JP2024110748A - Method for smelting nickel oxide ore - Google Patents

Abstract

[Problem] To provide a method for smelting nickel oxide ore, which can improve the grade of the obtained metal and efficiently produce high-quality metal by reducing a mixture containing nickel oxide ore. [Solution] The method for smelting nickel oxide ore includes a mixing step of mixing nickel oxide ore with a reducing agent to obtain a mixture, and a reduction step of subjecting the mixture to a reduction treatment, in which the reducing agent mixed with the nickel oxide ore in the reduction step contains starch and coal. [Selected Figure] Figure 1

Description

The present invention relates to a smelting method for obtaining ferronickel by subjecting a mixture containing nickel oxide ore and a reducing agent to a reduction treatment.

Methods for smelting nickel oxide ores called limonite or saprolite include the dry smelting method, which uses a smelting furnace to produce nickel matte by roasting with sulfur, the dry smelting method, which uses a rotary kiln or moving hearth furnace to produce an iron-nickel alloy (hereinafter also referred to as "ferronickel") by reducing with a reducing agent, and the wet smelting method, which uses an autoclave to leach nickel and cobalt with sulfuric acid, and adds a sulfurizing agent to the leachate obtained 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, the raw ore is first pretreated to form agglomerates or slurry. Specifically, when nickel oxide ore is agglomerated, that is, when converting the nickel oxide ore from a powder or fine grain form 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 agglomeration equipment to form agglomerates (pellets, briquettes, etc., hereinafter simply referred to as "pellets") of, for example, about 10 mm to 30 mm in size.

Pellets need to have a certain degree of breathability to allow the moisture they contain to evaporate. Furthermore, if reduction does not proceed uniformly within the pellets, the composition of the resulting reduced product will be non-uniform, resulting in problems such as metal dispersion or uneven distribution, 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 important 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 also necessary.

In addition, reducing smelting costs 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 metal oxides and a reducing agent are supplied onto the hearth of a moving-bed type reduction melting furnace, heated, and the metal oxides are 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 to obtain higher quality ferronickel by controlling the reaction that occurs inside the agglomerates to increase the reaction efficiency and progress the reduction reaction more uniformly.

In addition, in the method of using agglomerates having a specific diameter as described in Patent Document 1, it is necessary to remove those that do not have the specific diameter. As a result, the yield of agglomerates is low. In addition, the method disclosed in Patent Document 1 requires the laying density of the agglomerates to be adjusted to 0.5 to 0.8, and the agglomerates cannot be stacked, making it a method with low productivity. These reasons also lead to increased manufacturing costs.

As such, the technology of producing metals and alloys by mixing and reducing oxide ores such as nickel oxide ore has faced many technical challenges in terms of increasing productivity, reducing manufacturing costs, and improving metal quality.

JP 2011-256414 A

The present invention aims to provide a method for smelting nickel oxide ore that can improve the grade of the resulting metal and efficiently produce high-quality metal in a smelting method for producing metal by reducing a mixture containing nickel oxide ore.

The inventors of the present invention have conducted extensive research to solve the above-mentioned problems. As a result, they have discovered that high-quality ferronickel can be efficiently produced by subjecting nickel oxide ore to a reduction treatment using a reducing agent containing starch and coal, and have completed the present invention.

(1) The first aspect of the present invention is a method for smelting nickel oxide ore, comprising a mixing step of mixing nickel oxide ore with a reducing agent to obtain a mixture, and a reduction step of subjecting the mixture to a reduction treatment, in which the reducing agent mixed with the nickel oxide ore in the reduction step contains starch and coal.

(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 reducing agent mixed with the nickel oxide ore in the reduction step contains starch in an amount of 20% by mass or more and 80% by mass or less based on the total amount of the reducing agent.

(3) The third aspect of the present invention is a method for smelting nickel oxide ore according to the first or second invention, in which, in the mixing step, the reducing agent is mixed to obtain a mixture in a ratio of 25% by mass to 350% by mass, where the mass of the reducing agent required to reduce the total amount of nickel oxide and iron oxide contained in the mixture is taken as 100% by mass.

According to the present invention, a method for producing ferronickel by subjecting nickel oxide ore to a reduction treatment can be provided that can efficiently produce high-quality ferronickel.

FIG. 1 is a process diagram showing an example of a flow of a method for smelting nickel oxide ore. TG/DTA measurement results of starch. 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). FIG. 2 is a diagram showing the relationship between the starch addition ratio and the nickel metallization rate, recovery rate, and nickel grade measured in the examples.

The following describes in detail an embodiment of the present invention (hereinafter, "the present embodiment"). Note that the present invention is not limited to the following embodiment, and various modifications are possible without departing from the gist 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. Nickel oxide ore smelting method≫
The method for smelting nickel oxide ore according to the present embodiment is a method for forming pellets from nickel oxide ore and producing ferronickel metal and slag by subjecting the pellets to a reduction treatment. Specifically, nickel (nickel oxide) and iron (iron oxide) in the nickel oxide ore constituting the pellets are reduced to produce ferronickel metal and slag, which are iron-nickel alloys, and the metal is separated from the slag to produce ferronickel.

This smelting method is characterized by using a reducing agent containing starch and coal to reduce nickel oxide ore.

According to this method, the quality of the resulting metal can be improved by reducing nickel oxide ore using a reducing agent containing starch and coal.

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 mixed with a reducing agent to obtain a mixture, an agglomeration process S2 in which the resulting mixture is formed into a predetermined shape to form pellets, a drying process S3 in which the pellets are dried, a reduction process S4 in which the pellets are subjected to a reduction treatment, and a recovery process S5 in which slag is separated from the reduced product produced by the reduction to obtain ferronickel metal.

<2-1. Mixing process>
The mixing step S1 is a step of mixing raw material powder containing nickel oxide ore to obtain a mixture. Specifically, a reducing agent is added to the raw material ore, nickel oxide ore, and mixed, and an optional component is added. As the agent, powders of iron ore, flux components, binders, etc., 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 ).

In the smelting method according to the present embodiment, a reducing agent containing starch and coal is used as the reducing agent that is mixed with the nickel oxide ore to form the mixture in the mixing step S1. This allows for efficient production of high-quality ferronickel with high metal grade.

Here, one method for clarifying the behavior of the reducing agent in a mixture when the mixture is subjected to a reduction treatment is to measure TG 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 the TG and DTA curves can clarify the behavior of a sample, such as decomposition or phase transition, when a temperature change is applied to the sample. 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 raised 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 when the reduction treatment is performed using starch, the reduction reaction can proceed 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 rise in temperature to generate _H2 gas, forming a porous structure, and the bond between the carbon atoms constituting starch is weak.

On the other hand, Figure 3 shows the TG and DTA curves of "coal" measured using TG/DTA. Compared to starch, the TG curve of coal shows that the weight hardly changes even when the temperature is raised from room temperature, and the DTA curve of coal is almost 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 the decomposition temperature of starch. Therefore, it is presumed that when reduction treatment is performed using coal, the reduction reaction can proceed 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, so the carbon atoms derived from plants are concentrated, and the bonds between the carbon atoms that make up the coal are strong.

In the smelting method according to the present embodiment, a reducing agent containing starch, which has a relatively low decomposition temperature and is substantially free of other components such as oxides, and coal, which has a relatively high decomposition temperature and may contain oxides, is used, and a reduction process is carried out on a mixture obtained by mixing this reducing agent with nickel oxide ore. As a result, in the initial stage of the reduction process, the starch contained in the mixture can cause the reduction reaction of the nickel oxide ore to proceed at a high reaction rate, and after the desired reduction temperature is reached, the coal contained in the mixture can cause the reduction reaction of the nickel oxide ore to proceed for a long period of time.

In this way, by using a reducing agent containing at least two types of carbonaceous reducing agents with different decomposition temperatures and oxide contents, it is possible to effectively reduce the nickel oxide contained in the nickel oxide ore throughout the entire reduction process, thereby improving the quality of the resulting metal.

The starch content in the 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 reducing agent. The upper limit of the starch content in the 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 reducing agent.

The coal content in the 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 reducing agent. The upper limit of the coal content in the 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 reducing agent.

The total content of starch and coal in the 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, and it is most preferable that the reducing agent is composed only of starch and coal (i.e., the total content of starch and coal is 100% by mass of the total reducing agent).

By configuring the reducing agent so that the starch and coal contents are within these ranges, it becomes possible to proceed with the reduction reaction at a relatively low temperature in the initial stage of the reduction treatment, and it becomes possible to carry out the reduction treatment over a long period of time, so that high-quality ferronickel can be smelted more efficiently. The starch and coal contents may be appropriately set depending on the ore used as the raw material, the treatment temperature, the treatment time, etc.

The amount of reducing agent mixed in the mixture is preferably 25% by mass, more preferably 30% by mass or more, and even more preferably 35% by mass, when the amount of reducing agent required to reduce the nickel oxide and iron oxide that constitute the nickel oxide ore without excess or deficiency is taken as 100% by mass.

The upper limit of the amount of reducing agent mixed is not particularly limited, but is preferably 350% by mass or less, more preferably 250% by mass or less, and even more preferably 150% 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").

In this way, by setting the amount of reducing agent contained in the mixture (mixed amount of reducing agent) to a ratio of 25% by mass or more and 350% by mass or less when the total value of the chemical equivalents is 100% by mass, the reduction reaction can be efficiently carried out, and ferronickel with high nickel quality can be efficiently produced.

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 step S1. Note that the composition of the raw material powders is not limited to this.

In the mixing step S1, the raw powder containing nickel oxide ore can be mixed using a mixer or the like. When the raw powder is mixed to obtain a mixture, the raw 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 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 powders, 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, it is preferable for the extruder to be equipped with a twin-screw extruder. 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. It is also possible to knead effectively, 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 by forming 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 are preferably, for example, spherical, rectangular, cuboidal, cylindrical, or other shapes. By molding the mixture into such a shape, molding the mixture becomes easier, and molding costs can be reduced. In addition, the shape to be molded is not complicated, so the occurrence of defective pellets is reduced. This also makes it easier to maintain the strength of the pellets.

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 (mixture) dried in the drying step S3 are subjected to a reduction treatment. Specifically, the obtained pellets (mixture) are placed on the hearth of a reduction furnace, and the pellets (mixture) are subjected to a heating reduction treatment in the reduction furnace. Due to the heating reduction treatment in the reduction step S4, a smelting reaction (reduction reaction) proceeds based on the reducing agent (first reducing agent) in the pellets (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 thermal reduction process, in a short time of, 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 the metal also becomes liquid.

In the smelting method according to the present embodiment, as described above, in the mixing step S1, a reducing agent containing at least starch and coal, which have different decomposition temperatures and oxide contents, is used, and the reducing agent is mixed with nickel oxide ore to form a mixture to be subjected to the reduction treatment. Therefore, in the initial stage of the reduction treatment, the reduction reaction of the nickel oxide ore can be made to proceed at a high reaction rate mainly due to the action of starch, which can cause the reduction reaction to proceed at a relatively low temperature. In addition, in the stage where the temperature of the reduction treatment reaches the desired reduction temperature, the reduction reaction of the nickel oxide ore can be made to proceed at a high reaction rate mainly due to the action of coal, which can cause the reduction reaction to proceed for a long time at a relatively high temperature. As a result, nickel oxide contained in the nickel oxide ore can be effectively reduced throughout the entire reduction treatment.

Here, when using an organic reducing agent derived from a plant such as starch, which has a relatively low decomposition temperature, there is a possibility that it may burn during the heating reduction process. For this reason, it is preferable to carry out the reduction process in an atmosphere with a low oxygen concentration. Specifically, for example, it is preferable to carry out the reduction process in an atmosphere with an oxygen concentration of 3.0% by volume or less, and it is more preferable to carry out the reduction process in an atmosphere with an oxygen concentration of 1.0% by volume or less. The reduction process may also be carried out 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 heat required for reduction, calculated by multiplying the reduction temperature (℃) by the reduction time (min), is preferably in the range of 20,000 (℃ x min) to 40,000 (℃ x min). This allows for efficient production of high-quality metal.

The reduction furnace may be a fixed hearth, 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 if the treatment in each step were performed using separate furnaces. Furthermore, heat loss between each treatment is reduced, making more efficient operation possible. Below, the configuration of a rotary hearth furnace as an example of a moving hearth furnace is explained using Figure 4.

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 or the like.

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 or the like.

When the reduction treatment is performed using a rotary hearth furnace, the heat treatment may be performed stepwise at different temperatures. For example, the temperature in one treatment chamber may be controlled so that the first reduction treatment is performed at a reduction temperature in the range of 1150°C to 1250°C, and the temperature in the other treatment chamber may be controlled so that the second reduction treatment is performed at a reduction temperature in the range of 1350°C to 1450°C. By performing the heat treatment stepwise at different temperatures using a rotary hearth furnace having multiple treatment chambers in this way, the reduction proceeds with the highly reactive starch in the relatively low temperature range of the first stage, and then the reaction proceeds with the coal, which reacts slowly, in the relatively high temperature range of the second stage, so that the reducing atmosphere can be maintained for a long time and the variation in the degree of reduction is reduced throughout the entire reduction temperature range, making it possible to more effectively reduce the nickel oxide contained in the nickel oxide ore throughout the entire reduction process, thereby further improving the quality of the metal obtained.

The heating means for the reduction furnace is not particularly limited, and 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 as raw ore, iron ore, silica sand and limestone as flux components, binder, and reducing agent were mixed in a mixer while adding an appropriate amount of water to obtain a mixture. Starch and coal were used as reducing agents, and nickel oxide and iron oxide ( _Fe2O3 ) contained in the nickel oxide ore as raw _ore were contained in an amount of 55 mass% relative to the required chemical equivalent of 100 mass%.

The starch used as the reducing agent had a total carbon content of 38% by mass, all of which existed as free carbon (elementary carbon). On the other hand, the coal used as the reducing agent had a total carbon content of 72% by mass, of which 50% was free carbon.

[Agglomeration process]
Next, an appropriate amount of water was added to the mixture obtained in the mixing step, 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.

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

Here, the lumps were loaded into the reduction furnace _by first spreading ash (mainly _SiO2 with small amounts of oxides such as _Al2O3 and MgO as other components) on the hearth of the reduction furnace and then placing the lumps on top of the ash.

[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 and Figure 5 below show 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 reducing agent containing starch and coal was used as the reducing agent, good results were obtained in terms of nickel metallization rate, nickel content in metal, and metal recovery rate. 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 only coal was used as the reducing agent, and Comparative Example 2, in which only starch was used as the reducing agent, it was not possible to efficiently produce high-quality metal compared to the Examples.

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

Claims (3)

a mixing step of mixing nickel oxide ore and a reducing agent to obtain a mixture;
a reduction step of subjecting the mixture to a reduction treatment;
having
The reducing agent mixed with the nickel oxide ore in the reduction step contains starch and coal.
A method for smelting nickel oxide ores. 2. The method for smelting nickel oxide ore according to claim 1, wherein the reducing agent mixed with the nickel oxide ore in the reduction step contains starch in an amount of 20% by mass or more and 80% by mass or less based on a total amount of the reducing agent. 3. The method for smelting nickel oxide ore according to claim 1 or 2, wherein in the mixing step, the reducing agent is mixed to obtain a mixture in a ratio of 25 mass% to 350 mass%, where a mass of the reducing agent required to reduce all of the nickel oxide and iron oxide contained in the mixture is taken as 100 mass%.

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