Method and system for mineral processing

Abstract

The present invention relates to a method and system for mineral beneficiation. In particular, the present invention relates to the recovery of alloys, metals, and minerals from mining and process wastes, such as the recovery of ferrochrome (FeCr) from less desirable materials. The product produced by the disclosed mineral beneficiation method includes a chromium concentrate with 95% chromium units.

Description

[Technical field]

[0001] The present invention relates to methods and systems for mineral processing, in particular the recovery of alloys, metals and minerals from mining and process wastes, such as the recovery of ferrochrome (FeCr) from less desirable materials. [Background technology]

[0002] In the mining industry, beneficiation is used to produce high quality concentrates for downstream purification of minerals, oxides, or metals prior to smelting and refining steps.

[0003] During the process of beneficiation, target minerals, oxides, or metals are separated from undesirable elements (called gangue, which includes, for example, silica, alumina, and other low-value materials) in the mined ore body or waste material (such as furnace slag and process tailings). The resulting target concentrate is then further refined.

[0004] According to current practice, mineral beneficiation involves three stages of milling (particle size reduction by crushing, grinding, shearing, vibrating, or other means): primary milling (large milling), usually accomplished with jaw crushers or orbital compaction cones; secondary milling (small milling), realized with sage mills, cone crushers, or impact crushers; and tertiary milling (comminuted), typically performed with ball or rod mills to produce material less than 1 mm.

[0005] After milling is complete, the crushed and ground material is beneficiated (fractionated) into gangue, middlings (i.e., target material not completely released from the gangue), and concentrate (the desired target material).

[0006] However, such methods are inefficient because they are slow; they require significant electrical energy input; they require frequent and expensive replacement of wear liners, which leads to downtime of the processing plant; and, more importantly, the ore and slag are crushed inefficiently, i.e., not along the boundaries (such a term is used to mean the edges of the material that make up the aggregates), and therefore complete liberation is not obtained, which complicates the downstream beneficiation process.

[0007] Traditionally, crushing and grinding methods are based on attrition, a process in which minerals are worn away by particle-particle collisions. However, attrition does not achieve boundary separation.

[0008] Furthermore, although gravity separation is very efficient for particles with a difference in specific gravity of more than 3, when the specific gravities of different material particles are close, gravity separators cannot distinguish between particle size and particle gravity. For example, a 100 μm particle with a specific gravity of 2 will behave the same as a 200 μm particle with a specific gravity of 1. Because both particles have the same mass, they will experience the same attractive forces in the separator system. This conflict between particle size and particle gravity negates the ability of the gravity separation system to be able to separate based on specific gravity, limiting the efficiency of gravity separation. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention relates to a method and system for mineral processing, in particular the recovery of alloys, metals and minerals from mining wastes, such as the recovery of ferrochrome (FeCr) from less desirable materials. [Means for solving the problem]

[0010] According to one aspect, there is a mineral processing system that includes a roll crusher with hardfacing tiles facing a cylinder. The roll crusher may be a high pressure roll crusher. The feed material to the rollers may include ores, slags, mining waste, or other materials having relatively low concentrations of alloys, metals, and / or minerals to be recovered. The feed material may be crushed, preferably continuously, using one or more high pressure roll crushers with hardfacing tiles.

[0011] Each hardfacing tile may be a polygon or polygonal shape. They may all have an even number of sides or an odd number of sides. All hardfacing tiles may have the same number of polygonal sides. The hardfacing tiles may have polygonal sides that are all equal in length, or opposing polygonal sides may be equal in length, or every other polygonal side may be equal in length, or polygonal sides may be of different lengths. All hardfacing tiles may have the same shape, all hardfacing tiles may have the same size, or some of the hardfacing tiles may have a different shape or size than the other tiles. The hardfacing tiles may be square, rectangular, pentagonal, hexagonal, heptagonal, octagonal, or may have more sides.

[0012] Each hardfacing tile may be adjacent to one or more other hardfacing tiles secured to the cylindrical surface of the cylinder. The hardfacing tiles may be adjacent to each other in a pattern that places an edge of one hardfacing tile adjacent to an edge of another hardfacing tile. Typically, adjacent edges of adjacent hardfacing tiles are parallel to each other, although other configurations are possible.

[0013] Each hardfacing tile is adjacent on every other side to an edge of another hardfacing tile which is in turn adjacent on every other side to an edge of yet another hardfacing tile, and each edge that is not adjacent to another tile is at least one side length away from a parallel edge of another tile.

[0014] All or some of the hardfacing tiles on the cylinder may be in groups forming a pattern of tiles. There may be a group of hexagonal tiles. Each hexagonal tile may have three sides that are individually adjacent to a side of another hexagonal tile, which in turn may have three sides that are individually adjacent to a side of yet another hexagonal tile. The sides that are adjacent to the sides of another hexagonal tile may alternate with sides that are not adjacent to another tile. The sides that are not adjacent to another tile are at least one side length away from a parallel side of another tile. The sides of the hexagonal tiles that are not adjacent to the sides of other tiles may form spaces without tiles within the group. The spaces may be hexagons defined by the sides of the hardfacing tiles.

[0015] There may also be groups of octagonal tiles. Each octagonal tile may have four sides that are individually adjacent to a side of another octagonal tile, which in turn may have four sides that are individually adjacent to a side of yet another octagonal tile. The sides that are adjacent to the sides of another octagonal tile may alternate with sides that are not adjacent to another tile. The sides that are not adjacent to another tile are at least one side length away from a parallel side of another tile. The sides of the octagonal tiles that are not adjacent to the sides of other tiles form spaces within the group that are free of tiles. The spaces may be squares or rectangles defined by the sides of the hardfacing tiles.

[0016] Hardfacing tiles near the circular edge of the cylinder may only be adjacent to three other hardfacing tiles. Those hardfacing tiles close to the circular edge may only be adjacent to two other hardfacing tiles at the corners of the group of tiles. Those hardfacing tiles close to the rounded edge may only be adjacent to three other hardfacing tiles.

[0017] Thus, the tiles are spaced apart from one another by a separation gap, the separation gap distance between adjacent sides of the hardfacing tiles can be less than 2 mm, 3 mm, 4 mm, 5 mm, or 6 mm.

[0018] High pressure roll crushers may operate continuously for over 25,000 hours before the rolls must be fitted with new hardfacing tiles, and therefore the present invention advantageously minimizes "downtime" due to liner maintenance and replacement (e.g., over 25,000 hours of operation with liner replacement every 30,000 hours compared to 720-1,200 hours of operation with liner replacement every 720-1,200 hours).

[0019] According to one aspect, the method of beneficiation includes running the hardfacing tiles on the cylinders of the roll crusher continuously for over 25,000 hours before replacing them. Crushing can be accomplished in one embodiment in a single step by small gaps between the hardfacing tiles of the crusher (e.g., gaps of 6 mm to 4 mm or less) providing biting edges that cut into the feed material and pull it into the pinch points of the high pressure crushing rolls. Preferably, the maximum dimension of particles in the feed material to the roll crusher is 40 mm, 30 mm, 20 mm, or 400 micrometers or less so that the pinch points help grip the particles as the roll crusher tears and / or crushes them.

[0020] There may be a first sieve upstream of the roll crusher to prevent pre-ground debris having a maximum dimension of less than 40 mm, or 30 mm, or 20 mm, or 400 micrometers from being ground by the roll crusher. The first sieve is configured to operate at sonic speed with at least two-axis motion. A two-axis dry sieving system may be used to sieve oversized material. The oversized material may be recycled back to the high pressure roll crusher.

[0021] An advantage of the present invention is that the crushing step consumes less power, for example one-third to one-half the power, than conventional two or three step milling processes.

[0022] The crushed debris is discharged from the roll crusher outlet. There may then be a sieve for "standard" material, such as crushed debris particles having a maximum dimension of less than 600 micrometers, less than 400 micrometers, or less than 100 micrometers. The sieve may be a dry sieve and / or may include a sealed sieving device. Dust may be collected and recycled to the roll crusher. Oversized material may be recycled to the high pressure roll crusher for autogenous crushing. The standard crushed debris may pass through the dry sieve and be conveyed to a wet sieving device, which separates the debris into particle size ranges.

[0023] In the high pressure roll crusher, a 400% recirculation load (as such term is used herein to describe the number or average number of passes through the milling process that the crushed or ground material undergoes before it is reduced to the desired size) can be performed. This induces autogenous crushing (as such term is used to describe the material crushing on its own). Autogenous crushing, which is performed by returning the fine material subjected to the 400% recirculation load to the pre-crushed feed material entering the rolls, results in particle shaping. This is assisted by the maximum dimension of the pre-crushed feed having a particle size dimension of 30 mm. Particle shaping converts angular particles into subangular particles by rounding the corners of each particle. This converts the feed material, especially the amorphous glass phase of the slag, into valuable foundry sand products. High pressure roll crushing breaks gangue and / or amorphous glass slag from the target material along the boundaries between these component materials (which may be minerals and / or metals, etc., that make up the feed material). Thus, the minerals become more easily separated in the beneficiation process.

[0024] According to one aspect, a method of beneficiation includes using a roll crusher to break up particles of agglomerates along an intermediate boundary between the target material and the gangue. A beneficiation system used by this method may operate continuously for over 25,000 hours before replacing hardfacing tiles on the roll crusher cylinders.

[0025] The method may include separating crushed debris particles broken by the roll crusher into oversized particles having at least a preselected maximum dimension and conforming particles having a smaller maximum dimension, and returning the oversized particles with the incoming pre-crushed debris to the roll crusher for autogenous crushing. There may be a 200%, 300%, 400%, or 500% recycle load of crushed debris. The method may include using the roller crusher in a single step with or without returning crushed material to the incoming material.

[0026] The target material may include metallic minerals, native metals, or chromium or other metallic units. Depending on the hardfacing tiles, their hardness, composition, perimeter shape, and / or space gaps between the tile edges, gangue and / or amorphous glass slugs may be torn, ground, or crushed from the target material along the boundaries between them in the particles of the feed material to the roll crusher.

[0027] The sieving system may include a two-axis operation at sonic speed to sieve slags less than 40 mm, 30 mm, 20 mm, or 400 μm from the high pressure roll crusher. The first sieve may be configured to operate on the pre-ground debris in a dry state. Non-clogged sieves may be employed simultaneously on multiple (independent) sieving decks (e.g., four) to achieve high hourly yields (e.g., 400 tons) of dry fine sieving. The first sieve may include multiple sieving decks, each with a non-clogged sieve.

[0028] Thus, an advantage of the present invention is that it reduces the time, energy requirements, and costs of a standard dry sieving process by more than a factor of 5: for example, standard dry sieving would require more than 20 sieving units to achieve 400 tons per hour; oversized material after crushing, such as oversized slag, ore particles, and / or mining debris, is recycled back to the high pressure roll crusher for autogenous crushing.

[0029] Downstream of the roll crusher there may be a second sieve configured to act on the crushed debris provided by the roll crusher. The second sieve is configured to act on the crushed debris in a wet state. The crushed debris may be processed in a wet screening device directly after roll crushing or after passing through a dry screen in a closed screening device. The wet beneficiation device is upstream of the gravity separator and may perform beneficiation by separating relatively metal-rich particles from gangue and middlings.

[0030] The second sieve may comprise multiple decks for separating the crushed debris into separate particle size streams, each having a specific range of particle size. The second sieve may comprise multiple decks for separating the crushed debris. For example, the wet sieving device may comprise a wet triple deck sieving. The crushed slag and crushed debris may be separated into fragment sizes. For example, crushed debris with a maximum particle size of 400 mm is separated by a triple deck into four fragment sizes: 400 μm to 300 μm; 300 μm to 200 μm; 200 μm to 100 μm; and 100 μm to 10 μm. This creates a narrow bandwidth of particle sizes to overcome the tradeoff between specific gravity and particle size in gravity separation systems.

[0031] The process may be continuous and there may be a first different size stream of particles with a maximum dimension in the range of 300-400 micrometers, and / or a second different size stream of particles with a maximum dimension in the range of 200-300 micrometers, and / or a third different size stream of particles with a maximum dimension in the range of 100-200 micrometers, and / or a fourth different size stream of particles with a maximum dimension in the range of 10-100 micrometers. For example, the bandwidth of the maximum particle size in the streams may be 100 micrometers or 90 micrometers as in the above example. The bandwidth of each stream may be 500 micrometers, 300 micrometers, or 50 micrometers. All streams may have the same bandwidth, or a particular stream may have a different maximum particle size bandwidth than the other streams.

[0032] The relatively narrow bandwidth of maximum particle size in each stream compared to the particle size range of the crushed material immediately downstream of the roll crusher helps overcome the tradeoff between particle size and particle specific gravity that negates the ability of standard gravity separation systems to separate particles based on specific gravity; it also helps overcome the limitations of gravity separation for materials with a specific gravity difference of less than 3.

[0033] There may be a respective gravity separator downstream of each different particle size stream to separate the concentrate from the gangue and / or middlings.

[0034] For example, a stream of material with a bandwidth of less than 100 μm can be fed to a dedicated gravity separator to achieve complete or near complete fractionation. Desired materials, which may include metal oxides, can be produced. There can be separation of at least 70%, 80%, 85%, 90%, 93%, 95%, 97%, or 97% chromium concentrate by weight from the remainder of the amorphous glass slag component.

[0035] The gravity separator may apply a gravity force of less than 100g, 200g, 300g, 400g, or 600g. A concentrate of the desired material, which may include metal oxides, may be produced. A concentrate may be produced from the gravity separator as a chromium concentrate of at least 95% by weight of chromium units. Three phases of chromium units in the post-comminuted debris may be recovered from each stream by the gravity separator for that stream. For example, the chromium unit phases may be unconverted Cr2O3 ore, a partially reduced chromium phase called spinal, and a fully reduced chromium phase called ferrochrome metal.

[0036] According to one embodiment of the mineral beneficiation process utilizing the mineral beneficiation system disclosed herein, a product is produced that includes a chromium concentrate having at least 85% to 95% by weight of chromium units.

[0037] There may be a process water supply configured to wet the post-comminuted debris upstream of the second screen. The process water supply may include a binary compound in the water, which may chemically bond to the surface of the gangue and / or middlings particles.

[0038] Binary compounds may be added to the process water used in the wet sieving and wet beneficiation processes carried out by gravity separators. The binary compounds may be capable of chemically bonding to the surface of the material and sealing the surface of each particle with a layer of silicate glass. The binary compounds may include silicate-based compounds.

[0039] Such sealing of the surface of each particle advantageously prevents the tailings sand particles from leaching residual heavy metals into the environment.

[0040] According to one aspect of a mineral processing method utilizing the mineral processing system disclosed herein, there is a product produced that includes sand.

[0041] A further advantage is that such sealing of the surface of each particle allows the tailings sand to be used in downstream applications. For example, the sand produced by the disclosed method and system is thermally stable, shaped into subangular particles by a high pressure roller crusher, sealed by a binary compound, and classified as a non-hazardous material. Therefore, it can be used as a high value foundry sand.

[0042] The binary compound may also include a dispersant. The binary compound may break up and push particles smaller than 600 μm, 400 μm, 200 μm, or 100 μm apart in the process water suspension, thereby further improving the efficiency of the gravity separation process. The process water suspension may include post-comminuted debris suspended in the process water.

[0043] This binary compound may contain a highly alkaline solution that helps balance the pH of the plant process water. The highly alkaline solution may have a pH of 7.5, 8, 8.5, 9, 10, 11, 12 or higher. The highly alkaline solution may be sodium hydroxide, which is mixed with the downstream flow from the aqueous chemical storage tank to provide the process water. Then, after comminution, when the process water is used with the post-grinding debris, the process water may have a pH of 7.1, 7.5, 8, 8.5, 9, 10, 11 or higher.

[0044] There may be a dewatering sieve to remove water from the concentrate and / or gangue and / or middlings. The recovered target concentrate (e.g., FeCr) is passed through a dewatering sieve, which dewaters the concentrate to a low moisture content, e.g., less than 20% by weight. An ultrasonic dewatering sieve may be used. The recovered water is returned to the water storage tank for recirculation. The water storage tank may be downstream of the aqueous chemical storage tank and / or the binary compound storage tank. An ultrasonic dewatering sieve may be used to dewater both the produced target concentrate and the tailings sand. It is an advantage of the use of an ultrasonic dewatering sieve that the present invention allows for a water neutral or water positive process.

[0045] The product produced by the mineral processing method utilizing the mineral processing system described herein may include sand. This may be sand obtained from tailings. The sand produced may include primarily subangular particles. The particles may be sealed with a layer of silicate glass.

[0046] The products produced by the mineral processing methods utilizing the mineral processing systems described herein may include a chromium concentrate of at least 95% by weight chromium units.

[0047] The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0048] [Figure 1] FIG. 1 is a process diagram for using a roll crusher and a closed screening device for crushed material in a system and method for mineral processing. [Diagram 2] FIG. 2 is a process diagram of a feed and sieve device used to sieve particles in the material prior to crushing, upstream of the roll crusher shown in FIG. 1. [Diagram 3] FIG. 2 is a process diagram using a wet sieving device downstream of the roll crusher and enclosed sieving equipment shown in FIG. 1. [Figure 4]FIG. 4 is a process diagram for using the mineral processing apparatus shown in FIG. 3 with a gravity separator downstream of the wet sieving apparatus. [Diagram 5] FIG. 6 is a process diagram of a dewatering unit used to dry the tailings and dry the chromium concentrate downstream of the concentrator shown in FIG. [Figure 6] FIG. 1 shows a treated water storage and treatment apparatus for treating treated water with a binary compound and adjusting the alkalinity of the treated water. [Figure 7] FIG. 1 shows a roll crusher with hardfacing tiles facing the cylinder. [Figure 8] FIG. 1 shows four groups of octagonal hardfacing tiles on a cylinder. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] As shown in FIG. 1, a high pressure roll crusher 100 crushes, breaks, and tears apart pre-comminuted materials including non-crystalline glass slugs inhomogeneously bonded debris particles with target constituent materials.

[0050] 7 is a side view of roll 102 of roll crusher 100. Hardfacing tiles 106, 107, 108, 109 are shown on the cylindrical surface of roll 102. For purposes of illustration, the roll is shown with tiles only on a portion of its circumference, but in reality, in some embodiments, hardfacing tiles are present around the entire circumference.

[0051] As shown in Figure 8, adjacent sides of tiles 108, 109, 110, 111 have separation gaps 120, 123, 124, 125 between them. Each hardfacing tile 106, 107, 108, 109, 110, 111 is adjacent on every other side to a side of another hardfacing tile which is in turn adjacent on every other side to a side of yet another hardfacing tile. The tiles are octagonal. The sides of an octagonal tile that are not adjacent to the sides of other tiles form non-tiled spaces 130 within the group. Each side is substantially equal in length so that the spaces are substantially square.

[0052] Some of the sides of the hardfacing tiles 106 106, 107, 108, 109, 110, 111 are parallel or nearly parallel to the axis of the cylinder 102. These sides are straight or nearly straight to match the shape of the surface of the cylinder. Other sides of the hardfacing tiles 106 106, 107, 108, 109, 110, 111 are parallel or nearly parallel to the circular direction of the cylinder. These sides have an arcuate cross-sectional profile to match the shape of the cylindrical surface 104 of the cylinder 102 to which the faces of the hardfacing tiles are attached.

[0053] The roll crusher includes hard facing tiles facing the cylinders spaced by gaps 120, 121, 122, 123, 124, 125 of about 2, 4, 6, or 8 mm, so that the pre-crushed material is crushed in the roll crusher to 40 mm, 20 mm, 1000 μm, 400 μm, or 100 μm. The debris particles are broken in part or in large part along the boundary between the slag and the target material. The crushed material includes gangue / slag, middlings, and particles of the target material. This allows the target material to be more easily separated from the slag and middlings during the downstream beneficiation process.

[0054] As shown in Figure 2, upstream of the roll crusher 1, feed material including ore, tailings, mining waste, and / or slag debris is transported by conveyor system 7 to an infeed (primary) hopper 10. The conveyor 7 extends as the slag source (e.g., a slag dump) is depleted, allowing easy loading of slag by a front end loader 8. A water spray system 9 sprays the conveyor system to control dust.

[0055] The primary feed hopper 10 is, for example, a 4m x 4m feed hopper. Slag is continuously provided to the treatment plant, for example a 4m x 4m primary feed hopper 10 providing in excess of 130 tonnes of slag per hour.

[0056] The feeding hopper system is equipped with a water spray system 11 to minimize dust generation during loading.

[0057] The incoming slag passes through a scalping unit 12 to remove oversized slag and large debris. The oversized slag is returned to the crushing facility 14 for size reduction.

[0058] Particles of the feed material having a maximum dimension of 40mm or less proceed downstream through a scalping unit 12. The particles then pass through a magnetic screening system 13 to remove foreign metals from the feed material. The foreign metals are collected as tramp metal 16 and sent to a local recycling facility.

[0059] The feed material, with the foreign metals removed, proceeds downstream through a second vibratory feed hopper 17 and is fed to a dry mill with a roll crusher 100 as shown in FIG. 1. The unground feed material thus becomes ground material. Ground material with a particle size above 400 μm is sieved by a sealed sieving device 3 and returned by a conveyor 4 to the roller crusher 100. The milling process is sealed and equipped with a dust collection system 5 to extract any dust generated. Ground material with a particle size below 400 μm in its largest dimension is pumped downstream by a first pump to a slurry hopper 6.

[0060] In the dry mill shown in FIG. 1, a high pressure roll crusher 1 is used to crush ferrochrome slag and / or gangue and / or mining or grinding waste in a single step.

[0061] FIG. 7 shows a high pressure roll crusher equipped with hardfacing tiles on a cylinder. FIG. 8 shows a group of hardfacing tiles on a cylinder. The hardfacing tiles are shown as octagonal tiles in FIG. 8. The gap separation distance between adjacent sides of the hardfacing tiles is less than 2 mm, 3 mm, 4 mm, 5 mm, or 6 mm. Adjacent sides of adjacent hardfacing tiles are parallel to each other.

[0062] Crushing is carried out continuously for periods of more than 25,000 hours or even more than 30,000 hours, after which the roll crusher is serviced and new hardfacing tiles are installed. The gaps between the hardfacing tiles provide biting edges that cut into particles of pre-crushed material less than 20mm, 30mm, or 40mm in their largest dimension, drawing the particles into the "pinch point" of the high pressure crushing rolls.

[0063] As shown in FIG. 1, a dual-axis ultrasonic dry sieving system 3 sieves out oversized material and recycles it back to the high-pressure roll crusher 1. The "on-spec" material, e.g., material containing particles with a maximum dimension less than 400 μm, passes through the dry sieve 3 and enters the wet sieving process shown in FIG. 3. The wet sieving process separates the on-spec material into narrow bandwidths. The wet sieving process is accomplished by a first wet sieve 18, a second wet sieve 19, and a third wet sieve 20. The three wet sieves 18, 19, 20 process the streams in parallel. The sieving equipment 3 and the transfer conveyor 4 shown in FIG. 1 allow for a 400% recirculation load in the high-pressure roll crusher 1. This induces autogenous crushing. Autogenous crushing by recycling fine material back into the incoming <30mm pre-grind material provides particle shaping, thereby rounding the corners of each particle, turning angular particles into subangular particles. This converts the amorphous glassy phase of the slag into a valuable foundry sand product.

[0064] The post-comminuted debris having a maximum dimension less than 400 μm passes through a sieving system 3 and proceeds to a slurry hopper 6. The slurry hopper 6 and the first pump are shown in FIGS.

[0065] The dual-axis ultrasonic dry sieving system 3 employs non-clogging sieves on multiple independent sieving decks to achieve a dry fine sieving capacity of several hundred tons per hour. For example, a dual-axis ultrasonic dry sieving system employs non-clogging sieves on four independent sieving decks to achieve a dry fine sieving capacity of 400 tons per hour.

[0066] The dry milling and sieving system 3 is connected to a central dust collection system 5 shown in FIG. 1. The central dust collection system 5 includes an air / dust separation cyclone and a baghouse filtration system. The collected dust is fed to a slurry hopper and processed in the wet beneficiation system together with the crushed slag. For example, the dust collection system collects about 0.64 tons per hour of fine dust generated by the milling and sieving system, which is transferred to the wet slurry hopper 6 via a closed screw conveyor, thereby preventing the dust from becoming airborne in the plant. The crushed post-grinding debris and the fine debris from the dust collection system are mixed with water in the slurry hopper 6 to generate a 40% by weight solids slurry for wet beneficiation. The slurry is continuously agitated and fed to the wet beneficiation circuit shown in FIGS. 3 and 4. The wet sieves 18, 19, 20 include a wet triple deck. As shown in FIG. 3, the post-milling debris with a maximum particle size of less than 400 micrometers is fractionated into various fragment sizes. In some embodiments, the post-milling debris with a maximum particle size of less than 600 micrometers, less than 200 micrometers, or less than 100 micrometers is fractionated. For example, four fragment sizes are shown in FIG. 3, including a first fragment size 21, 25, 29 of 300 μm to 400 μm shown in FIG. 3. There are also a second fragment size 22, 26, 30 of 200 μm to 300 μm, a third fragment size 23, 27, 31 of 100 μm to 200 μm, and a fourth fragment size 24, 28, 32 of 10 μm to 100 μm. The first fragment size is 50% to 70% by weight, typically 60%. The second fragment size is 10% to 30% by weight, typically 20%. The third particle size is 5% to 20% by weight, typically 15%. The fourth particle size is 1% to 10% by weight, typically 5%. The sum is 100%, so if the first particle size is, for example, 70%, one or all of the other particle sizes will be closer to the lower end of their range accordingly.

[0067] Thus, a narrow bandwidth of particle sizes is created. The process is continuous and there is a first stream of 300 μm to 400 μm particles provided by a slurry hopper and second pump 33 to a first gravity separator 37. There is also a second stream of 200 μm to 300 μm particles provided by a slurry hopper and third pump 34 to a second gravity separator 40, a third stream of 100 μm to 200 μm particles provided by a slurry hopper and fifth pump 35 to a fourth gravity separator 37, and a fourth stream of 10 μm to 100 μm particles provided by a slurry hopper and fifth pump 36 to a fourth gravity separator 45.

[0068] In some embodiments, the crushed debris is provided to a gravity separator at less than 1000 micrometers, less than 600 micrometers, less than 200 micrometers, or less than 100 micrometers. The narrow bandwidth stream is then adjusted. The bandwidth can be adjusted proportionally or in another manner depending on the target material and gangue.

[0069] A narrow bandwidth of particle size streams overcomes the tradeoff between specific gravity and particle size in the gravity separation system shown in Figure 4. Feeding the 100 μm or less bandwidth to dedicated gravity separators 37, 40, 43, 46, 39, 42, 45, 48 allows for near complete separation of the chromium concentrate from the residual amorphous glass slag components, or at least to levels greater than 70%, 80%, 85%, 90%, 93%, 95%, 97%, or 97% by weight.

[0070] Four slurry hoppers and sixth, seventh, eighth and ninth pumps 38, 41, 33, 47 feed four separate streams of narrow bandwidth particles to fifth, sixth, seventh and eighth gravity separators 39, 42, 45, 48 respectively.

[0071] The wet beneficiation circuit shown in Figures 3 and 4 uses a 100 cubic process water storage tank 62 shown in Figure 6 to supply water to the slurry hopper 6 and first pump to produce a 40% by weight solids slurry for wet beneficiation.

[0072] The slurry passes through several beneficiation systems, such as the one that separates the chromium units from the gangue (tailings) as shown in Figure 4. In some embodiments, there may be up to 2, 4, 6, 8, or 10 beneficiation systems.

[0073] A fifth stream of tailings is withdrawn from the gravity separators 37, 40, 43, 46, 39, 42, 45, 48. The fifth stream is sent to a slurry transfer pump station 49 shown in Figures 4 and 5 and then to a first dewatering screen 51 shown in Figure 5.

[0074] A sixth stream of target concentrate is withdrawn from gravity separators 37, 40, 43, 46, 39, 42, 45, 48. The sixth stream is sent to a second dewatering screen 50 shown in Figures 4 and 5.

[0075] The pH of the treated water is monitored and adjusted accordingly, for example with sodium hydroxide 61 as shown in FIG. 6, to keep the pH of the treated water neutral and avoid acid corrosion of the treatment equipment.

[0076] In one embodiment, the mineral processing system is a closed loop system installed on a concrete floor and surrounded by an enclosure to prevent any spilled treated water from leaking into the environment.

[0077] The treated water is filtered through a cross-flow filtration system 64, shown in Figures 5 and 6, to remove ultrafine particles. The cross-flow filter backflows into a small settling tank 63, shown in Figure 6, where the water is returned to the beneficiation system and the ultrafine particles are mixed into the tailings.

[0078] Gravity separators 37, 40, 43, 46, 39, 42, 45, 48 shown in Figure 4 apply a gravitational force of up to 300 g and allow for the beneficiation of up to 70%, 80%, 85%, 90%, 93%, 95%, 97%, or 97% by weight of chromium elements from the amorphous glass slag. The chromium element phases include unconverted Cr2O3 ore, a partially reduced chromium phase called spinal, and a fully reduced chromium phase called ferrochrome metal.

[0079] As shown in Figure 6, a chemical stormwater tank 60 with an off-load pump feeds a water reservoir with a water transfer pump 62. A binary compound (silicate-based) is added to the process water 62 used in the wet screening and beneficiation processes shown in Figures 3 and 4. The binary compound coats the surface of each particle and seals it with a layer of silicate glass. This prevents the tailings sand particles from leaching residual heavy metals into the environment and allows the tailings sand to be used in downstream applications. The water transfer pumps 54, 54 shown in Figure 5 pump the water back to the main reservoir 62 through a cross-flow filtration system 64 and a settling tank 63.

[0080] In one embodiment, the tailings sand shown in Figure 5 is produced by the ferrochrome slag beneficiation process described herein. This tailings sand is a high value foundry sand that is thermally stable, composed of subangular particles, sealed by binary compounds, and therefore classified as non-hazardous. A dewatering screen 51 upstream of the railcar loading section 52 removes up to 18% moisture from the sand.

[0081] This binary compound is also a strong dispersant, breaking up and pushing apart all particles in the process water suspension that have a maximum dimension less than 600 micrometers, 400 micrometers, or 100 micrometers, which further increases the efficiency of the gravity separation process.

[0082] This binary compound is a colorless, odorless, highly alkaline solution that helps balance the pH of the plant's effluent. A sodium hydroxide dosing system 61, shown in Figure 6, also helps regulate the pH of the plant's effluent.

[0083] The second stage gravity separators 39, 42, 45, 48 shown in Figure 4 provide a 73% metallic mineral, native metal, or chromium or other metal unit concentrate to the second dewatering screen 50 shown in Figure 5. In some embodiments, the concentrate is 50%, 60%, 70%, 80%, or 90% or more metallic mineral, native metal, or chromium unit, or other metal or target mineral unit.

[0084] The recovered target concentrate 56 (e.g., FeCr) is passed through an ultrasonic dewatering sieve 50, which dewaters the concentrate to a moisture content of 18% by weight (i.e., below the moisture content of the raw slag entering the processing plant). In some embodiments, the moisture content is reduced to 30%, 20%, 10%, or 5% or less by weight. The recovered water is returned by a water transfer pump 55 to a 100 cubic treated water storage tank 62 for recirculation. Water neutral or water positive operation is achieved.

[0085] The target concentrate 56 may be accumulated on a concrete pad with an enclosure to prevent water runoff, and water slowly escaping from the concentrate is returned to the treated water circuit.

[0086] The target concentrate (eg, FeCr) is transported to a drying and mixing facility located within the smelting building for smelting.

[0087] The present invention has been described only for purposes of illustration. Thus, the foregoing is considered as merely illustrative of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation as illustrated and described, and therefore, all suitable modifications and equivalents may be resorted to within the scope of the appended claims.

Claims

1. An ore dressing system comprising a roll crusher having a hard facing tile facing a cylinder.

2. The ore dressing system according to claim 1, wherein the tile is octagonal.

3. The ore dressing system according to claim 1 or 2, wherein the tiles are spaced apart from each other by a separation gap.

4. The ore dressing system according to claim 3, wherein the separation gap is less than 6 mm.

5. The ore dressing system according to claim 1 or 2, further comprising a first screen upstream of the roll crusher to prevent debris before crushing with a maximum dimension of less than 400 micrometers from being crushed by the roll crusher.

6. The ore dressing system according to claim 5, wherein the first screen is configured to operate at the speed of sound with at least two-axis movement.

7. The ore dressing system according to claim 5, wherein the first screen comprises a plurality of screening decks each having a screen that is not clogged.

8. The ore dressing system according to claim 5, wherein the first screen is configured to act on the debris before crushing in a dry state.

9. The ore dressing system according to claim 1 or 2, further comprising a second screen downstream of the roll crusher and configured to act on the debris after crushing provided by the roll crusher.

10. The ore dressing system according to claim 9, wherein the second screen comprises a plurality of decks for separating the debris after crushing into separate particle size streams each having a specific range of particle sizes.

11. The ore dressing system according to claim 9, wherein the second screen separates the debris after crushing into a first different particle size stream of particles having a maximum dimension in the range of 300 - 400 micrometers, and / or a second different particle size stream of particles having a maximum dimension in the range of 200 - 300 micrometers, and / or a third different particle size stream of particles having a maximum dimension in the range of 100 - 200 micrometers, and / or a fourth different particle size stream of particles having a maximum dimension in the range of 10 - 100 micrometers, and comprises a plurality of decks for this purpose.

12. The ore dressing system according to claim 9, wherein the second screen is configured to act on the debris after crushing in a wet state.

13. The beneficiation system according to claim 10, comprising respective gravity separators downstream of streams of respective different particle sizes to separate a concentrate from gangue and / or middling.

14. The beneficiation system according to claim 13, wherein each gravity separator is configured to apply a gravity of less than 300 g to produce the concentrate as a chromium concentrate of at least 95% by weight of chromium units.

15. wherein the chromium unit is unconverted Cr ２ O ３ The beneficiation system according to claim 14, comprising ore, spinel of a partially reduced chromium phase, and / or ferrochrome metal of a completely reduced chromium phase.

16. The beneficiation system according to claim 13, comprising a process water supply unit configured to wet the crushed debris upstream of the second sieve.

17. The beneficiation system according to claim 16, wherein the process water supply unit contains a binary compound in water, and the binary compound can chemically bond to the surfaces of gangue and / or middling particles.

18. The beneficiation system according to claim 17, wherein the binary compound contains a silicate-based binary compound, and each of the particles is sealed with a layer of silicate glass.

19. The beneficiation system according to claim 17, wherein the binary compound contains a dispersant that repels particles having a maximum dimension of less than 400 micrometers from each other in a suspension containing the process water and the crushed debris.

20. The beneficiation system according to claim 17, wherein the binary compound contains an alkaline solution having a pH of 8, 10, 12 or higher.

21. The beneficiation system according to claim 13, comprising a dewatering sieve for removing water from the concentrate and / or gangue and / or middling.

22. A product produced by a beneficiation method using the beneficiation system according to claim 1 or 2 and containing sand.

23. A product produced by the beneficiation method according to claim 22, wherein the sand mainly contains sub-angular particles.

24. A product produced by the beneficiation method according to claim 22 and containing particles sealed with a layer of silicate glass.

25. A product produced by a beneficiation method using the beneficiation system according to claim 1 or 2 and containing a chromium concentrate of at least 95% by weight of chromium units.

26. A beneficiation method using the beneficiation system according to claim 1 or 2, the method comprising the step of using the roll crusher to break the particles of the agglomerate along the boundary line between the target substance and the gangue.

27. A beneficiation method using the beneficiation system according to claim 1 or 2, the beneficiation method continuously operating for more than 25,000 hours until the hard-facing tiles on the cylinder of the roll crusher are replaced.

28. The beneficiation method according to claim 26, comprising separating the particles of the crushed debris crushed by the roll crusher into oversized particles having at least a preselected maximum size and conforming particles having a maximum size smaller than that, and returning the oversized particles to the debris before crushing flowing into the roll crusher for autogenous crushing.

29. The beneficiation method according to claim 28, including a 400% recycle load of the crushed debris.

30. The beneficiation method according to claim 26, including using the roller crusher in a single step, with or without the return of the crushed material to the incoming material.

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