Method for filtering a coarse particle slurry

Abstract

The invention relates to a method for filtering a coarse particle slurry to obtain a filtered coarse cake, the coarse particle slurry having a particle size distribution wherein at least 90% of the particles of the coarse particle slurry have a size larger than 25 pm. The method is carried out by a filter device (14) comprising a filter pan (26), and comprises, for each filter cell (48) of the filter pan (26), a treatment cycle comprising: - discharging the coarse particle slurry on top of the filter cell (48); - applying a pressure difference between an inner volume and the exterior of the filter cell (48), so that a liquid of the coarse particle slurry is led towards the inner volume of the filter cell (48) and so that the filtered coarse cake is obtained on top of the medium filter.

Description

[0001] Method for filtering a coarse particle slurry

[0002] The present invention concerns a method for filtering a coarse particle slurry and a process for filtering tailings, in particular mine tailings, using such a method.

[0003] Tailings filtration plants are used to desaturate the tailings, before their placement in dry stack facilities and get the appropriate water content for compaction to reach their maximum bulk density. Compaction will allow to densify the material to what is known as “dilatant” state and avoid the liquefaction effect, which can only take place when the particles are saturated and loose (known in the geotechnical profession as “contractive” state). This is particularly important as conventional tailings dams can catastrophically fail if this liquefaction effect occurs.

[0004] Current known solutions to treat tailings before stacking separately filter fine particles in filter presses and coarse ones in dewatering screens, and then mix both streams before compaction to achieve the targeted water content in the mixed material. It would be typically desired that both fractions are respectively around 50% saturation at the end of both filtrations to obtain the targeted water content of the mixed blend.

[0005] However, this process is not cost efficient since the pressure filtration is expensive. Further, the dewatering screens used for filtering the coarse fine particles deliver a filtered material that is typically highly saturated, with a saturation above 80%, or close to 100% saturation.

[0006] There is a need to provide a method for improving the filtration of coarse particle slurry.

[0007] For this purpose, different types of filter device are known for filtering tailings.

[0008] A first known type of filter device comprises vertical disk filters that are through-fed. More specifically, either cloth or ceramic filtration media disks are placed vertically and rotate into a slurry chamber, form a cake and then get out of the slurry and continue to get deliquored.

[0009] However, such a through-fed disk filter is not appropriate for filtering coarse particle slurry as the coarse particles settle fast and will tend to accumulate in the bottom. Agitation and / or high rotation speeds are then required which are not cost efficient. Consequently, this first type of filter is not satisfactory for replacing dewatering screens for filtering coarse particle slurry.

[0010] A second known type of filter device is a top-fed cloth filter such as a pan filter or a vacuum belt filter, wherein the slurry is discharged on top of a moving medium on which a filter cloth is stretched, and vacuum suction is carried out to drain the liquid of the discharged slurry through the filter cloth. However, with such cloth-type filters, high vacuums are difficult or very expensive to create for coarse particle slurries, The working vacuum level is therefore maintained at a relatively low level and the slurry does not get the expected water content reduction that would be possible at the maximum vacuum pressure possible of 1 bar (at sea level).

[0011] An aim of the invention is therefore to provide a method for treating a coarse particle slurry achieving high desaturation in a cost effective manner.

[0012] To this end, the invention relates to a method for filtering a coarse particle slurry to obtain a filtered coarse cake, the coarse particle slurry having a particle size distribution wherein at least 90% of the particles of the coarse particle slurry have a size larger than 25 pm, the method being carried out by a filter device comprising a filter pan, a base frame and a vacuum device, the filter pan being movable with respect to the base frame, the filter pan comprising a plurality of filter cells, each filter cell delimiting an inner volume and being configured so that a pressure difference may be generated in the inner volume with respect to an exterior of the filter cell by the vacuum device, each filter cell comprising a filter medium for filtering the coarse particle slurry, the filter medium comprising at least one filter plate, the or each filter plate comprising at least a layer of semipermeable material, the method comprising, for each filter cell, at least one treatment cycle comprising, while the filter pan moves with respect to the base frame:

[0013] - discharging the coarse particle slurry on top of an upper surface of the filter medium of the filter cell;

[0014] - applying a pressure difference between the inner volume and the exterior of the filter cell by the vacuum device, so that a liquid of the coarse particle slurry present on top of the filter medium is led towards the inner volume of the filter cell and so that the filtered coarse cake is obtained on top of the medium filter.

[0015] The use of such a semipermeable material allows to operate with very high vacuums, near perfect -1 atm (101 kPa), as there is no gas flow so the vacuum device is able to constantly work close to the maximum vacuum level. Further, the filter medium placed horizontally is perfectly suited for processing the coarse particle slurry, the particles of which settle rapidly.

[0016] The method can further comprise the following features, considered alone or according to any technically feasible combination:

[0017] - the filter pan is movable with respect to the base frame in a rotatable manner about a vertical axis of rotation, and wherein the filter pan preferably comprises a central pan hub mounted in a rotatable manner with respect to the base frame, the filter cells being fixed to the central pan hub to form an angular sector, the angular sector being for example 360°; - the layer of semipermeable material has a thickness of 30 mm or below, advantageously 20 mm or below;

[0018] - the semipermeable material is porous and has an average pore size of 4.0 pm or below, preferably 3.5 pm or below, better 3.0 pm or below; and / or wherein the semipermeable material is porous and has an average pore size of 0.5 pm or above, preferably 1.5 pm or above, better 2.0 pm or above;

[0019] - the semipermeable material comprises a ceramic material and / or a polymeric membrane material;

[0020] - the filtered coarse cake has 30% or less of saturation, preferably 20% or less of saturation, advantageously 15% or less of saturation;

[0021] - the method comprises the repetition of the treatment cycle in a continuous process induced by the movement of the filter pan with respect to the base frame;

[0022] - the upper surface of the filter medium is sensibly horizontal;

[0023] - the coarse particle slurry is from iron ore tailing;

[0024] - the filter medium comprises only one filter plate or wherein the filter medium comprises a plurality of filter plates, each filter plate having a radial length smaller than the radial length of the filter cell;

[0025] - the filter plate forms a multilayer stack structure comprising said layer of semipermeable material and at least one other layer, the other layer being arranged more inward compared to the layer of semipermeable material, and, preferably, the inner the layer of the multilayer structure, the more porous and / or the more robust;

[0026] The invention further relates to a process for filtering tailings comprising the following steps:

[0027] - providing the tailing to be filtered and separating the tailing to be filtered into a coarse particle slurry and a fine particle slurry, so that the filtered coarse particle slurry has a particle size distribution wherein at least 90% of the particles have a size larger than 25 pm;

[0028] - filtering the coarse particle slurry to obtain a filtered coarse cake by a method according to any one of the previous claims;

[0029] - dewatering the fine particle slurry to obtain a dewatered fine stream; and

[0030] - blending the filtered coarse cake and the dewatered fine stream into a blended material to reach a targeted water content in the blended material.

[0031] The process can further comprise the following features, considered alone or according to any technically feasible combination:

[0032] - the blended material resulting from blending for example comprises from 40% to 85% by weight of filtered coarse cake, preferably from 50% to 85% by weight, advantageously more than 70% by weight, the rest being dewatered fine stream; - the dewatered fine stream has at least 90% of saturation;

[0033] - the targeted water content is 50% or below, preferably 20% or below.

[0034] Other aspects and advantages of the invention will appear upon reading the following description given by way of example and made in reference to the appended drawing, wherein:

[0035] - figure 1 is a schematic organigram of an installation for filtering tailing;

[0036] - figure 2 is a schematic side view of an example of a filter device for filtering a slurry of coarse particles; and

[0037] - figure 3 is a schematic perspective view of the filter device of figure 2;

[0038] - figure 4 is a schematic perspective view of a filter device according to a second embodiment; and

[0039] - figure 5 is an organigram of a process for filtering tailings.

[0040] An installation 10 for filtering tailings is schematically illustrated in figure 1.

[0041] The installation 10 comprises a separating apparatus 12 for separating a tailing to be filtered into a slurry of coarse particles 20 (in the following “coarse particle slurry”) and a slurry of fine particles 22 (in the following “fine particle slurry”).

[0042] The installation 10 comprises a filter device 14 for filtering the coarse particle slurry 20 and a dewatering apparatus 16 for dewatering the fine particle slurry 22.

[0043] The installation 10 further comprises a blending system 18 for blending the filtered materials from both filter device 14 and dewatering apparatus 16.

[0044] The tailing may be an iron ore tailings. Iron ore tailings are the industrious solid waste discharged by concentrating mills after processing iron ores and selecting the valuable components.

[0045] The separating apparatus 12 is known to the skilled person and will not be disclosed in more details.

[0046] The separating apparatus 12 is configured for receiving the tailings to be filtered and separating the tailing in a separation chamber for example through the use of hydrocyclones, hydraulic classifiers, vibratory screens or any other size classification units.

[0047] The separating apparatus 12 is configured for outputting the coarse particle slurry 20 and outputting the fine particle slurry 22.

[0048] The coarse particle slurry 20 is for example from iron ore tailings. The coarse particle slurry is for example a mineral concentrate. In the coarse particle slurry, the particles are in suspension in a liquid. The liquid for example comprises water.

[0049] The coarse particle slurry has a particle size distribution wherein at least 90% of the particles have a size larger than 25 pm. Advantageously, 10% or less of the particles of the coarse particle slurry have a size of less than 100 pm.

[0050] Preferably, at least 95% of the particles have a size less than 3000 pm, advantageously less than 2000 pm, for example less than 1500 pm.

[0051] The particle size distribution is for example determined by sieve analysis. The sieve analysis is for example performed following the standard ISO 4701 :2019. Alternatively, the particle size distribution of the tailings stream is determined by dynamic image analysis following the standard ISO 13322-2:2021.

[0052] The coarse particle slurry has preferably a permeability of at least 10'6m / s (in other words 10A(-6) m / s). The coarse particle slurry has advantageously a permeability of at least 10'5m / s (in other words 10A(-5) m / s).

[0053] The permeability is for example determined following the standard ISO 17892- 11 :2019.

[0054] The fine particle slurry is for example from iron ore tailings. The fine particle slurry is for example a mineral concentrate.

[0055] In the fine particle slurry, the particles are in suspension in a liquid. The liquid for example comprises water.

[0056] Preferably, the particle size distribution of the fine particle slurry has a median particle size of less than 100 pm. The particle size distribution is for example determined by sieve analysis. The sieve analysis is for example performed following the standard ISO 4701 :2019. Alternatively, the particle size distribution of the tailings stream is determined by dynamic image analysis following the standard ISO 13322-2:2021.

[0057] The fine particle slurry has preferably a permeability less than 10'6m / s.

[0058] The permeability is for example determined following the standard ISO 17892- 11 :2019.

[0059] A first embodiment of the filter device 14 for filtering the coarse particle slurry is schematically illustrated in more details in figures 2 and 3.

[0060] The filter device 14 is configured to filter the coarse particle slurry to obtain a filtered coarse cake (referenced by arrow 24 in figure 1). As will be explained in more details below, the filter device 14 is configured to reach a saturation (or degree of saturation) of 30% or less in the filtered coarse cake, preferably 20% or less, advantageously 15% or less.

[0061] Such a saturation is for example determined by calculation after the determination of the solids particle density ps(for example as in ISO 17892-3-2015), the dry density pd of the cake (for example as in ISO 17892-2-2014), its water content w (for example as in ISO 17892-1-2014) and the density p of the liquid remaining in the cake (for example as in ISO

[0062] 758:1976).

[0063] The filter device 14 comprises a filter pan 26 and a base frame 28, the filter pan 26 being movable with respect to the base frame 28.

[0064] The filter device 14 comprises a motor system (not shown) configured for rotating the filter pan 26 with respect to the base frame 28 along the vertical axis.

[0065] The filter device 14 comprises an application station 30 for applying the coarse particle slurry to be filtered on the filter pan 26.

[0066] The filter device 14 further for examples comprises at least one additional treatment station 32 of the slurry discharged on top of the filter pan 26.

[0067] The filter device 14 further comprises a vacuum device 34.

[0068] The filter device 14 further comprises a liquid filtrate reservoir 36 and a central control head 38, the filter pan 26 being connected to the liquid filtrate reservoir 36 though the central control head 38.

[0069] The filter device 14 further comprises a removal station 40 for removing the filtered coarse cake.

[0070] The application station 30 is configured for discharging the coarse particle slurry and adequately distributing the slurry on top of the filter pan 26.

[0071] The application station 30 comprises a slurry reservoir 42 containing the coarse particle slurry to be filtered and a device 44 for moving the coarse particle slurry from the reservoir to the filter pan 26. The device 44 for moving the slurry for example comprises a conduit, the conduit having at least one outlet 46 arranged above the filter pan 26. The device 44 for moving the slurry further for example comprises a pump or for example functions by gravity only if the slurry reservoir 42 is arranged on top of the filter pan 26. The application station 30 is configured for adequately distributing the slurry homogeneously over the filter pan 26 depending on the different linear speeds at different radial distance from the center of the rotation.

[0072] The technical design of such an application station 30 is known to the skilled person and will not be disclosed in more details.

[0073] The additional treatment station 32 for example corresponds to a washing station wherein the filtered coarse cake formed on top of the filter pan 26 is washed with a washing liquid.

[0074] The additional treatment 32 for example corresponds to a steam deliquoring or desaturation station, wherein the filtered coarse cake formed on top of the filter pan 26 is further desaturated through the use of steam addition.

[0075] The filter device 14 may include at least one or both of these stations.

[0076] The technical design of such a washing or steaming station is known to the skilled person and will not be disclosed in more details.

[0077] The filter pan 26 is preferably movable with respect to the base frame 28 in a rotatable manner about a vertical axis of rotation.

[0078] The filter pan 26 comprises a central pan hub 47 mounted in a rotatable manner with respect to the base frame 28 and a plurality of filter cells 48.

[0079] The motor system of the filter device 14 is then for example configured for rotating the filter pan 26 by rotating the central pan hub 47 with respect to the base frame 28 along the vertical axis.

[0080] The central pan hub 47 comprises a housing. The housing has for example a drum shape. The housing of the central pan hub 47 delimits, for each filter cell 48, a corresponding outlet opening for evacuating the liquid filtrate.

[0081] The central pan hub 47 further comprises, for each filter cell 48, a filtrate pipe 50 for evacuating the liquid filtrate of the filter cell 48 through the corresponding outlet opening.

[0082] The filter pan 26 has for example an outer diameter comprised between 3 m and 15 m.

[0083] In the illustrated exemplary embodiment, the filter pan 26 comprises at least 10 filter cells 48, for example at least 14 filter cells 48.

[0084] Each filter cell 48 forms an angular segment. The filter cells 48 are fixed to the central pan hub 47 to form an angular sector. The angular sector is preferably 360°, so that the filter cells 48 form together a ring shape around the central pan hub 47 as illustrated in figure 3.

[0085] Each filter cell 48 for example has a disk-segment shape or a cake-piece shape.

[0086] Each filter cell 48 delimits an inner volume and is configured so that a vacuum may be generated in the inner volume. Each filter cell 48 is thus airtight with respect to the outside of the filter cell 48.

[0087] Each filter cell 48 comprises a support structure 52 and a filter medium 54 for filtering the coarse particle slurry.

[0088] The support structure 52 comprises support sheets preferably including a bottom support sheet 56, two lateral support sheets 58, an outer radial support sheet 60.

[0089] The support sheets are for example made of metal.

[0090] Here and in the following, the term “radial” is to be understood with respect to the axis of rotation of the filter pan 26 with respect to the base frame 28.

[0091] The support structure 52 further comprises for example cross members to ensure mechanical resistance of the structure and / or support of the filter medium 54.

[0092] The bottom support sheet 56 is for example inclined radially inward and downward so as to enable drainage of the liquid filtrate towards the central pan hub 47.

[0093] The lateral support sheets 58 extends from the bottom support sheet 56 for example in the vertical direction.

[0094] The support structure 52 further comprises an inner radial support part 62.

[0095] The inner radial support part 62 faces the corresponding inlet opening of the central pan hub 47. The filtrate pipe 50 of the central pan hub 47 extends through the inner radial support part 62 to open in the inner volume of the filter cell 48.

[0096] When the filter cell 48 is fixed to the central pan hub 47, the liquid filtrate can flow via the filtrate pipe 50 through the inner radial support part 62 and the inlet opening of the central pan hub 47.

[0097] The filtrate pipe 50 is fixed to the support structure 52 for example by bayonet mounts. Such bayonet mounts could be used to quickly fasten / unfasten the filtrate pipe 50.

[0098] Further, the inner radial support part 62 is configured for fixing the filter cell 48 to the central pan hub 47 in a pressure-sealed manner. Preferably, the inner radial support part 62 is fixed to the central pan hub 47 in a releasable manner, for example by way of screw connections. This releasable fixation is advantageous for maintenance purpose.

[0099] The filter medium 54 is configured for filtering the coarse particle slurry.

[0100] The filter medium 54 is supported by the support structure 52. The filter medium 54 is fixed to the support structure 52 in a pressure-sealed manner. For example, the filter medium 54 is pressure sealed to the support structure 52 with silicone, and / or any other fluid sealants, and / or adequately prepared rubber groove-type seals.

[0101] The filter medium 54 is for example screwed on top of the support structure 52. Alternatively, the filter medium 54 is fixed to the support structure 52 by latches, snap fasteners or any other fasteners.

[0102] The filter medium 54 is for example arranged on an upper edge of the support structure 52 and faces the bottom support sheet 56.

[0103] The filter medium 54 and the support structure 52 delimit together the inner volume of the filter cell 48.

[0104] The filter medium 54 has an upper surface 64 on which the coarse particle slurry is discharged and a lower surface delimiting the inner volume of the filter cell 48. Especially, the application station 30 is configured for discharging the coarse particle slurry on top of the filter medium 54.

[0105] The upper surface 64 of the filter medium 54 is arranged substantially horizontal.

[0106] Here and in the following, by horizontal, it is meant perpendicular to the vertical axis.

[0107] The upper surface 64 of the filter medium 54 extends over an area that will vary depending on the diameter of the pan and the number of filter cells. For example, for a pan divided into 24 filter cells, the upper surface 64 of the filter medium 54 extends over an area comprised from 0.3 to 7.4 m2for a pan diameter from 3 to 15 m.

[0108] The filter medium 54 comprises at least one filter plate.

[0109] In an embodiment, the filter medium 54 comprises only one filter plate. The filter plate then for example has a radial length greater than 90% of the radial length of the filter cell 48.

[0110] Alternatively, the filter medium 54 comprises a plurality of filter plates. Each filter plate then has a radial length smaller than the radial length of the filter cell 48, for example smaller than 30% of the radial length of the filter cell 48. The radial length of each filter plate is for example greater than 10% of the radial length of the filter cell 48. Each individual plate is then more easily handled by a single person based on its weight and dimensions.

[0111] The filter medium 54 further comprises, for each filter plate or for the only filter plate, a frame for fixing the filter plate to the support structure 52 as explained above. The frame is fixed to the respective filter plate of the filter medium 54 in a pressure-sealed manner.

[0112] The or each filter plate is a self supporting part.

[0113] The or each filter plate comprises at least a layer of semipermeable material. The layer of semipermeable material has preferably a thickness of at least 10 mm, advantageously at least 12 mm. The layer of semipermeable material has preferably a thickness of 30 mm or below, advantageously 20 mm or below. The thickness is for example measured along the vertical axis. Such a thickness is for example for mechanical resistance purposes and for providing some resistance to abrasion / damage.

[0114] Preferably, the layer of semipermeable material is in contact with the coarse particle slurry, when the slurry is discharged on the filter cell 48. The upper surface 64 of the filter medium 54 is then defined by the layer of semipermeable material.

[0115] The layer of semipermeable material is preferably continuous over an upper surface of the filter plate. By continuous, it is meant that there is no hole within the layer.

[0116] By a semi-permeable material, it is meant a material that physically separate a liquid phase and a gas phase by capillary forces. The semi permeability of the filter may be regulated via its pore size.

[0117] The semipermeable material is configured for preventing air flow between the upper surface 64 and the lower surface of the filter medium 54. The semipermeable material is configured for filtrating the slurry by capillary action.

[0118] To this end, the semipermeable material is porous.

[0119] In a preferred embodiment, the semipermeable material has an average pore size of 4.0 pm or below, preferably 3.5 pm or below, better 3.0 pm or below. Advantageously, the semipermeable material has an average pore size of 0.5 pm or above, preferably 1.5 pm or above, better 2.0 pm or above.

[0120] Such ranges of average pore size are chosen because the pore size which has a capillary pressure of 101 kPa (1 atm) for a fully hydrophilic material at 25°C is 2.8 pm based on the Young Laplace equation. Thus, such ranges of average pore size allow the pores of the semipermeable material to remain saturated under any vacuum applied, as the capillary force will be greater than the maximum potential vacuum applied.

[0121] Further, since the actual operating pressures on the filter medium 54 will usually still be lower than 1 atm, larger average pore sizes, up to 4.0 pm, are still acceptable. The inventors found that the pores having an average size of 4.0 pm will remain saturated at 72 kPa effective pressure.

[0122] Although such low average pore size may be eventually blinded by fine particles, the use of such filter medium 54 for filtering coarse particles (as in the invention) significantly reduces the need of replacement and maintenance of the filter medium 54.

[0123] In a first embodiment of the semipermeable material, the semipermeable material comprises a ceramic material. The ceramic material for example comprises silicate, aluminosilicate, oxide, silicon carbide, corundum, cordierite and / or aluminium oxide with or without silicon carbide.

[0124] In a second embodiment of the semipermeable material, the semipermeable material comprises a polymeric membrane material. The polymeric membrane material comprises for example cellulose, PTFE and / or polyamide. Such a polymeric membrane material can be manufactured at the desired average pore size for this purpose.

[0125] In an optional embodiment of the filter plate, the filter plate forms a multilayer stack structure comprising said layer of semipermeable material and at least one other layer. The other layer is arranged more inward compared to the layer of semipermeable material. The layers are stack to one another. Each layer then defines an upper surface and a lower surface separated from the upper and lower surface of the other layer(s).

[0126] Preferably, the inner the layer of the multilayer structure, the more porous, i.e. the greater the average pore size of the layer, and / or the more robust material, i.e. the greater the tensile strength of the layer.

[0127] The vacuum device 34 of the filter device 14 is configured for generating a pressure difference in the inner volume of each filter cell 48 with respect to an exterior of the filter cell 48, for example for generating a relative pressure of at least -70 kPa and as low as -101 kPa inside the inner volume compared with the atmosphere exterior to the filter cell 48.

[0128] The vacuum device 34 is for example configured for generating the pressure difference through the corresponding filtrate pipe 50 of each filter cell 48.

[0129] The vacuum device 34 for example comprises a vacuum pump and / or a barometric leg.

[0130] The vacuum device 34 is stationary with respect to the base frame 28. The vacuum device 34 does not rotate with respect to the base frame 28, when the filter pan 26 rotates with respect to the base frame 28.

[0131] Due to the pressure difference applied between the inner volume and the exterior of the filter cell 48 by the vacuum device 34, the liquid is led away from the coarse particle slurry towards the inner volume of the filter cell 48 and drained inwards to the central pan hub 47, through the filtrate pipe 50, to form the liquid filtrate.

[0132] More specifically, the liquid of the coarse particle slurry is suctioned from the upper surface 64 of the filter medium 54 towards the lower surface thereof. As a result, the filtered coarse cake is gradually formed on the filter medium 54 until the filter cell 48 reaches the removal station 40.

[0133] The use of such a semipermeable material allows to operate with very high vacuums, near perfect -101 kPa, as there is no gas flow so the vacuum device 34 is able to constantly work close to the maximum vacuum level. Such a filtration with no airflow eliminates one of the main cost drivers in conventional cloth filtration.

[0134] The control head 38 comprises a valve and a plurality of channels connected to the filtrate pipes 50, for draining off the liquid filtrate from the filtrate pipes 50 of the central pan hub 47. The channels are connected to the liquid filtrate reservoir 36 wherein the liquid filtrate accumulates during the filtration method.

[0135] The control head 38 is arranged in the center of the filter pan 26.

[0136] The control head 38 is stationary with respect to the base frame 28. The control head 38 does not rotate with respect to the base frame 28, when the filter pan 26 rotates with respect to the base frame 28.

[0137] Unlike in non-semipermeable filter, there is no air flow passing through the filter medium 54 so no vacuum loss. Consequently, the design of the control head 38 can remain simple. In particular, there is no need to have a complex control head 38 with separate sections for cake discharge or to account for separation of air and liquid flows.

[0138] The removal station 40 is configured for removing the filter cake formed on the filter medium 54 of the filter cell 48.

[0139] The removal station 40 for example comprises a filtered coarse cake reservoir 66 wherein the filtered coarse cake, removed from the filter cells 48, accumulates during the filtration method.

[0140] The removal station 40 for example comprises a washing system 67 for washing the filter medium 54 after the filtered coarse cake is removed from the filter medium 54. The washing system 67 is for example configured for injecting a pressured fluid on the medium filter 54.

[0141] In a first embodiment as illustrated in figure 3, each filter cell 48 is for example configured for tilting the support structure 52 with respect to the central pan hub 47, notably for removing the filtered coarse cake in the removal station 40.

[0142] When the filter cell 48 is in the removal station 40, the filter cell 48 is configured for tilting the support structure 52 with respect to the central pan hub 47, for removing the filter cake.

[0143] In a second preferred embodiment, as shown in figure 4, the removal station 40 comprises an endless rotating screw 80 configured for removing the filter cake formed on the filter medium 54 of the filter cell 48. In this second preferred embodiment, and contrary to the first embodiment, none of the filter cell 48 is configured for tilting the support structure 52.

[0144] The endless rotating screw 80 is aligned with a radius of the filter pan and is arranged on top of the filter pan.

[0145] The endless rotating screw 80 is arranged so that a gap between an edge of the endless rotating screw 80 and the filter medium 54 is comprised from 2 to 20 mm, in order to ensure complete removal of the slurry without damaging the filter medium 54.

[0146] The endless rotating screw 80 is configured to push the cake out of the pan in the radial direction towards the filtered coarse cake reservoir 66.

[0147] Other embodiments for removing the filtered coarse cake are known by the skilled person and will not be described in more details.

[0148] The dewatering apparatus 16 for dewatering the fine particle slurry is not particularly limited in the context of the invention. The dewatering apparatus 16 is configured to dewater the fine particle slurry to obtain a dewatered fine stream (referenced by arrow 68 in figure 1).

[0149] The dewatered fine stream is for example a cake or a slurry (in particular a highly concentrated slurry).

[0150] For example, the dewatering apparatus 16 is configured to reach a saturation of at least 90% in the dewatered fine stream. Such a saturation is for example determined as explained above.

[0151] Examples of dewatering apparatus 16 include high density thickeners (for example including a continuously raked settling cylinder), paste thickeners, lamella thickeners, decanter centrifuges. Such dewatering apparatus 16 are usually inexpensive.

[0152] The blending system 18 is configured for blending the filtered coarse cake and the dewatered fine cake from both filter device 14 and dewatering apparatus 16 into a blended material and to reach a targeted water content in the blended material.

[0153] The filtered coarse cake corresponds to the cake which accumulates in the removal station 40 during the filtration method.

[0154] The blended material resulting from blending for example comprises from 40% to 85% by weight of filtered coarse cake, preferably from 50% to 85% by weight, advantageously more than 70% by weight, the rest being dewatered fine stream.

[0155] The targeted water content in the blended material is typically chosen to produce a target dry density after compaction. This can be a value close to the optimum water content determined by ASTM D698 (Standard Proctor) for example 50% or below, preferably 25 % or below, advantageously 20% or below (geotechnical water content) or any other target determined after geotechnical assessment.

[0156] Such a water content after blending is for example determined by ISO 17892-1-2014. Such a blending system 18 is known by the skilled person and will not be disclosed in more details. An example of a blending system 18 is specialized soil reclaimers such as those used for lime stabilization for blending after deposition, but blending systems before disposal can also be considered such as the screw mixers in use in paste backfill plants.

[0157] Thanks to the above listed advantages of the filter device 14 of the invention for filtering the coarse particle slurry, it is possible to use any low cost dewatering apparatus 16 for treating the fine particle slurry.

[0158] Indeed, the filter device 14 of the invention allows reaching very low saturated filtered coarse cake from the coarse particle slurry. This low saturation filtered coarse cake compensates the high saturation dewatered fine stream (cake or high density slurry), to reach comparatively the same targeted water content in the blended material in a more efficient and flexible way.

[0159] A process 100 for filtering tailing will now be disclosed in reference to figure 5. The process 100 is for example carried out by the installation 10 disclosed above.

[0160] The process 100 comprises a step 102 of providing the tailing to be filtered and separating the tailing to be filtered into the coarse particle slurry and the fine particle slurry described above.

[0161] The process 100 comprises a method 104 for filtering the coarse particle slurry to obtain a filtered coarse cake. The method 104 for filtering the coarse particle slurry is for example carried out by the above described filter device 14.

[0162] For example, the filtered coarse cake having 30% or less of saturation, preferably 20% or less of saturation, advantageously 15% or less of saturation.

[0163] The method 104 comprises, for each filter cell 48, at least one treatment cycle, while the filter cell 48 rotates with respect to the base frame 28.

[0164] The treatment cycle comprises discharging 104A the coarse particle slurry on top of the filter cell 48 when the filter cell 48 reaches the application station 30.

[0165] The treatment cycle then comprises applying 104B a pressure difference between the inner volume and the exterior of the filter cell 48 by the vacuum device 34. Due to the applied pressure difference, the liquid of the coarse particle slurry on top of the filter medium 54 is led towards the inner volume of the filter cell 48 and drained inwards to the central pan hub 47, through the filtrate pipe 50, to form the liquid filtrate. When the filter cell 48 reaches the removal station 40, the filtered coarse cake is obtained on top of the filter medium 54 and the treatment cycle comprises removing 104C the filtered coarse cake in the removal station 40.

[0166] The treatment cycle then for example comprises washing 104D the filter medium 54.

[0167] Subsequently, in a continuous process induced by the constant rotation of the filter pan 26, the filter cell 48 runs through a new treatment cycle.

[0168] The process 100 further com prises a method 106 for dewatering the fine particle slurry to obtain a dewatered fine cake or highly concentrated fine particle slurry.

[0169] The method 106 for dewatering the fine particle slurry is not particularly limited in the context of the invention.

[0170] The method 106 for dewatering the fine particle slurry is for example carried out by the above described dewatering apparatus 16.

[0171] For example, the method 106 for dewatering the fine particle results in a high saturated dewatered fine cake, for example a saturation of at least 90% in the dewatered fine cake.

[0172] The process 100 then comprises blending 108 the filtered coarse cake and the dewatered fine cake into a blended material to reach a targeted water content in the blended material.

[0173] The targeted water content, for example determined by ISO 17892-1 , is for example 50% or below, preferably 20% or below. The targeted water content is for example 15% or below.

[0174] The blending is for example carried out by the above described blending system 18 for blending the materials from both filter device 14 and dewatering apparatus 16.

[0175] The blended material resulting from blending for example comprises between 40% and 85% by weight of filtered coarse cake, preferably between 50% and 85% by weight, advantageously more than 70% by weight, the rest being dewatered fine stream.

[0176] The process 100 then for example comprises compaction 110 of the blended material and storage in a dedicated location.

[0177] The invention will now be illustrated by the following example, which is by no way limitative.

[0178] A tailings stream with the following particle size distribution is fed to a separating apparatus. In the example, the separating apparatus is a hydrocyclone. The particle size distribution of the tailings stream is determined by dynamic image analysis following the standard ISO 13322-2:2021 and is reported in Table 1 below. Table 1 - particle size distribution of the tailings stream

[0179] The result of the separation in the separating apparatus is an underflow coarse particle slurry and an overflow fine particle slurry with the following particle size distributions reported in Table 2:

[0180] Table 2- particle size distributions of the coarse and fine particle slurries

[0181] In this case, the median size of the particles of the fine particle slurry is 39 pm. The coarse particle slurry has a particle size distribution wherein 97% of the mass has particle size larger than 25pm and with a permeability of 4.3*1 O'5m / s.

[0182] Coarse particle filtration

[0183] The coarse particle slurry is then filtered with a method according to the invention by feeding it on top of a filter device. This filter device is a horizontally-placed capillary action filter plate having a layer of semipermeable material.

[0184] In this case, this is a ceramic filter medium with a pore size of 1.5pm in a plate of 24 mm thickness made of aluminium oxide.

[0185] To this end, a cylindrical slurry dam of 50mm diameter is prepared to contain the coarse particle slurry on top of the ceramic media.

[0186] The ceramic media extends over an area of 18810 mm2.

[0187] A filtrate receiver flask is connected to a vacuum pump and to the capillary action filter plate. The filtrate receiver flask has a manometer to confirm the vacuum level. A relative pressure of -98 kPa was applied during filtering.

[0188] After filtering, the filtered coarse cake thickness (in mm), wet and dry cake weights (in grams) are measured with a calliper and scale. The solids density is known to be 2.82 t / m3. Four independent test results are shown in Table 3 below.

[0189] The average results of the four top-fed ceramic filtration tests are thus 5.8% water content for a 14.3% degree of saturation.

[0190] Table 3 - independent test results for the filtered coarse cake

[0191] Fine particle dewatering

[0192] The fine particle slurry can be dewatered by various approaches to obtain a dewatered fine stream. For example, the use of high density thickeners has been tested through various tests, including a continuously raked settling cylinder. This testwork has shown that up to 73.5% by weight solids concentration can be obtained on such a high density thickener, as reported in Table 4 below. Table 4 - Solids concentration in the dewatered fine stream depending on dewatering duration

[0193] Blending

[0194] A target water content of 15% (corresponding to 13% moisture) has been considered for the blended material after geotechnical assessment.

[0195] The resulting water content after blending of the filtered coarse cake and the dewatered fine stream can be calculated. An example calculation for 100 tons of tailings is shown in Table 5 below. In this specific example, as long as the dewatered fine stream has a solids concentration of 65.9% by weight, the total tailings blend will be on target for compaction.

[0196] Table 5 - Calculation of the minimum % solids required in the fine particle stream

[0197] Now using the maximum achievable solids concentration in the fine particle slurry (73%wt), these tests show that the invention makes it possible to obtain a water content of the overall blend that would even be below the target water content for compaction, as shown in Table 6 below.

[0198] Table 6 - Calculation of the achievable blend water content when considering the maximum solids concentration of the dewatered fine stream

Claims

CLAIMS1.- A method (104) for filtering a coarse particle slurry to obtain a filtered coarse cake, the coarse particle slurry having a particle size distribution wherein at least 90% of the particles of the coarse particle slurry have a size larger than 25 pm, the method being carried out by a filter device (14) comprising a filter pan (26), a base frame (28) and a vacuum device (34), the filter pan (26) being movable with respect to the base frame (28), the filter pan (26) comprising a plurality of filter cells (48), each filter cell (48) delimiting an inner volume and being configured so that a pressure difference may be generated in the inner volume with respect to an exterior of the filter cell (48) by the vacuum device (34), each filter cell (48) comprising a filter medium (54) for filtering the coarse particle slurry, the filter medium (54) comprising at least one filter plate, the or each filter plate comprising at least a layer of semipermeable material, the method (104) comprising, for each filter cell (48), at least one treatment cycle comprising, while the filter pan (26) moves with respect to the base frame (28):- discharging (104A) the coarse particle slurry on top of an upper surface (64) of the filter medium (54) of the filter cell (48);- applying (104B) a pressure difference between the inner volume and the exterior of the filter cell (48) by the vacuum device (34), so that a liquid of the coarse particle slurry present on top of the filter medium (54) is led towards the inner volume of the filter cell (48) and so that the filtered coarse cake is obtained on top of the medium filter.2.- Method (104) according to claim 1 , wherein the filter pan (26) is movable with respect to the base frame (28) in a rotatable manner about a vertical axis of rotation, and wherein the filter pan (26) preferably comprises a central pan hub (47) mounted in a rotatable manner with respect to the base frame (28), the filter cells (48) being fixed to the central pan hub (47) to form an angular sector, the angular sector being for example 360°.3.- Method (104) according to claim 1 or 2, wherein the layer of semipermeable material has a thickness of 30 mm or below, advantageously 20 mm or below.4.- Method (104) according to any one of claims 1 to 3, wherein the semipermeable material is porous and has an average pore size of 4.0 pm or below, preferably 3.5 pm or below, better 3.0 pm or below; and / or wherein the semipermeable material is porous and has an average pore size of 0.5 pm or above, preferably 1 .5 pm or above, better 2.0 pm or above.5.- Method (104) according to any one of claims 1 to 4, wherein the semipermeable material comprises a ceramic material and / or a polymeric membrane material.6.- Method (104) according to any one of claims 1 to 5, wherein the filtered coarse cake has 30% or less of saturation, preferably 20% or less of saturation, advantageously 15% or less of saturation.7.- Method (104) according to any one of claims 1 to 6, wherein the method comprises the repetition of the treatment cycle in a continuous process induced by the movement of the filter pan (26) with respect to the base frame (28).8.- Method (104) according to any one of claims 1 to 7, wherein the upper surface (64) of the filter medium (54) is sensibly horizontal.9.- Method (104) according to any one of claims 1 to 8, wherein the coarse particle slurry is from iron ore tailing.10.- Method (104) according to any one of claims 1 to 9, wherein the filter medium (54) comprises only one filter plate or wherein the filter medium (54) comprises a plurality of filter plates, each filter plate having a radial length smaller than the radial length of the filter cell (48).11.- Method (104) according to any one of claims 1 to 10, wherein the filter plate forms a multilayer stack structure comprising said layer of semipermeable material and at least one other layer, the other layer being arranged more inward compared to the layer of semipermeable material, and, preferably, the inner the layer of the multilayer structure, the more porous and / or the more robust.12.- Process (100) for filtering tailing comprising the following steps:- providing (102) the tailing to be filtered and separating the tailing to be filtered into a coarse particle slurry and a fine particle slurry, so that the filtered coarse particle slurry has a particle size distribution wherein at least 90% of the particles have a size larger than 25 pm;- filtering (104) the coarse particle slurry to obtain a filtered coarse cake by a method according to any one of the previous claims;- dewatering (106) the fine particle slurry to obtain a dewatered fine stream; and- blending (108) the filtered coarse cake and the dewatered fine stream into a blended material to reach a targeted water content in the blended material.13.- Process (100) according to claim 12, wherein the blended material resulting from blending for example comprises from 40% to 85% by weight of filtered coarse cake, preferably from 50% to 85% by weight, advantageously more than 70% by weight, the rest being dewatered fine stream. 14.- Process (100) according to claims 12 or 13, wherein the dewatered fine stream has at least 90% of saturation.15.- Process (100) according to, any one of claims 12 to 14 wherein the targeted water content is 50% or below, preferably 20% or below.

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