks.

6. The comminution device of claim 5, wherein the disks are coaxially arranged.

7. The comminution device of claim 6, further comprising a shaft that rotatably supports at least one of the disks.

8. The comminution device of any one of claims 5 to 7, wherein the inlet is configured to direct fluid between the pair of opposing disks and the outlet isconfigured to offtake fluid from between the pair of opposing disks, and the outlet is radially offset from the inlet.

9. The comminution device of any one of the preceding claims, wherein the inlet has a tapered portion that tapers over a length, from a first diameter to a second diameter that is smaller than the first diameter.

10. The comminution device of any one of the preceding claims, wherein the electromagnetic field generator is configured to produce a three-phase power supply.

11. The comminution device of any one of the preceding claims, wherein the electromagnetic field generator comprises a power source, a transformer and a pair of opposing electrode assemblies.

12. The comminution device of claim 11, wherein the pair of opposing electrode assemblies comprises a positive electrode assembly and a negative electrode assembly, wherein the positive electrode assembly comprises a positive electrode and the negative electrode assembly comprises a plurality of electrically isolated negative electrodes, each of the plurality of electrically isolated negative electrodes being configured to deliver a phase of a three-phase alternating current to the positive electrode.

13. The comminution device of any one of the preceding claims, wherein the electromagnetic field generator comprises a controller that is configured to allow adjustment of a strength of the electromagnetic field between the surfaces.

14. The comminution device of any one of the preceding claims, wherein at least one of the surfaces is magnetic.

15. The comminution device of claim 14, wherein the magnetic surface produces a magnetic field that is between 0.5 Tesla and 1.5 Tesla when the electromagnetic field generator is not generating the electromagnetic field between the surfaces.

16. The comminution device of claim 14, configured such that, when theelectromagnetic field generator is generating the electromagnetic field between the surfaces, a magnetic field between the surfaces is between 5 Tesla and 20 Tesla.

17. A process for reducing size of particles of material in a fluid, the process including: feeding a fluid containing particles of material of a size between a pair of opposing surfaces that are separated by a distance; moving one of the surfaces relative to the other surface in a direction transverse to at least one of the surfaces; during said moving, generating an electromagnetic field between the surfaces, wherein particles of material of a reduced size are obtained through subjecting the fluid to the movement of the surfaces and the electromagnetic field therebetween; and removing particles of material of a reduced size from between the surfaces.

18. The process of claim 17, wherein the distance is between 0.1mm and 10mm.

19. The process of claim 17 or claim 18, comprising moving one or both surfaces at a speed that is between 0.1 meters per second and 250 meters per second.

20. The process of any one of claims 17 to 19, comprising producing an electrical potential difference between the surfaces of less than 100 volts.

21. The process of any one of claims 17 to 20, comprising producing an electrical current through the fluid.

22. The process of claim 21, wherein the electrical current is such that the electrical current density is between 1 milliamp / cm2and 50 amps / cm2.

23. The process of any one of claims 21 or claim 22, wherein the electrical current is at an electrical frequency of between 1 hertz to 500 hertz.

24. A slurry containing particles of material of a reduced size obtained using the process according to any one of claims 17 to 23.

25. A process of recovering a valuable mineral from a slurry containing particles of material of a reduced size, wherein the slurry according to claim 24 comprises avaluable mineral and the process comprises: subjecting the slurry to a recovery process to yield a valuable mineral.

26. A valuable mineral obtained according to the process of claim 25.

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