JP7639496B2 - Method for smelting nickel oxide ore - Google Patents

Description

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

Methods for smelting nickel oxide ores called limonite or saprolite include the dry smelting method, which uses a smelting furnace to produce nickel matte by roasting with sulfur, the dry smelting method, which uses a rotary kiln or moving hearth furnace to produce an iron-nickel alloy (hereinafter also referred to as "ferronickel") by reducing with a carbonaceous reducing agent, and the wet smelting method, which uses an autoclave to leach nickel and cobalt with sulfuric acid, and adds a sulfurizing agent to the leachate obtained to produce a mixed sulfide.

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

Pellets need to have a certain degree of breathability to allow the moisture they contain to evaporate. Furthermore, if reduction does not proceed uniformly within the pellets, the composition of the resulting reduced material will be non-uniform, resulting in problems such as metal dispersion or uneven distribution, so it is important to mix the mixture uniformly and to maintain as uniform a temperature as possible during the reduction process of the pellets.

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

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

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

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

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

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

JP 2011-256414 A

The present invention has been proposed in light of these circumstances, and aims to provide a method for producing ferronickel by forming pellets from nickel oxide ore and reducing them, which is highly productive and efficient, and can produce high-quality ferronickel at low cost.

The inventors of the present invention have conducted extensive research to solve the above-mentioned problems. As a result, they have discovered that high-quality ferronickel can be efficiently produced by forming a mixture containing nickel oxide ore and a carbonaceous reducing agent into pellets, applying a carbonaceous reducing agent, at least a portion of which is a plant-derived component, onto the surfaces of the formed pellets, and subjecting the pellets to a reduction heat treatment. This has led to the completion of the present invention.

(1) The first invention of the present invention is a smelting method for producing ferronickel 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, in which in the mixture forming process, a carbonaceous reducing agent is applied to the surface of the pellets, and at least a part of the carbonaceous reducing agent applied to the pellets is a plant-derived component.

(2) The second invention of the present invention is a method for smelting nickel oxide ore according to the first invention, in which the carbonaceous reducing agent of the plant-derived component is starch.

(3) The third invention of the present invention is a method for smelting nickel oxide ore according to the first or second invention, in which, in the mixture forming step, the carbonaceous reducing agent is applied to the pellets in an amount of 2% by mass or more and 50% by mass or less, assuming that the amount of carbon in the carbonaceous reducing agent required to reduce the iron oxide and nickel oxide contained in the nickel oxide ore constituting the pellets without excess or deficiency is 100% by mass.

(4) The fourth invention of the present invention is a method for smelting nickel oxide ore according to any one of the first to third inventions, further comprising a separation step of separating slag from the reduction product obtained through the reduction step to obtain ferronickel.

According to the present invention, a method for producing ferronickel by forming pellets from nickel oxide ore and reducing them can be provided that is highly productive and efficient, and can produce high-quality ferronickel at low cost.

FIG. 1 is a diagram showing an example of a flow of a method for smelting nickel oxide ore. FIG. 2 is a flow chart showing an example of a process flow in a mixture molding step.

The following describes in detail an embodiment of the present invention (hereinafter, "the present embodiment"). Note that the present invention is not limited to the following embodiment, and various modifications are possible without departing from the gist of the present invention. In this specification, the expression "X to Y" (X and Y are arbitrary numbers) means "X or more and Y or less."

The nickel oxide ore smelting method according to this embodiment is a method in which pellets are formed from a mixture containing nickel oxide ore, which is the raw ore, and a reducing agent, and the pellets are charged into a reduction furnace and subjected to a reduction process to produce ferronickel metal and slag. Specifically, the nickel (nickel oxide) and iron (iron oxide) in the nickel oxide ore that constitutes the pellets are reduced to produce ferronickel metal and slag, which are iron-nickel alloys, and the metal is separated from the slag to produce ferronickel.

This 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.

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

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 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 ferro-nickel metal.

[Mixing process]
The mixing process S1 is a process for mixing raw material powders including nickel oxide ore to obtain a mixture. Specifically, a carbonaceous reducing agent is added to the nickel oxide ore as the raw material 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.

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

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

The amount of carbonaceous reducing agent mixed is not particularly limited, but is preferably 50% by mass or less, and more preferably 40% by mass or less, assuming that the amount of carbonaceous reducing agent required to reduce the nickel oxide and iron oxide that constitute the nickel oxide ore without excess or deficiency is 100% by mass. The amount of 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 all of the 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").

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

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% to 50 mass% when the total value of the chemical equivalents is 100 weight%, the reduction reaction can be efficiently carried out, and ferronickel with high nickel quality can be efficiently produced.

The iron ore, which is an optional additive, is not particularly limited, but examples include iron ore with an iron content of about 50% by mass or more, and hematite obtained by wet smelting of nickel oxide ore. Examples of binders include bentonite, polysaccharides, resins, water glass, and dehydrated cake. Examples of flux components include calcium oxide, calcium hydroxide, calcium carbonate, and silicon dioxide.

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

In the mixing process S1, the raw material powder containing nickel oxide ore can be mixed using a mixer or the like. When the raw material powder is mixed to obtain a mixture, the raw material powder may be kneaded to improve mixability. This applies shear force to the mixture, which breaks down 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.

[Mixture molding process]
The mixture forming step S2 is a step of forming the mixture of raw material powders obtained in the mixing treatment 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.

Figure 2 is a flow diagram showing an example of the process flow in the mixture forming step S2. As shown in Figure 2, the mixture forming step S2 includes an agglomeration process step S21 in which the mixture is formed into lumps, a coating process S22 in which a carbonaceous reducing agent is applied to the obtained lumps, and a drying process S23 in which the coated lumps are dried. 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 agent is attached to only a part of the pellet surface.

(1) Agglomeration Step In the agglomeration step S21, the mixture obtained in the mixing step S1 is formed into agglomerates of a predetermined shape and size.

The shape into which the mixture is 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 an elliptical, cubic, rectangular, cylindrical, or spherical shape is preferable. Molding the mixture into such a shape makes the molding process easier and reduces the costs required for molding. Furthermore, the simpler the molded shape, the more likely it is that the number of defective pellets will be reduced and the easier it will be to maintain the strength of the pellets.

In the agglomeration process S21, the mixture can be molded, for example, using a pellet molding device. There are no particular limitations on the pellet molding device, but it is preferable that the pellet molding device is capable of kneading and molding the mixture at high pressure and high shear force. By kneading the mixture at high pressure and high shear, it is possible to break up agglomerations in the raw powder mixture, to effectively knead the mixture, and to increase the strength of the resulting pellets.

It is also possible to use a briquette press to mold the pellets. The appropriate equipment should be selected taking into consideration the equipment, pellet strength, yield, etc.

(2) Coating Step In the coating step S22, the surface of the obtained lump (pellet) is coated with a carbonaceous reducing agent. 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, a powdered carbonaceous reducing agent may be applied by rolling it on a spread floor surface.

As mentioned above, the coating on the surface of the pellets may be applied not only to the entire surface, but also to only a portion of the surface.

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, etc. Among these, starch is preferably used. In this way, by applying a carbonaceous reducing agent containing at least a portion of a plant-derived component to the pellet surface, reduction treatment can be performed inexpensively and efficiently, and reoxidation of the generated metal can be effectively suppressed.

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, and it is 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 characteristics, 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 high in purity and has little variation in quality, so contamination caused by the reducing agent can be avoided, and as a result, high-quality ferronickel can be obtained.

Specifically, starch is a structure consisting of carbon (C), hydrogen (H), and oxygen (O), as shown in the following chemical formula. When this starch is heated and decomposed in the treatment in the reduction step, it is first decomposed into H ₂ O and the like and volatilized, leaving carbon. 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.

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

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. Furthermore, if it exceeds 50% by mass, over-reduction may occur, which may reduce the nickel content in the metal.

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

Here, the lumps obtained by the pellet-shape agglomeration process contain excess moisture, for example, about 50% by mass. Therefore, if pellets containing excess moisture are suddenly heated to the reduction temperature, the moisture will evaporate all at once, causing expansion and destruction of the lumps. 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 during the reduction heating process in the next reduction process 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.

Specifically, the drying process in the drying process step S23 is not particularly limited, but for example, hot air at 200°C to 400°C is blown onto the pellets to dry them. Note that by keeping the temperature of the pellets below 100°C during the drying process, damage to the pellets can be prevented, and the process can be carried out preferably.

When drying large pellets, it is acceptable for them to have cracks or breaks 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 it is unlikely to cause a major problem. Also, if the pellets are in a form that will not break, the drying process in the drying process step S22 may be omitted.

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

[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 ferronickel metal, which is an iron-nickel alloy, and slag is produced.

In particular, in the method according to the present embodiment, a highly reactive carbonaceous reducing agent is applied to the pellet surface in advance, which allows the reduction reaction to proceed more efficiently and prevents the metal generated in the pellet from being oxidized by oxygen, water, etc. that inevitably enter the reduction furnace. In addition, because the carbonaceous reducing agent applied to the pellet surface contains plant-derived components, the area around the pellet can be more effectively maintained in a reducing atmosphere, allowing the production of high-quality ferronickel.

Specifically, in the reduction heat treatment, pellets containing nickel oxide ore are stacked on the hearth of the 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.

In the reduction heat treatment, for example, in a short time of about one minute, the 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, forming a shell (hereinafter also referred to as the "shell"). Meanwhile, within the shell, the slag components in the pellet gradually melt as the shell is formed, and liquid slag is generated. As a result, ferronickel metal (hereinafter also simply referred to as "metal") and slag made of oxides (hereinafter simply referred to as "slag") are generated separately within one pellet. Then, when the reduction heat treatment time 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 absorbed into the iron-nickel alloy, lowering the melting point. As a result, the iron-nickel alloy melts and becomes liquid.

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

The pellet stack that has been subjected to the reduction heat treatment becomes a mixture of large lumps of metal and slag. By performing the reduction heat treatment on pellets with a large apparent volume, it becomes easier to form large lumps of metal, which reduces the effort required to recover them from the reduction furnace and effectively prevents a decrease in the metal recovery rate. The volume of the resulting mixture shrinks to about 50% to 60% by volume compared to the pellet stack that is charged.

In addition, in the reduction heat treatment, additional reducing agent may be added during the reduction reaction. Once the reduction reaction has progressed 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. It is preferable to add the reducing agent from the top of the pellets. By adding the reducing agent from the top of the pellets, where the oxidized metal frequently comes into contact with gas, reoxidation can be effectively prevented.

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

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.

Furthermore, by carrying out the treatment in a moving hearth furnace, heat loss between each treatment is reduced, allowing for more efficient operation. In other words, if the reaction is carried out using separate furnaces, the temperature drops when the pellet stack is moved between furnaces, resulting in heat loss and a change in the reaction atmosphere, and so the reaction does not proceed immediately when the pellets are recharged into the furnace. In contrast, by carrying out each treatment in a single facility using a moving hearth furnace, heat loss is reduced and the atmosphere inside the furnace can be precisely controlled, allowing the reaction to proceed more effectively. As a result, metal with a high nickel content can be obtained more effectively.

[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.

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

The obtained metal phase and slag phase can be easily separated due to their poor wettability. For example, by dropping the large mixture obtained by the reduction step S3 described above over a predetermined drop or by applying a certain amount of vibration during sieving, the metal phase and slag phase can be easily separated from the mixture.

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

[Mixing of raw powders]
For each sample, nickel oxide ore as raw ore, iron ore, silica sand and limestone as flux components, binder, and carbonaceous reducing agent (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 reducing agent, and the content was set in the ratio shown in Table 4 below, assuming that the amount required to properly reduce nickel oxide (NiO) and iron oxide (Fe ₂ O ₃ ) contained in the nickel oxide ore as raw ore is 100 mass %.

[Molding of 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.

[Carbonaceous Reductant 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 also determined as an addition ratio 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 was taken as 100 mass %.

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

Next, each sample was dried by blowing hot nitrogen air at 150°C to 200°C onto it so that the solid content was approximately 70% by mass and the moisture content was approximately 30% by mass. Table 3 below shows the solid content composition (excluding carbon) of the pellets after drying.

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

The pellets were then subjected to a reduction heat treatment at the temperature and for the time shown in Table 4 below. After the reduction treatment, the pellets were quickly cooled to room temperature in a nitrogen atmosphere and then removed into the air.

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.

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 mixture ÷ (total amount of metalized Ni and Fe in mixture) × 100 (%)

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 recovered Ni / (amount of charged oxide ore x Ni content in oxide ore) x 100 (%)

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

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

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

Claims (2)

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 in an amount of 2.3% by mass or more and 48.0% by mass or less, where 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 in an adequate amount is taken as 100% by mass.
A method for smelting nickel oxide ores. The process further comprises a separation step of obtaining ferronickel by separating slag from the reduction product obtained through the reduction step.
2. The method for smelting nickel oxide ore according to claim 1 .

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