JP7735851B2 - Nickel oxide ore smelting method - Google Patents

Description

The present invention relates to a method for smelting nickel oxide ore, in which ferronickel is produced by reducing a mixture of nickel oxide ore (raw material) and a carbonaceous reducing agent.

Known methods for smelting nickel oxide ores called limonite or saprolite include the pyrometallurgical method, which uses a smelting furnace to produce nickel matte, the pyrometallurgical method, which uses a rotary kiln or moving hearth furnace to produce ferronickel, and the hydrometallurgical method, which uses an autoclave to produce mixed sulfides.

When smelting nickel oxide ore, the raw ore is first treated to agglomerate, form a slurry, etc. (a "pretreatment" prior to the reduction process). Specifically, in this pretreatment, the nickel oxide ore is agglomerated, i.e., converted from powder or fine particles into agglomerates. Typically, the ore is first mixed with components other than the nickel oxide ore, such as a binder and a reducing agent, to form a mixture. After adjusting the moisture content, the mixture is then loaded into an agglomeration machine to form agglomerates (pellets, briquettes, etc.; hereafter simply referred to as "pellets") of approximately 10 mm to 30 mm in size.

Pellets require a certain degree of breathability, for example, to allow moisture to evaporate. Furthermore, if reduction is not carried out uniformly within the pellet, the composition may become uneven, causing the metal to disperse and become unevenly distributed. For this reason, it is important to mix the mixture uniformly and maintain as uniform a temperature as possible during pellet reduction.

In addition, it is also important to coarsen the ferronickel produced by reduction. If the ferronickel produced is, for example, a few tens to a few hundreds of microns in size, it becomes difficult to separate from the slag, and the yield of ferronickel drops significantly. For this reason, a technology is needed to effectively coarsen the ferronickel produced after reduction.

In addition, in recent years, ores with high nickel grade and few impurities have become scarce, so in order to produce high-quality ferronickel, it is necessary to efficiently process a variety of ores and accumulate data.

For example, a small amount of pellets may be loaded into a reduction furnace, reduction treatment performed, and the resulting reduced product removed to examine various properties. However, the treatment temperature is high, around 1000°C to 1500°C, making loading and unloading pellets difficult. Previously, such operations involved loading pellets into the furnace and unloading the resulting reduced product using a special ladle made of metal that can withstand relatively high temperatures. However, the high temperature would cause the ladle to bend, resulting in problems such as the ladle getting caught on the furnace wall during removal, making it take longer than necessary and making it difficult to obtain accurate findings.

Furthermore, not just reduction furnaces, but furnaces in general require openings for the loading and unloading of samples and other processed products. To prevent oxygen entrapment, heat diffusion, and the influence of outside air, it is preferable for the opening to be small. However, particularly in the case of relatively small-scale furnaces such as test furnaces, the opening size tends to be relatively large, which can lead to errors in the data obtained from tests.

Furthermore, if the furnace opening is made smaller, there is the problem that when using a ladle to remove samples, the ladle tends to get caught on the furnace wall, making it difficult to remove. If the ladle cannot be removed smoothly, accurate data on the reduction status inside the furnace cannot be obtained, making it difficult to reflect this in operations.

In addition, in small furnaces, it is generally not easy to stably adjust and maintain the degree of reduction inside the reduction furnace, which is at a high temperature. For example, if a burner or other device is used to heat the reduction furnace, a large amount of air is used for fuel combustion, and oxygen contamination is unavoidable. On the other hand, if coal or LNG is used as heating fuel, the fuel contains moisture and water is generated during combustion, which can accelerate the oxidation of the ferronickel metal produced.

As described above, in order to efficiently obtain ferronickel metal by mixing nickel oxide ore with a carbonaceous reducing agent and reducing it, it was necessary to be able to carry out various experiments accurately and efficiently.

Japanese Patent Application Laid-Open No. 2018-178252

The present invention was proposed in light of the above-mentioned circumstances, and aims to provide a smelting method for producing ferronickel by reducing a mixture containing nickel oxide ore, which minimizes deterioration in the quality of the reduced product obtained and enables ferronickel to be produced through efficient operations.

After extensive research, the inventors discovered that the above-mentioned problems could be solved by using a reduction furnace equipped with a heat treatment section that heats the mixture to perform a reduction process and a coal throwing section connected to the heat treatment section, and by moving the mixture from the heat treatment section to the coal throwing section midway through the reduction process and supplying additional carbonaceous reducing agent to the mixture. When additional carbonaceous reducing agent is supplied, the bottom plate of the reducing agent container located above the coal throwing section is slid out and removed, allowing the carbonaceous reducing agent inside the reducing agent container to fall and be supplied to the mixture. This led to the completion of the present invention.

(1) The first aspect of the present invention is a method for smelting nickel oxide ore, which produces ferronickel by reducing a mixture containing nickel oxide ore as raw ore and a carbonaceous reducing agent, and includes a mixing process for mixing the nickel oxide ore with the carbonaceous reducing agent, and a reduction process for charging the mixture into a reduction furnace and heating the mixture to perform a reduction process. In the reduction process, the reduction furnace is equipped with a heat treatment section for heating the mixture to perform a reduction process, and a coal injection section connected to the heat treatment section, and a reducing agent storage container containing a carbonaceous reducing agent is installed at the top of the coal injection section. The reducing agent storage container has a bottom plate that can slide horizontally and and a plurality of partition plates that are erected vertically at predetermined intervals from the bottom plate and divide the interior into a plurality of spaces. During the reduction process, the mixture is moved from the heat treatment section to the coal throwing section, and a carbonaceous reducing agent is additionally supplied to the mixture in the coal throwing section. The mixture to which the carbonaceous reducing agent has been added is then moved again to the heat treatment section and subjected to reduction treatment. When additional carbonaceous reducing agent is added in the coal throwing section, the bottom plate of the reducing agent storage container provided above the coal throwing section is slid and removed, causing the carbonaceous reducing agent in the reducing agent storage container to drop and be supplied to the mixture. This is a method for smelting nickel oxide ore.

(2) The second aspect of the present invention is a method for smelting nickel oxide ore according to the first aspect, in which, after the reduction treatment is completed, the resulting reduced material is moved to the coal-throwing section and cooled in the coal-throwing section.

(3) A third aspect of the present invention is a method for smelting nickel oxide ore according to the first or second aspect, wherein the coal-feeding section in the reduction furnace has a structure that allows gas replacement.

(4) A fourth aspect of the present invention is a method for smelting nickel oxide ore according to any one of the first to third aspects, wherein in the reduction step, a sample ladle having a handle and a sample mounting portion connected to the tip of the handle is used, the mixture is placed on the sample mounting portion while the reduction treatment is carried out in the heat treatment portion of the reduction furnace, and the mixture is moved between the heat treatment portion and the coal throwing portion in the reduction furnace by moving the sample ladle.

(5) A sixth aspect of the present invention is a method for smelting nickel oxide ore according to any one of the first to fourth aspects, wherein the reduction step involves performing reduction treatment at a reduction temperature of 1200°C or higher and 1500°C or lower.

According to the present invention, in a smelting method for producing ferronickel by reducing a mixture containing nickel oxide ore, deterioration in the quality of the resulting reduced product can be suppressed and ferronickel can be produced through efficient operations.

FIG. 1 is a process diagram showing the flow of a method for smelting nickel oxide ore. FIG. 1 is a diagram showing an example of the configuration of a reducing furnace, and is a diagram for explaining the configuration of a heat treatment unit that serves as a main body of the reducing furnace. FIG. 2 is a diagram showing an example of the configuration of a reduction furnace, illustrating the configuration of a coal throwing unit connected to a heat treatment unit of the reduction furnace. FIG. 4 is a diagram for explaining the configuration of a reducing agent storage container in a coal throwing section. FIG. 2 is a top view of the reducing agent storage container; FIG. 2 is a diagram showing an example of the configuration of a sample ladle.

Specific embodiments of the present invention (hereinafter referred to as "present embodiments") are described in detail below. Note that the present invention is not limited to the following embodiments, and various modifications are possible without departing from the spirit of the present invention. Furthermore, in this specification, the expression "X to Y" (X and Y are arbitrary numerical values) means "greater than or equal to X and less than or equal to Y."

≪1. Nickel oxide ore smelting method≫
In the method for smelting nickel oxide ore according to the present embodiment, nickel oxide ore, which is a raw material ore, is mixed with a carbonaceous reducing agent, and the mixture is subjected to a reduction treatment in a smelting furnace (reduction furnace), thereby producing ferronickel metal and slag.

Specifically, the method for smelting nickel oxide ore includes at least a mixing process in which nickel oxide ore is mixed with a carbonaceous reducing agent, and a reduction process in which the resulting mixture is charged into a reduction furnace and heated to perform a reduction process.

In this case, in the smelting method according to this embodiment, the reduction process is carried out using a reduction furnace equipped with a heat treatment section that heats the mixture and performs the reduction process, and a coal throwing section connected to the heat treatment section. During the reduction process, the mixture is moved from the heat treatment section of the reduction furnace to the coal throwing section, and additional carbonaceous reducing agent is supplied to the coal throwing section. The mixture to which the additional carbonaceous reducing agent has been supplied is then moved again to the heat treatment section and reduced.

The reduction furnace used has a reducing agent container containing a carbonaceous reducing agent located at the top of the coal-feeding section. The reducing agent container has a horizontally slidable bottom plate and multiple partition plates that stand vertically at predetermined intervals from the bottom plate and divide the interior into multiple spaces. When additional carbonaceous reducing agent is to be supplied to the coal-feeding section of the reduction furnace, the bottom plate of the reducing agent container located at the top of the coal-feeding section is slid and removed, allowing the carbonaceous reducing agent inside the reducing agent container to fall and be supplied to the mixture.

This method allows for the uniform addition of carbonaceous reducing agent through extremely simple operations, making it possible to re-reduce metal that has been partially oxidized by oxygen or moisture during the reduction process. This makes it possible to efficiently produce ferronickel metal with improved quality and properties.

As will be described in more detail below, preferably, a sample ladle having a handle and a sample mounting portion connected to the end of the handle is used, and the mixture is placed on the sample mounting portion while the reduction treatment is carried out in the heat treatment portion of the reduction furnace. The mixture is moved between the heat treatment portion and the coal feeding portion of the reduction furnace by moving the sample ladle. This method allows the mixture to be moved appropriately with simple operations to supply additional carbonaceous reducing agent, and can then be returned to the heat treatment portion to continue the reduction treatment. This makes it possible to efficiently produce ferronickel while minimizing deterioration in quality.

≪2. About the smelting process≫
As described above, the method for smelting nickel oxide ore involves heating a mixture of nickel oxide ore, which is a raw material ore, and a carbonaceous reducing agent in a reduction furnace to reduce nickel (nickel oxide) and iron (iron oxide), thereby producing metal of an iron-nickel alloy (ferronickel).Ferronickel can be obtained by separating the metal from the reduction product obtained by the reduction treatment (separating the metal from the slag).

Specifically, as shown in FIG. 1, the nickel oxide ore smelting method according to this embodiment includes a mixing process S1 in which a raw material containing nickel oxide ore is mixed with a carbonaceous reducing agent; a mixture forming process S2 in which the resulting mixture is formed into a predetermined shape; a reduction process S3 in which the formed mixture is reduced and heated at a predetermined reduction temperature in a reduction furnace; and a recovery process S4 in which the metal and slag produced in the reduction process S3 are separated and the metal is recovered.

[Mixing process]
The mixing step S1 is a step of mixing raw material powders containing nickel oxide ore to obtain a mixture. Specifically, the raw material ore, nickel oxide ore, is mixed with a carbonaceous reducing agent, and optional additives such as iron ore, flux components, and binders, each having a particle size of about 0.2 mm to 0.8 mm, are mixed to obtain a mixture. The mixing process can be performed using a mixer or the like.

In the mixing process S1, kneading may be performed to improve mixability. For example, by kneading the mixture using a twin-screw kneader or the like, shear force is applied to the mixture, which breaks down agglomerations of the carbonaceous reducing agent, raw material powder, etc., resulting in more uniform mixing. This also increases the adhesion between particles, making it easier to perform a uniform reduction process on the resulting mixture.

The nickel oxide ore as the raw material ore is not particularly limited, and may be limonite ore, saprolite ore, etc. Nickel oxide ore contains nickel oxide (NiO) and iron oxide (Fe ₂ O ₃ ) as constituents.

As described above, in the mixing process S1, a specific amount of carbonaceous reducing agent is added to nickel oxide ore and mixed to form a mixture. The carbonaceous reducing agent is not particularly limited, but examples include coal powder and coke powder. It is preferable that the carbonaceous reducing agent has the same particle size as the nickel oxide ore, which is the raw material ore. Having the same particle size for the carbonaceous reducing agent and nickel oxide ore facilitates uniform mixing, which in turn allows the reduction reaction to occur uniformly, which is preferable.

The amount of carbonaceous reducing agent mixed is not particularly limited, but is preferably 50.0% or less, and more preferably 40.0% or less, when the amount of carbonaceous reducing agent required to properly reduce the nickel oxide and iron oxide that make up the nickel oxide ore is taken as 100%. Here, the amount of carbonaceous reducing agent required to properly reduce the nickel oxide and iron oxide can be rephrased as the sum of the chemical equivalent required to reduce all of the nickel oxide to nickel metal and the chemical equivalent required to reduce the iron oxide to iron metal (hereinafter also referred to as the "total chemical equivalents"). Thus, by setting the amount of carbonaceous reducing agent mixed at a ratio of 50.0% or less, when the total chemical equivalents are taken as 100%, the reduction reaction can proceed efficiently. The lower limit of the amount of carbonaceous reducing agent mixed is not particularly limited, but is preferably 10.0% or more, and more preferably 15.0% or more, when the total chemical equivalents are taken as 100%.

In addition to nickel oxide ore and carbonaceous reducing agent, iron ore may be added as an optional component, but is not limited to such. Examples include iron ore with an iron content of approximately 50% or more, and hematite obtained by hydrometallurgy of nickel oxide ore. Examples of binders include bentonite, polysaccharides, resins, water glass, and dehydrated cake. Examples of flux components include calcium oxide, calcium hydroxide, calcium carbonate, and silicon dioxide.

Table 1 below shows an example of the composition (weight %) of some of the raw material powders mixed in the mixing process S1. Note that the composition of the raw material powders is not limited to this.

[Mixture forming process]
The mixture forming step S2 is a step of forming the mixture obtained in the mixing treatment step S1. Specifically, the mixture obtained by mixing the raw material powders is formed into a mass of a certain size or larger so that the mixture can be loaded, for example, in a stacked form, into a reduction furnace during the reduction treatment in the subsequent reduction step S3.

The agglomerates (also called pellets) obtained by molding the mixture can be cuboid, cylindrical, spherical, or other shapes. Such shapes make it easy to mold the mixture and reduce molding costs. Furthermore, because these shapes are not complex, there are almost no defective products and the molding yield is extremely high. Furthermore, rectangular, cylindrical, or spherical shapes make it easy to stack them in the reduction furnace, making it possible to increase the amount processed during reduction. Furthermore, the amount processed during reduction can be increased without making each pellet larger, they are easy to handle, and they do not collapse when loaded into the reduction furnace, making it less likely to produce defects.

The volume of the pellets of the molded (agglomerated) mixture is not particularly limited, and can be, for example, 8000 ^mm3 or more. If the pellet volume is too small, the molding cost will be high and it may be troublesome to charge them into a reduction furnace. Furthermore, if the pellet volume is small, the proportion of the surface area in the entire pellet will be high, which will make it easier to see differences in reduction between the surface and the interior, and may affect the quality of ferronickel. By setting the volume of the pellets of the mixture to 8000 ^mm3 or more, molding costs can be reduced and handling is easy, which is preferable. Furthermore, high-quality ferronickel can be produced.

After the mixture has been molded, it may be subjected to a drying process. Depending on the moisture content of the mixture, the rapid temperature rise during the reduction process may cause the moisture in the mixture to evaporate and expand all at once, causing the mixture to shatter. For this reason, a drying process may be performed after the mixture molding process to dry the mixture. For example, the drying process can be performed so that the solids content of the mixture is approximately 70% by weight and the moisture content is approximately 30% by weight.

There are no particular limitations on the method used to dry the mixture; for example, hot air at 150°C to 400°C can be blown onto the lumps to dry them. Note that if the mixture is in relatively large chunks, it is acceptable for the mixture to have cracks or fissures before or after drying. For large chunks, even if the surface area increases due to cracks, the impact is minimal.

Table 2 below shows an example of the solid composition (parts by weight) of the mixture (after drying). Note that the composition of the mixture is not limited to this.

[Reduction process]
(Regarding reduction treatment)
In the reduction step S3, the mixture (molded product) obtained in the mixture molding step S2 is heated in a reduction furnace to a predetermined reduction temperature. This reduction treatment causes a smelting reaction (reduction reaction) of the mixture containing nickel oxide ore to proceed, producing metal and slag.

The temperature for the reduction treatment (reduction temperature) is preferably 1200°C or higher and 1500°C or lower, and more preferably 1250°C or higher and 1450°C or lower. By setting the reduction temperature within this range, the reduction reaction can proceed efficiently and reliably, resulting in ferronickel with the desired properties.

During the reduction process, the slag in the mixture becomes semi-molten, resulting in a mixture of liquid and solid phases, but the metal and slag that have already separated do not mix together, and subsequent cooling results in a mixture of separate phases: metal solid and slag solid. The volume of this mixture has shrunk to about 50% to 60% of the volume of the mixture being charged.

(Regarding the reduction furnace)
In the present embodiment, a reduction furnace used in the reduction treatment is characterized in that it includes a heat treatment section that heats the mixture to perform the reduction treatment, and a coal throwing section that is connected to the heat treatment section.

Figure 2 is a perspective view of a reduction furnace, illustrating the configuration of the heat treatment section, which forms the main body of the reduction furnace. As shown in Figure 2, the reduction furnace 1 can be a box-shaped furnace. Inside this box-shaped furnace body, a reduction process is carried out in which the mixture to be treated is heated and reduced. In other words, the reduction furnace 1 forms the heat treatment section 11.

The reduction furnace 1 is not particularly limited, but can be a burner furnace in which a burner 12 is installed at a predetermined position and the reduction process is carried out by heating with the burner. Using burner heating (burner furnace) as the heating method for the reduction furnace 1 is preferable, as it allows the interior of the heat treatment section 11 to be heated with excellent combustibility. The burner fuel can be any of gaseous fuels such as LPG, liquid fuels such as heavy oil, and solid fuels such as coal and coke, but LPG is preferred due to its superior combustibility.

The heat treatment section 11 is provided with a sample stage 13 placed in contact with a predetermined surface of the box (the inner surface of the furnace). The sample stage 13 is a stage on which the mixture to be treated is placed and the reduction treatment is carried out. A reducing agent such as a carbonaceous reducing agent may be laid on the top surface of the sample stage 13. As will be described in detail later, the reduction treatment is carried out using a sample ladle 3 having a handle 31 and a sample placement portion 32 connected to the tip of the handle 31, with the mixture to be treated placed on the sample placement portion 32 (see Figure 3). Therefore, the sample ladle 3 with the mixture placed on it is placed on the sample stage 13.

A partition plate 11a is provided on the side of the heat treatment section 11 to separate the inside from the outside. The partition plate 11a has a door-like structure that can be opened and closed. In the heat treatment section 11, the mixture to be treated is loaded through the partition plate 11a, and the mixture and the reduced product obtained after treatment are removed through the partition plate 11a. The partition plate 11a can be made of a plate-shaped insulating board, brick, insulating wool, etc. In the heat treatment section 11, after the mixture to be treated is loaded inside, the partition plate 11a is closed and the reduction process is carried out. In this way, by the simple operation of closing the partition plate 11a, the internal space of the heat treatment section 11 can be made into an airtight space, preventing a drop in temperature within the heat treatment section 11.

The reduction furnace 1 also has an exhaust port 14, for example on its upper surface (ceiling surface), for exhausting gas from within the furnace (inside the heat treatment section 11).

Figure 3 is a side view of the reduction furnace 1 and is a diagram illustrating the configuration of the coal throwing unit 21 connected to the heat treatment unit 11 of the reduction furnace 1. As shown in Figure 3, in the reduction furnace 1, the coal throwing unit 21 is connected to the heat treatment unit 11. The coal throwing unit 21 has, for example, a box-like shape similar to the heat treatment unit 11, and is connected to a predetermined surface of the heat treatment unit 11.

The heat treatment section 11 and the coal throwing section 21 are connected via the partition plate 11a in the heat treatment section 11 and the partition plate 21a on the heat treatment section 11 side in the coal throwing section 21. Like the partition plate 11a in the heat treatment section 11, the partition plate 21a in the coal throwing section 21 also has a door-like structure that can be opened and closed. Therefore, the mixture to be treated is loaded into the coal throwing section 21, and then passes through the door-like partition plates 21a and 11a and is loaded into the heat treatment section 11.

The partition plate 21a can also be made of a plate-shaped insulating board, brick, insulating wool, etc. Furthermore, the partition plate 11a of the heat treatment section 11 and the partition plate 21a of the coal throwing section 21 can be constructed with a common structure.

In the coal throwing section 21, a carbonaceous reducing agent is supplied to the mixture being treated. More specifically, during the reduction process, the mixture is moved from the heat treatment section 11 to the coal throwing section 21, and then additional carbonaceous reducing agent is supplied to the mixture at the coal throwing section 21. The process for supplying additional carbonaceous reducing agent will be described in detail later. Furthermore, prior to the start of the reduction process, the coal throwing section 21 may supply carbonaceous reducing agent to the mixture being charged into the heat treatment section 11 via the coal throwing section 21, or to the surrounding area of the mixture (the sample placement area of the sample ladle). In this way, the coal throwing section 21 functions as a reducing agent supply chamber for the mixture.

A reducing agent container is fixed to the upper part of the coal-feeding section 21. The reducing agent container contains a carbonaceous reducing agent and is a so-called supply device that allows additional carbonaceous reducing agent to be added to the mixture with simple operation.

Figure 4 shows an example of the internal configuration of the coal throwing section 21, and in particular is a diagram to explain the configuration of the reducing agent storage container provided within the coal throwing section 21. The reducing agent storage container 4 has a dish-shaped storage section 41 that stores a carbonaceous reducing agent, and a support rod 42 that supports and fixes it to the upper part of the coal throwing section 21.

In the reducing agent storage container 4, the storage section 41 stores the carbonaceous reducing agent by placing it on the bottom plate 41a, which forms the bottom surface of the dish-shaped recess. As described above, the reducing agent storage container 4 is fixedly installed above the coal-feeding section 21. When adding additional carbonaceous reducing agent from the reducing agent storage container 4 to the mixture, the mixture is placed in a position facing the bottom surface (the back surface of the bottom plate 41a) of the reducing agent storage container 4, and the bottom plate 41a of the reducing agent storage container 4 is slid horizontally and removed, as described below, to allow the carbonaceous reducing agent to fall downward and be supplied. Note that Figure 4 shows the sample placement section 32 of the sample ladle 3, which will be described in detail later, positioned in a position facing the bottom surface of the reducing agent storage container 4.

More specifically, in the reducing agent storage container 4, the support rod 42 is used to fix and support the reducing agent storage container 4 above the coal throwing section 21. One end of the support rod 4 is connected to the wall surface of the coal throwing section 21, and the other end is connected to the reducing agent storage container 4, and the reducing agent storage container 4 is fixed to the top of the coal throwing section 21 via this support rod 4.

As described above, the reducing agent storage container 4 is equipped with a bottom plate 41a that forms the bottom (floor surface, mounting surface) of the storage section 41. The bottom plate 41a is configured to be slidable horizontally (laterally). By sliding the bottom plate 41a, the bottom of the storage section 41 of the reducing agent storage container 4 opens, allowing the carbonaceous reducing agent placed on the bottom plate 41a to fall downward.

Here, Figure 5 is a top view of the reducing agent storage container 4 as viewed from above. The reducing agent storage container 4 is provided with multiple partition plates 43 that stand vertically from the bottom plate 41a that forms the bottom of the storage section 41. Note that "standing vertically from the bottom plate 41a" means that the ends of the partition plates 43 are in contact with the bottom plate 41a and are arranged vertically relative to the surface of the bottom plate 41a. As shown in Figure 5, the partition plates 43 are arranged to divide, i.e., partition, the interior of the storage section 41 into multiple spaces.

A slide rod 5 is connected to the end of the bottom plate 41a of the reducing agent storage container 4 for sliding the bottom plate 41a horizontally (in the direction of arrow H in Figures 4 and 5). The bottom plate 41a itself slides horizontally when the connected slide rod 5 is grasped and moved horizontally. As shown in the example configuration of the coal throwing section 21 in Figure 4, a bottom plate removal hole 21c is provided in the wall of the coal throwing section 21, specifically in the same wall surface where the loading/unloading opening 21b (described below) is provided. Therefore, in the reducing agent storage container 4, by sliding the bottom plate 41a with the slide rod 5 and pulling it out through the bottom plate removal hole 21c, the bottom plate 41a can be removed from the coal throwing section 21 and the bottom of the storage section 41 of the reducing agent storage container 4 can be opened.

With this configuration, the carbonaceous reducing agent stored in the storage section 41 can be efficiently and effectively added to the mixture by simply sliding the bottom plate 41a of the reducing agent storage container 4 horizontally to remove it.

Furthermore, in the reducing agent storage container 4, multiple partition plates 43 are provided vertically from the bottom plate 41a. By removing the bottom plate 41a to allow the carbonaceous reducing agent to fall, the carbonaceous reducing agent can be uniformly supplied to the mixture. For example, if a bottom plate without partition plates, such as the one described above, were to be removed by sliding it horizontally to open the bottom of the storage compartment and allow the carbonaceous reducing agent to fall, the sliding of the bottom plate could cause the carbonaceous reducing agent to fall unevenly in the direction of the slide, resulting in an uneven supply to the mixture. In this regard, in the present embodiment, the sliding-removable bottom plate 41a is provided with multiple partition plates 43 that are vertically provided in contact with the bottom plate 41a. Therefore, even when the bottom plate 41a is slid horizontally, the upright partition plates 43 act as walls (resistors) to prevent the carbonaceous reducing agent from falling unevenly. This allows the carbonaceous reducing agent to fall evenly to the mixture located below, suppressing variations in reduction and enabling effective reduction processing.

The coal throwing section 21 also functions as a cooling chamber for cooling the reduced material obtained after reduction treatment in the heat treatment section 11. After reduction treatment in the heat treatment section 11, the reduced material obtained is moved to the coal throwing section 21 via door-like partition plates 11a, 21a, where it is cooled to a predetermined temperature.

The coal throwing section 21 preferably has a structure capable of replacing the atmospheric gas. The replacing gas is preferably an inert gas. By flowing an inert gas to replace the atmosphere, oxidation of the generated metal can be suppressed, even when additional carbonaceous reducing agent is supplied to the mixture in the coal throwing section 21 during the reduction process, as described in detail below. Furthermore, when the resulting reduced product is cooled in the coal throwing section 21, the circulating inert gas acts as a cooling gas to promote cooling. Furthermore, the use of an inert gas during cooling can suppress oxidation of the resulting reduced product (metal), preventing deterioration in quality. The inert gas is not particularly limited, but can be nitrogen, argon, or the like, as these are relatively inexpensive and readily available. Carbon dioxide is also acceptable.

The coal-throwing section 21 is provided with a loading/unloading port 21b opposite the partition plate 21a, through which the mixture to be treated is charged and through which the reduced material obtained by the reduction treatment is removed. The loading/unloading port 21b is a lid, and like the partition plate 21a, has a door-like structure that can be opened and closed. It is also preferable that the loading/unloading port 21b be a double-door structure to minimize air intrusion. When the mixture is charged into the coal-throwing section 21, the loading/unloading port 21b is open. During reduction treatment in the heat treatment section 11, when a reducing agent is supplied to the coal-throwing section 21, and when cooling in the coal-throwing section 21, each operation is performed with the loading/unloading port 21b closed.

(Regarding the reduction process)
In the reduction treatment using the reduction furnace 1 having the above-described configuration, first, the loading/unloading port 21b of the coal-feeding section 21 is opened and the material is loaded inside, and then the partition plates 11a and 21a are opened and the material is loaded into the heat treatment section 11 connected to the coal-feeding section 21, and then the material is placed on the sample stage 13.

During the reduction process, a sample ladle is used to load and unload the mixture sample to be treated. Figure 6 shows an example of the configuration of a sample ladle 3. The sample ladle 3 comprises a handle 31 and a sample mounting portion 32 connected to the tip of the handle 31. In the sample ladle 3, the handle 31 is the part that an operator holds by hand or mechanically and is composed of a rod-shaped body. The sample mounting portion 32 is connected to the tip of the handle 31, and the sample, i.e., the mixture to be treated, is placed on its upper surface (mounting surface 32a). Note that Figure 6 shows an example in which the sample mounting portion 32 is configured as a rectangular parallelepiped, but this is not limited to this. For example, the mounting surface for the sample mixture forms a recess, and the mounting surface may be configured like a container with upright walls on all four sides and an open top.

In the reduction process, the sample mixture is placed on the sample placement section 32 of the sample ladle 3, and then the handle 31 is grasped by hand or by machine and inserted into the coal-feeding section 21. The partition plates 11a and 21a are then opened from inside the coal-feeding section 21, and the handle 31 of the sample ladle 3 is pushed in, inserting the sample placement section 32 into the heat-treating section 11.

At this time, the sample ladle 3 placed inside the heat treatment section 11 is moved to near the center of the sample stage 13, and then the sample ladle 3 itself is placed on the sample stage 13. The reduction process begins in this state (with the sample ladle 3 containing the mixture still placed there). In other words, during the reduction process, heating begins while the sample ladle 3 remains inside the heat treatment section 11. This method allows the reduction process to be carried out simply by placing the mixture to be treated on the sample ladle 3 and then moving the sample ladle 3 into and out of the heat treatment section 11 via the coal injection section 21. This prevents erroneous operation, such as the mixture falling from the sample stage 13 when transferring the mixture from the sample ladle 3 onto the sample stage 13. It also prevents problems such as uneven heating by the burner.

In this case, ash or a carbonaceous reducing agent may be placed on the sample placement portion 32 of the sample ladle 3. This prevents the mixture from fusing to the placement surface of the sample placement portion 32.

Furthermore, when the sample ladle 3 is left in the heat treatment section 11, the main part of the handle 31 of the sample ladle 3 is located in the coal throwing section 21 (see Figure 3). By starting the reduction process with the handle 31 of the sample ladle 3 located within the coal throwing section 21, it is possible to prevent the handle 31 of the sample ladle 3 from being thermally deformed by the heat of the reduction process. Because the reduction process is performed under high-temperature conditions, for example, at approximately 1200°C to 1500°C, the handle 31 of the sample ladle 3 may be thermally deformed and bent. In this regard, by keeping the handle 31 located within the coal throwing section 21, thermal deformation can be prevented.

For example, by forming a semicircular hole, for example, at the lower end of the partition plates 11a, 21a separating the coal-throwing section 21 and the heat-treating section 11, through which the handle 31 of the sample ladle 3 can pass, the partition plates 11a, 21a can ensure airtightness within the heat-treating section 11 even when the sample ladle 3 is left inside the heat-treating section 11 and the partition plates 11a, 21a are closed.

In the method according to this embodiment, during the reduction process, the mixture being reduced is moved from the heat treatment section 11 to the coal throwing section 21, where additional carbonaceous reducing agent is supplied to the mixture. After that, the mixture to which the additional carbonaceous reducing agent has been supplied is moved back to the heat treatment section 11, and the reduction process continues.

In this way, by supplying additional carbonaceous reducing agent, i.e., by replenishing it, during the reduction process, it is possible to reduce again the metal that was partially oxidized by the oxygen and moisture contained in the combustion gas during the reduction process, thereby improving the quality and characteristics. Furthermore, when the mixture sample is heated again, the presence of the reducing agent on its surface helps to suppress oxidation.

Furthermore, as mentioned above, the coal-feeding section 21 is connected continuously to the heat treatment section 11. Therefore, even when replenishing the carbonaceous reducing agent to the mixture during the reduction process, the mixture can be done without being released into the atmosphere, preventing oxidation of the metal being produced.

Furthermore, in the method according to this embodiment, when additional carbonaceous reducing agent is supplied at the coal supply unit 21, the bottom plate 41a of the reducing agent storage container 4 provided above the coal supply unit 21 is slid and removed, causing the carbonaceous reducing agent in the reducing agent storage container 4 to fall through the open bottom of the reducing agent storage container 4 and be supplied to the mixture (see Figures 4 and 5). The configuration of the reducing agent storage container 4 is as described above, but this simple operation of horizontally sliding and removing the bottom plate 41a of the reducing agent storage container 4 and allowing the carbonaceous reducing agent to fall allows the carbonaceous reducing agent to be efficiently and effectively replenished to the mixture.

Furthermore, in the method according to this embodiment, even when the bottom plate 41a is slid horizontally, the upright partition plate 43 acts as a wall (resistance element) to prevent the carbonaceous reducing agent from shifting to one side. This allows the carbonaceous reducing agent to be uniformly dropped onto the mixture, suppressing variations in reduction and enabling effective reduction processing.

Here, the mixture is moved between the heat treatment section 11 and the coal throwing section 21 in the reduction furnace 1 by moving the sample ladle 3.

As described above, in the reduction process, the mixture to be treated is placed on the sample placement portion 32 of the sample ladle 3, and the reduction process is carried out in the heat treatment portion 11. When moving the mixture from the heat treatment portion 11 to the coal throwing portion 21 during the reduction process, the partition plates 11a, 21a are opened, and the handle 31 of the sample ladle 3 is grasped and the sample ladle 3 is pulled out from the coal throwing portion 21 side, moving the portion of the sample placement portion 32 on which the mixture is placed into the coal throwing portion 21. Then, in the coal throwing portion 21, carbonaceous reducing agent is added and replenished to the mixture placed on the sample placement portion 32.

When moving the mixture replenished with carbonaceous reducing agent back into the heat treatment section 11, the handle 31 of the sample ladle 3 is grasped and the sample ladle 3 is pushed out from the coal injection section 21 side, moving the sample placement section 32 containing the mixture into the heat treatment section 11. The reduction process is then continued in the heat treatment section 11.

In this way, the mixture can be moved between the heat treatment section 11 and the coal throwing section 21 by moving the sample ladle 3, allowing for smooth and reliable operation.

Furthermore, after the reduction process is completed, the partition plates 11a, 21a are opened from inside the coal throwing section 21, and the reduced material obtained by the reduction process is removed from the heat treatment section 11 via the coal throwing section 21.

When the reduced material is removed, it is cooled in the coal throwing section 21. As described above, the coal throwing section 21 has a structure that allows gas replacement by circulating an inert gas. This allows the circulating inert gas to act as a cooling gas, efficiently and quickly cooling the reduced material to a predetermined temperature. Furthermore, in the environment inside the coal throwing section 21, which is filled with inert gas, oxidation of the metal in the reduced material can be suppressed, preventing a deterioration in quality.

The reduced material is cooled in the coal throwing section 21 with the partition plates 11a, 21a closed from inside the coal throwing section 21. This prevents high-temperature heat from the heat treatment section 11 from entering the coal throwing section 21, allowing for efficient cooling. There are no particular restrictions on the cooling time as long as the reduced material can be cooled to the specified temperature, but it is preferably cooled for 10 minutes or more. Cooling for 10 minutes or more can lower the temperature of the reduced material to below 1000°C, and even if the reduced material is then removed from the coal throwing section 212, oxidation of the generated metal can be suppressed.

In addition, because the coal throwing section 21 is connected continuously to the heat treatment section 11, the reduced material obtained by the reduction process in the heat treatment section 11 can be cooled without being released into the atmosphere. If the reduced material heated to a high temperature were released directly into the atmosphere, oxidation of the generated metal would proceed rapidly, degrading the metal's properties and significantly reducing the metal recovery rate. In this regard, by performing the reduction process using a reduction furnace 1 in which the coal throwing section 21 is connected to the heat treatment section 11, the cooling operation for the high-temperature reduced material can be carried out efficiently in the coal throwing section 21, effectively preventing oxidation of the metal.

By performing the reduction process in reduction step S3 as described above, ferronickel can be produced accurately, reliably, and efficiently.

[Recovery process]
In the recovery step S4, the metal and slag produced in the reduction step S3 are separated and the metal is recovered. Specifically, the metal phase is separated and recovered from a mixture (inclusion) containing a metal phase (metal solid phase) and a slag phase (slag solid phase) obtained by subjecting the mixture filled in a container to a reduction heat treatment.

Methods for separating the metal and slag phases from the solid mixture of metal and slag phases include, for example, removing unwanted materials by sieving, as well as methods such as separation by specific gravity or magnetic force.

Furthermore, the resulting metal and slag phases can be easily separated due to their poor wettability. For example, by subjecting the large impurities obtained by the reduction process S3 described above to an impact, such as by dropping them over a predetermined drop or by applying a predetermined vibration during sieving, the metal and slag phases can be easily separated from the impurities.

By separating the metal phase and slag phase in this way, the metal phase, i.e., ferronickel, is recovered.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples in any way.

[Examples and Comparative Examples]
A nickel oxide ore smelting method was carried out to produce ferronickel by reducing a mixture of nickel oxide ore as a raw material ore and a carbonaceous reducing agent under the conditions shown below.

(Mixing process)
A mixture was obtained by mixing nickel oxide ore as raw ore, iron ore, silica sand and limestone as flux components, a binder, and a carbonaceous reducing agent (coal powder (pulverized coal): carbon content 73 wt %, average particle size approximately 73 μm) using a mixer while adding an appropriate amount of water. The carbonaceous reducing agent was contained in an amount that was 32.0% when the amount necessary to exactly reduce the nickel oxide and iron oxide (Fe ₂ O ₃ ) contained in the nickel oxide ore as raw ore was taken as 100%.

(Mixture forming process)
The resulting mixture was then granulated using a pan granulator and sieved to a size of φ15.0±0.8 mm. Thereafter, the sample was dried by blowing hot air at 170°C to 250°C onto it to achieve a solid content of approximately 70% by weight and a moisture content of approximately 30% by weight before reduction. Table 3 below shows the solid composition (excluding carbon) of the sample after drying.

(Reduction step)
Next, the sieved sample (mixture sample) was divided into 14 pieces (Examples 1 to 11, Comparative Examples 1 to 3), and each was heated in a reduction furnace (burner furnace) to undergo reduction treatment.

In this example, a reduction furnace 1 connected to a coal-throwing section 21, as shown in the schematic diagrams of Figures 2 to 5, was used. Specifically, the reduction furnace 1 was a box-shaped burner furnace equipped with a heat treatment section 11 that heated and reduced the mixture sample, and a coal-throwing section 21 connected to the heat treatment section 11. The coal-throwing section 21 had a structure that allowed for gas replacement with an inert gas. A reducing agent container 4 containing a carbonaceous reducing agent was provided above the coal-throwing section 21. The reducing agent container 4 was further provided with a horizontally slidable bottom plate 41a and multiple partition plates 43 that stood vertically at predetermined intervals from the bottom plate 41a and divided the interior into multiple spaces. Furthermore, in the reduction furnace 1, the coal-throwing section 21 and the heat treatment section 11 were connected via partition plates 21a and 11a made of plate-shaped insulating boards, and the partition plates 21a and 11a could be opened and closed from inside the coal-throwing section 21. The reduction furnace was equipped with a burner, and pulverized coal, LPG, heavy oil, and coke were used as fuel.

The sample mixture was charged into the reduction furnace 1 using a sample ladle 3 as shown in the schematic diagram of Fig. 6. The sample ladle 3 has a handle 31 and a sample mounting portion 32 located at the tip of the handle 31. Ash (mainly composed of _SiO2 with small amounts _of oxides such as _Al2O3 and MgO as other components) was spread on the upper surface of the sample mounting portion 32, and the mixture sample was placed on top of it.

When loading the mixture into the reduction furnace 1, the mixture sample placed on the sample ladle 3 was first loaded into the coal-feeding section 21 by opening the lid (loading/unloading port 21b) and then opening the partition plates 21a and 11a from the coal-feeding section 21 side, allowing the mixture sample to be loaded into the heat-treating section 11 and placed on the sample stage 13. The sample ladle 3 containing the mixture was then placed directly on the sample stage 13. The partition plates 11a and 21a were then closed, and the heat-treating section 11 was made into an airtight space, and heating with a burner was initiated to carry out the reduction process.

In addition, in this example, during the reduction process, specifically 8 minutes before the end of the reduction time, the mixture sample was returned from the heat treatment unit 11 to the coal throwing unit 21, and additional carbonaceous reducing agent (pulverized coal) was supplied from above the mixture sample. To supply additional carbonaceous reducing agent, the carbonaceous reducing agent was stored in the reducing agent storage container 4 located above the coal throwing unit 21, and after the mixture sample was returned to the coal throwing unit 21, the bottom plate 41a of the reducing agent storage container 4 was slid horizontally (sideways) and removed, allowing the carbonaceous reducing agent to fall from the open bottom and be supplied to the mixture sample.

The amount of pulverized coal added was 30% when the amount of pulverized coal in the mixture was 100%. When additional carbonaceous reducing agent was added, inert gas was supplied into the coal-feeding section 21.

After replenishment of pulverized coal, the material was moved back to the heat treatment section 11, where the reduction treatment continued.

After the specified reduction time had elapsed, the partition plates 21a and 11a were opened from inside the coal-throwing section 21, and the sample ladle 3 containing the resulting reduced product was removed. At this time, the reduced product was cooled within the coal-throwing section 21 without being released into the atmosphere. In the coal-throwing section 21, inert gas (nitrogen) was continuously circulated at a flow rate of 20 L/min, and the reduced product was cooled over a 15-minute cooling period using the inert gas as a cooling gas.

After cooling was completed, the reduced material was removed from the coal-throwing section 21 and the nickel metallization rate and nickel content in the metal were measured, as shown below.

On the other hand, in the comparative example, a reducing agent storage container was used that did not have a partition plate on the bottom plate. Other than this, the comparative example was the same as the example. That is, as in the example, when additional carbonaceous reducing agent (pulverized coal) was supplied from above the mixture sample during the reduction process, the bottom plate (which did not have a partition plate) of the reducing agent storage container containing the carbonaceous reducing agent was removed by sliding it horizontally, and the carbonaceous reducing agent was dropped through the open bottom. After the reduction process was completed, the reduced material was cooled and collected in the coal injection section 21.

[evaluation]
After cooling each sample, the nickel metallization rate and nickel content in the metal, defined by the following formula, were analyzed and calculated using an ICP emission spectrometer (SHIMAZU S-8100).
Nickel metal ratio = amount of metalized Ni in the mixture ÷ (total amount of Ni in the mixture) × 100 (%) ... [1] Nickel content in metal = amount of metalized Ni in the mixture ÷ (total amount of metalized Ni and Fe in the mixture) × 100 (%) ... [2]

Table 4 below shows the reduction treatment conditions and the calculated nickel metal ratio and nickel content in the metal.

As shown in Table 4, in Examples 1 to 11, in which the bottom plate 41a with the partition plate installed was removed by sliding it horizontally during the reduction process and additional carbonaceous reducing agent was dropped through the open bottom to perform the reduction process, both the nickel metallization rate and metal content were good. This is thought to be because the carbonaceous reducing agent could be uniformly added to the mixture during reduction, allowing the partially oxidized metal to be reduced again, resulting in a more thorough reduction process.

On the other hand, in Comparative Examples 1 to 3, in which additional carbonaceous reducing agent was supplied but the bottom plate, which did not have a partition plate, was slid open, both the nickel metallization rate and metal content were lower than in the Examples. This is thought to be because the sliding of the bottom plate caused the carbonaceous reducing agent to become significantly uneven, preventing it from being supplied evenly to the mixture sample, resulting in insufficient reduction treatment and making it impossible to re-reduce the partially oxidized metal.

REFERENCE SIGNS LIST 1 reduction furnace 11 heat treatment section 12 burner 13 sample stage 14 exhaust port 21 coal throwing section 11a, 21a partition plate 21b loading/unloading port 21c bottom plate removal hole 3 sample ladle 31 handle 32 sample placement section 4 reducing agent storage container 41 storage section 41a bottom plate 42 support rod 43 partition plate 5 slide rod

Claims (5)

A method for smelting nickel oxide ore to produce ferronickel by reducing a mixture containing nickel oxide ore as a raw material ore and a carbonaceous reducing agent, comprising:
a mixing step of mixing the nickel oxide ore with the carbonaceous reducing agent;
a reduction step of charging the mixture into a reduction furnace and heating the mixture to perform a reduction treatment;
Including,
In the reduction step,
The reduction furnace used is a furnace that includes a heat treatment section that heats the mixture to perform a reduction treatment, and a coal throwing section that is connected to the heat treatment section, and a reducing agent storage container that stores a carbonaceous reducing agent is provided at an upper part of the coal throwing section, and the reducing agent storage container is provided with a bottom plate that is slidable in the horizontal direction, and a plurality of partition plates that are vertically arranged at predetermined intervals from the bottom plate and divide the interior into a plurality of spaces,
In the course of the reduction treatment, the mixture is moved from the heat treatment section to the coal throwing section, and a carbonaceous reducing agent is additionally supplied to the mixture in the coal throwing section, and thereafter, the mixture to which the carbonaceous reducing agent has been additionally supplied is moved again to the heat treatment section, and a reduction treatment is performed thereon;
When the carbonaceous reducing agent is additionally supplied to the coal throwing unit, a bottom plate of the reducing agent storage container provided at the top of the coal throwing unit is slid and removed, so that the carbonaceous reducing agent in the reducing agent storage container falls and is supplied to the mixture.
A method for smelting nickel oxide ore. After the reduction treatment is completed, the obtained reduced material is moved to the coal throwing section and cooled in the coal throwing section.
The method for smelting nickel oxide ore according to claim 1. The coal throwing section in the reduction furnace has a structure capable of gas replacement.
3. The method for smelting nickel oxide ore according to claim 1 or 2. In the reduction step,
using a sample ladle having a handle and a sample placement portion connected to the tip of the handle, and carrying out a reduction treatment in a heat treatment portion of the reduction furnace while the mixture is placed on the sample placement portion;
The mixture is moved between the heat treatment section and the coal throwing section in the reduction furnace by moving the sample ladle.
4. The method for smelting nickel oxide ore according to claim 1. In the reduction step,
A reduction treatment is carried out at a reduction temperature of 1200°C or higher and 1500°C or lower.
5. The method for smelting nickel oxide ore according to claim 1.