JP7687079B2 - Apparatus for distributing chromite-containing slurry and method for recovering chromite using the same - Google Patents

Description

The present invention relates to a distributor that distributes and supplies a chromite-containing slurry prepared by adding water to crushed nickel oxide ore to multiple separation devices that separate chromite from nickel oxide ore, and a method for recovering chromite using the distributor.

Nickel oxide ore, which is used as a raw material in nickel hydrometallurgy, contains chromite, a mineral whose main component is the element chromium. This chromite, which exists in the form of chromite ore within nickel oxide ore, has a higher true specific gravity and a larger particle size than other ore components, so that in the ore slurry prepared by adding water to crushed nickel oxide ore, the chromite ore has high settling properties.

In addition, as can be seen from the fact that chromite is used industrially as an abrasive and the like, it is harder than other ore components contained in nickel oxide ore, so if chromite is contained in the ore slurry processed in a nickel hydrometallurgical plant, there is a concern that the parts of the equipment, piping, etc. that come into contact with the ore slurry will be significantly worn out. For this reason, it has been necessary to implement costly anti-wear measures at the parts of equipment that handles chromite-containing ore slurry, such as liquid delivery pumps, piping, and valves, that come into contact with the ore slurry.

Therefore, when chromite is contained in nickel oxide ore used as a raw material in a nickel hydrometallurgy process, it has been proposed to separate and recover the chromite in an upstream process. For example, Patent Documents 1, 2, and 3 disclose a technology for separating and recovering chromite in a high pressure acid leaching process in which sulfuric acid is added to the raw nickel oxide ore and acid leaching is performed under high temperature and pressure, in which the nickel oxide ore is crushed and then water is added to prepare an ore slurry, and before the acid leaching is performed, the ore slurry is treated in a classification process that utilizes centrifugal force and specific gravity difference to separate and recover chromite.

JP 2012-107289 A JP 2017-052991 A JP 2017-052992 A

In the classification process using the specific gravity difference, the ore slurry is introduced into a settling tank, where chromite, which has a high true specific gravity, settles by gravity in the settling tank and is collected from the bottom of the tank, while the slurry containing particles with a lower true specific gravity than chromite overflows as a supernatant liquid and can be collected from a trough at the top of the tank. However, commercially available classification devices using the specific gravity difference have limited processing capacity, and when a large amount of ore slurry is continuously processed, such as in the case of wet smelting of low-grade nickel oxide ore, a single classifier may not be sufficient. In this case, it is necessary to uniformly distribute the ore slurry to multiple classifiers installed in parallel and continuously supply each at a constant flow rate.

As a method for distributing and delivering equal amounts of ore slurry to multiple classification devices as described above, one method is to branch the ore slurry supply pipe for each classification device, provide a valve on each branch pipe, and adjust the opening of the valve. Alternatively, one method is to provide a liquid delivery pump on each branch pipe and control the flow rate of the liquid delivery pump. However, both of these methods are prone to wear inside the valves and inside the casing of the liquid delivery pump, which is time-consuming and costly to repair, and the operation of the device must be stopped during repairs, which can reduce the plant's operating rate.

The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a distribution and supply device that can distribute equal amounts of chromite-containing slurry, such as ore slurry prepared by adding water to crushed nickel oxide ore, to multiple separation devices installed in parallel in order to separate and recover chromite contained in nickel oxide ore used as a raw material in the nickel hydrometallurgy process, and continuously supply each at a constant flow rate.

In order to achieve the above object, the present invention provides a chromite-containing slurry distribution device that evenly distributes and supplies a chromite-containing slurry to a plurality of separation devices that separate chromite from the chromite-containing slurry, and is characterized in that it comprises a substantially cylindrical distribution tank in which a plurality of weirs that can be moved in the vertical direction are provided at equal intervals in the circumferential direction, the same number as the number of the separation devices, and an agitator provided in the center of the distribution tank, in which the supply portions of the plurality of separation devices are located lower than the upper ends of the plurality of weirs when they are at their lowest positions, and the inner wall surface of the distribution tank is provided with a plurality of flow path portions with both upper and lower ends open to guide the chromite-containing slurry that overflows the plurality of weirs .

According to the present invention, it is possible to distribute equal amounts of chromite-containing slurry, such as ore slurry prepared by adding water to crushed nickel oxide ore, to multiple parallel separation devices that separate and recover chromite from nickel oxide ore used as a raw material in the nickel hydrometallurgy process, and continuously supply each at a constant flow rate.

FIG. 1 is a process flow diagram of a nickel hydrometallurgical refining method to which the distributing device for a chromite-containing slurry of the present invention is suitably applied. FIG. 2 is a process flow diagram of a specific example of a chromite recovery process in the hydrometallurgical process of FIG. 1. FIG. 2 is a plan view of the chromite-containing slurry distributor according to the embodiment of the present invention with the top plate portion removed. FIG. 4 is a longitudinal sectional view of the distributor of FIG. 3 taken along line IV-IV. FIG. 4 is an exploded perspective view of the dispensing device of FIG. 3 . FIG. 1 is a front view of a spiral concentrator preferably used in a chromite recovery method according to an embodiment of the present invention. FIG. 1 is a vertical cross-sectional view of a density separator preferably used in a chromite recovery method according to an embodiment of the present invention. FIG. 2 is a plan view of a shaking table preferably used in the chromite recovery method according to the embodiment of the present invention.

Below, an embodiment of the distributor for a slurry containing chromite (hereinafter also referred to as a chromite-containing slurry) according to the present invention will be described, taking as an example a case in which the chromite-containing slurry is a coarse-particle slurry discharged from a bottom-side discharge outlet when an ore slurry prepared by crushing nickel oxide ore and adding water is introduced into a hydrocyclone. Note that the distributor for a chromite-containing slurry of the present invention is not limited to the following embodiment, and includes various modifications and alternative examples within the scope of the present invention. In other words, the scope of the rights of the present invention extends to the scope of the claims and their equivalents.

1. Nickel hydrometallurgy method The chromite-containing slurry distributor according to the embodiment of the present invention is used in the upstream process of separating and recovering chromite from an ore slurry prepared by adding water to pulverized nickel oxide ore used as a raw material in a nickel hydrometallurgy method. First, the nickel hydrometallurgy method will be described. The nickel hydrometallurgy method is a method in which a leachate containing valuable metals such as nickel obtained by acid leaching an ore slurry under high temperature and high pressure is subjected to a sulfidation treatment to recover the valuable metals in the form of sulfides.

More specifically, as shown in FIG. 1, the nickel hydrometallurgy process includes a pretreatment step S1 in which the raw material nickel oxide ore is subjected to pretreatment such as crushing and sieving and water is added to prepare an ore slurry having a predetermined slurry concentration; a chromite recovery step S2 in which chromite is separated from the ore slurry and recovered as a by-product; a leaching step S3 in which sulfuric acid and high-pressure steam are added to the ore slurry after the chromite has been separated and removed in an autoclave to perform an acid leaching process under high temperature and pressure; and a flash drum is used to reduce the pressure and temperature of the leached slurry containing nickel and cobalt as valuable metals leached by the acid leaching process, after which the leached slurry is cooled and cooled. It is generally composed of a countercurrent multi-stage washing process S4 in which the leaching residue is separated and removed while being washed with washing water introduced at the most downstream side by introducing the leaching residue into the most upstream side of a series of multiple thickeners; a neutralization process S5 in which a neutralizing agent is added to the leachate after the leachate residue has been separated and removed to separate and remove impurity elements contained in the leachate as neutralized precipitates; a sulfurization process S6 in which a sulfurizing agent is added to the final neutralization liquid after the neutralized precipitates have been separated and removed to recover nickel and cobalt in the form of a mixed sulfide; and a final neutralization process S7 in which a neutralizing agent is added to the nickel-poor liquid discharged during the recovery of the mixed sulfide and the leachate removed in the countercurrent multi-stage washing process S4 to perform a detoxification process.

The nickel oxide ores used as raw materials in the above-mentioned nickel hydrometallurgy method are mainly so-called laterite ores such as limonite ore and saprolite ore. The nickel content of laterite ore is generally 0.8-2.5% by mass, and nickel is contained as hydroxide or hydrous magnesium silicate (magnesium silicate) mineral. The iron content of laterite ore is generally 10-50% by mass, and in this case, the iron is mainly in the form of trivalent hydroxide (goethite), but some divalent iron is contained in hydrous magnesium silicate minerals, etc.

The above-mentioned laterite ore further contains chromium, magnesia, and silicon. Of these, most of the chromium is contained in the laterite ore as chromite minerals containing iron and magnesium, usually at about 1 to 5 mass%. Magnesia is contained in hydrous silicic earth minerals, as well as in unweathered, hard silicic earth minerals that contain almost no nickel. Silica is contained in silica minerals such as quartz and cristobalite (amorphous silica), and hydrous silicic earth minerals. These chromite minerals, silicic earth minerals, and silica minerals contained in laterite ore contain almost no nickel, and are called gangue components.

2. Chromite Recovery Step Next, the chromite recovery step S2 in the above-mentioned nickel hydrometallurgy method will be described with reference to FIG. The chromite recovery process S2 is a centrifugation process S21 in which the chromite-containing ore slurry (also referred to as chromite-containing ore slurry) prepared in the pretreatment process S1 is centrifuged in a hydrocyclone to discharge a coarse-particle slurry containing coarse chromite from a bottom-side outlet and a dechromite ore slurry containing fine particles such as goethite from a top-side outlet; a distribution process S22 in which the coarse-particle slurry is distributed according to the number of devices in the subsequent process; a specific gravity separation process S23 in which goethite contained in the distributed coarse-particle slurry is separated by utilizing a specific gravity difference; a concentration process S24 in which the coarse-particle slurry after the goethite separation in the specific gravity separation process S23 is introduced into a concentration device to further increase the concentration of chromite; and a magnetic separation process S25 in which magnetized substances contained in the coarse-particle slurry in which the chromite concentration has been increased in the concentration process S24 are separated by using a magnetic force.

As described above, even if the nickel oxide ore used as a raw material in the nickel hydrometallurgy process contains chromite, the particle size is preferably adjusted to 45 μm or more and 1.4 mm or less by crushing and sieving in the pretreatment process S1, and water is added to prepare an ore slurry to a predetermined slurry concentration. Then, the chromite is separated from this ore slurry in the chromite recovery process S2. This makes it possible to prevent the problem of significant wear of the liquid-contacting parts of equipment such as pipes and pumps by chromite in the subsequent leaching process S3 and thereafter.

This not only reduces the equipment maintenance costs, but also the frequency of shutdowns for maintenance, thereby improving the operating efficiency of the hydrometallurgical plant. In this specification, the particle size A or more and B or less means that the particle size is on the sieve with mesh size A and below the sieve with mesh size B. Each step constituting the chromite recovery process S2 will be specifically described below.

2.1 Centrifugal separation step The centrifugal separation step S21 is a step of classifying the chromite-containing ore slurry prepared in the pretreatment step S1 using a hydrocyclone. The hydrocyclone is a classification device consisting of a cylindrical section and an inverted cone-shaped reduced diameter section connected to the lower end of the cylindrical section. By introducing the chromite-containing ore slurry pressurized by a pump into the cylindrical section from the tangential direction, the chromite-containing ore slurry can be caused to descend while swirling at high speed along the inner wall surface. The centrifugal force generated by this causes the chromite, which is a coarse particle having a high true density and a large particle diameter, to be discharged from the bottom discharge port as a coarse particle side slurry (also called underflow "U/F").

Only a portion of the ore slurry introduced into the hydrocyclone is discharged from this bottom discharge outlet, so the remaining ore slurry rises from the center and is discharged from the top discharge outlet as fine particle side slurry (also called overflow "O/F") containing fine particles such as goethite. This fine particle side slurry is joined by fine particles mainly consisting of goethite separated in the subsequent gravity separation process S23, concentration process S24, and magnetic separation process S25, and is subjected to acid leaching treatment in the subsequent leaching process S3 as a dechromite ore slurry.

The above classification of chromite and goethite can be achieved by setting the classification particle size (classification point) of the chromite-containing ore slurry to be classified within an appropriate range, and this classification particle size can be adjusted by the operating conditions of the hydrocyclone. Specifically, to effectively classify the chromite-containing ore slurry, the classification particle size is preferably in the range of 20 to 150 μm, and more preferably in the range of 45 to 75 μm.

If the classification particle size is less than 20 μm, the proportion of fine particles mixed into the coarse-particle slurry will be high, resulting in insufficient quality of the recovered chromite. In addition, the proportion of nickel that should be contained in the chromite-free ore slurry processed in the subsequent leaching step S3 that is mixed into the coarse-particle slurry will increase, resulting in increased nickel loss. Conversely, if the classification particle size exceeds 150 μm, the proportion of coarse chromite, magnesia, and silica minerals mixed into the fine-particle slurry will increase, which may cause wear and reduce processing capacity in the steps following the leaching step S3. In addition, in this centrifugation step S21, it is preferable that the chromite concentration of the coarse-particle slurry is concentrated to 41 mass% or more.

Examples of operating conditions of the hydrocyclone that are adjusted appropriately to achieve the above classification particle size include the slurry concentration (pulp concentration) of the chromite-containing ore slurry introduced into the hydrocyclone, the operating pressure of the hydrocyclone, the slurry concentration (pulp concentration) of the coarse particle slurry, the amount of chromite-containing ore slurry supplied to the hydrocyclone, and the shape of the hydrocyclone, as represented by the inner diameter.

Among the above operating conditions, the pulp concentration of the chromite-containing ore slurry supplied to the hydrocyclone is not particularly limited, but is preferably adjusted to about 10 to 30% by mass, and more preferably adjusted to about 15 to 20% by mass. Even if the pulp concentration is less than 10% by mass, classification can be performed to some extent by the hydrocyclone, but a large amount of water is required to prepare the ore slurry in the pretreatment step S1, and water must be removed in a subsequent step, for example by sedimentation concentration, which may increase processing costs. Conversely, if the pulp concentration exceeds 30% by mass, the viscosity of the chromite-containing ore slurry may become too high, making classification by the hydrocyclone difficult.

The operating pressure of the hydrocyclone, i.e., the pressure of the chromite-containing ore slurry supplied to the hydrocyclone, is not particularly limited, but is preferably within the range of about 0.1 to 0.3 MPaG, taking into consideration classification performance, processing speed, etc. Furthermore, the pulp concentration of the coarse-particle slurry as the underflow of the hydrocyclone is preferably 15% by mass or more. The pulp concentration of this underflow can be adjusted, for example, by the opening of a valve installed at the bottom-side discharge outlet of the hydrocyclone.

As described above, among the operating conditions of the hydrocyclone taking into consideration classification performance, processing speed, etc., it is particularly preferable to adjust the pressure of the ore slurry supplied to the hydrocyclone and the pulp concentration of the ore slurry so that the proportion of particles with a particle size of -45 μm (that can pass through a screen with 45 μm openings) in the solid content of the coarse-particle slurry is 30 mass% or less. In other words, it is desirable for the proportion of particles with a particle size of -45 μm to be as close to 0 mass% as possible for the particles contained in the coarse-particle slurry, but the closer the proportion of -45 μm particles is to 0 mass%, the more likely it is that low-nickel-grade coarse particles will be mixed into the fine-particle slurry, which may be a factor in nickel recovery losses in the hydrometallurgical process.

As mentioned above, chromite has a higher true density and generally larger particle size than iron hydroxides such as goethite, so by using a hydrocyclone as a classification device, it is possible to accurately separate coarse chromite particles from fine particles such as goethite. In other words, it is possible to almost completely eliminate the distribution of chromite to the fine-particle slurry discharged from the top outlet as an overflow. In addition, since hydrocyclones have no moving parts, they are suitable for processing large amounts of ore slurry at low cost, and are particularly suitable for processing when the amount of ore discharged from the top side is greater than the amount of ore discharged from the bottom side. The number of stages in the hydrocyclone is not limited to one as mentioned above, and may be two or more.

2.2 Distribution Step The distribution step S22 is a step of distributing the coarse-particle-side slurry separated in the above-mentioned centrifugation step S21 using a distribution device. Specifically, the distribution device is composed of a cylindrical distribution tank 10 with a bottom and an agitator 20 provided on the central axis of the distribution tank 10, as shown in Figures 3 to 5. The distribution tank 10 has a plurality of substantially rectangular cutouts 10a (four cutouts 10a are shown in Figure 3) at equal intervals in the circumferential direction at its upper end, the number of which is the same as the number of the gravity separation devices in the subsequent stage. A plurality of weirs 11 are provided so as to be movable in the vertical direction so as to block each of the plurality of cutouts 10a from the inside and to change the overflow liquid level. The distribution tank 10 is preferably covered with a disk-shaped lid 12, and a motor 21 of the agitator 20 is installed in the approximate center of the lid.

With this configuration, the coarse-particle slurry discharged from the bottom-side discharge port of the hydrocyclone in the previous process is pressurized by a slurry pump provided as necessary, and then introduced into the distribution tank 10 through a feed pipe (not shown). The slurry is mixed uniformly by the stirring blade 23 provided at the tip of the shaft 22 of the agitator 20, and then overflows the multiple weirs 11, so that it is distributed in equal amounts. The coarse-particle slurry that overflows the multiple weirs 11 is temporarily received in the storage section 13 provided corresponding to each weir 11 outside the distribution tank 10, and then discharged from the opening 13a provided at the bottom and sent to the downstream specific gravity separation device (not shown) through the discharge pipe 14 connected to the opening 13a.

The distributor of the above structure is installed so that the supply parts of the above-mentioned multiple specific gravity separators are located lower than the upper ends of the above-mentioned multiple weirs 11 when they are located at the lowest position. This allows the coarse-particle-side slurry evenly distributed in equal amounts by the distributor to be continuously sent to the above-mentioned multiple specific gravity separators using only the height difference. The height difference is preferably 3 m or more. If the height difference is less than 3 m, there is a risk that the slurry cannot be sent stably when there is a pressure loss in the discharge pipe 14 or a fluctuation in the particle size or pulp concentration of the coarse-particle-side slurry. In addition, the flow rate of the coarse-particle-side slurry overflowing each of the above-mentioned multiple weirs 11 is preferably 10 m ³ /hr or more and 200 m ³ /hr or less. If the flow rate overflowing each weir 11 is within the range of 10 m ³ /hr or more and 200 m ³ /hr or less, the coarse-particle-side slurry can be stably overflowed from these multiple weirs 11, making it possible to distribute it more evenly.

In the distribution tank 10, the stirring by the stirring blades 23 of the agitator 20 creates ripples on the liquid surface, which can cause variations in the flow rate overflowing the multiple weirs 11. To suppress this variation in flow rate, multiple flow passages 15 with open upper and lower ends that guide the coarse-particle slurry overflowing the multiple weirs 11 are provided on the inner wall surface of the distribution tank 10. These multiple flow passages 15 can also function as baffles that prevent the stirring blades 23 of the agitator 20 from rotating the slurry in the distribution tank 10 along the inner wall surface.

2.3 Gravity Separation Step The gravity separation step S23 is a step in which each of the coarse-particle slurries distributed in the distribution step S22 is subjected to gravity separation processing using a gravity separator to separate fine particles such as goethite contained in the coarse-particle slurry, which also makes it possible to concentrate chromite. That is, in the above-mentioned centrifugal separation step S21, the coarse-particle slurry recovered as the underflow from the bottom-side outlet of the hydrocyclone mainly contains chromite, but also contains some fine particles such as goethite.

Therefore, in this gravity separation step S23, the coarse-particle slurry containing fine particles in addition to chromite is subjected to gravity separation treatment, so that the fine particles such as goethite can be effectively separated from the chromite. In other words, the chromite in the coarse-particle slurry is further concentrated. The fine particles containing goethite separated in this gravity separation step S23 can be mixed with the overflow of the hydrocyclone mentioned above to produce a chromite-free ore slurry that is treated by the acid leaching process in the wet smelting process.

It is preferable to use at least a spiral concentrator as the density separation device used in the density separation step S23. In this case, it is preferable to provide at least one more stage of density separation device selected from a density separator, a shaking table, and a spiral concentrator downstream of the spiral concentrator. Among these combinations, it is preferable to provide one stage of a spiral concentrator and one stage of a density separator suitable for large-volume processing in succession. These density separation devices are described in detail below.

(Spiral concentrator)
As shown in Fig. 6, the spiral concentrator has a structure in which a gutter is provided in a spiral shape around a central axis extending in the vertical direction, and by supplying slurry from a feed section located at the top and causing it to flow downward while rotating due to gravity toward a discharge outlet located at the bottom, the slurry containing fine particles such as goethite with a low specific gravity is pushed to the outer periphery by the centrifugal force generated at that time, and the slurry containing chromite with a high specific gravity flows on the inner periphery side. As a result, by separately collecting the inner and outer periphery sides at the discharge outlet at the bottom, it becomes possible to separate the fine particles such as goethite from the chromite.

In the gravity separation process using the spiral concentrator, although there are no particular limitations, it is preferable that the pulp concentration of the slurry supplied to the feed section is more than 15% by mass and less than 35% by mass, and more preferably more than 20% by mass and less than 30% by mass. If the pulp concentration is 15% by mass or less, separation performance may deteriorate, and conversely, if it is 35% by mass or more, the flow of particles may stagnate on the inner side of the spiral concentrator, which is the concentrated side of the chromite during the gravity separation process, making it easier for build-up to occur, and the above separation may not be performed well.

In addition, in gravity separation processing using a spiral concentrator, multiple spiral concentrators may be connected in series to perform gravity separation of the slurry to be treated in a multi-stage device. In this case, it is preferable to supply the slurry containing chromite recovered as the slurry on the inner circumference side of the spiral concentrator to the subsequent spiral concentrator. This allows the chromite components contained in the slurry to be treated to be effectively concentrated to a higher concentration, further increasing the chromite recovery rate.

(Density separator)
The density separator is also called a theeter-bed separator, and is composed of a cylindrical section and an inclined section located at the lower part thereof, and a plurality of pipes for supplying water called theeter water are provided at the lower end part of the cylindrical section, as shown in Fig. 7. With this configuration, fine particles contained in the slurry introduced from the upper part of the cylindrical section are made to overflow at the upper end part of the cylindrical section along with the upward flow of the theeter water, and coarse particles contained in the slurry are made to settle against the upward flow of the theeter water and are deposited in the inclined section, and then can be collected from the bottom as an underflow.

In the gravity separation treatment using the density separator, although there is no particular limitation, it is preferable to set the supply amount of teeter water to 0.5 to 7.0 ^{m 3} · h ^-1 /m ^2. If the supply amount is less than 0.5 m ³ · h ^-1 /m ² , the effect of interference settling becomes small, and gravity separation may not be performed efficiently. Conversely, if the supply amount exceeds 7.0 ^{m 3} · h ^-1 /m ² , chromite particles may rise and move to the overflow side. In this case, the recovery rate of chromite decreases, and the chromite content in the ore slurry supplied to the leaching treatment increases, making it difficult to reduce the Cr grade in the hematite.

In the above-mentioned gravity separation process using a density separator, a plurality of density separators may be connected in series to separate the slurry to be treated by gravity in a multi-stage device. This allows chromite to be separated more effectively, and the chromite quality ( _Cr2O3 quality) in the slurry extracted as an underflow from the _final -stage density separator can be further increased.

(Shaking table)
As shown in Fig. 8, the shaking table is a substantially rectangular table that is reciprocated horizontally by a drive unit, and slurry is supplied to one corner of the table, and water is supplied from the corner through a plurality of openings in a pipe extending in the longitudinal direction of the table. With this configuration, fine particles such as goethite fall from the other side of the table opposite to the end of the table where the pipe is provided, along with the flow of water supplied from the pipe, whereas coarse particles of chromite are not affected by the flow of water and are transported from one end to the other in the longitudinal direction by the vibration of the table, and are collected at the corner opposite to the one corner.

In the gravity separation process using the shaking table described above, although there are no particular limitations, it is preferable to adjust the pulp concentration of the slurry supplied from one corner of the table to more than 15% by mass and less than 35% by mass, and more preferably more than 20% by mass and less than 30% by mass.

The concentration step S24 is a step of adjusting the slurry concentration of the pre-concentrated slurry treated in the preceding gravity separation step S23 so as to obtain a slurry concentration suitable for the supply conditions of the magnetic separator employed in the following magnetic separation step S25. There is no particular limitation on the type of thickening device used in this concentration step S24, but a gravity settling device such as a thickener that can thicken the slurry at a relatively low cost is preferred.

2.5 Magnetic Separation Step The magnetic separation step S25 is a step of removing magnetized matter from the concentrated slurry concentrated in the previous concentration step S24 using a magnetic separator. The coarse-particle slurry separated and classified to the coarse-particle side in the centrifugation step S21 is mainly composed of chromite, but may contain magnetite and also goethite. In the magnetic separation step S25, the concentrated slurry containing other mineral components in addition to chromite is subjected to magnetic separation treatment, so that magnetite as a magnetized matter can be separated from chromite as a non-magnetized matter, which means that the chromite is further concentrated.

The mixture containing magnetite as a magnetized material separated in this magnetic separation step S25 can be mixed with the overflow of the hydrocyclone described above to produce a chromite-free ore slurry that is treated in the acid leaching process of the hydrometallurgical process. In addition, if the concentrated slurry that is the target of this magnetic separation process contains trace amounts of goethite, this magnetic separation process can cause it to be included in the mixture containing magnetite, and the ore slurry can be supplied to the acid leaching process together with magnetite.

The above magnetic separation device is not particularly limited, but it is preferable to use a high magnetic field magnetic separation device that generates a relatively high magnetic field strength in the range of 5 to 20 kGauss. This allows chromite to be separated and removed extremely efficiently. If the magnetic field strength is less than 5 kGauss, there is a risk that the magnetite in the magnetized material cannot be effectively separated. Conversely, if the magnetic field strength exceeds 20 kGauss, there is a risk that the chromite will also be magnetized at the same time.

As described above, both magnetite and goethite can be separated and removed by using a high magnetic field magnetic separation device, but magnetized magnetite is attracted even to magnets with relatively low magnetic field strength, so if the magnetic field strength is too high, it becomes difficult to remove from the magnet. On the other hand, goethite is not attracted to magnets with relatively low magnetic field strength, but is attracted to magnets with high magnetic field strength. Therefore, in this magnetic separation step S25, it is preferable to perform magnetic separation using a low magnetic field magnetic separation device that generates a magnetic field strength of about 500 to 2000 Gauss, which is smaller than the magnetic field strength of the high magnetic field magnetic separation device, before magnetic separation with the high magnetic field magnetic separation device.

As explained above, the chromite-containing slurry distribution device of the embodiment of the present invention does not require pumps, valves, etc. in particular, so the number of such devices that are prone to wear can be reduced, thereby reducing the construction and maintenance costs of the facility, and the frequency of equipment troubles and maintenance due to wear is reduced, so the plant's operating rate can be increased. In addition, the number of driving parts can be reduced, so operating costs can also be reduced. Furthermore, because the height difference is used to send the slurry containing chromite, which is prone to wear on equipment, from the distribution device, the flow rate in the piping can be slower than when the liquid is sent by a pump. As a result, wear on the piping and on valves installed as necessary can be suppressed.

[Reference example]
As shown in Figures 3 to 5, a distribution device was prepared, which includes a distribution tank 10 having cutouts 10a and vertically slidable gates 11 covering the cutouts 10a at four locations (A, B, C, D) at the top end at equal intervals, and an agitator 20 provided on the central shaft of the distribution tank 10. Then, water at a temperature of 20 to 30°C was supplied while rotating the agitator 20 at a rotation speed of 103 rpm, and it was examined whether water overflowed evenly from the four gates 11. The four gates 11 provided on the distribution tank 10 were all adjusted to the same height. The measurement results are shown in Table 1 below.

As can be seen from Table 1 above, the flow rates of the water overflowing from the four weirs 11 (A, B, C, D) at the top end of the distribution tank 10 varied within a range of -2.9% to +3.0% from their average value. However, when recovering chromite from an ore slurry prepared as a raw material in a nickel hydrometallurgy method, the allowable range of variation when distributing to multiple separation devices installed in parallel is usually 5% or less, so it was found that the water can be distributed evenly by the distribution tank 10.

[Example]
In a nickel hydrometallurgical plant, nickel oxide ore, which is a raw material for producing a nickel-cobalt mixed sulfide by a high-pressure acid leaching method, contains chromite. Thus, water is added to nickel oxide ore made of powder particles whose particle diameter is adjusted to 45 μm or more and 1.4 mm or less by a crusher and a screen to prepare an ore slurry having a slurry concentration of 20 mass %, and the chromite is separated and recovered from the ore slurry by processing the ore slurry in the order of the centrifugal separation step S21, the distribution step S22, and the specific gravity separation step S23 in the process flow diagram shown in FIG. 2 .

Specifically, in the centrifugation step S21, a hydrocyclone manufactured by Salter Cyclones Limited was used, and the above-mentioned ore slurry was pressurized to 0.2 MPaG by a pump and fed, and a coarse-particle slurry with a pulp concentration of 15% by mass was extracted from the bottom outlet of the hydrocyclone. In the distribution step S22, the coarse-particle slurry was distributed using a distribution device as shown in Figures 3 to 5 while rotating the agitator 20 at a rotation speed of 103 rpm, and the slurry was fed to four spiral concentrators installed in parallel, respectively, for classification in the gravity separation step S23. Note that when all four weirs 11 of the distribution tank 10 of the distribution device were positioned at the lowest position, their upper ends were 3 m higher than the feed section of the spiral concentrator.

As a result, the coarse-particle slurry could be made to overflow at a flow rate of about 20 ^m3 /hr at each of the four weirs 11 of the distribution tank 10, and the variation from the average value of these flow rates could be suppressed to 5% or less. In addition, it became possible to stably operate the four spiral concentrators to recover chromite, and no severe wear was observed in the wetted parts of the nickel hydrometallurgy plant.

REFERENCE SIGNS LIST 10 distribution tank 10a cutout portion 11 weir 12 lid 13 storage portion 13a opening 14 discharge pipe 15 flow path portion 20 mixer 21 motor 22 shaft 23 mixing blade

Claims (5)

A chromite-containing slurry distribution device that uniformly distributes and supplies a chromite-containing slurry to a plurality of separation devices that separate chromite from the chromite-containing slurry,
a mixing vessel having a cylindrical shape and a plurality of weirs movable in the vertical direction, the number of which is equal to the number of separation devices, and a stirrer provided in the center of the mixing vessel, wherein the supply portions of the separation devices are located lower than the upper ends of the weirs when they are at their lowest positions , and the inner wall surface of the mixing vessel is provided with a plurality of flow paths having open upper and lower ends for guiding the chromite-containing slurry overflowing the weirs . 2. The apparatus for distributing a chromite-containing slurry according to claim 1 , wherein a difference in height between upper ends of the plurality of weirs when they are located at their lowest position and supply portions of the plurality of separation devices is 3 m or more. 3. The apparatus for distributing a chromite-containing slurry according to claim 1 or 2 , wherein a flow rate of the chromite-containing slurry overflowing each of the plurality of weirs is 10 m ³ /hr or more and 200 m ³ /hr or less. A method for recovering chromite contained in an ore slurry prepared by crushing nickel oxide ore used as a raw material in a nickel hydrometallurgy process and then adding water, comprising the steps of:
3. A method for recovering chromite comprising: a centrifugation step of introducing the ore slurry into a hydrocyclone to separate it into a chromite-containing slurry and a chromite-free ore slurry; and a separation step of distributing the chromite-containing slurry to a plurality of separation devices and introducing the slurry into each of the separation devices to separate fine particles contained in the chromite-containing slurry, wherein the distribution device according to claim 1 or 2 is used for distributing the chromite-containing slurry. 5. The method for recovering chromite according to claim 4 , wherein the ore slurry has a particle size of 45 μm or more and 1.4 mm or less.

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