JP2024122340A - Method for smelting nickel oxide ore - Google Patents

Abstract

[Problem] To provide a method for smelting nickel oxide ore, which produces metal by reducing a mixture containing an oxide ore such as nickel oxide ore, and which can improve the grade of the metal obtained and efficiently produce high-quality metal. [Solution] The method for smelting nickel oxide ore includes a mixing process in which nickel oxide ore is mixed with a first reducing agent to obtain a mixture, and a reduction process in which the mixture is charged into a reduction furnace and reduced, in which a second reducing agent containing starch, charcoal, and coal is placed on the hearth of the reduction furnace, and the mixture is placed on top of the second reducing agent to perform the reduction process. [Selected Figure] Figure 1

Description

The present invention relates to a method for smelting nickel oxide ore.

Methods for smelting nickel oxide ore, known as limonite or saprolite, include the dry smelting method, in which nickel matte is produced by roasting with sulfur in a smelting furnace; the dry smelting method, in which a carbonaceous reducing agent is used in a rotary kiln or moving hearth furnace to reduce the ore and produce an iron-nickel alloy (hereafter also referred to as "ferronickel"); and the wet smelting method, in which nickel and cobalt are leached with sulfuric acid in an autoclave, and a sulfurizing agent is added to the leachate to produce a mixed sulfide.

Among the various smelting methods mentioned above, when nickel oxide ore is smelted by reduction together with a carbon source, first, pretreatment is carried out to turn the raw ore into agglomerates or slurry. Specifically, when turning nickel oxide ore into agglomerates, that is, turning it from powder or fine particles into agglomerates, the nickel oxide ore is generally mixed with a binder, a reducing agent, etc., and then the moisture is adjusted before being charged into a lump-making machine to turn it into agglomerates (pellets, briquettes, etc.; hereinafter simply referred to as "pellets") of, for example, about 10 mm to 30 mm in size.

These pellets need to have a certain degree of breathability to "evaporate" the moisture they contain. Also, if the reduction does not proceed uniformly within the pellets, the composition of the resulting reduced material will be non-uniform, leading to problems such as the metal being dispersed or unevenly distributed, so it is important to mix the mixture uniformly and to maintain as uniform a temperature as possible during the reduction process of the pellets.

In addition, it is also an important technology to coarsen the ferronickel produced by reduction. This is because if the ferronickel produced is fine, for example, tens to hundreds of microns in size, it becomes difficult to separate it from the slag produced at the same time, and the recovery rate (yield) of ferronickel drops significantly. For this reason, a process to coarsen the ferronickel after reduction is necessary.

In addition, keeping smelting costs as low as possible is also an important technical issue, and there is a demand for continuous processing that can be operated using compact facilities.

For example, Patent Document 1 discloses a method for producing granular metals in which agglomerates containing a metal oxide and a carbonaceous reducing agent such as coal or coke are supplied onto the hearth of a moving-bed type reduction melting furnace, heated, and the metal oxide is reduced and melted. The method discloses a method in which agglomerates having an average diameter of 19.5 mm to 32 mm are supplied onto the hearth and heated so that the laying density is 0.5 to 0.8, where the laying density is the relative value of the projected area ratio of the agglomerates onto the hearth to the maximum projected area ratio of the agglomerates onto the hearth when the distance between the agglomerates is 0. This method discloses that the productivity of granular metallic iron can be increased by controlling both the laying density and the average diameter of the agglomerates.

However, the method disclosed in Patent Document 1 is a technique for controlling the reaction that occurs outside the agglomerates, and does not focus on controlling the reaction that occurs inside the agglomerates, which is the most important factor in the reduction reaction. On the other hand, there is a demand for controlling the reaction that occurs inside the agglomerates to increase the reaction efficiency and progress the reduction reaction more uniformly, thereby obtaining a higher quality metal (metal, alloy).

In addition, the method of using a specific diameter as the agglomerates as described in Patent Document 1 has a low yield when producing agglomerates because it is necessary to remove those that do not have the specific diameter. In addition, the method described in Patent Document 1 has a low productivity because it is necessary to adjust the laying density of the agglomerates to 0.5 to 0.8 and it is not possible to stack the agglomerates. For these reasons, the method described in Patent Document 1 has high manufacturing costs.

Patent Document 2 also discloses a smelting method for producing metals by reducing a mixture containing an oxide ore such as nickel oxide ore, which increases the metal recovery rate and improves productivity, while also producing high-quality metals cheaply and efficiently.

Specifically, in a smelting method in which a mixture obtained by mixing an oxide ore with a carbonaceous reducing agent is heated and subjected to a reduction treatment to obtain a metal and slag as reduced products, the mixture is subjected to the reduction treatment in the presence of an oxidation inhibitor. As the oxidation inhibitor, for example, an oxide mixture having an oxide content of 90 mass% or more, or an oxidation inhibitor mixture containing an oxide mixture having an oxide content of 90 mass% or more and a carbonaceous reducing product is used. These oxidation inhibitors can be placed on the top surface of the mixture to allow them to coexist, or can be surrounded by the oxidation inhibitor to allow them to coexist.

However, even when using the method of Patent Document 2, it was not easy to control the atmosphere inside the furnace so as to completely suppress oxidation of the mixture, especially when using an industrial-scale furnace.

As such, the technology of mixing and reducing oxide ores to produce metals and alloys has many challenges in terms of increasing productivity, reducing manufacturing costs, and improving metal quality.

JP 2011-256414 A JP 2018-178219 A

The present invention aims to provide a method for smelting oxide ores, which produces metal by reducing a mixture containing an oxide ore such as nickel oxide ore, and which can improve the grade of the resulting metal and efficiently produce high-quality metal.

The inventors of the present invention have conducted extensive research to solve the above-mentioned problems. As a result, they discovered that the above problems could be solved by placing a reducing agent containing starch, charcoal, and coal on the hearth and placing the mixture on top of it in the reduction process, which 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 comprises a mixing process step of mixing nickel oxide ore with a first reducing agent to obtain a mixture, and a reduction process step of loading the mixture into a reduction furnace and subjecting it to a reduction process, in which a second reducing agent containing starch, charcoal, and coal is laid on the hearth of the reduction furnace, and the mixture is placed on top of the second reducing agent and subjected to a reduction process.

(2) The second aspect of the present invention is a method for smelting nickel oxide ore according to the first aspect of the present invention, in which the total content of starch and charcoal in the reduction step is 20% by mass or more and 80% by mass or less of the total amount of the second reducing agent.

The oxide ore smelting method of the present invention allows for efficient production of high-quality metals.

FIG. 1 is a process diagram showing an example of the flow of a method for smelting nickel oxide ore. TG/DTA measurement results of starch. TG/DTA measurement results of charcoal. 1 shows the TG/DTA measurement results of coal. FIG. 1 is a diagram (plan view) showing an example of the configuration of a reducing furnace (rotary hearth furnace).

Specific embodiments of the present invention 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. In this specification, the expression "X to Y" (X and Y are arbitrary numbers) means "X or more and Y or less."

1. Overview of the present invention
The present invention relates to a method for smelting an oxide ore, which uses nickel oxide ore as a raw material, and produces ferronickel metal as a reduction product by mixing the oxide ore with a reducing agent and reducing the resulting mixture.

This smelting method is characterized by placing a reducing agent containing starch, charcoal, and coal on the hearth of a reduction furnace, placing the mixture on top of it, and carrying out the reduction process.

According to this method, a reducing agent containing starch, charcoal, and coal is placed on the hearth and a reduction process is performed on a mixture containing nickel oxide ore, thereby improving the quality of the resulting metal.

Figure 1 is a diagram showing an example of the flow of a method for smelting nickel oxide ore. As shown in Figure 1, this smelting method includes a mixing process S1 in which nickel oxide ore is used as a raw material and mixed with a first reducing agent to obtain a mixture, an agglomeration process S2 in which the obtained mixture is formed into a predetermined shape to form pellets (agglomerates), a drying process S3 in which the pellets (mixture) are dried, a reduction process S4 in which the pellets (mixture) are subjected to a reduction process, and a separation process S5 in which slag is separated from the reduced material produced by the reduction to obtain ferronickel metal.

[Mixing process]
The mixing process S1 is a process for mixing raw material powders including nickel oxide ore to obtain a mixture. Specifically, a first reducing agent is added to the raw material nickel oxide ore and mixed, and powders of optional additives such as iron ore, flux components, binders, etc., each having a particle size of, for example, about 0.2 mm to 0.8 mm, are mixed to obtain a mixture.

The nickel oxide ore as the raw material ore is not particularly limited, but limonite ore, saprolite ore, etc. Representative components of nickel oxide ore include nickel oxide (NiO) and iron oxide (Fe ₂ O ₃ ).

The first reducing agent is not particularly limited, but examples thereof include carbonaceous reducing agents such as coal powder and coke powder. In addition, a part or all of the first reducing agent may be composed of a plant-derived component, such as starch. It is preferable that the carbonaceous reducing agent has a particle size and particle size distribution equivalent to that of the nickel oxide ore, which is the raw material ore, because this makes it easier to mix uniformly and the reduction reaction also tends to proceed uniformly.

The amount of the first reducing agent mixed is not particularly limited, but when the amount of reducing agent required to adequately reduce the nickel oxide and iron oxide that constitute the nickel oxide ore is taken as 100 mass%, it is preferably 25 mass%, more preferably 30 mass% or more, and even more preferably 35 mass%.

The upper limit of the amount of reducing agent mixed is not particularly limited, but is preferably 300% by mass or less, more preferably 200% by mass or less, more preferably 100% by mass or less, and even more preferably 50% by mass or less, when the total value of the chemical equivalents is 100%. The amount of reducing agent required to reduce nickel oxide and iron oxide without excess or deficiency can be defined as the total value of the chemical equivalent required to reduce all of the nickel oxide contained in the mixture to nickel metal and the chemical equivalent required to reduce the iron oxide contained in the mixture to iron metal (hereinafter also referred to as the "total value of chemical equivalents").

The iron ore, which is an optional additive, is not particularly limited, but examples include iron ore with an iron content of about 50% by mass or more, and hematite obtained by wet smelting 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 (mass%) 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.

In the mixing process S1, the raw material powder containing nickel oxide ore can be mixed using a mixer or the like. When the raw material powder is mixed to obtain a mixture, the raw material powder may be subjected to a kneading process to improve mixability. This applies shear force to the mixture, which breaks down agglomerations of the reducing agent, raw material powder, etc. and allows for more uniform mixing, improves the adhesion of each particle, and reduces voids, making it easier to perform a uniform reduction process and shortening the reaction time of the reduction reaction. It also reduces quality variation.

The kneading process can be carried out using a batch kneader such as a Brabender, a Banbury mixer, a Henschel mixer, a helical rotor, a roll, a single-screw kneader, a twin-screw kneader, or the like. By kneading the mixture, a shear force is applied to the mixture, which breaks down agglomerations of the reducing agent and raw material powder, etc., allowing for uniform mixing, improved adhesion between particles, and reduced voids. This makes it easier for the reduction reaction to occur in the mixture and allows the reaction to occur uniformly, shortening the reaction time for the reduction reaction. It also reduces quality variation.

Also, after mixing, or after mixing and kneading, the mixture may be extruded using an extruder. This applies pressure (shear force) to the mixture, breaking up agglomerations of the reducing agent, raw material powder, etc., and making the mixture more uniformly mixed. Furthermore, voids within the mixture can be reduced. As a result, the reduction reaction of the mixture is more likely to occur uniformly in the reduction step S3 described below, the quality of the resulting metal can be improved, and high-quality metal can be produced.

The extruder is preferably one that can knead and mold the mixture under high pressure and high shear force, and examples of such extruders include single-screw extruders and twin-screw extruders. In particular, one equipped with a twin-screw extruder is preferable. By kneading the mixture under high pressure and high shear force, it is possible to break up agglomerations in the mixture of raw material powders. In addition, it is possible to effectively knead the mixture, and the strength of the mixture can be increased. Furthermore, by using an extruder equipped with a twin-screw extruder, it is possible to obtain the mixture while maintaining a continuous high productivity.

<2-2. Clumping process>
The agglomeration step S2 is a step of forming the mixture of raw material powders obtained in the mixing step S1 into pellets. The agglomeration step is not an essential step, but it is necessary to form the mixture into a predetermined shape. The pellets may have any shape as long as they can be stacked on the hearth of the reduction furnace, and may be, for example, spherical, rectangular, cubic, cylindrical, or other shapes. It is preferable. By molding the mixture into such a shape, molding of the mixture becomes easy, and therefore the cost of molding can be reduced. In addition, since the shape to be molded is not complicated, the occurrence of defective pellets can be reduced. This can reduce the amount of oxygen that can be absorbed, and the strength of the pellets can be easily maintained.

Among these, it is preferable that the pellets have a shape that allows them to be placed on the hearth as densely as possible, for example an elliptical or cylindrical shape. By placing the pellets on the hearth of the reduction furnace at a high density and carrying out the reduction process, the proportion of oxygen and water that is inevitably contained and consumed is reduced, and therefore the reducing atmosphere can be maintained efficiently.

In the agglomeration step S2, the mixture can be molded using, for example, a pellet molding device. There are no particular limitations on the pellet molding device, but it is preferable that the pellet molding device is capable of kneading and molding the mixture at high pressure and high shear force. By kneading the mixture at high pressure and high shear, it is possible to break up agglomerations in the raw material powder mixture, to effectively knead the mixture, and to increase the strength of the resulting pellets.

<2-3. Drying treatment>
In the drying step S3, the obtained pellets are subjected to a drying process. Although the drying step is not essential, the lumps obtained by the pellet-shaped agglomeration process contain excess moisture, for example, about 50% by mass. Therefore, if the pellets containing excess moisture are suddenly heated to the reduction temperature, the moisture may evaporate all at once, expand, and destroy the lumps. Therefore, by subjecting the obtained pellets to a drying process so that the solid content is about 70% by mass and the moisture content is about 30% by mass, the pellets can be prevented from collapsing in the reduction heat treatment in the next reduction step S3. This also prevents the pellets from becoming difficult to remove from the reduction furnace. Furthermore, since the pellets are often sticky due to excess moisture, the drying process can make them easier to handle.

The method for drying the pellets is not particularly limited, and any conventionally known method can be used, such as maintaining the pellets at a predetermined drying temperature (e.g., 200°C to 400°C) or blowing hot air at a predetermined drying temperature onto the mixture to dry it. This drying process can be used to make the pellets have a solid content of about 70% by mass and a moisture content of about 30% by mass. It is preferable that the temperature of the mixture itself during this drying process be less than 100°C, which can prevent the mixture from bursting due to bumping of moisture, etc.

This drying process may be carried out outside the reduction furnace, which will be described later, or the lumps may be placed in the reduction furnace, which will be described later, and the drying process may be carried out inside the furnace.

Here, when drying pellets that are particularly large in volume, it is acceptable for the pellets to have cracks or breaks before and after drying. When the pellets are large in volume, they melt and shrink during reduction, which often results in cracks and breaks. However, when the pellets are large in volume, the effects of cracks and breaks, such as an increase in surface area, are minimal, so it is unlikely to cause any major problems. Therefore, it is acceptable for the pellets to have cracks or breaks before reduction.

The drying process may be carried out continuously at once or in multiple steps. By carrying out the drying process in multiple steps, the mixture can be more effectively prevented from bursting. When the drying process is carried out in multiple steps, the drying temperature from the second step onwards is preferably 150°C or higher and 400°C or lower. Drying within this range makes it possible to dry without the reduction reaction proceeding.

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

<2-4. Reduction step>
In the reduction step S4, the pellets dried in the drying step S3 are subjected to a reduction treatment. Specifically, the obtained lumps (pellets) are placed on the hearth of a reduction furnace, and the mixture is subjected to a heating reduction treatment in the reduction furnace. The heating reduction treatment in the reduction step S4 causes a smelting reaction (reduction reaction) to proceed based on the reducing agent (first reducing agent) in the mixture, and ferronickel metal (hereinafter simply referred to as "metal") and ferronickel slag (hereinafter simply referred to as "slag") are generated separately in the mixture. In the following, the pellets to be subjected to the reduction treatment are referred to as a mixture for convenience.

In the heating reduction process, in a short time, for example about one minute, the nickel oxide and iron oxide in the mixture are first reduced and metalized to ferronickel near the surface of the mixture where the reduction reaction is most likely to occur, forming a shell. Meanwhile, within the shell, the slag components gradually melt as the shell forms, producing liquid slag. As a result, metal and slag are produced separately within the mixture.

After about 10 minutes of processing, the excess reducing agent that is not involved in the reduction reaction is absorbed into the metal, lowering its melting point and turning the metal into a liquid phase. This makes it possible to steadily increase the quality of the resulting metal, resulting in a high-quality metal.

In the reduction step S4, a second reducing agent containing starch, charcoal, and coal is laid on the hearth of the reduction furnace, and the mixture is placed on the bedding material and subjected to reduction treatment. One method for clarifying the behavior of a sample in a reduction furnace is to measure TG curves and DTA curves using a TG/DTA (differential thermal/thermogravimetric simultaneous measurement device). TG/DTA is a device that can simultaneously perform differential thermal analysis and thermogravimetry, and can clarify the behavior of a sample, such as decomposition and phase transition, when a temperature change is applied to the sample, using TG curves and DTA curves. Note that a TG curve represents the weight of a sample versus temperature, and a DTA curve represents the temperature difference between a sample and a reference material versus temperature.

FIG. 2 shows the TG curve and DTA curve of "starch" measured using TG/DTA. The TG curve of starch shows that the weight loss occurs rapidly at around 240°C when the temperature is increased from room temperature, and the DTA curve of starch shows a large maximum value at around 600°C. This shows that the decomposition temperature of starch is relatively low compared to the decomposition temperature of coal. Therefore, it is presumed that starch can proceed with a reduction reaction at a high reaction rate under relatively low temperature conditions. This is because starch is a polymer made of carbon, hydrogen, and oxygen, and the bond between the hydrogen and carbon is broken by the increase in temperature to generate _H2 gas, forming a porous structure, and the bond between the carbon atoms constituting starch is weak.

Figure 3 shows the TG and DTA curves of "charcoal" measured using TG/DTA. The TG curve of charcoal shows that weight loss occurs immediately when the temperature is raised from room temperature, and the DTA curve of charcoal shows a large maximum value around 600°C. This shows that the decomposition temperature of charcoal is relatively low compared to that of coal. For this reason, it is presumed that charcoal can promote reduction reactions at a high reaction rate under relatively low temperature conditions. This is because charcoal is produced by steaming the wood material to evaporate the moisture in the wood, resulting in a porous structure and weak bonds between the carbon atoms that make up the charcoal.

On the other hand, Figure 4 shows the TG and DTA curves of "coal" measured using TG/DTA. Compared to charcoal, the TG curve of coal shows that the weight hardly changes even when the temperature is raised from room temperature, and is also a broad curve. The weight loss at around 420°C is thought to be due to the decomposition and evaporation of volatile organic matter. This shows that the decomposition temperature of coal is relatively high compared to that of charcoal. Therefore, it is presumed that coal can proceed with reduction reactions for a long period of time under relatively high temperature conditions. This is because coal is a fossil fuel produced by the transformation (coalification) of plants and oxides by exposure to geothermal heat and geopressure for a long period of time, and therefore the carbon atoms derived from plants are concentrated, and the bonds between the carbon atoms that make up coal are strong.

In the smelting method according to the present embodiment, a second reducing agent containing starch and charcoal, which have a relatively low decomposition temperature and are substantially free of other components such as oxides, and coal, which has a relatively high decomposition temperature and may contain oxides, is laid on the hearth of a reduction furnace, and the mixture is placed on top of the second reducing agent and reduced. As a result, even if part of the metal obtained is reoxidized by oxygen inevitably mixed in from the recovery port or charging port, oxygen supplied by the burner, or water generated by the combustion of the burner fuel, it is possible to reduce it again by the second reducing agent containing starch, charcoal, and coal, and it is possible to suppress further oxidation of part of the obtained metal, thereby improving the quality of the obtained metal.

The phrase "laying the second reducing agent on the hearth of the reduction furnace" means that when the mixture is placed on the second reducing agent, the lower part of the mixture (the part placed on the mixture) comes into contact with the second reducing agent. For example, the second reducing agent may be laid on at least a part of the hearth of the reduction furnace, or the second reducing agent may be laid over the entire hearth of the reduction furnace.

In addition, placing the mixture on the second reducing agent does not necessarily mean that all of the mixture charged into the reduction furnace is placed on the second reducing agent, but may mean that at least a portion of the mixture charged into the reduction furnace is placed on the second reducing agent. For example, the mixture (pellets) may be shaped like an ellipse or a cylinder, and placed on the second reducing agent in several layers. This makes it possible to place the pellets on the hearth of the reduction furnace at a high density and perform the reduction process.

In addition, in order to prevent the second reducing agent on the hearth from being blown away by the combustion gas in the reduction furnace, the hearth surface of the reduction furnace may be shaped to have a depression, and the second reducing agent may be laid in the depression. This makes it possible to prevent the second reducing agent from being blown away from the hearth or from spilling off the hearth.

The material of the hearth of the reduction furnace is not particularly limited, and for example, brick or ceramics can be used. These materials will not react with the second reducing agent, and the hearth can be used for a long period of time without maintenance.

It is also possible to lay a hearth material on the hearth beforehand, and then lay the second reducing agent on top of the hearth material. By laying the hearth material on the hearth beforehand, the reaction between the hearth and the slag can be suppressed, and the hearth can be protected. An example of a material for the hearth material is silicon carbide (SiC). SiC (silicon carbide) is preferable because it has excellent durability at high temperatures, and even if the slag does soak into the hearth, it is less likely to react with the slag, and has a long life as a hearth material.

The starch content in the second reducing agent is not particularly limited, but is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, based on the total amount of the second reducing agent. The upper limit of the starch content in the second reducing agent is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less, based on the total amount of the second reducing agent.

The charcoal content in the second reducing agent is not particularly limited, but is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, based on the total amount of the second reducing agent. The upper limit of the charcoal content in the second reducing agent is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less, based on the total amount of the second reducing agent.

The coal content in the second reducing agent is not particularly limited, but is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, based on the total amount of the second reducing agent. The upper limit of the coal content in the second reducing agent is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less, based on the total amount of the second reducing agent.

The total content of starch and charcoal in the second reducing agent is not particularly limited, but is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, based on the total amount of the second reducing agent. The total content of starch and charcoal in the second reducing agent is not particularly limited, but is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less, based on the total amount of the second reducing agent.

The content ratio of starch and charcoal in the second reducing agent is not particularly limited, but the mixing ratio of the chemical equivalent of starch mixed with the nickel oxide ore and the chemical equivalent of charcoal mixed with the nickel oxide ore is preferably in the range of 30:70 to 70:30, more preferably in the range of 40:60 to 60:40, and even more preferably in the range of 45:55 to 55:45. By setting the ratio of the chemical equivalent of charcoal to starch in such a range, the quality of the obtained metal can be improved. The chemical equivalent is defined as the sum of the chemical equivalent required to reduce all of the nickel oxide contained in the mixture to nickel metal and the chemical equivalent required to reduce the iron oxide contained in the mixture to iron metal.

The total content of starch, charcoal, and coal in the second reducing agent is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, of the total amount of the second reducing agent, and it is most preferable that the second reducing agent is composed only of starch, charcoal, and coal (i.e., the total content of starch, charcoal, and coal is 100% by mass of the total amount of the reducing agent).

The second reducing agent contained in the bedding material may be a reducing agent different from starch, charcoal, and coal. An example of such a reducing agent is bamboo charcoal.

The amount of the second reducing agent contained in the bedding material is not particularly limited, but when the amount of reducing agent required to reduce the iron oxide and nickel oxide contained in the nickel oxide ore constituting the pellets without excess or deficiency is taken as 100 mass%, it is preferable that the amount is in the range of 3 mass% to 100 mass%, more preferably in the range of 5 mass% to 70 mass%, and even more preferably in the range of 7 mass% to 50 mass%. By making the amount of the second reducing agent 3 mass% or more, it is possible to more effectively suppress the reoxidation of the generated metal. In addition, by making the amount of the second reducing agent 100 mass% or less, it is possible to reduce the possibility of over-reduction, and therefore to suppress the deterioration of the nickel grade in the metal.

When using a plant-derived organic reducing agent such as charcoal or starch as the second reducing agent, there is a possibility that the plant-derived organic reducing agent in the mixture or the plant-derived organic reducing agent laid on the hearth of the reduction furnace may burn during the heating and reduction treatment. Therefore, it is preferable to perform the reduction treatment on the mixture in an atmosphere of low oxygen concentration inside the reduction furnace. For example, the reduction treatment is preferably performed in an atmosphere of low oxygen concentration, where the oxygen concentration is preferably 3.0% by volume or less, and more preferably 1.0% by volume or less. The reduction treatment may also be performed in an inert gas atmosphere such as nitrogen or argon.

The temperature in the reduction process (reduction temperature) is not particularly limited, but is preferably in the range of 1200°C to 1450°C, and more preferably in the range of 1300°C to 1400°C. By performing reduction within such a temperature range, the reduction reaction can occur uniformly, and ferronickel can be produced with reduced quality variation. Furthermore, by performing reduction at a reduction temperature in the range of 1300°C to 1400°C, the desired reduction reaction can occur in a relatively short time.

The time for the reduction process (treatment time) is set according to the temperature of the reduction furnace, but is preferably 10 minutes or more, and more preferably 15 minutes or more. On the other hand, the upper limit of the time for performing the reduction heat treatment may be set to 50 minutes or less, or 40 minutes or less, from the viewpoint of suppressing an increase in manufacturing costs.

It is preferable that the cumulative heat required for reduction, calculated by multiplying the reduction temperature (°C) by the reduction time (min), is in the range of 20,000 (°C x min) to 40,000 (°C x min). By carrying out the reduction process with this amount of heat, high-quality metal can be produced efficiently.

The reduction furnace used in the reduction heat treatment is not particularly limited. For example, a fixed hearth or a moving hearth furnace may be used, but it is preferable to use a moving hearth furnace. By using a moving hearth furnace as such a reduction furnace, the mixture can be treated more efficiently. In addition, by using a moving hearth furnace, the reduction reaction proceeds continuously and the reaction can be completed in one facility, and the treatment temperature can be controlled more accurately than when the treatment in each step is performed using separate furnaces. Furthermore, the heat loss between each treatment is reduced, making it possible to operate more efficiently. Below, the configuration of a rotary hearth furnace as an example of a moving hearth furnace is explained using Figure 5.

Figure 4 is a diagram (plan view) showing an example of the configuration of a rotary hearth furnace with a rotating hearth. As shown in Figure 4, a rotary hearth furnace 2 that is circular and divided into a plurality of processing chambers 20a to 20d can be used. In the rotary hearth furnace 2, each process is performed in each region while rotating in a predetermined direction. In this rotary hearth furnace, the processing temperature in each region can be adjusted by controlling the time it takes to pass through each region (travel time, rotation time), and the mixture 1 is smelted every time the rotary hearth furnace rotates. Here, the rotary hearth furnace 2 may be provided with a preheating chamber outside the furnace. In addition, the rotary hearth furnace 2 may be provided with a cooling chamber outside the furnace. The moving hearth furnace may be a roller hearth kiln, etc.

When performing reduction treatment using a rotary hearth furnace, the heat treatment may be performed in stages at different temperatures. For example, the temperature in one treatment chamber may be controlled so that the first stage reduction treatment is performed at a reduction temperature in the range of 1150°C to 1250°C, the temperature in one treatment chamber may be controlled so that the second stage reduction treatment is performed at a reduction temperature in the range of 1250°C to 1350°C, and the temperature in the other treatment chamber may be controlled so that the third stage reduction treatment is performed at a reduction temperature in the range of 1350°C to 1450°C. By using a rotary hearth furnace having multiple treatment chambers in this way to perform heat treatment in stages at different temperatures, it is possible to reduce the reoxidized metal by highly reactive starch again and suppress the oxidation of the metal in the low temperature range of the first stage, then reduce the reoxidized metal by charcoal, which has the second highest reactivity after starch, again and suppress the oxidation of the metal in the temperature range of the second stage, and then reduce the reoxidized metal by coal, which reacts slowly, again and suppress the oxidation of the metal in the relatively high temperature range of the third stage. This makes it possible to maintain a reducing atmosphere for a long time and to reduce the reoxidized metal again and suppress the oxidation of the metal over the entire reduction temperature range, making it possible to more effectively reduce the nickel oxide contained in the nickel oxide ore throughout the reduction process, and further improving the quality of the resulting metal.

The heating means for the reduction furnace is not particularly limited, but may be a burner or electricity. A burner is preferable because it can effectively perform heating and reduction treatment on the mixture in a short time. When using a reduction furnace with a burner, for example, LPG, LNG, coal, coke, pulverized coal, etc. are used as fuel. The cost of these fuels is very low, and the equipment costs and maintenance costs can be kept significantly lower than those of electric furnaces, etc.

<2-5. Recovery process>
In the recovery step S5, the metal is recovered from the reduced product obtained in the reduction step S4. Specifically, the reduced product (mixture) containing a metal phase and a slag phase obtained by the heating and reduction treatment is cooled, and if necessary, pulverized to form a powder, and the metal (metal powder particles) is separated and recovered.

Methods for separating the metal phase and the slag phase from the mixture of metal phase and slag phase obtained as a solid include, for example, removing unnecessary materials by sieving, as well as separation by specific gravity or by magnetic force.

The obtained metal phase and slag phase have poor wettability and can be easily separated. For example, by dropping the large mixture obtained by the reduction step S4 described above over a predetermined drop or by applying a certain amount of vibration during sieving, the metal phase and slag phase can be easily separated from the mixture.

In this way, the metal phase is separated from the slag phase and the metal phase is recovered.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[Mixing process]
For each sample, nickel oxide ore (limonite ore with Ni content = 0.75 mass%) as raw ore, iron ore, silica sand and limestone as flux components, binder, and a first reducing agent were mixed in a mixer while adding an appropriate amount of water to obtain a mixture. Note that coal was used as the reducing agent, and nickel oxide and iron oxide ( _{Fe2O3 )} contained in the nickel oxide ore as raw ore were contained in an amount of 32 mass% relative to the required chemical equivalent of 100 mass%.

[Agglomeration process]
Next, an appropriate amount of water was added to the mixture obtained in the mixing process, and the mixture was formed into spheres with a pelletizer to obtain lumps (samples) having a diameter of 15±0.2 mm.

[Drying process]
Next, the aggregates obtained in the agglomeration step were subjected to a drying treatment by blowing hot air at 200°C to 250°C onto them so that the solid content was about 70% by mass and the moisture content was about 30% by mass. Table 3 below shows the solid content composition (excluding carbon) of the aggregates (samples) after the drying treatment.

[Reduction process]
Next, the lumps (samples) obtained in the drying step were each charged into a reduction furnace under a nitrogen atmosphere substantially free of oxygen. The temperature condition during charging into the reduction furnace was 500±20° C.

At this time, in Examples 1 to 5, the second reducing agent was spread on the hearth and the reduction treatment was performed. A mixture of starch, charcoal, and coal was used as the second reducing agent. The amount of the second reducing agent spread on the hearth was 18 mass %, assuming that the chemical equivalent required for reducing nickel oxide and iron oxide (Fe ₂ O ₃ ) contained in the nickel oxide ore, which is the raw material ore, is 100 mass %. The mixture ratio of coal contained in the second reducing agent is shown in Table 4 below. In Examples 1 to 5 and Comparative Example 2, the mass ratio of starch and charcoal was 50:50. Meanwhile, in Comparative Example 1, coal was used as the reducing agent placed on the hearth.

Next, the mixture pellets were subjected to a reduction heat treatment at a reduction temperature of 1380°C for 25 minutes. After the reduction treatment, the pellets were quickly cooled to room temperature in a nitrogen atmosphere and then removed into the air.

[Recovery process]
After the reduction heat treatment, each reduced product (sample) was crushed by wet processing, and the metal was recovered by magnetic separation. The nickel metallization rate and the nickel content in the metal were analyzed and calculated using an ICP emission spectrometer (SHIMAZU S-8100 model).

The nickel metallization rate, the nickel content in the metal, and the nickel metal recovery rate were calculated by the following formulas (1), (2), and (3).
Nickel metallization rate = mass of nickel in metal / (mass of all nickel in reduced product) x 100 (%) ... (1) Nickel content in metal = mass of nickel in metal / (total mass of nickel and iron in metal) x 100 (%) ... (2) Nickel metal recovery rate = amount of nickel recovered / (amount of ore input x nickel content in ore) x 100 ... (3)

Table 4 below shows the nickel metallization rate, nickel content in the metal, and nickel metal recovery rate for each sample.

As shown in the results in Table 4, in Examples 1 to 5, in which a second reducing agent containing starch, charcoal, and coal was laid on the hearth of the reduction furnace, the mixture was placed on top of the second reducing agent, and reduction treatment was performed, good results were obtained in terms of nickel metallization rate and nickel content in metal. This shows that the oxide ore smelting method according to the present invention can efficiently produce high-quality metal.

On the other hand, in Comparative Example 1, in which a reducing agent containing only coal was placed on the hearth of the reduction furnace, the mixture was placed on the reducing agent, and a reduction treatment was performed, and in Comparative Example 2, in which a reducing agent containing only starch and charcoal was placed on the hearth of the reduction furnace, the mixture was placed on the reducing agent, and a reduction treatment was performed, the Ni metallization rate, Ni content, and metal recovery rate were all lower than those of the Examples, and the effects of the present invention were not achieved.

1 Charging inlet 2 Rotary hearth furnace 20a to 20d Treatment chamber 21 Preheating chamber 22 Cooling chamber

Claims (2)

a mixing step of mixing the nickel oxide ore with a first reducing agent to obtain a mixture;
a reduction step of charging the mixture into a reduction furnace and subjecting it to a reduction treatment;
having
In the reduction step, a second reducing agent containing starch, charcoal and coal is laid on the hearth of the reduction furnace, and the mixture is placed thereon and subjected to reduction treatment. The method for smelting nickel oxide ore according to claim 1 , wherein in the reduction step, a total content of starch and charcoal is 20 mass % or more and 80 mass % or less of the total amount of the second reducing agent.

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