Method for smelting nickel oxide ore

Abstract

To provide a method for producing ferronickel by forming pellets from nickel oxide ore and reducing the pellets which can produce high-quality ferronickel at low cost with high productivity and efficiency.SOLUTION: A melting method for producing ferronickel by forming pellets from nickel oxide ore and reducing the pellets includes: a mixing step of mixing at least nickel oxide ore and carbonaceous reducing agent; a mixture molding step of molding the resulting mixture into pellets; and a reduction step of heating the pellets at a predetermined reduction temperature in a reduction furnace. In the mixture molding step, the carbonaceous reducing agent is applied to the surface of the pellets, and at least part of the carbonaceous reducing agent applied to the pellets is a plant-derived component.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for smelting nickel oxide ores. [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 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 wet smelting 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, first, a pretreatment is performed to turn the raw material ore into agglomerates, slurry, etc. Specifically, when turning nickel oxide ore into agglomerates, that is, turning it from a powder or fine particle state 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 turn it into agglomerates (referring to pellets, briquettes, etc., hereinafter simply referred to as "pellets") of about 10 mm to 30 mm in size.

[0004] The pellets need to have a certain degree of breathability to allow the moisture contained therein to evaporate. Also, if the 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. Therefore, it is important to mix the mixture uniformly and to maintain as uniform a temperature as possible during the reduction treatment of the pellets.

[0005] In addition, it is also important to coarsen the ferronickel produced by reduction. This is because, if the produced ferronickel has a fine 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 is significantly reduced. For this reason, a process for coarsening the ferronickel after reduction is also necessary.

[0006] In addition, reducing smelting costs is also an important technological issue, and there is a demand for continuous processing that can be operated in compact facilities.

[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 are supplied onto the hearth of a moving-bed type reducing melting furnace, heated, and the metal oxide is reduced and melted, in which agglomerates having an average diameter of 19.5 mm to 32 mm are supplied onto the hearth and heated so as to have a laying density of 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. In this method, it is disclosed that the productivity of granular metallic iron can be increased by controlling both the laying density and the average diameter of the agglomerates.

[0008] However, the method disclosed in Patent Document 1 is a technique 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 is a demand for obtaining higher quality ferronickel by controlling the reaction occurring inside the agglomerates to increase the reaction efficiency and to advance the reduction reaction more uniformly.

[0009] 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. Therefore, 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, so that the method has low productivity. These reasons also cause the manufacturing cost to increase.

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

[0011] [Patent Document 1] JP 2011-256414 A Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been proposed in view of the above circumstances, and has an object to provide a method for producing ferronickel by forming pellets from nickel oxide ore and reducing the pellets, which has high productivity and efficiency and can produce high-quality ferronickel at low cost. [Means for solving the problem]

[0013] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have found that high-quality ferronickel can be efficiently produced by forming a mixture containing nickel oxide ore and a carbonaceous reducing agent into pellets, coating the surfaces of the formed pellets with a carbonaceous reducing agent at least a part of which is a plant-derived component, and subjecting the pellets to a reduction heat treatment, and have thus completed the present invention.

[0014] (1) A first invention of the present invention is a smelting method for producing ferro-nickel by forming pellets from nickel oxide ore and reducing the pellets, the method comprising a mixing process step of mixing at least the nickel oxide ore with a carbonaceous reducing agent, a mixture forming process step of forming the resulting mixture into pellets, and a reduction process step of heating the pellets at a predetermined reduction temperature in a reduction furnace, wherein in the mixture forming process, a carbonaceous reducing agent is applied to the surfaces of the pellets, and at least a part of the carbonaceous reducing agent applied to the pellets is a plant-derived component.

[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 carbonaceous reducing agent of plant origin is starch.

[0016] (3) A third aspect of the present invention is a method for smelting nickel oxide ore according to the first or second aspect of the present invention, wherein in the mixture forming step, the carbonaceous reducing agent is applied to the pellets in an amount of 2 to 50 mass % when an amount of carbon in the carbonaceous reducing agent required for reducing iron oxide and nickel oxide contained in the nickel oxide ore constituting the pellets without excess or deficiency is taken as 100 mass %.

[0017] (4) A fourth aspect of the present invention is a method for smelting nickel oxide ore according to any one of the first to third aspects of the present invention, further comprising a separation step of obtaining ferronickel by separating slag from a reduction product obtained through the reduction step. Effect of the Invention

[0018] According to the present invention, in a method for producing ferronickel by forming pellets from nickel oxide ore and reducing the pellets, it is possible to provide a method which is highly productive and efficient and capable of producing high-quality ferronickel at low cost. [Brief description of the drawings]

[0019] [Figure 1]FIG. 1 is a diagram showing an example of a flow of a method for smelting nickel oxide ore. [Diagram 2] FIG. 2 is a flow chart showing an example of a process flow in a mixture molding step. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail below. 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 addition, in this specification, the expression "X to Y" (X and Y are arbitrary numerical values) means "X or more and Y or less."

[0021] The method for smelting nickel oxide ore according to the present embodiment is a method for forming pellets from a mixture containing nickel oxide ore as a raw material ore and a reducing agent, charging the pellets into a reduction furnace and subjecting them to a reduction treatment to generate ferronickel metal and slag. Specifically, nickel (nickel oxide) and iron (iron oxide) in the nickel oxide ore constituting the pellets are reduced to generate ferronickel metal and slag, which are iron-nickel alloys, and the metal is separated from the slag to produce ferronickel.

[0022] This method is characterized in that in the mixture molding step, a carbonaceous reducing agent is applied to the surface of the pellets, and a plant-derived component is used as at least a part of the carbonaceous reducing agent applied to the pellets.

[0023] The term "pellet" refers to a compact made from a mixture containing nickel oxide ore and a carbonaceous reducing agent, and has a lump shape. The shape of the pellet may be any shape, such as a sphere, an ellipse, a cube, a rectangular solid, or a cylinder.

[0024] Fig. 1 is a diagram showing an example of the flow of a method for smelting nickel oxide ore. As shown in Fig. 1, this smelting method includes a mixing process S1 in which nickel oxide ore is used as a raw material and mixed with a carbonaceous reducing agent to obtain a mixture, a mixture forming process S2 in which the obtained mixture is formed into a predetermined shape to form pellets, a reduction process S3 in which the pellets are heated at a predetermined reduction temperature in a reduction furnace, and a separation process S4 in which slag is separated from the reduced product produced by reduction to recover ferronickel metal.

[0025] [Mixing process] The mixing process S1 is a process for mixing raw powders including nickel oxide ore to obtain a mixture. Specifically, a carbonaceous reducing agent is added to the raw material ore, nickel oxide ore, and mixed, and powders having a particle size of, for example, about 0.2 mm to 0.8 mm, such as iron ore, flux components, and binders, are mixed as optional additives to obtain a mixture.

[0026] The nickel oxide ore as the raw material ore is not particularly limited, but limonite ore, saprolite ore, etc. Typical components of nickel oxide ore include nickel oxide (NiO) and iron oxide (Fe2O3).

[0027] The carbonaceous reducing agent is not particularly limited, but examples thereof include coal powder, coke powder, etc. Also, a part or all of the carbonaceous reducing agent may be composed of a plant-derived component, such as starch, etc. It is preferable that the carbonaceous reducing agent has a particle size and particle size distribution equivalent to that of the nickel oxide ore, which is the raw material ore, because this makes it easier to mix uniformly and the reduction reaction also tends to proceed uniformly.

[0028] The amount of the carbonaceous reducing agent mixed is not particularly limited, but is preferably 50% by mass or less, and more preferably 40% by mass or less, when the amount of the carbonaceous reducing agent required to reduce the nickel oxide and iron oxide constituting the nickel oxide ore without excess or deficiency is taken as 100% by mass. The amount of the carbonaceous reducing agent required to reduce the nickel oxide and iron oxide without excess or deficiency can be defined as the total value of the chemical equivalent required to reduce the entire amount of nickel oxide contained in the pellet to nickel metal and the chemical equivalent required to reduce the iron oxide contained in the pellet to iron metal (hereinafter also referred to as the "total value of chemical equivalents").

[0029] Furthermore, the lower limit of the amount of the carbonaceous reducing agent mixed is not particularly limited, but is preferably 20 mass% or more, and more preferably 23 mass% or more, when the total value of the chemical equivalents is 100%.

[0030] In this way, by setting the amount of carbonaceous reducing agent contained in the pellets (mixed amount of carbonaceous reducing agent) to a ratio of 20 mass % or more and 50 mass % or less when the total value of the chemical equivalents is 100 mass %, the reduction reaction can be efficiently progressed and ferronickel with high nickel grade can be efficiently produced.

[0031] The iron ore, which is an optional additive, is not particularly limited, and examples thereof include iron ore with an iron content of about 50 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.

[0032] Table 1 below shows an example of the composition (mass %) of some of the raw material powders mixed in the mixing process S1, but the composition of the raw material powder is not limited to this.

[0033] [Table 1]

[0034] In the mixing process S1, the raw material powder containing nickel oxide ore can be mixed using a mixer or the like. When the raw material powder is mixed to obtain a mixture, the raw material powder may be kneaded to improve mixability. This applies a shear force to the mixture, which breaks down the agglomerations of the carbon reducing agent, raw material powder, etc., allowing for more uniform mixing, and also increases the adhesion of each particle, making it easier to perform a uniform reduction process.

[0035] [Mixture forming process] The mixture forming step S2 is a step of forming the mixture of raw material powders obtained in the mixing step S1 into pellets. The method according to the present embodiment is characterized in that after forming the pellets in the mixing forming step S2, a carbonaceous reducing agent, at least a part of which is a plant-derived component, is applied to the surface of the pellets.

[0036] Fig. 2 is a flow diagram showing an example of the process flow in the mixture forming step S2. As shown in Fig. 2, the mixture forming step S2 includes an agglomeration step S21 for forming the mixture into lumps, a coating step S22 for coating the obtained lumps with a carbonaceous reducing agent, and a drying step S23 for drying the coated lumps. Note that "coating" includes the meaning of coating the surface of the pellets, and may refer not only to a mode in which the entire pellet surface is covered, but also to a mode in which the pellet surface is adhered to a part of the pellet surface.

[0037] (1) Agglomeration process In the agglomeration process S21, the mixture obtained in the mixing process S1 is formed into chunks of a predetermined shape and size.

[0038] The shape of the mixture to be molded, i.e., the shape of the pellets, is not particularly limited as long as it can be stacked on the hearth of the reduction furnace, but is preferably an ellipse, a cube, a rectangular parallelepiped, a cylinder, or a sphere. Molding the mixture into such a shape makes the molding process easier and reduces the cost required for molding. In addition, the simpler the molded shape, the more likely it is that the number of pellets with molding defects will be reduced and the easier it is to maintain the strength of the pellets.

[0039] In the agglomeration step S21, 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. By kneading the mixture under high pressure and high shear, it is possible to break up the agglomerations of the raw material powder mixture, to effectively knead the mixture, and to increase the strength of the resulting pellets.

[0040] It is also possible to form the powder using a briquette press. The appropriate equipment can be selected in consideration of the equipment, pellet strength, yield, etc.

[0041] (2) Coating process In the coating step S22, the carbonaceous reducing agent is coated on the surface of the obtained lump (pellet). The carbonaceous reducing agent can be coated on the pellet by, for example, spraying or sprinkling, but a method capable of coating the pellet surface uniformly is preferable. For example, in the case of spherical or rod-shaped pellets, the powdered carbonaceous reducing agent may be applied by rolling it on a spread floor surface.

[0042] As described above, the coating on the surface of the pellet may be applied not only to the entire surface but also to only a part of the surface.

[0043] Here, the carbonaceous reducing agent applied to the pellet surface contains at least a portion of a plant-derived component. Examples of plant-derived components include starch, oil, wheat flour, cellulose, sucrose, lactose, glucose (α-glucose), fructose, and the like. Among these, starch is preferably used. By applying the carbonaceous reducing agent containing at least a portion of a plant-derived component to the pellet surface in this manner, reduction treatment can be performed inexpensively and efficiently, and reoxidation of the generated metal can be effectively suppressed.

[0044] For example, starch, which is a plant-derived component, is cheaper than fossil fuels and there is no concern about depletion. In addition, when considering the production to consumption of plant-derived components, there is no increase in CO2, which is considered to be a greenhouse gas, making it a very environmentally friendly material. In addition, starch does not contain moisture like materials such as coal, so there is no need for energy to evaporate water and there is no risk of deterioration in properties, and there is virtually no risk of explosion or fire, and it is non-toxic, so it is easy to store and handle. Therefore, it is easy to apply to smelting processing and heating costs can be effectively reduced. Furthermore, starch is a product that is highly pure and has little quality variation, so contamination caused by reducing agents can be avoided, and as a result, high-quality ferronickel can be obtained.

[0045] Specifically, starch is a structure consisting of carbon (C), hydrogen (H), and oxygen (O), as shown in the chemical formula below. When this starch is heated and decomposed during the treatment in the reduction process, it is first decomposed into H2O and the like and volatilized, leaving carbon behind. As a result, the fine carbon from which oxygen and hydrogen have been removed becomes a reducing agent and is highly reactive. This makes it possible to uniformly reduce the ore and produce high-quality ferronickel with little quality variation. Examples of starch include corn starch, wheat starch, rice starch, bean starch, potato starch, sweet potato starch, tapioca starch, potato starch, bracken starch, kudzu starch, and the like.

[0046] [ka]

[0047] The amount of carbonaceous reducing agent applied to the pellets is not particularly limited, but it is preferable to apply the carbonaceous reducing agent so that the amount of carbon in the carbonaceous reducing agent required for reducing the iron oxide and nickel oxide contained in the nickel oxide ore constituting the pellets without excess or deficiency is in the range of 2% by mass to 50% by mass, where 100% by mass is taken as the amount of carbon in the carbonaceous reducing agent. Note that the amount of the carbonaceous reducing agent does not include only the amount of plant-derived components contained in at least a part of the carbonaceous reducing agent, but also includes the amount of components other than the plant-derived components.

[0048] If the amount of carbonaceous reducing agent applied to the pellets is less than 2% by mass, it may not be possible to effectively suppress the reoxidation of the generated metal, and if it exceeds 50% by mass, it may cause over-reduction, which may lower the nickel content in the metal.

[0049] (3) Drying process In the drying process S23, a drying process is performed on the pellets (lumps) obtained by coating the surface of the carbonaceous reducing agent in the coating process S22.

[0050] Here, the aggregates obtained by the agglomeration process into pellets 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 will evaporate all at once, expanding and the aggregates may be destroyed. Therefore, by subjecting the obtained pellets to a drying process so that the solid content is, for example, about 70% by mass and the moisture content is about 30% by mass, it is possible to prevent the pellets from collapsing in the reduction heat treatment in the next reduction step S3. This also makes it possible to prevent 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.

[0051] Specifically, the drying process in the drying process step S23 is not particularly limited, but for example, hot air of 200° C. to 400° C. is blown onto the pellets to dry them. Note that by maintaining the temperature of the pellets at less than 100° C. during the drying process, damage to the pellets can be prevented, and the process can be preferably performed.

[0052] When drying large pellets, cracks or breaks may occur before or after drying. When the pellets are large in volume, they melt and shrink during reduction, which often results in cracks or breaks, but the effect of the increase in surface area caused by the cracks or breaks is small, so this is unlikely to cause a major problem. In addition, if the pellets are in a form that does not break, the drying process in the drying process step S22 may be omitted.

[0053] An example of the composition (parts by weight) of the solid content in the pellets after drying is shown in the following Table 2. Note that the composition of the pellets is not limited to this.

[0054] [Table 2]

[0055] [Reduction process] In the reduction step S3, the pellets obtained in the mixture molding step S2 are charged into a reduction furnace and heated to a predetermined reduction temperature for reduction treatment (reduction heat treatment). By such treatment, a reduction product containing ferro-nickel metal, which is an iron-nickel alloy, and slag is produced.

[0056] In particular, in the method according to the present embodiment, since the pellet surface is coated in advance with a highly reactive carbonaceous reducing agent, the reduction reaction proceeds more efficiently and the metal generated in the pellet can be prevented from being oxidized by oxygen, water, etc. that inevitably enter the reduction furnace. In addition, since the carbonaceous reducing agent coated on the pellet surface contains a plant-derived component, the periphery of the pellet can be more effectively maintained in a reducing atmosphere, and high-quality ferronickel can be produced.

[0057] Specifically, in the reduction heat treatment, pellets containing nickel oxide ore are stacked on the hearth of a reduction furnace, and the pellet stack is heated to a temperature of, for example, 1250°C to 1450°C, more preferably, about 1300°C to 1400°C.

[0058] In the reduction heat treatment, for example, in a short time of about 1 minute, nickel oxide and iron oxide contained in the pellet are first reduced and metalized near the pellet surface where the reduction reaction is likely to proceed, becoming an iron-nickel alloy, and forming a shell (hereinafter also referred to as the "shell"). Meanwhile, in the shell, the slag components in the pellet gradually melt as the shell is formed, and a liquid phase slag is generated. As a result, ferronickel metal (hereinafter also referred to simply as "metal") and slag (hereinafter simply referred to as "slag") made of oxides are generated separately in one pellet. Then, when the processing time of the reduction heat treatment in the heat treatment has passed about 10 minutes, the carbon components of the surplus carbonaceous reducing agent that are not involved in the reduction reaction are taken into the iron-nickel alloy, lowering the melting point. As a result, the iron-nickel alloy melts and becomes a liquid phase.

[0059] The time (treatment time) of the reduction heat treatment in the reduction furnace is not particularly limited and can be set according to the temperature of the reduction furnace. For example, it can be 10 minutes or more, and more preferably 15 minutes or more. On the other hand, the upper limit of the treatment time is preferably 50 minutes or less, and more preferably 40 minutes or less, from the viewpoint of suppressing an increase in manufacturing costs.

[0060] The pellet stack that has been subjected to the reducing heat treatment becomes a mixture of large lumps of metal and slag. By performing the reducing heat treatment on pellets with a large apparent volume, large lumps of metal are easily formed, which reduces the effort required for recovery from the reduction furnace and effectively prevents a decrease in the metal recovery rate. The volume of the resulting mixture is shrunk to about 50% to 60% by volume compared to the pellet stack that is charged.

[0061] In the reduction heat treatment, a reducing agent may be added during the reduction reaction. When the reduction reaction progresses to a certain extent, oxidation of the generated metal may occur due to oxygen that is inevitably brought into the furnace and moisture generated by fuel combustion. In this case, reoxidation of the metal can be prevented by adding additional reducing agent during the reduction reaction. The reducing agent is preferably added from the top of the pellets. Reoxidation of the generated oxidized metal can be efficiently prevented by adding the reducing agent from the top of the pellets, where the oxidized metal frequently comes into contact with gas.

[0062] The proportion of the carbonaceous reducing agent in the additional addition of the reducing agent is not particularly limited, but is preferably in the range of about 1% by mass to 30% by mass when the carbonaceous reducing agent contained in the pellets to be subjected to the thermal reduction treatment is taken as 100% by mass. By additionally adding the reducing agent in such a range, oxidation can be efficiently suppressed and over-reduction can be prevented.

[0063] The reduction furnace used in the reduction heat treatment is not particularly limited. For example, a moving hearth furnace can be used. By using a moving hearth furnace as the reduction furnace, the pellets can be treated more efficiently in the reduction furnace. In addition, by using a moving hearth furnace, the reduction reaction proceeds continuously and the reaction can be completed in one facility, and the treatment temperature can be controlled more accurately than when the treatment in each process is performed using separate furnaces.

[0064] Furthermore, by using a moving hearth furnace, the heat loss between each process is reduced, enabling more efficient operation. In other words, if the reaction is carried out using separate furnaces, the temperature drops and heat loss occurs when the pellet stack is moved between furnaces, and the reaction atmosphere changes, so that the reaction does not proceed immediately when the pellets are recharged into the furnace. In contrast, by using a moving hearth furnace to carry out each process in one facility, heat loss is reduced and the atmosphere in the furnace can be accurately controlled, allowing the reaction to proceed more effectively. As a result, a metal with a high nickel content can be obtained more effectively.

[0065] [Separation process] The separation step S4 is a step of separating the metal and slag produced in the reduction step S3 and recovering the metal. Specifically, the metal phase is separated and recovered from a mixture (reduced product) containing a metal phase (metal solid phase) and a slag phase (slag solid phase) obtained by the reduction heat treatment of the pellets.

[0066] Methods for separating the metal phase and the slag phase from the mixture of the metal phase and the slag phase obtained as a solid include, for example, sieving to remove unnecessary materials, as well as separation by specific gravity or magnetic force.

[0067] Furthermore, 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 S3 described above from a predetermined drop or by applying a predetermined vibration during sieving, the metal phase and slag phase can be easily separated from the mixture. EXAMPLES

[0068] 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 in any way.

[0069] [Mixing raw powders] For each sample, nickel oxide ore as raw ore, iron ore, silica sand and limestone as flux components, binder, and carbonaceous reductant (coal powder, carbon content: 45% by weight, average particle size: about 150 μm) were mixed in a mixer while adding an appropriate amount of water to obtain a mixture. Pulverized coal was used as the carbonaceous reductant, and the content was set at the ratio shown in Table 4 below, assuming that the amount required to reduce nickel oxide (NiO) and iron oxide (Fe2O3) contained in the nickel oxide ore as raw ore without excess or deficiency is 100 mass%.

[0070] [Molding the mixture] Next, the mixture obtained for each sample was formed into pellets using a pelletizer, and the pellets obtained were then sieved to collect pellets with a diameter of 15±0.3 mm for use in the test.

[0071] [Carbonaceous reducing agent coating] Next, for samples No. 1 to No. 12 (Examples 1 to 12) which are examples, the pellet surfaces were coated with a carbonaceous reducing agent in the ratio shown in Table 4 below. Starch was used as the carbonaceous reducing agent. For sample No. 13 (Example 13), a mixture of starch and pulverized coal was used as the carbonaceous reducing agent for coating. The amount of the carbonaceous reducing agent applied was determined as an addition ratio when the amount of carbon in the carbonaceous reducing agent required for reducing the iron oxide and nickel oxide contained in the nickel oxide ore constituting the pellets without excess or deficiency was taken as 100 mass%.

[0072] On the other hand, for samples No. 14 to No. 16 (Comparative Examples 1 to 3) which are comparative examples, the pellet surfaces were not coated with a carbonaceous reducing agent.

[0073] Next, each sample was dried by blowing hot nitrogen air at 150°C to 200°C onto it 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 pellets after drying.

[0074] [Table 3]

[0075] [Reducing heat treatment of pellets] The dried sample pellets were then charged into a reduction furnace with a nitrogen atmosphere substantially free of oxygen, with the temperature in the furnace being 500±20°C.

[0076] Next, the pellets were subjected to a reducing heat treatment at the temperature and for the time shown in the following Table 4. After the reducing treatment, the pellets were quickly cooled to room temperature in a nitrogen atmosphere, and then taken out into the air.

[0077] Here, the pellets 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 pellets on top of the ash.

[0078] For each sample after the reduction heat treatment, the nickel metallization rate and the nickel content in the metal were analyzed and calculated using an ICP emission spectrometer (SHIMAZU S-8100 type). Specifically, the nickel metallization rate and the nickel content in the metal were calculated using the following formula. Nickel metallization rate = amount of metallized Ni in the mixture ÷ (total amount of Ni in the mixture) × 100 (%) Nickel content in metal = amount of metalized Ni in the mixture ÷ (total amount of metalized Ni and Fe in the mixture) × 100 (%)

[0079] After the reduction heat treatment, each sample was crushed by wet processing, and the metal was recovered by magnetic separation. The nickel metal recovery rate was calculated from the content of nickel oxide ore in the pellet stack charged into the reduction furnace, the nickel content in the nickel oxide ore, and the amount of recovered nickel. The nickel metal recovery rate was calculated using the following formula. Nickel metal recovery rate = amount of Ni recovered ÷ (amount of oxide ore charged × Ni content in oxide ore) × 100 (%)

[0080] Table 4 below shows the nickel metallization rate, nickel content in the metal, and nickel metal recovery rate for each sample.

[0081] [Table 4]

[0082] As shown in the results in Table 4, in Examples 1 to 13, by coating the pellet surface with a carbonaceous reducing agent, reoxidation of the generated metal could be effectively suppressed, and good results were obtained.

[0083] In contrast, in Comparative Examples 1 to 3, the Ni metallization rate, Ni content, and metal recovery rate were all lower than those of the Examples. This is believed to be due to the occurrence of reoxidation of the metal obtained by the reduction heat treatment.

Claims

1. 1. A smelting method for producing ferro-nickel by forming pellets from nickel oxide ore and reducing the pellets, comprising: a mixing step of mixing at least the nickel oxide ore with a carbonaceous reductant; a mixture forming step of forming the resulting mixture into pellets; A reduction step of heating the pellets in a reduction furnace at a predetermined reduction temperature, In the mixture molding step, starch is applied to the surface of the pellets, The starch is applied to the pellets so that the proportion of the starch is 2.3% by mass or more and 48.0% by mass or less, when the amount of carbon in the carbonaceous reducing agent necessary for reducing the iron oxide and nickel oxide contained in the nickel oxide ore constituting the pellets without excess or deficiency is taken as 100% by mass. A method for smelting nickel oxide ores.

2. The process further comprises a separation step of separating slag from the reduction product obtained through the reduction step to obtain ferronickel.

2. The method for smelting nickel oxide ore according to claim 1.

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