JP7552289B2 - How to smelt oxide ores - Google Patents

Description

The present invention relates to a smelting method in which pellets made from an oxide ore such as nickel oxide ore and a reducing agent are smelted by reducing and heating them at high temperatures in a reduction furnace to obtain reduced products such as ferronickel.

Methods for smelting nickel oxide ore, known as 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 reduce the ore with a carbonaceous reducing agent to produce an iron-nickel alloy (hereafter also referred to as "ferronickel"), 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 to produce a mixed sulfide.

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

These lumps need to have a certain degree of breathability to "evaporate" the moisture they contain. Also, if reduction does not proceed uniformly within the lumps, the composition of the resulting reduced product will be non-uniform, leading to 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 when reducing the lumps.

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 necessary.

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

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

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

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

As described above, the technology for producing metals and alloys by mixing and reducing oxide ores has many problems in terms of increasing productivity, reducing production costs, and improving the quality of metals. In addition, there are environmental problems with fossil fuels such as coal, which have a limited amount that can be used, and which increase _CO2 in the environment after being used for reduction.

JP 2011-256414 A

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

The inventors of the present invention have conducted extensive research to solve the above-mentioned problems. As a result, they have found that the above-mentioned problems can be solved by using a reducing agent containing a plant-derived reducing agent as the reducing agent in the mixing step, and by subjecting the mixture to a drying treatment in advance in an atmosphere with an oxygen concentration equal to or lower than a predetermined concentration when subjecting the mixture to a reduction treatment, and have thus completed the present invention.

(1) A first aspect of the present invention is a method for producing a mixture containing an oxide ore and a reducing agent;
The method for smelting an oxide ore includes a drying step of subjecting the mixture to a drying treatment, and a reducing step of subjecting the mixture that has been subjected to the drying step to a reduction treatment, in which a reducing agent containing a plant-derived reducing agent is used as the reducing agent in the mixing step, and in which the mixture is dried at a drying temperature of 100° C. or higher and 500° C. or lower in an atmosphere having an oxygen concentration of 3.0 vol. % or lower in the drying step.

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

(3) The third aspect of the present invention is a method for smelting oxide ore according to the first or second invention, in which the content of the reducing agent in the mixture is mixed in a ratio of 20% by mass or more and 80% by mass or less relative to 100% by mass of the chemical equivalent required to reduce the oxide ore.

(4) The fourth aspect of the present invention is a method for smelting oxide ore according to any one of the first to third inventions, in which the oxide ore is nickel oxide ore, and in the reduction step, a mixture containing the nickel oxide ore is subjected to a reduction treatment to produce ferronickel.

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

FIG. 1 is a process diagram showing an example of the flow of a method for smelting nickel oxide ore. FIG. 1 is a diagram (plan view) showing an example of the configuration of a reducing furnace (rotary hearth furnace).

Specific embodiments of the present invention are described in detail below. Note that the present invention is not limited to the following embodiments, and various modifications are possible without departing from the gist of the present invention.

1. Overview of the present invention
The present invention relates to a method for smelting an oxide ore, for example, nickel oxide ore, which is a raw material, and produces a metal as a reduced product by mixing the oxide ore with a reducing agent and reducing the resulting mixture. For example, when nickel oxide ore is used as the raw material ore, ferro-nickel metal, an alloy of iron and nickel, is produced as the reduced product.

Specifically, the method for smelting oxide ore according to the present invention is characterized in that a reducing agent containing a plant-derived reducing agent is used as a reducing agent to be mixed with the raw oxide ore, and when subjecting the mixture to a reduction treatment, the mixture is first subjected to a drying treatment at a drying temperature of 100°C or higher and 500°C or lower in an atmosphere with an oxygen concentration of 3.0% by volume or lower.

According to this method, the quality of the resulting metal can be improved by performing a reduction process on a mixture containing a predetermined amount of a plant-derived reducing agent as the reducing agent.

≪2. Nickel oxide ore smelting method≫
Hereinafter, as a specific embodiment of the present invention (hereinafter referred to as "the present embodiment"), a smelting method will be described as an example in which nickel oxide ore is used as a raw ore, and the nickel (nickel oxide) and iron (iron oxide) contained in the nickel oxide ore are metallized by reducing the nickel oxide ore to produce an iron-nickel alloy (ferronickel).

Specifically, as shown in FIG. 1, the method for smelting nickel oxide ore according to this embodiment includes a mixing process S1 for obtaining a mixture containing an oxide ore and a reducing agent, an agglomeration process S2 for forming the resulting mixture into a predetermined shape to form an agglomerate, a drying process S3 for drying the resulting agglomerate, a reduction process S4 for subjecting the agglomerate (mixture) to a reduction treatment, and a recovery process S5 for recovering metal from the resulting reduced product (mixture).

<2-1. Mixing process>
In the mixing step S1, a nickel oxide ore and a reducing agent are mixed to obtain a mixture. Specifically, in the mixing step S1, a reducing agent is first added to the nickel oxide ore, which is the raw material ore, and mixed. As optional additives, powders of iron ore, flux components, binders, etc., having a particle size of, for example, about 0.2 mm to 0.8 mm, are added and mixed to obtain a mixture. This can be done using a machine or the like.

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

Here, a reducing agent containing a plant-derived reducing agent is used as a reducing agent to be mixed with the nickel oxide ore in the mixing step S1 to form the mixture. Examples of plant-derived reducing agents include organic reducing agents derived from plants that have the function of reducing the oxide ore, and charcoal or bamboo charcoal made by carbonizing wood or bamboo derived from plants. In addition, waste materials or food waste containing these may also be used.

By subjecting a mixture containing a plant-derived reducing agent to a reduction process, the quality of the resulting metal can be improved.

Furthermore, plant-derived reducing agents are generally cheaper than fossil fuels such as coal and are easily renewable. Also, unlike fossil fuels, plant-derived reducing agents are not subject to depletion. Furthermore, from production to consumption, plant-derived reducing agents do not increase _CO2 , which is considered a greenhouse gas, and are therefore environmentally friendly.

The use of refined plant-derived organic reducing agents makes it possible to efficiently and stably increase the quality of the resulting metal, but unrefined plant-derived reducing agents or waste materials or food waste containing plant-derived organic reducing agents may also be used. This not only reduces costs, but also the environmental impact. In this case, it is preferable to control the proportion of plant-derived reducing agent and moisture within an acceptable range.

The plant-derived reducing agent is preferably an organic reducing agent derived from a plant. Since the plant-derived organic reducing agent is a compound (including a monomer, oligomer, and polymer) consisting of carbon, hydrogen, and oxygen, when the organic reducing agent in the mixture is heated in the drying step S3 or the reduction step S4 described later, the hydrogen and oxygen constituting the organic reducing agent are released while generating _H2O , and the remaining carbon constituting the organic reducing agent remains uniformly in the mixture. Then, in the reduction step S4 described later, the uniformly remaining carbon makes it possible to uniformly reduce the oxide ore, and the grade of the obtained metal can be efficiently and stably improved.

Examples of plant-derived organic reducing agents include starch, oil, wheat flour, cellulose, sucrose, lactose, glucose (α-glucose), fructose, etc. Among these, starch is particularly preferred. Starch is a polymer of α-glucose, for example, as represented by the following formula (1).

Starch is a polymer made up of carbon, hydrogen, and oxygen, so it is easy to mix evenly into a mixture. Furthermore, starch has the property of increasing viscosity when it absorbs water, so it also functions as a binder, making it easy to mold the mixture.

Furthermore, there is an established method for refining starch, and it is easy to obtain starch with high purity and little variation in composition. Therefore, by using a reducing agent containing starch, it is possible to efficiently and stably increase the quality of the resulting metal.

Examples of starches include corn starch, wheat starch, rice starch, bean starch, potato starch, sweet potato starch, tapioca starch, potato starch, bracken starch, kudzu starch, etc.

The content of the plant-derived reducing agent is preferably 50% by mass or more of the total amount of reducing agent contained in the mixture, more preferably 70% by mass or more, and even more preferably 90% by mass or more, and it is most preferable that the reducing agent contained in the mixture consists only of plant-derived reducing agents (i.e., the content of the plant-derived reducing agent is 100% by mass of the total amount of reducing agent contained in the mixture).

It is preferable that the reducing agent has the same particle size and particle size distribution as the nickel oxide ore, which is the raw material ore described above. This is because the particle size and particle size distribution are the same, which makes it easier to mix uniformly and allows the reduction reaction to occur uniformly.

The amount of reducing agent mixed is preferably 80% by mass or less, and more preferably 65.0% by mass or less, when the amount of reducing agent required to reduce the nickel oxide and iron oxide that make up the nickel oxide ore without excess or deficiency is taken as 100% by mass. The lower limit of the amount of reducing agent mixed is not particularly limited, but is preferably 20.0% by mass or more, and more preferably 23.0% by mass or more, relative to the total value of the chemical equivalents, which is 100% by mass.

The amount of reducing agent required to reduce nickel oxide and iron oxide without excess or deficiency can be rephrased as the sum of the chemical equivalent required to reduce all of the nickel oxide to nickel metal and the chemical equivalent required to reduce the iron oxide to iron metal (hereinafter also referred to as the "total value of chemical equivalents").

As the optional additive iron ore, for example, iron ore with an iron content of about 50% by mass or more, hematite obtained by wet smelting of nickel oxide ore, etc. can be used. In addition, as the flux component, for example, calcium oxide, calcium hydroxide, calcium carbonate, silicon dioxide, etc. can be used. In addition, as the binder, for example, bentonite, polysaccharides, resin, water glass, dehydrated cake, etc. can be used.

When mixing, kneading may be performed simultaneously to improve mixability, or after mixing. Kneading can be performed using a batch kneader such as a Brabender, a Banbury mixer, a Henschel mixer, a helical rotor, a roll, a single-shaft kneader, or a twin-shaft kneader. Kneading the mixture applies shear force to the mixture, which breaks down agglomerations of the reducing agent and raw material powder, allowing for uniform mixing, improving the adhesion of each particle, and reducing voids. This makes it easier for the reduction reaction to occur in the mixture and allows the reaction to occur uniformly, shortening the reaction time for the reduction reaction. It also reduces quality variation.

Also, after mixing, or after mixing and kneading, the mixture may be extruded using an extruder. This applies pressure (shear force) to the mixture, breaking up agglomerations of the reducing agent, raw material powder, etc., and making the mixture more uniformly mixed. Furthermore, voids within the mixture can be reduced. As a result, the reduction reaction of the mixture is more likely to occur uniformly in the reduction step S2 described below, the quality of the resulting metal can be improved, and high-quality metal can be produced.

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

In the mixing step S1, a mixture is obtained by uniformly mixing the raw material powders containing nickel oxide ore. Table 1 below shows an example of the composition (mass%) of some of the raw material powders mixed in the mixing step S1, but the composition of the raw material powders is not limited to this.

<2-2. Clumping process>
In the agglomeration step S2, the mixture is molded into a predetermined shape to form agglomerates (pellets). The agglomeration step is not an essential step, but molding the mixture into a predetermined shape improves handling. The shape of the lumps (pellets) may be any shape that allows them to be stacked on the hearth of the reduction furnace, and is preferably, for example, a spherical, rectangular, cuboid, cylindrical, or other shape. By molding the mixture into such a shape, molding the mixture becomes easier, and molding costs can be reduced. In addition, the shape to be molded is not complicated, so the occurrence of defective pellets is reduced. It is possible.

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

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.

<2-3. Drying process>
In the drying step S3, the aggregates obtained in the agglomeration step S2 are dried. When the mixture is mixed with a large amount of water in the kneading in the mixing step S1 or the agglomeration step S2 or in the molding of the aggregates, By subjecting the lump (mixture) to a drying treatment, the amount of moisture contained in the atmospheric gas in the reduction furnace can be reduced.

Furthermore, when a reducing agent containing starch is used, when the aggregates are subjected to a drying treatment and the starch in the aggregates is heated, at least a part of the hydrogen and oxygen constituting the starch is released as H ₂ O. Drying the aggregates obtained in the agglomeration step S2 can prevent the aggregates from collapsing, which can prevent the aggregates from becoming difficult to remove from the reduction furnace. Furthermore, the amount of moisture contained in the atmospheric gas in the reduction furnace can be more effectively reduced, and oxidation of the metal contained in the aggregates can be more effectively suppressed.

However, because plant-derived reducing agents are relatively susceptible to decomposition and oxidation, the mixture may burn if a large amount of oxygen is present during drying, making it impossible to carry out the reduction process properly in the reduction step described below, which leads to a decrease in the quality of the resulting metal.

Therefore, when the mixture is subjected to a reduction treatment, the mixture is dried in advance at a drying temperature of 100°C or higher and 500°C or lower in an atmosphere with an oxygen concentration of 3.0% by volume or lower. This prevents the mixture from burning due to the presence of oxygen during drying, and allows the reduction treatment to be appropriately performed in the reduction process described below while maintaining the mixture ratio of the oxide ore and the reducing agent at the desired ratio.

If the drying temperature is less than 100°C, the drying will not be sufficient and it will not be possible to prevent the collapse of the lumps. Furthermore, it will not be possible to reduce the amount of moisture contained in the atmospheric gas in the reduction furnace, making it impossible to suppress the oxidation of the metal. If the drying temperature is more than 500°C, a reduction process will be performed in the drying process, and the reduction process described below will not be able to perform an appropriate reduction process, which will result in a decrease in the quality of the resulting metal.

In particular, when a reducing agent containing starch is used, at least a portion of the hydrogen and oxygen constituting the starch generates H ₂ O and cannot escape, causing a decrease in the metal grade.

The drying temperature is preferably 200°C or higher, and more preferably 250°C or higher. The drying temperature is preferably 490°C or lower. The oxygen concentration is preferably 2.8% by volume or lower.

The method for drying the lumps is not particularly limited as long as it involves subjecting the mixture to a drying treatment at a drying temperature of 100°C to 500°C in an atmosphere with an oxygen concentration of 3.0% by volume or less. Conventional means can be used, such as a method of keeping the lumps at a drying temperature of 100°C to 500°C or a method of blowing hot air at a predetermined drying temperature onto the mixture to dry it. This drying treatment can be used to make the lumps have a solid content of about 70% by mass and a moisture content of about 30% by mass, for example. The temperature of the mixture itself during this drying treatment is preferably less than 100°C, which can prevent the mixture from bursting due to bumping of moisture, etc.

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

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

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

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

<2-4. Reduction step>
In the reduction step S4, the lumps (mixture) obtained in the drying step are subjected to a reduction treatment. Specifically, the lumps (mixture) obtained are charged into a reduction furnace, and the mixture is subjected to a heating reduction treatment. The heating reduction treatment in the reduction step S2 causes a smelting reaction (reduction reaction) to proceed based on the reducing agent in the mixture, and ferronickel metal (hereinafter simply referred to as "metal") and ferronickel slag (hereinafter simply referred to as "slag") are generated separately in the mixture.

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

After about 10 minutes of processing, the excess reducing agent that is not involved in the reduction reaction is absorbed into the metal, lowering its melting point and causing the metal to become liquid.

In this case, the quality of the resulting metal can be improved by subjecting the mixture, which contains a plant-derived reducing agent, to a reduction treatment.

Furthermore, in the reduction process described above, the mixture is dried at a drying temperature of 100°C or higher and 500°C or lower in an atmosphere with an oxygen concentration of 3.0% by volume or lower, which prevents the mixture from burning due to the presence of oxygen during drying, making it possible to appropriately perform the reduction process while maintaining the mixture ratio of the oxide ore and the reducing agent at the desired ratio.

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

In addition, when a reducing agent containing a plant-derived organic reducing agent is used, when the organic reducing agent in the mixture is heated, the hydrogen and oxygen constituting the organic reducing agent generate _H2O and are released, while the remaining carbon remains in the mixture. As a result, the remaining carbon acts as a reducing agent to uniformly reduce the ore.

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

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

The heat required for reduction, calculated by multiplying the reduction temperature (℃) by the reduction time (min), is preferably in the range of 20,000 (℃ x min) to 40,000 (℃ x min). This allows for efficient production of high-quality metal.

The reduction furnace may be a fixed hearth, but it is preferable to use a moving hearth furnace. By using a moving hearth furnace as such a reduction furnace, the mixture can be treated more efficiently. In addition, by using a moving hearth furnace, the reduction reaction proceeds continuously and the reaction can be completed in one facility, and the treatment temperature can be controlled more accurately than if each process were performed using separate furnaces. Furthermore, heat loss between each process is reduced, making more efficient operation possible. Below, the configuration of a rotary hearth furnace as an example of a moving hearth furnace is explained using Figure 2.

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

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

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

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

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

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

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

[Mixing process]
For each sample, nickel oxide ore as raw material ore, iron ore, silica sand and limestone as flux components, and a reducing agent were mixed in a mixer while adding an appropriate amount of water to obtain a mixture. As the reducing agent, a plant-derived reducing agent (starch) or pulverized coal (coal) was used, and nickel oxide and iron oxide ( _{Fe2O3 )} contained in the nickel oxide ore as raw material ore were contained in the amounts shown in Table 4 relative to the required chemical equivalent of 100 mass%.

[Agglomeration process]
Next, the mixture obtained for each sample was formed into a sphere using a pelletizer to obtain a lump (sample) having a diameter of 15±0.3 mm.

[Drying process]
Next, the aggregates obtained in the agglomeration step were subjected to a drying treatment under the conditions shown in Table 3 so that the solid content was about 70% by mass and the moisture content was about 30% by mass. The drying time was 2 hours in each case.

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

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

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

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

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

Table 4 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 Tables 3 and 4, in Examples 1 to 15, in which a reducing agent containing a plant-derived reducing agent was used as the reducing agent and the mixture was dried at a drying temperature of 100°C to 500°C in an atmosphere with an oxygen concentration of 3.0% by volume or less, good results were obtained in terms of the nickel metallization rate and nickel content in the metal. This shows that the oxide ore smelting method according to the present invention can efficiently produce high-quality metal.

On the other hand, in Comparative Example 1, in which the mixture was dried at a drying temperature of more than 500°C, and in Comparative Example 2, in which the mixture was dried in an atmosphere with an oxygen concentration of more than 3.0% by volume, it was not possible to efficiently produce high-quality metal. Also, in Reference Examples 1 and 2, in which a reducing agent containing a plant-derived reducing agent was not used as a reducing agent, it was not possible to efficiently produce high-quality metal.

1 Mixture 2 Rotary bed furnace 20a to 20d Treatment chamber 21 Preheating chamber 40 Cooling chamber

Claims (2)

A mixing step for obtaining a mixture containing nickel oxide ore and a reducing agent;
a drying step of subjecting the mixture to a drying treatment;
A reduction step of producing ferronickel by subjecting the mixture that has been subjected to the drying step to a reduction treatment,
In the mixing step, a plant-derived organic reducing agent is used as the reducing agent,
In the reduction step, a value obtained by multiplying the reduction temperature (° C.) and the reduction time (min.) is 20,000 (° C.×min.) or more and 40,000 (° C.×min.) or less;
In the drying step, the mixture is dried at a drying temperature of 280 ° C. or more and 490 ° C. or less in an atmosphere having an oxygen concentration of 1.5 vol. % or more and 2.8 vol. % or less. The plant-derived organic reducing agent is starch;
The starch is mixed in the mixture so that the content of the starch in the mixture is 21% by mass or more and 48% by mass or less with respect to 100% by mass of a chemical equivalent necessary for reducing nickel oxide and iron oxide constituting the nickel oxide ore.
A method for smelting oxide ores according to claim 1.

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