Nickel oxide ore smelting method

Abstract

The present invention provides a method for smelting an oxide ore, with which it is possible to enhance the quality of a metal obtained thereby and to efficiently produce a high-quality metal.　The present invention specifically provides a method for smelting a nickel oxide ore, the method comprising: a mixing step in which a nickel oxide ore and a first reducing agent are mixed so as to obtain a mixture; and a reduction step in which the mixture is charged into a reduction furnace and a second reducing agent is put into the reduction furnace so as to reduce the mixture.

Description

[Technical Field]

[0001] The present invention relates to a smelting method for obtaining a reduced product such as ferronickel by smelting pellets produced from an oxide ore such as nickel oxide ore and a reducing agent by reducing and heating them at high temperatures in a reduction furnace. [Background technology]

[0002] Known methods for smelting nickel oxide ores called limonite or saprolite include a dry smelting method in which nickel matte is produced by sulfurizing and roasting together with sulfur using a smelting furnace, a dry smelting method in which an iron-nickel alloy (hereinafter also referred to as "ferronickel") is produced by reduction using a carbonaceous reducing agent using a rotary kiln or a moving hearth furnace, and a hydrometallurgical method in which nickel and cobalt are leached with sulfuric acid using an autoclave, and a sulfiding agent is added to the leachate obtained to produce a mixed sulfide.

[0003] Among the various smelting methods described above, when nickel oxide ore is smelted by reduction together with a carbon source, the raw material ore is first subjected to pretreatment to form agglomerates, slurry, etc. Specifically, when nickel oxide ore is agglomerated, that is, when converting powder or fine particles into agglomerates, the nickel oxide ore is generally mixed with a binder, a reducing agent, etc., and then subjected to moisture adjustment, etc. before being charged into an agglomeration machine to form agglomerates (referring to pellets, briquettes, etc.; hereinafter simply referred to as "pellets") of, for example, about 10 mm to 30 mm.

[0004] These pellets need to have a certain degree of breathability to "evaporate" the moisture they contain. 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 dispersion or uneven distribution of the metal. Therefore, it is important to mix the mixture uniformly and maintain as uniform a temperature as possible during the reduction treatment of the pellets.

[0005] In addition, it is also an important technology to coarsen the ferronickel produced by reduction. This is because if the produced ferronickel has a small size of, for example, several tens of μm to several hundreds of μm, 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.

[0006] Furthermore, how to keep smelting costs as low as possible is also an important technical issue, and continuous processing that can be operated in compact facilities is desired.

[0007] 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 reducing melting furnace, heated, and the metal oxide is reduced and melted. The method involves supplying and heating agglomerates having an average diameter of 19.5 mm to 32 mm onto the hearth so that the bed density is 0.5 to 0.8, where the bed 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 describes that the productivity of granular metallic iron can be increased by controlling both the bed density and the average diameter of the agglomerates.

[0008] However, the method disclosed in Patent Document 1 is a technology for controlling the reaction occurring outside the agglomerates, and does not focus on controlling the reaction occurring inside the agglomerates, which is the most important factor in the reduction reaction. On the other hand, there has been a demand for controlling the reaction occurring inside the agglomerates to increase reaction efficiency and promote the reduction reaction more uniformly, thereby obtaining higher quality metals (metals, alloys).

[0009] Furthermore, the method of using a specific diameter as the agglomerates, as described in Patent Document 1, requires the removal of agglomerates that do not have the specific diameter, resulting in a low yield when producing agglomerates. Furthermore, the method described in Patent Document 1 requires the agglomerates to have a bed density of 0.5 or more and 0.8 or less, and does not allow the agglomerates to be stacked, resulting in low productivity. For these reasons, the method described in Patent Document 1 has high manufacturing costs.

[0010] As described above, the technology for producing metals and alloys by mixing and reducing oxide ores has had many challenges in terms of increasing productivity, reducing production costs, and improving the quality of the metals. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-256414 Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to provide a method for smelting oxide ore, in which a metal is produced by reducing a mixture containing an oxide ore such as nickel oxide ore, that can improve the grade of the obtained metal and efficiently produce high-quality metal. [Means for solving the problem]

[0013] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by adding a second reducing agent containing at least one of charcoal and starch to a reduction furnace and subjecting the mixture to a reduction treatment, thereby completing the present invention.

[0014] (1) The first aspect of the present invention is a method for producing a nickel oxide ore, comprising: a mixing step of mixing a nickel oxide ore with a first reducing agent to obtain a mixture; and a reduction step of charging the mixture into a reduction furnace and adding a second reducing agent to the reduction furnace to reduce the mixture. In the reduction step, a reducing agent containing coal as the second reducing agent and further containing at least one of charcoal and starch is used. This is a method for smelting nickel oxide ore.

[0015] (2) A second aspect of the present invention is a method for smelting nickel oxide ore according to the first aspect of the present invention, wherein the reduction step uses a reducing agent containing coal and charcoal as the second reducing agent.

[0016] (3) A third aspect of the present invention is a method for smelting nickel oxide ore according to the first aspect of the present invention, wherein the second reducing agent used in the reduction step is a reducing agent containing coal and starch.

[0017] (4) A fourth aspect of the present invention is a method for smelting nickel oxide ore according to the first aspect of the present invention, wherein the reduction step uses a reducing agent containing coal, starch, and charcoal as the second reducing agent.

[0018] (5) A fifth aspect of the present invention is a method for smelting nickel oxide ore according to any one of the first to fourth aspects of the present invention, wherein the reduction step includes a first reduction step of introducing at least a part of the second reducing agent into the reduction furnace and subjecting the mixture to a reduction treatment, and a second reduction step of introducing the remaining second reducing agent into the reduction furnace and subjecting the mixture to a reduction treatment.

[0019] (6) A sixth aspect of the present invention is a method for smelting nickel oxide ore according to the fifth aspect of the present invention, wherein in the first reduction step, a reducing agent containing coal is introduced into the reduction furnace to subject the mixture to a reduction treatment, and in the second reduction step, a reducing agent containing at least one of charcoal and starch is introduced into the reduction furnace to subject the mixture to a reduction treatment. [Effects of the Invention]

[0020] According to the method for smelting oxide ore of the present invention, high-quality metal can be efficiently produced. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a process diagram showing an example of the flow of a method for smelting nickel oxide ore. [Figure 2] TG / DTA measurement results of starch. [Figure 3] This is the result of TG / DTA measurement of charcoal. [Figure 4] This shows the results of TG / DTA measurements of coal. [Figure 5] FIG. 1 is a diagram (plan view) showing an example of the configuration of a reducing furnace (rotary hearth furnace). DETAILED DESCRIPTION OF THE INVENTION

[0022] Specific embodiments of the present invention will be described in detail below. Note that the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the present invention. In addition, in this specification, the expression "X to Y" (X and Y are arbitrary numerical values) means "at least X and at most Y."

[0023] 1. Overview of the Invention The present invention is a method for smelting an oxide ore, which uses nickel oxide ore as a raw material, by mixing the oxide ore with a reducing agent and reducing the resulting mixture to produce ferronickel metal as a reduction product.

[0024] This smelting method is characterized by introducing a reducing agent (second reducing agent) containing coal and at least one of charcoal and starch into a reduction furnace, thereby subjecting the mixture to a reduction treatment.

[0025] According to this method, the quality of the resulting metal can be improved by adding a reducing agent (second reducing agent) containing coal and at least one of charcoal and starch to a reduction furnace and subjecting the mixture to reduction treatment.

[0026] 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 agglomerating 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 treatment, and a recovery process S5 in which metal is recovered from the reduced material produced by the reduction.

[0027] <2-1. Mixing process> The mixing step S1 is a step of mixing raw material powders containing nickel oxide ore to obtain a mixture. Specifically, a first reducing agent is added to the raw material nickel oxide ore and mixed with the mixture. 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 also mixed to obtain a mixture.

[0028] The nickel oxide ore used as the raw material ore is not particularly limited, but examples include limonite and saprolite. Nickel oxide ores typically contain nickel oxide (NiO) and iron oxide (FeO).

[0029] The first reducing agent is not particularly limited, but examples thereof include carbonaceous reducing agents such as coal powder and coke powder. It may also be composed entirely or partially of plant-derived components, such as starch. It is preferable for the carbonaceous reducing agent to have a particle size and particle size distribution similar to that of the nickel oxide ore, which is the raw material ore, because this facilitates uniform mixing and promotes uniform reduction reactions.

[0030] The amount of the first reducing agent mixed is not particularly limited, but when the amount of reducing agent necessary to reduce the nickel oxide and iron oxide constituting the nickel oxide ore in the exact amount is taken as 100% by mass, the amount is preferably 25% by mass or more, more preferably 30% by mass or more, and even more preferably 35% by mass or more.

[0031] Furthermore, the upper limit of the amount of the first 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%. Note that the amount of reducing agent required to reduce nickel oxide and iron oxide without excess or deficiency can be 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 (hereinafter also referred to as the "total value of chemical equivalents").

[0032] The iron ore, which is an optional additive, is not particularly limited, but examples thereof include iron ore with an iron content of about 50% by mass 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.

[0033] The following Table 1 shows an example of the composition (mass %) of some of the raw material powders mixed in the mixing treatment step S1, but the composition of the raw material powder is not limited to this.

[0034] [Table 1]

[0035] In the mixing step S1, the raw material powder containing nickel oxide ore can be mixed using a mixer or the like. When mixing the raw material powders to obtain a mixture, the raw material powders may be subjected to a kneading process to improve mixability. This applies shear force to the mixture, breaking down agglomerates of the reducing agent, raw material powder, etc., allowing for more uniform mixing, improving the adhesion between particles, and reducing voids, making it easier to perform a uniform reduction process and shortening the reaction time of the reduction reaction. This also reduces quality variations.

[0036] 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. Kneading the mixture applies shear force to the mixture, which breaks down agglomerations of the reducing agent and raw material powder, resulting in uniform mixing, improved adhesion between particles, and reduced voids. This facilitates the reduction reaction in the mixture, allowing it to react uniformly, shortening the reduction reaction time. It also reduces quality variations.

[0037] Alternatively, 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 agglomerates of the reducing agent, raw material powder, etc., and making the mixture more uniformly mixed. Furthermore, it reduces voids within the mixture. As a result, the reduction reaction of the mixture in the reduction step S3 described below is more likely to occur uniformly, improving the quality of the resulting metal and enabling the production of high-quality metal.

[0038] The extruder is preferably one that can knead and mold the mixture under high pressure and high shear force, and examples thereof include a single-screw extruder and a twin-screw extruder. In particular, one equipped with a twin-screw extruder is preferred. Kneading the mixture under high pressure and high shear can break up agglomerations in the raw material powder mixture. This also allows for effective kneading, thereby increasing the strength of the mixture. Furthermore, by using one equipped with a twin-screw extruder, the mixture can be obtained continuously while maintaining high productivity.

[0039] <2-2. Agglomeration process> The agglomerating step S2 is a step in which the mixture of raw material powders obtained in the mixing step S1 is molded to obtain pellets. The agglomerating step is not an essential step, but molding the mixture into a predetermined shape can improve handleability. The shape of the pellets may be any shape that can be stacked on the hearth of the reduction furnace, but shapes such as spheres, rectangular parallelepipeds, cubes, and cylinders are preferred. Molding the mixture into such shapes makes it easier to mold the mixture, thereby reducing molding costs. Furthermore, because the molded shape is not complex, the occurrence of defective pellets can be reduced and the strength of the pellets can be more easily maintained.

[0040] Among these, a shape that allows the pellets to be placed on the hearth as densely as possible, such as an elliptical or cylindrical shape, is preferable. By placing the pellets on the hearth of the reduction furnace at a high density and subjecting them to reduction treatment, the proportion of oxygen and water that are inevitably contained in the pellets is reduced, thereby making it possible to efficiently maintain a reducing atmosphere.

[0041] In the agglomerating step S2, the mixture can be molded using, for example, a pellet molding device. The pellet molding device is not particularly limited, but is preferably one that can knead and mold the mixture under high pressure and high shear force. Kneading the mixture under high pressure and high shear can break up agglomerations in the raw material powder mixture, enable effective kneading, and increase the strength of the resulting pellets.

[0042] <2-3. Drying process> In the drying step S3, the obtained pellets are subjected to a drying treatment. Although the drying step is not essential, the pellets obtained by the pellet-shape agglomeration treatment contain excessive moisture, for example, about 50% by mass. Therefore, if pellets containing excessive moisture are suddenly heated to the reduction temperature, the moisture will suddenly evaporate, expanding and causing the pellets to break. Therefore, by subjecting the obtained pellets to a drying treatment so that the solid content is, for example, about 70% by mass and the moisture content is about 30% by mass, the pellets can be prevented from collapsing during 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 the excess moisture, the drying treatment makes them easier to handle.

[0043] 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 reduces the pellets to a solids content of approximately 70% by mass and a moisture content of approximately 30% by mass. The temperature of the mixture itself during this drying process is preferably less than 100°C, which can prevent the mixture from bursting due to bumping of moisture.

[0044] This drying step may be carried out outside the reduction furnace, which will be described later, or the pellets may be placed in the reduction furnace, which will be described later, and the drying treatment may be carried out in the reduction furnace.

[0045] Here, when drying pellets having a particularly large volume, cracks or breaks may occur in the pellets before or after drying. When the pellets have a large volume, they melt and shrink during reduction, which often causes cracks or breaks. However, when the pellets have a large volume, the effects of cracks or breaks, such as an increase in surface area, are minimal, and therefore, no major problems are likely to occur. Therefore, it is acceptable for the pellets to have cracks or breaks before reduction.

[0046] 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 exploding. When the drying process is carried out in multiple steps, the drying temperature for the second and subsequent steps is preferably 150°C or higher and 400°C or lower. Drying within this range makes it possible to dry the mixture without causing a reduction reaction to proceed.

[0047] An example of the composition (parts by mass) of the solid content in the pellets (mixture) after drying is shown in the following Table 2. However, the composition of the pellets (mixture) is not limited to this.

[0048] [Table 2]

[0049] <2-4. Reduction process> 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 heat reduction treatment in the reduction furnace. By the heat reduction treatment in the reduction step S4, a smelting reaction (reduction reaction) proceeds 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. Note that, hereinafter, the pellets to be subjected to the reduction treatment will be referred to as a mixture for convenience.

[0050] In the thermal reduction treatment, for example, in a short time of about one minute, 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, slag components gradually melt as the shell forms, producing liquid slag. As a result, metal and slag are produced separately within the mixture.

[0051] After about 10 minutes of treatment, excess reducing agent that is not involved in the reduction reaction is absorbed into the metal, lowering its melting point and turning it into a liquid. This makes it possible to steadily improve the quality of the resulting metal, resulting in a high-quality metal.

[0052] The temperature in the reduction treatment (reduction temperature) is not particularly limited, but is preferably in the range of 1200°C or higher and 1450°C or lower, and more preferably in the range of 1300°C or higher and 1400°C or lower. By carrying out reduction within such a temperature range, the reduction reaction can occur uniformly, and ferronickel can be produced with reduced quality variation. Furthermore, by carrying out reduction at a reduction temperature more preferably in the range of 1300°C or higher and 1400°C or lower, the desired reduction reaction can occur in a relatively short time.

[0053] The time for the reduction treatment (treatment time) is set depending on the temperature of the reduction furnace, but is preferably 10 minutes or more, more preferably 15 minutes or more. On the other hand, the upper limit of the time for 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 production costs.

[0054] The cumulative heat required for reduction, calculated by multiplying the reduction temperature (°C) by the reduction time (minutes), is preferably in the range of 20,000 (°C x min) to 40,000 (°C x min). By carrying out reduction treatment with this heat amount, high-quality metal can be produced efficiently.

[0055] The reduction step S4 is characterized by adding a reducing agent (second reducing agent) containing coal and at least one of charcoal and starch to reduce the mixture. One method for clarifying the behavior of samples in a reduction furnace is to measure TG and DTA curves using a TG / DTA (differential thermal analysis / thermogravimetry) analyzer. TG / DTA is an instrument that can simultaneously perform differential thermal analysis and thermogravimetry, and the TG and DTA curves can reveal behavior such as sample decomposition and phase transitions exhibited when the sample is subjected to temperature changes. The TG curve represents the weight of the sample versus temperature, and the DTA curve represents the temperature difference between the sample and a reference material versus temperature.

[0056] Figure 2 shows the TG and DTA curves of starch measured using TG / DTA. The TG curve of starch shows a rapid weight loss around 240°C when heated from room temperature, and the DTA curve of starch shows a large maximum around 600°C. This indicates that the decomposition temperature of starch is relatively low compared to that of coal. Therefore, it is speculated that starch can undergo a rapid reduction reaction at relatively low temperatures. This is thought to be because starch is a polymer composed of carbon, hydrogen, and oxygen. When heated, the bonds between these hydrogen and carbon are broken, generating H2 gas, creating a porous structure, and the bonds between the carbon atoms that make up starch are weak.

[0057] 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 indicates that the decomposition temperature of charcoal is relatively low compared to that of coal. Therefore, it is speculated that charcoal can promote reduction reactions at a fast reaction rate even at relatively low temperatures. This is because charcoal is produced by steaming wood, which evaporates the moisture in the wood, resulting in a porous structure and weak bonds between the carbon atoms that make up charcoal.

[0058] Figure 4 shows the TG and DTA curves of "coal" measured using TG / DTA. Compared to charcoal, the TG curve of coal shows almost no weight change when heated from room temperature, and is also almost broad. The weight loss around 420°C is thought to be due to the decomposition and evaporation of volatile organic matter. This indicates that the decomposition temperature of coal is relatively higher than that of charcoal. Therefore, it is speculated that coal can undergo 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 (carbonization) of plants and oxides through long-term exposure to geothermal heat and geopressure. Therefore, it is thought that the carbon atoms derived from plants are concentrated, resulting in strong bonds between the carbon atoms that make up coal.

[0059] In the smelting method according to the present embodiment, a second reducing agent containing at least one of charcoal and starch, which have a relatively low decomposition temperature and are substantially free of other components such as oxides, and coal, which have a relatively high decomposition temperature and may contain oxides, is introduced into a reducing furnace to reduce the mixture. As a result, even if a portion of the metal obtained is re-oxidized due to oxygen inevitably mixed in through the reduced material recovery port, the mixture inlet, the second reducing agent inlet, oxygen supplied by the burner, or water generated by combustion of the burner fuel, the second reducing agent containing starch and coal can reduce the metal again, preventing further oxidation of the metal obtained, thereby improving the quality of the metal obtained.

[0060] In the smelting method according to the present embodiment, a reducing agent containing coal and charcoal may be used as the second reducing agent, which can prevent a portion of the resulting metal from being oxidized, thereby improving the quality of the resulting metal.

[0061] In the smelting method according to the present embodiment, a reducing agent containing coal and starch may be used as the second reducing agent, which can prevent a portion of the resulting metal from being oxidized, thereby improving the quality of the resulting metal.

[0062] In the smelting method according to the present embodiment, a reducing agent containing coal, starch, and charcoal may be used as the second reducing agent, which can prevent a portion of the resulting metal from being oxidized, thereby improving the quality of the resulting metal.

[0063] The second reducing agent can be introduced into the reducing furnace through a predetermined inlet of the reducing furnace. The location of introduction is not particularly limited, and it may be near the mixture, near a heat source (for example, a burner flame), or between the mixture and a heat source (for example, a burner flame). In particular, the introduction location is preferably near the mixture.

[0064] The second reducing agent may be introduced into the reducing furnace at any timing. For example, the second reducing agent may be introduced into the reducing furnace before the reduction treatment is performed, the second reducing agent may be introduced into the reducing furnace while the temperature is rising to a set reduction temperature, the second reducing agent may be introduced into the reducing furnace when the set reduction temperature is reached, the second reducing agent may be introduced into the reducing furnace when the reduction reaction has progressed to a certain extent after the reduction temperature is reached (or while the set reduction temperature is being maintained), or the second reducing agent may be introduced into the reducing furnace when the reduction reaction is completed.

[0065] The amount (feed amount) of the second reducing agent fed into the reduction furnace is not particularly limited, but is preferably set to a ratio of 3% by mass to 100% by mass, more preferably 4% by mass to 70% by mass, and even more preferably 5% by mass to 50% by mass, where 100% by mass is the amount of reducing agent required to adequately reduce the iron oxide and nickel oxide contained in the nickel oxide ore that constitutes the mixture. By setting the amount of the second reducing agent to 3% by mass or more, reoxidation of the generated metal can be more effectively suppressed. Furthermore, by setting the amount of the second reducing agent to 100% by mass or less, the possibility of over-reduction can be reduced, thereby suppressing a decrease in the nickel grade in the metal.

[0066] The second reducing agent is not particularly limited, and may be, for example, a carbonaceous reducing agent such as coal or coke, or a plant-derived organic reducing agent such as charcoal, bamboo charcoal, or starch.

[0067] When a plant-derived organic reducing agent is used as the second reducing agent, there is a possibility that the plant-derived organic reducing agent may burn during the thermal reduction treatment. Therefore, it is preferable to perform the reduction treatment on the mixture in a reduction furnace under an atmosphere with a low oxygen concentration. For example, the reduction treatment under an atmosphere with a low oxygen concentration is preferably performed under an atmosphere with an oxygen concentration of 3.0% by volume or less, and more preferably under an atmosphere with an oxygen concentration of 1.0% by volume or less. The reduction treatment may also be performed under an inert gas atmosphere such as nitrogen or argon.

[0068] When a reducing agent containing coal and charcoal is used as the second reducing agent, the amount of coal added to the second reducing agent is not particularly limited, but is preferably 1% by mass or more and 15% by mass or less, more preferably 3% by mass or more and 12% by mass or less, and even more preferably 6% by mass or more and 11% by mass or less, when the amount of reducing agent necessary to adequately reduce the nickel oxide and iron oxide that constitute the nickel oxide ore is taken as 100% by mass.

[0069] When a reducing agent containing coal and charcoal is used as the second reducing agent, the amount of charcoal added to the second reducing agent is not particularly limited, but when the amount of reducing agent necessary to properly reduce the nickel oxide and iron oxide that constitute the nickel oxide ore is taken as 100 mass%, the amount of charcoal is preferably 1.0 mass% or more and 10.0 mass% or less, more preferably 1.3 mass% or more and 7.0 mass% or less, and even more preferably 1.5 mass% or more and 4.5 mass% or less.

[0070] When a reducing agent containing coal and charcoal is used as the second reducing agent, the total content of charcoal and coal in the second reducing agent is preferably 50 mass% or more of the total amount of the second reducing agent, preferably 70 mass% or more, and more preferably 90 mass% or more, and it is most preferable that the second reducing agent consists only of charcoal and coal (i.e., the total content of charcoal and coal is 100 mass% of the total amount of the reducing agent).

[0071] When a reducing agent containing coal and starch is used as the second reducing agent, the amount of coal added to the second reducing agent is not particularly limited, but is preferably 0.01% by mass or more and 15% by mass or less, more preferably 0.03% by mass or more and 12% by mass or less, and even more preferably 0.05% by mass or more and 11% by mass or less, when the amount of reducing agent necessary to adequately reduce the nickel oxide and iron oxide that constitute the nickel oxide ore is taken as 100% by mass.

[0072] When a reducing agent containing coal and starch is used as the second reducing agent, the amount of starch added in the second reducing agent is not particularly limited, but is preferably 0.01% by mass or more and 15% by mass or less, more preferably 0.03% by mass or more and 10% by mass or less, and even more preferably 0.05% by mass or more and 6% by mass or less, when the amount of reducing agent necessary to adequately reduce the nickel oxide and iron oxide that constitute the nickel oxide ore is taken as 100% by mass.

[0073] When a reducing agent containing coal and starch is used as the second reducing agent, the total content of starch and coal in the second reducing agent is preferably 50 mass% or more of the total amount of the second reducing agent, preferably 70 mass% or more, and more preferably 90 mass% or more, and it is most preferable that the second reducing agent consists only of starch and coal (i.e., the total content of starch and coal is 100 mass% of the total amount of the reducing agent).

[0074] When a reducing agent containing coal, charcoal, and starch is used as the second reducing agent, the total amount of starch and charcoal added in the second reducing agent is not particularly limited, but is preferably 0.01% by mass or more and 15% by mass or less, more preferably 0.03% by mass or more and 10% by mass or less, and even more preferably 0.05% by mass or more and 6% by mass or less, when the amount of reducing agent necessary to properly reduce the nickel oxide and iron oxide that constitute the nickel oxide ore is taken as 100% by mass.

[0075] When a reducing agent containing coal, charcoal, and starch is used as the second reducing agent, the ratio of the starch to the charcoal in the second reducing agent is not particularly limited, but the mixing ratio of the chemical equivalent of the starch mixed with the nickel oxide ore to the chemical equivalent of the 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.

[0076] When a reducing agent containing coal, charcoal, and starch is used as the second reducing agent, the total content of starch, coal, and charcoal 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 consists only of starch, coal, and charcoal (i.e., the total content of starch, coal, and charcoal is 100% by mass of the total amount of the reducing agent).

[0077] Furthermore, the introduction of the second reducing agent into the reducing furnace may be carried out in two or more stages. Specifically, the reduction process may be divided into two stages: a first reduction stage in which at least a portion of the second reducing agent is introduced into the reducing furnace in an early stage of the reduction treatment to reduce the mixture, and a second reduction stage in which the remaining second reducing agent is introduced into the reducing furnace in a later stage of the reduction treatment to reduce the mixture. In this case, the second reducing agent may be introduced into the reducing furnace through a single inlet, or may be introduced separately through multiple inlets of the reducing furnace.

[0078] When the reduction process includes a first reduction step and a second reduction step, the amount of the second reducing agent added in the first reduction step is not particularly limited, but is preferably 1% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less, when the amount of reducing agent necessary to reduce the nickel oxide and iron oxide constituting the nickel oxide ore in the exact amount is taken as 100% by mass.

[0079] When the reduction process includes a first reduction step and a second reduction step, the amount of the second reducing agent added in the second reduction step is not particularly limited, but is preferably 1% by mass or more and 7% by mass or less, and more preferably 1% by mass or more and 4% by mass or less, when the amount of reducing agent necessary to reduce the nickel oxide and iron oxide constituting the nickel oxide ore in the exact amount is taken as 100% by mass.

[0080] Furthermore, in the case of a reduction process having a first reduction step and a second reduction step, in the first reduction step, which is an early stage of the reduction treatment, a reducing agent containing coal is introduced into a reduction furnace to reduce the mixture, and in the second reduction step, which is a later stage of the reduction treatment, a reducing agent containing at least one of charcoal and starch is introduced into the reduction furnace to reduce the mixture. The decomposition temperature of coal is relatively high compared to the decomposition temperature of charcoal. Therefore, by introducing coal, which is relatively difficult to decompose, into the reduction furnace in the first reduction step, which is an early stage of the reduction treatment, a reducing atmosphere can be maintained for a long period of time. Furthermore, by introducing at least one of charcoal and starch, which are relatively easy to decompose and can cause the reduction reaction to proceed at a fast reaction rate, into the reduction furnace in the second reduction step, which is a later stage of the reduction treatment, it is possible to effectively re-reduce the reoxidized metal.

[0081] In this case, the "reducing agent containing coal" and the "reducing agent containing at least one of charcoal and starch" may be charged through the same charging port. Alternatively, the reduction furnace may be provided with multiple charging ports, and the "reducing agent containing at least one of charcoal and starch" may be charged through one charging port and the "reducing agent containing coal" may be charged through another charging port.

[0082] In a reduction process including a first reduction step and a second reduction step, the first reduction step and the second reduction step may be heat-treated in stages at different temperatures. For example, the temperature in the treatment chamber may be controlled so that the first reduction step is performed at a reduction temperature in the range of 1150°C to 1350°C, and the temperature in the other treatment chamber may be controlled so that the second reduction step is performed at a reduction temperature in the range of 1350°C to 1450°C. By performing heat treatment in stages at different temperatures in this manner, by adding coal, which is relatively difficult to decompose in the relatively low temperature range of the first reduction step, to the reduction furnace, a reducing atmosphere can be maintained for a long time, the reduction reaction can be carried out uniformly, and metal can be efficiently produced. In addition, by adding a reducing agent containing at least one of charcoal and starch, which is relatively easy to decompose in the relatively high temperature range of the second reduction step and can cause the reduction reaction to proceed at a high reaction rate, to the reduction furnace, reoxidization of the reoxidized metal can be effectively suppressed in a short time.

[0083] For example, when a reducing agent containing coal and charcoal is used as the second reducing agent to be charged into the reduction furnace, the temperature inside the treatment chamber may be controlled so that the reduction treatment in the first reduction step can be performed at a reduction temperature in the range of 1250°C to 1350°C, and the temperature inside the other treatment chamber may be controlled so that the reduction treatment in the second reduction step can be performed at a reduction temperature in the range of 1350°C to 1450°C.

[0084] For example, when a reducing agent containing coal and starch is used as the second reducing agent to be charged into the reduction furnace, the temperature inside the treatment chamber may be controlled so that the reduction treatment in the first reduction step can be performed at a reduction temperature in the range of 1150°C to 1250°C, and the temperature inside the other treatment chamber may be controlled so that the reduction treatment in the second reduction step can be performed at a reduction temperature in the range of 1350°C to 1450°C.

[0085] For example, when a reducing agent containing coal, charcoal, and starch is used as the second reducing agent to be charged into the reduction furnace, the temperature inside the treatment chamber may be controlled so that the reduction treatment in the first reduction step can be performed at a reduction temperature in the range of 1150°C to 1350°C, and the temperature inside the other treatment chamber may be controlled so that the reduction treatment in the second reduction step can be performed at a reduction temperature in the range of 1350°C to 1450°C.

[0086] The reduction furnace used in the reduction heat treatment is not particularly limited. For example, a fixed hearth or a mobile hearth furnace may be used, but a mobile hearth furnace is preferably used. By using a mobile hearth furnace as such a reduction furnace, the mixture can be treated more efficiently. Furthermore, by using a mobile hearth furnace, the reduction reaction proceeds continuously and the reaction can be completed in one facility, allowing for more accurate control of the treatment temperature than if the treatments in each step were performed using separate furnaces. Furthermore, heat loss between each treatment is reduced, allowing for more efficient operation. Below, the configuration of a rotary hearth furnace as an example of a mobile hearth furnace is described using Figure 4.

[0087] FIG. 4 is a diagram (plan view) showing an example of the configuration of a rotary hearth furnace with a rotating hearth. As shown in FIG. 4, a circular rotary hearth furnace 2 that is divided into multiple treatment chambers 20a to 20d can be used. In the rotary hearth furnace 2, each treatment is performed in each zone while rotating in a predetermined direction. In this rotary hearth furnace, the treatment temperature in each zone can be adjusted by controlling the time it takes to pass through each zone (travel time, rotation time), and the mixture 1 is smelted with each rotation of the rotary hearth furnace. Here, the rotary hearth furnace 2 may be provided with a preheating chamber outside the furnace. Furthermore, 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.

[0088] When performing reduction treatment using a rotary hearth furnace, heating treatment may be performed in stages at different temperatures. When the reduction process includes a first reduction step in which a reducing agent containing at least one of charcoal and starch is introduced into a reduction furnace to reduce the mixture, and a second reduction step in which a reducing agent containing coal is introduced into the reduction furnace to reduce the mixture, it is preferable to perform the reduction treatment using a rotary hearth furnace. Specifically, the temperature in one treatment chamber is controlled so that the reduction treatment in the first reduction step is performed at a reduction temperature ranging from 1150°C to 1350°C, and the temperature in the other treatment chamber is controlled so that the reduction treatment in the second reduction step is performed at a reduction temperature ranging from 1350°C to 1450°C. By introducing relatively difficult-to-decompose coal into a treatment chamber controlled at a temperature ranging from 1150°C to 1350°C, the reducing atmosphere can be maintained for a long period of time, allowing the reduction reaction to occur uniformly and metal to be efficiently produced. Furthermore, by introducing at least one of charcoal and starch, which are relatively easy to decompose and can cause the reduction reaction to proceed at a fast reaction rate, into a treatment chamber whose temperature is controlled to a range of 1350°C or higher and 1450°C or lower, it is possible to effectively suppress the reoxidation of the reoxidized metal in a short period of time.

[0089] For example, when a reducing agent containing coal and charcoal is used as the second reducing agent to be charged into the reduction furnace, the temperature in one treatment chamber may be controlled so that the reduction treatment in the first reduction step can be 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 reduction treatment in the second reduction step can be performed at a reduction temperature in the range of 1350°C to 1450°C.

[0090] For example, when a reducing agent containing coal and starch is used as the second reducing agent to be charged into the reduction furnace, the temperature in one treatment chamber may be controlled so that the reduction treatment in the first reduction step can be 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 reduction treatment in the second reduction step can be performed at a reduction temperature in the range of 1350°C to 1450°C.

[0091] For example, when a reducing agent containing coal, charcoal, and starch is used as the second reducing agent to be charged into the reduction furnace, the temperature in one treatment chamber may be controlled so that the reduction treatment in the first reduction step can be performed at a reduction temperature in the range of 1150°C to 1350°C, and the temperature in the other treatment chamber may be controlled so that the reduction treatment in the second reduction step can be performed at a reduction temperature in the range of 1350°C to 1450°C.

[0092] In this case, it is preferable to provide multiple inlets for each treatment chamber of the reducing furnace so that the charcoal-containing reducing agent and the coal-containing reducing agent can be fed into different treatment chambers of the reducing furnace, and to feed the "reducing agent containing at least one of charcoal and starch" and the "coal-containing reducing agent" from each inlet. Furthermore, the "starch-containing reducing agent" and the "charcoal-containing reducing agent" may be fed from the same inlet, or the "starch-containing reducing agent" and the "charcoal-containing reducing agent" may be fed from different inlets.

[0093] The heating means for the reducing furnace is not particularly limited, and may be a burner or a device using electricity, etc. A burner is preferred because it can effectively subject the mixture to a heating and reduction treatment in a short period of time. When a reducing furnace having a burner is used, 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.

[0094] <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 thermal reduction treatment is cooled, and if necessary, pulverized to form a powder, and the metal (metal powder particles) is separated and recovered.

[0095] As a method for separating the metal phase and the slag phase from the mixture of the metal phase and the slag phase obtained as a solid, in addition to removing unnecessary substances by sieving, methods such as separation by specific gravity or separation by magnetic force can be used.

[0096] Furthermore, the resulting metal phase and slag phase can be easily separated due to their poor wettability. For example, by subjecting the large inclusions obtained by the reduction step S4 described above to an impact, such as by dropping them over a predetermined drop or by applying a predetermined vibration during sieving, the metal phase and slag phase can be easily separated from the inclusions.

[0097] By separating the metal phase from the slag phase in this manner, the metal phase is recovered. [Example]

[0098] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to the following examples in any way.

[0099] (First embodiment) [Mixing process] For each sample, nickel oxide ore as raw ore, iron ore, silica sand and limestone as flux components, a binder, and a first reducing agent were mixed in a mixer while adding an appropriate amount of water to obtain a mixture. Coal was used as the reducing agent, and the nickel oxide and iron oxide (Fe2O3) contained in the nickel oxide ore as raw ore were contained in an amount of 30 to 45 mass% relative to the required chemical equivalent of 100 mass%.

[0100] [Clumping process] Next, an appropriate amount of water was added to the mixture obtained in the mixing process, and the mixture was pelletized using a pelletizer to obtain lumps (samples) with a diameter of 15±0.2 mm.

[0101] [Drying process] Next, the lumps obtained in the agglomeration step were dried by blowing hot air at 200 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 composition (excluding carbon) of the lumps (samples) after drying.

[0102] [Table 3]

[0103] [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, with the temperature condition for charging into the reduction furnace being 500±20°C.

[0104] Next, the mixture pellets were subjected to a reduction heat treatment at a reduction temperature of 1380°C for 50 minutes. At this time, 10 minutes after the start of reduction, coal was charged into the reduction furnace as a second reducing agent through one of the inlets of the reduction furnace (reduction step 1). Also, 40 minutes after the start of reduction, charcoal was charged into the reduction furnace as a second reducing agent through the other inlet of the reduction furnace (reduction step 2). The reduction furnace was purged with nitrogen to create a substantially oxygen-free nitrogen atmosphere, thereby preventing oxygen from the outside air from entering the furnace through the inlet. Table 4 below shows the amount of the second reducing agent added. In Comparative Examples 1-1 to 1-3, the second reducing agent was not charged into the reduction furnace. After the reduction treatment, the samples were quickly cooled to room temperature in the nitrogen atmosphere and then removed into the air.

[0105] [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 nickel content in the metal were then analyzed and calculated using an ICP emission spectrometer (SHIMAZU S-8100 model).

[0106] The nickel metallization rate, nickel content in the metal, and nickel metal recovery rate were calculated using the following formulas (1), (2), and (3). Nickel metallization rate = mass of nickel in metal / (mass of all nickel in the reduced product) × 100 (%) (1) Nickel content in metal = mass of nickel in metal / (total mass of nickel and iron in metal) × 100 (%) (2) Nickel metal recovery rate = amount of recovered nickel / (amount of ore input × nickel content in ore) × 100 (3)

[0107] Table 4 below shows the nickel metallization rate, nickel content in the metal, and nickel metal recovery rate for each sample.

[0108] [Table 4]

[0109] As shown in the results in Table 4, in Examples 1-1 to 1-5 in which the second reducing agent was added to the reduction furnace and the mixture was subjected to reduction treatment, good results were obtained in terms of the nickel metallization rate and the nickel content in the metal.

[0110] Among these, in Examples 1-3 to 1-5, in which a reducing agent containing coal and charcoal was used as the second reducing agent, better results were obtained in terms of nickel metallization rate and nickel content in metal compared to Examples 1-1 and 1-2.

[0111] On the other hand, in Comparative Examples 1-1 to 1-3, in which the mixture was subjected to reduction treatment without adding a second reducing agent to the reduction furnace, 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.

[0112] (Second embodiment) [Mixing process] For each sample, nickel oxide ore as raw ore, iron ore, silica sand and limestone as flux components, a binder, and a first reducing agent were mixed in a mixer while adding an appropriate amount of water to obtain a mixture. Coal was used as the reducing agent, and the nickel oxide and iron oxide (Fe2O3) contained in the nickel oxide ore as raw ore were contained in an amount of 30 to 45 mass% relative to the required chemical equivalent of 100 mass%.

[0113] [Clumping process] Next, an appropriate amount of water was added to the mixture obtained in the mixing process, and the mixture was pelletized using a pelletizer to obtain lumps (samples) with a diameter of 15±0.2 mm.

[0114] [Drying process] Next, the lumps obtained in the agglomeration step were dried by blowing hot air at 200 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 5 below shows the solid composition (excluding carbon) of the lumps (samples) after drying.

[0115] [Table 5]

[0116] [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, with the temperature condition for charging into the reduction furnace being 500±20°C.

[0117] Next, the mixture pellets were subjected to a reduction heat treatment at a reduction temperature of 1380°C for 50 minutes. At this time, 10 minutes after the start of reduction, coal was charged into the reduction furnace as a second reducing agent through one of the inlets of the reduction furnace (reduction step 1). Also, 40 minutes after the start of reduction, starch was charged into the reduction furnace as a second reducing agent through the other inlet of the reduction furnace (reduction step 2). Nitrogen purging was performed inside the reduction furnace to create a substantially oxygen-free nitrogen atmosphere, thereby preventing oxygen from the outside air from entering the furnace through the inlet. Table 6 below shows the amount of the second reducing agent added. In Examples 2-1 to 2-5, the starch was charged into the reduction furnace and then quickly cooled to room temperature within the reduction furnace 10 minutes later, and the sample was then removed into the atmosphere. In Comparative Examples 1 to 4, on the other hand, no second reducing agent was charged into the reduction furnace.

[0118] [Recovery process] After the reduction heat treatment, each reduced product (sample) was crushed by wet processing, and then the metal was recovered by magnetic separation. Then, as in the first embodiment, the nickel metallization rate, the nickel content in the metal, and the nickel metal recovery rate were measured.

[0119] Table 6 below shows the nickel metallization rate, nickel content in the metal, and nickel metal recovery rate for each sample.

[0120] [Table 6]

[0121] As shown in the results in Table 6, in Examples 2-1 to 2-5, in which a second reducing agent containing coal and starch was added to the reduction furnace and the mixture was subjected to reduction treatment, good results were obtained in terms of nickel metallization rate and nickel content in the metal.

[0122] On the other hand, in Comparative Examples 2-1 to 2-4, in which the mixture was subjected to reduction treatment without adding a second reducing agent to the reduction furnace, 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.

[0123] (Third embodiment) [Mixing process] For each sample, nickel oxide ore as raw ore, iron ore, silica sand and limestone as flux components, a binder, and a first reducing agent were mixed in a mixer while adding an appropriate amount of water to obtain a mixture. Coal was used as the reducing agent, and the nickel oxide and iron oxide (Fe2O3) contained in the nickel oxide ore as raw ore were contained in an amount of 30 to 45 mass% relative to the required chemical equivalent of 100 mass%.

[0124] [Clumping process] Next, an appropriate amount of water was added to the mixture obtained in the mixing process, and the mixture was pelletized using a pelletizer to obtain lumps (samples) with a diameter of 15±0.2 mm.

[0125] [Drying process] Next, the lumps obtained in the agglomeration step were dried 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 7 below shows the solid composition (excluding carbon) of the lumps (samples) after drying.

[0126] [Table 7]

[0127] [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, with the temperature condition for charging into the reduction furnace being 500±20°C.

[0128] Next, the mixture pellets were subjected to a reduction heat treatment at a reduction temperature of 1380°C for 50 minutes. Ten minutes after the start of reduction, coal was introduced into the reduction furnace as a second reducing agent through one of the furnace's inlets (reduction step 1). Forty minutes after the start of reduction, starch and charcoal were introduced into the reduction furnace as second reducing agents through the other inlet (reduction step 2). The weight ratio of the starch and charcoal reducing agents was 1:1. Nitrogen purging was performed inside the reduction furnace to create a substantially oxygen-free nitrogen atmosphere, preventing oxygen from the outside air from entering the furnace through the inlet. Table 8 below shows the amount of the second reducing agent added. For Examples 3-1 to 3-5, the starch and charcoal were introduced into the reduction furnace, and 10 minutes later, the samples were quickly cooled to room temperature in the reduction furnace and then removed into the atmosphere. For Comparative Examples 3-1 to 3-4, no second reducing agent was introduced into the reduction furnace.

[0129] [Recovery process] After the reduction heat treatment, each reduced product (sample) was crushed by wet processing, and then the metal was recovered by magnetic separation. Then, as in the first embodiment, the nickel metallization rate, the nickel content in the metal, and the nickel metal recovery rate were measured.

[0130] Table 8 below shows the nickel metallization rate, nickel content in the metal, and nickel metal recovery rate for each sample.

[0131] [Table 8]

[0132] As shown in the results in Table 8, in Examples 3-1 to 3-5, in which a second reducing agent containing starch and charcoal was added to the reduction furnace and the mixture was subjected to reduction treatment, good results were obtained in terms of nickel metallization rate and nickel content in the metal.

[0133] On the other hand, in Comparative Examples 3-1 to 3-4, in which the mixture was subjected to reduction treatment without adding a second reducing agent to the reduction furnace, 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. [Explanation of symbols]

[0134] 1 charging port 2 Rotary hearth furnace 20a~20d Processing chamber 21 Preheating chamber 22 Cooling room

Claims

1. 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 adding a second reducing agent to the reduction furnace to subject the mixture to a reduction treatment; and In the reduction step, a reducing agent containing coal as the second reducing agent and further containing at least one of charcoal and starch is used; The reduction step a first reduction step of introducing at least a portion of the second reducing agent into the reduction furnace to perform a reduction treatment on the mixture; a second reduction step of introducing the remaining second reducing agent into the reduction furnace to subject the mixture to a reduction treatment; and In the first reduction step, a reducing agent containing coal is introduced into the reduction furnace to subject the mixture to a reduction treatment; In the second reduction step, a reducing agent containing at least one of charcoal and starch is introduced into the reduction furnace to perform a reduction treatment on the mixture. A method for smelting nickel oxide ore.

2. In the reduction step, a reducing agent containing coal and charcoal is used as the second reducing agent. The method for smelting nickel oxide ore according to claim 1.

3. In the reduction step, a reducing agent containing coal and starch is used as the second reducing agent. The method for smelting nickel oxide ore according to claim 1.

4. In the reduction step, a reducing agent containing coal, starch, and charcoal is used as the second reducing agent. The method for smelting nickel oxide ore according to claim 1.

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