JP4782091B2 - Method for coating nickel oxide particles - Google Patents

Description

Background of the Invention

The present invention relates to a method of coating nickel oxide particles with a metal oxide, which method is particularly suitable for the production of reduced nickel by contacting the nickel oxide particles with a reducing gas.

BACKGROUND ART Conventionally, reduced nickel is produced by bringing a reducing gas into contact with solid nickel oxide. As the reducing gas, ammonia, carbon monoxide, hydrogen, natural gas containing these, propane gas, or the like is used. In general, it is considered that a method of obtaining a metal by reducing a metal oxide with a reducing gas basically undergoes the following chemical reaction.
MnOm + 1/2 mC → nM + 1/2 mCO ₂
(Or MnOm + 2mH → nM + mH ₂ O)
MnOm + mCO → nM + mCO ₂

  In such a method, it is effective to secure a large number of contact opportunities between the gas and the metal oxide in order to promote the reaction. In practice, however, a reduced metal layer is first formed in the surface region of the metal oxide in contact with the gas. This metal layer may suppress gas diffusion and hinder the promotion of the reaction. Further, since this metal layer is chemically extremely active in a high temperature region where gas reduction occurs, it is easy to bond to a metal formed in another reaction zone. In fact, in the production of reduced nickel, the reduced nickel particles produced in the gas reduction process are fused together to inhibit the progress of the reaction, and the reduced nickel may adhere to the reaction vessel. It will cause a drop in speed or interruption.

  In order to avoid such a situation, a method has been proposed in which nickel oxide particles are coated with an oxide that is thermodynamically and chemically stable in a temperature range that allows a reduction reaction. For example, a method is known in which a magnesium sulfate solution is blown into a nickel oxide fluidized bed at a high temperature of 1000 ° C. or higher to coat the surface of nickel oxide particles with magnesium oxide (for example, Patent Document 1 (Japanese Patent Publication No. 59-45740)). Issue gazette)). However, this method requires a large amount of heat energy for evaporation of moisture from the magnesium sulfate solution and thermal decomposition of the magnesium sulfate, which increases the manufacturing cost. In addition, since the magnesium sulfate is partly removed from the nickel oxide as the water evaporates, the yield is usually as low as about 80%.

  On the other hand, since it is extremely difficult to make magnesium oxide into an aqueous solution, it is practically impossible to coat nickel oxide particles with magnesium oxide at a low temperature using the solution.

  Under the circumstances as described above, a more efficient and economical method for producing reduced nickel is required.

Japanese Patent Publication No.59-45740

Summary of the Invention

  The inventors of the present invention now have excellent adhesion to an oxide protective coating that is chemically stable even in the reduction reaction temperature range on the surface of the nickel oxide particles simply by mixing the nickel oxide particles and a certain type of oxide powder. The knowledge that it can be formed efficiently and economically. Then, when the coated nickel oxide particles are subjected to a gas reduction process, the reaction is prevented from being inhibited by the fusion of the reduced nickel particles, and the reduced nickel is prevented from adhering to the reaction vessel, so that efficient and economical reduction is achieved. The knowledge that nickel can be produced was also obtained.

  Accordingly, an object of the present invention is to efficiently and economically form an oxide protective coating that is chemically stable even on the surface of nickel oxide particles even in a reduction reaction temperature range with excellent adhesion. It is another object of the present invention to efficiently and economically produce reduced nickel by preventing reaction due to fusion of the reduced nickel particles and preventing reduction nickel from adhering to the reaction vessel.

  That is, the nickel oxide particle coating method provided by the present invention comprises mixing nickel oxide particles and at least one powdery coating oxide selected from the group consisting of magnesium oxide, aluminum oxide, and silicon oxide. Thus, nickel oxide particles coated with the coating oxide are obtained.

  Further, the coated nickel oxide particles provided by the present invention are at least one selected from the group consisting of the nickel oxide particles and magnesium oxide, aluminum oxide, and silicon oxide formed on the surface of the particles. It is manufactured by the above method.

Furthermore, in the method for producing reduced nickel provided by the present invention, nickel oxide particles coated with a coating oxide are formed by the above method, and the coated nickel oxide particles are sintered at 750 ° C. or higher. Heating to a non-temperature, supplying a reducing gas to the heated particles to reduce the nickel oxide, thereby producing reduced nickel.

Detailed description of the invention

Nickel Oxide Particle Coating Method In the nickel oxide particle coating method of the present invention, first, nickel oxide particles and a powdery coating oxide are prepared. As the oxide for coating, magnesium oxide, aluminum oxide, silicon oxide, or a mixture thereof is used. Any of these oxides is a chemically stable substance in the temperature range when reducing nickel oxide particles. The nickel oxide particles coated with the coating oxide can be obtained simply by mixing these nickel oxide particles and the powdered coating oxide. Since the oxide coating thus obtained is difficult to peel off even when physically stirred in a fluidized bed or the like, a high yield rate can be realized. Here, this mixing is a very simple technique that can be performed at room temperature in the atmosphere, and no special treatment such as heat treatment, pressure treatment, or addition of additives is required. This is nothing but an unexpected finding from the conventional technical common sense that it was necessary to add a magnesium sulfate solution at a high temperature of 1000 ° C. or higher for coating nickel oxide. In this way, a chemically stable oxide protective coating can be efficiently and economically formed on the nickel oxide particle surface with excellent adhesion even under reducing reaction conditions. The coated nickel oxide particles are protected by oxides that are chemically stable even under reducing reaction conditions. Therefore, when the nickel oxide particles are subjected to a gas reduction step, the particles of the reduced nickel particles are fused. It is possible to prevent the reaction from being hindered due to the adhesion and the reduction nickel from adhering to the reaction vessel, and to avoid the significant reduction or interruption of the reduction reaction. For this reason, extremely efficient and economical reduction nickel manufacture becomes possible. In addition, it can be said that the method of the present invention is environmentally friendly because energy consumption can be remarkably reduced by a very simple method and a conventionally used magnesium sulfate solution is unnecessary.

  The nickel oxide particles used in the method of the present invention are particles composed of nickel oxide, but it is allowed to contain inevitable impurities depending on the quality of the raw material to be obtained. The purity of nickel oxide in the nickel oxide particles may be about 98.0% by mass, preferably 98.5% by mass or more, more preferably 98.7% by mass or more, and further preferably 99% by mass or more. The size of the nickel oxide particles is not particularly limited, but may be appropriately determined according to the characteristics of the equipment to be employed. When it is assumed that the particles are subjected to a gas reduction process later, the particles are sufficiently reduced to the inside. It is desirable to make it as large as possible. According to a preferred embodiment of the present invention, the nickel oxide particles preferably have a diameter of 0.1 mm or more, more preferably 0.1 to 5 mm, still more preferably 0.2 to 3 mm, most preferably. 0.21 to 0.29 mm. In addition, it is not necessary for all the particles of nickel oxide particles to be used to have the above preferred particle size, and it is preferable that at least 10% by mass of all the nickel oxide particles have the above preferred particle size, more preferably It is at least 30% by weight, more preferably at least 50% by weight, still more preferably at least 70% by weight, even more preferably at least 90% by weight, most preferably 99% by weight or more.

  As the coating oxide used in the method of the present invention, magnesium oxide, aluminum oxide, silicon oxide, or a mixture thereof is used. These oxides are substances that are chemically stable in the temperature range when the nickel oxide particles are reduced. The coating oxide is in the form of powder, and the particle size is not particularly limited, but it is desirable that the coating oxide has a size that can cover the surface of the nickel oxide particles so as not to prevent the progress of the reduction reaction of nickel oxide. According to a preferred embodiment of the present invention, the particle diameter of the powdery coating oxide is preferably 45 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. These particle sizes can be measured by sieve analysis. Within such a range, the reduction promoting effect by the oxide coating can be sufficiently exhibited when the gas reduction step is applied later. The lower limit of the particle diameter of the powdery coating oxide is not limited, but is preferably 0.1 μm, more preferably 1 μm from the viewpoint of workability.

  According to a preferred embodiment of the present invention, the amount of the coating oxide added may be trace amount and is not particularly limited, but is 0.02 mass relative to the total mass of nickel oxide and coating oxide in terms of metal element. % Or more, and more preferably 0.03 to 0.10% by mass. An addition of about 0.05% by mass has a sufficient effect. Even in such an extremely small addition amount, the reduction promoting effect by the oxide coating can be sufficiently exerted when subjected to the subsequent gas reduction step. In addition, metal element conversion means having used the value converted into the mass of the metal element which comprises the coating oxide instead of using the mass of coating oxide itself.

  As described above, in the method of the present invention, the mixing can be performed at room temperature, that is, without preheating and heating, but it goes without saying that the mixing may be performed at a temperature other than room temperature as long as coating is not hindered. For example, the temperature may be within a range of 0 ° C to 100 ° C. Further, the mixing time is not particularly limited as long as the time for coating can be surely selected according to the kind of coating oxide to be added and the amount added, but is generally about 1 minute or longer and about 10 minutes at the longest. In general, the desired coating effect will be obtained. The mixing method is not particularly limited as long as the nickel oxide particles and the powdery coating oxide can be mixed uniformly, but it is preferably performed by a V-type mixer or a concrete mixer.

For example, when a coated sample is produced with a small amount of nickel oxide such as 600 g, it is preferable to use a V-type mixer (SVM type, manufactured by Seishin Corporation) for coating. In this case, when nickel oxide and coating oxide are put into a mixer and mixed at a rotation speed of 108 rpm = 108 min ⁻¹ for at least 1 minute and at most 10 minutes, a generally desired coating effect can be obtained. On the other hand, when a coated sample is produced with a large amount of nickel oxide such as 100 kg, it is preferable to use a concrete mixer (PM-3, manufactured by Takemura) (open top, lateral rotation) for kneading. In this case, nickel oxide and coating oxide are put into a mixer and mixed at least for 1 minute and at most 10 minutes at a rotational speed of approximately 22 rpm = 22 min ⁻¹ and a tilt angle of 40 to 45 degrees, and generally desired. The coating effect can be obtained. In addition, when only a small amount of sample is required as in the laboratory level, it is preferable to employ a V-type mixer.

  By the above mixing, nickel oxide particles having an oxide coating formed on the surface are obtained. The coated nickel oxide particles are preferably used as a raw material powder in a method for producing reduced nickel described later, but are not limited to this application.

Method for Producing Reduced Nickel The coated nickel oxide particles obtained by the method of the present invention are suitably used for producing reduced nickel by reduction of nickel oxide. The production of reduced nickel can be performed by heating the coated nickel oxide particles to a temperature at which sintering does not occur at 750 ° C. or higher, and supplying the reducing gas to reduce the nickel oxide. A preferable heating temperature is 750 ° C. or more and less than 950 ° C., more preferably 750 ° C. to 900 ° C., and further preferably 800 to 900 ° C. In such a temperature range, undesired sintering of particles can be effectively prevented while increasing the speed of the reduction reaction. The reducing gas is not particularly limited as long as it is generally used for the reduction of metal oxides, and is preferably, for example, ammonia, hydrogen, carbon monoxide, or natural gas or propane gas containing these. Supply and cause a reduction reaction. The nickel oxide becomes reduced nickel by the reduction reaction.

  According to a preferred aspect of the present invention, the reduction is preferably performed while fluidizing the coated nickel oxide particles with nitrogen gas. As a result, the nickel oxide particles are physically agitated, more contact opportunities between the reducing gas and nickel oxide are ensured, and the efficiency of the reduction reaction can be improved. In particular, in the oxide-coated nickel oxide particles of the present invention, the oxide film is difficult to peel off even when physically stirred, so that the effect of the oxide coating can be sufficiently exerted even in a fluidized bed. it can.

  As described above, reduced nickel particles are obtained. The oxide coating may still remain on the surface of the reduced nickel particles, and it does not impair the quality of the final product.

The present invention will be specifically described based on the following examples, but the present invention is not limited to these examples.
In addition, the raw material used in the following examples is as follows.

(1) Nickel oxide particles (quality and particle size: as follows)
・ Grade
Ni Co Cu Fe O other
76.81 1.06 0.14 0.53 21.40 0.06 (% by mass)
・ Particle size (measured by sieve analysis)
〜850μm −850〜425μm −425〜212μm −212〜150μm −150μm
2 30 60 7 1 (mass%)
In addition, the particle size analysis (sieving analysis) of nickel oxide is performed using a low-tap type sieve shaker (IIDA SIEVE SHAKER, manufactured by Iida Seisakusho) at an impulse number of 156 times / minute and a rotation number of 290 times / minute. It was. At this time, a test sieve defined in JIS Z8801-1 was used as a standard sieve. This sieve is a metal mesh sieve having an inner frame size of 200 mm and a depth of 45 mm, and five types of openings 1700, 850, 425, 212, and 150 μm were used. The mass percentage of the screened sample was calculated to obtain the particle size distribution.

(2) Oxide for coating a) Magnesium oxide powder (Grade: Particle size by sieve analysis: 2.1 μm or less as follows)
・ Grade
MgO CaO SiO ₂ SO ₃ O
97 or more 0.90 0.18 1.81 0.06 (mass%)
b) Aluminum oxide powder (Grade: Al ₂ O ₃ ; 99.99% by mass or more, particle size by sieve analysis: 3.0 μm or less)
c) Silicon oxide powder (Grade: SiO ₂ ; 99.7% by mass or more, particle size by sieve analysis: 5.5 μm or less)

Example 1: Evaluation of Adhesiveness of Magnesium Oxide Coating 1.56 g of magnesium oxide powder was added to 600 g of nickel oxide particles and mixed for 5 minutes at room temperature with a V-type mixer (SVM type, manufactured by Seishin Enterprise). The particles were coated with magnesium oxide. At this time, the addition amount of the magnesium oxide powder was set to 0.15% by mass with respect to the total mass of nickel oxide and coating oxide in terms of metal elements. The nickel oxide particles thus coated were heated to 900 ° C. and nitrogen was blown to form a fluidized bed having a space velocity of 1.83 m / sec. In order to confirm whether or not magnesium oxide delamination occurs in the fluidized bed, particles are taken out at each processing time shown in Table 1, and the Mg content is determined by ICP-emission spectrophotometer (VISTA-PRO, manufactured by Varian). ). The results were as shown in Table 1.

  As shown in Table 1, the magnesium oxide film coated on the nickel oxide particles by the method of the present invention does not peel even in a considerably intense flow state with a space velocity of 1.83 m / sec. It remained well on the particle surface. That is, it can be seen that the magnesium oxide coating is deposited on the nickel oxide with excellent adhesion.

Example 2: Influence of magnesium oxide addition amount and mixing time on coating effect Magnesium oxide powder was added to 600 g of nickel oxide particles at the magnesium addition rate shown in Table 2, and a V-type mixer (SVM type, manufactured by Seishin Enterprise) Was mixed for 5 minutes at room temperature to coat the nickel oxide particles with magnesium oxide. In addition, an addition rate is the mass% with respect to the total mass of nickel oxide and the oxide for a coating in conversion of a metal element. 10 g of nickel oxide particles thus coated were weighed and placed in a magnetic crucible. After heating the reaction apparatus to 900 ° C., a magnetic crucible charged with nickel oxide particles was put, and reduction reaction treatment was performed for 20 minutes while supplying hydrogen as a reducing gas at a flow rate of 0.2 m ³ / hr. By this reduction reaction treatment, the nickel oxide particles were reduced to become reduced nickel particles. After the reduced nickel particles were cooled to room temperature under an inert atmosphere, the magnetic crucible was taken out and turned over. At this time, the presence or absence of sintering was confirmed by observing whether the sample spilled out without being sintered. The results were as shown in Table 2.

  As shown in Table 2, the coating effect was obtained with a shorter mixing time as the Mg addition rate increased.

Example 3: Covering effect by aluminum oxide Aluminum oxide powder was added to 600 g of nickel oxide particles at the aluminum addition rate shown in Table 3, and mixed at room temperature for 5 minutes with a V-type mixer (SVM type, manufactured by Seishin Enterprise). The nickel oxide particles were coated with aluminum oxide. In addition, an addition rate is the mass% with respect to the total mass of nickel oxide and the oxide for a coating in conversion of a metal element. 10 g of nickel oxide particles thus coated were weighed and placed in a magnetic crucible. After heating the reaction apparatus to 900 ° C., a magnetic crucible charged with nickel oxide particles was put in, and a reduction reaction treatment was performed for 20 minutes while supplying 0.2 Nm ³ / hr of hydrogen as a reducing gas. By this reduction reaction treatment, the nickel oxide particles were reduced to become reduced nickel particles. After the reduced nickel particles were cooled to room temperature under an inert atmosphere, the magnetic crucible was taken out and turned over. At this time, the presence or absence of sintering was confirmed by observing whether the sample spilled out without being sintered. The results were as shown in Table 3.

  As shown in Table 3, no sintering was observed when 0.02% or more of aluminum oxide was added. This shows that unwanted sintering is avoided by the aluminum oxide coating.

Example 4: Covering effect by silicon oxide Silicon oxide powder was added to 600 g of nickel oxide particles at the silicon addition rate shown in Table 4, and mixed at room temperature for 5 minutes with a V-type mixer (SVM type, manufactured by Seishin Enterprise). The nickel oxide particles were coated with silicon oxide. In addition, an addition rate is the mass% with respect to the total mass of nickel oxide and the oxide for a coating in conversion of a metal element. 10 g of nickel oxide particles thus coated were weighed and placed in a magnetic crucible. After heating the reaction apparatus to 900 ° C., a magnetic crucible charged with nickel oxide particles was put, and reduction reaction treatment was performed for 20 minutes while supplying hydrogen as a reducing gas at a flow rate of 0.2 m ³ / hr. By this reduction reaction treatment, the nickel oxide particles were reduced to become reduced nickel particles. After the reduced nickel particles were cooled to room temperature under an inert atmosphere, the magnetic crucible was taken out and turned over. At this time, the presence or absence of sintering was confirmed by observing whether the sample spilled out without being sintered. The results were as shown in Table 4.

  As shown in Table 4, no sintering was observed when 0.03% by mass or more of silicon oxide was added. This shows that unwanted sintering is avoided by the silicon oxide coating.

Example 5: Effect of reduction treatment temperature on aluminum oxide coating and Ni quality Aluminum oxide powder was added to 600 g of nickel oxide particles at the aluminum addition rate shown in Table 5, and a V-type mixer (SVM type, manufactured by Seishin Enterprise) Was mixed at room temperature for 5 minutes to coat the nickel oxide particles with aluminum oxide. In addition, an addition rate is the mass% with respect to the total mass of nickel oxide and the oxide for a coating in conversion of a metal element. 10 g of nickel oxide particles thus coated were weighed and placed in a magnetic crucible. The reactor was heated to the temperature shown in Table 5, and then a magnetic crucible charged with nickel oxide particles was put in, and a reduction reaction treatment was performed for 20 minutes while supplying hydrogen as a reducing gas at a flow rate of 0.2 m ³ / hr. . By this reduction reaction treatment, the nickel oxide particles were reduced to become reduced nickel particles. After the reduced nickel particles were cooled to room temperature under an inert atmosphere, the magnetic crucible was taken out and turned over. At this time, the presence or absence of sintering was confirmed by observing whether the sample spilled out without being sintered. The quality of the obtained reduced nickel was measured with an ICP-emission spectroscopic analyzer (VISTA-PRO, manufactured by Varian). These results were as shown in Table 5.

  As shown in Table 5, the higher the reduction treatment temperature, the easier the sintering tendency appears, and the lower the treatment temperature, the less the sintering. This shows that it is desirable to perform the treatment at the lowest possible reduction temperature.

Example 6: Effect of reduction treatment temperature on silicon oxide coating Silicon oxide powder was added to 600 g of nickel oxide particles at the silicon addition rate shown in Table 6 and then at room temperature using a V-type mixer (SVM type, manufactured by Seishin Enterprise). Mix for 5 minutes to coat the nickel oxide particles with silicon oxide. In addition, an addition rate is the mass% with respect to the total mass of nickel oxide and the oxide for a coating in conversion of a metal element. 10 g of nickel oxide particles thus coated were weighed and placed in a magnetic crucible. The reactor was heated to the temperature shown in Table 6, and then a magnetic crucible charged with nickel oxide particles was put in, and a reduction reaction treatment was performed for 20 minutes while supplying hydrogen as a reducing gas at a flow rate of 0.2 m ³ / hr. . By this reduction reaction treatment, the nickel oxide particles were reduced to become reduced nickel particles. After the reduced nickel particles were cooled to room temperature under an inert atmosphere, the magnetic crucible was taken out and turned over. At this time, the presence or absence of sintering was confirmed by observing whether the sample spilled out without being sintered. The quality of the obtained reduced nickel was measured with an ICP-emission spectroscopic analyzer (model name: VISTA-PRO, manufactured by Varian). These results were as shown in Table 6.

As shown in Table 6, the higher the reduction treatment temperature, the more likely the sintering tendency appears, and the lower the treatment temperature, the less sintering occurred. This shows that it is desirable to perform the treatment at the lowest possible reduction temperature.

Example 7: Observation of magnesium oxide coating layer before reduction Magnesium oxide powder was added to 600 g of nickel oxide particles and mixed at room temperature for 5 minutes with a V-type mixer (SVM type, manufactured by Seishin Enterprise). Coated with magnesium oxide. At this time, the addition amount of the magnesium oxide powder was set to 0.15% by mass with respect to the total mass of nickel oxide and coating oxide in terms of metal elements. When the cross section of the obtained sample was scanned and analyzed with an energy dispersive X-ray analyzer (GENESIS 2000, manufactured by EDX), it was confirmed that magnesium was present on the particle surface as shown in FIG. The obtained EPMA analysis image is shown in FIG. FIG. 1 shows that a magnesium-based layer having a thickness of about 3 μm was formed on the particle surface. Moreover, when the surface of the obtained particle | grains was observed by SEM, the image shown by FIG. 2 was obtained. Furthermore, elemental analysis was performed at each point a, b, c, and d shown in FIG. 2 using (SEM; Hitachi S4100) and an energy dispersive X-ray analysis method (EDX; Horiba EMAX5770). Mg was confirmed. FIG. 3 shows an elemental analysis chart at point b.

Example 8: Observation of reduced magnesium oxide coating layer 10 g of the coated nickel oxide particles obtained in Example 7 were weighed and the reactor placed in a magnetic crucible was heated to 900 ° C. and then charged with nickel oxide particles. The magnetic crucible was put in, and a reduction reaction treatment was performed for 20 minutes while supplying hydrogen as a reducing gas at 0.2 m ³ / hr. By this reduction reaction treatment, the nickel oxide particles were reduced to become reduced nickel particles. When the cross section of the obtained particle was scanned and analyzed with an energy dispersive X-ray analyzer (GENESIS 2000, manufactured by EDX), it was confirmed that magnesium was present on the particle surface as shown in FIG. The obtained EPMA analysis image is shown in FIG. FIG. 4 shows that a magnesium-based layer having a thickness of about 2 μm was formed on the particle surface. Further, when the surface of the obtained particle was observed with an SEM, an image shown in FIG. 5 was obtained. Furthermore, when elemental analysis was performed with a scanning electron microscope (SEM; Hitachi S4100) and an energy dispersive X-ray analysis method (EDX; Horiba EMAX5770) at points a, b, c and d shown in FIG. Mg was confirmed at each point. FIG. 6 shows an elemental analysis chart at point c.

Example 9: Magnesium oxide powder was added to 1650 g of reduction-treated nickel oxide particles using a fluidized bed, and mixed for 5 minutes at room temperature with a V-type mixer (SVM type, manufactured by Seishin Enterprise Co., Ltd.). Coated with. At this time, the addition amount of the magnesium oxide powder was set to 0.10% by mass with respect to the total mass of nickel oxide and coating oxide in terms of metal elements. 1650 g of the coated nickel oxide particles were weighed and placed in a cylindrical stainless steel flow apparatus (siliconit furnace, manufactured by Siliconit Co.) having an inner diameter of 90 mmΦ. This fluidizing device was heated to 900 ° C. from the outside, and nitrogen gas was introduced from the bottom at a flow rate of ³ m ³ / hr to form a fluidized bed. The reduction reaction was continuously carried out for 7 minutes 30 seconds while supplying propane as a reducing gas at a flow rate of 0.4 m ³ / hr. At this time, when the CO concentration and CO ₂ concentration in the gas discharged from the fluidized bed were continuously analyzed with an INFRARED GAS ANALYZER apparatus (ZRG2GNP2-0B0YY-YY0YYFY, manufactured by Fuji Electric Co., Ltd.), the progress of the reduction reaction was observed. 7 as shown. After the reduction treatment, the heating and supply of the reducing gas were stopped, and the mixture was cooled to room temperature while introducing nitrogen gas. The obtained processed product was sampled and analyzed by an ICP-emission spectroscopic analyzer (VISTA-PRO, manufactured by Varian) to grasp the degree of progress of reduction. As a result, the achieved Ni quality of the obtained reduced product was 95.7% by mass, and the oxygen content of the product was 1.88% (oxygen analyzer, RO-600, manufactured by LECO). From these results, it can be seen that the flow state was maintained until the end, the reduction reaction proceeded smoothly, and a target Ni-grade product was obtained. From this, it can be seen that by applying the MgO coating to the nickel oxide particles, the reduction reaction proceeds smoothly and the desired Ni quality can be obtained.

Example 10: Magnesium oxide powder was added to 1650 g of reduction-treated nickel oxide particles using a fluidized bed, and mixed for 5 minutes at room temperature with a V-type mixer (SVM type, manufactured by Seishin Enterprise). Coated with. At this time, the addition amount of the magnesium oxide powder was set to 0.005 mass% with respect to the total mass of nickel oxide and coating oxide in terms of metal elements. 1650 g of the coated nickel oxide particles were weighed and placed in a cylindrical stainless steel flow apparatus (siliconit furnace, manufactured by Siliconit Co.) having an inner diameter of 90 mmΦ. This fluidizing device was heated to 900 ° C. from the outside, and nitrogen gas was introduced from the bottom at a flow rate of ³ m ³ / hr to form a fluidized bed. The reduction reaction was continuously carried out for 2 minutes while supplying propane as a reducing gas at a flow rate of 0.4 m ³ / hr. At this time, when the CO concentration and CO ₂ concentration in the gas discharged from the fluidized bed were continuously analyzed with an INFRARED GAS ANALYZER apparatus (ZRG2GNP2-0B0YY-YY0YYFY, manufactured by Fuji Electric Co., Ltd.), the progress of the reduction reaction was observed. As shown in FIG. After the reduction treatment, the heating and supply of the reducing gas were stopped, and the mixture was cooled to room temperature while introducing nitrogen gas. The obtained processed material was sampled and analyzed by an ICP-emission spectroscopic analyzer (VISTA-PRO, manufactured by Varian) to grasp the degree of progress of reduction. As a result, the achieved Ni quality of the obtained reduced product was 78.9% by mass. From these results, it can be seen that the flow state disappeared immediately after the start, the reduction reaction also stagnated, and the target Ni-grade product was not obtained. From this, it can be seen that when the coating is insufficient, sintering occurs, the fluidized bed is not maintained, and the reduction reaction is stagnant.

In Example 7, it is the image which analyzed the cross section of the MgO covering nickel oxide particle before reduction | restoration by EPMA. 8 is an image obtained by photographing the surface of MgO-coated nickel oxide particles before reduction in Example 7 with an SEM. 3 is an elemental analysis chart measured at point b in FIG. 2. In Example 8, it is the image which analyzed the cross section of the MgO covering nickel particle after reduction | restoration by EPMA. In Example 8, it is the image which image | photographed the surface of the MgO covering nickel particle after reduction | restoration by SEM. 6 is an elemental analysis chart measured at point c in FIG. 5. FIG. 10 is a graph showing changes with time in CO concentration and CO ₂ concentration in gas discharged from a fluidized bed measured in Example 9. Measured in Example 10, it shows the time course of CO concentration and the CO ₂ concentration in the gas discharged from the fluidized bed.

Claims (16)

Mixing nickel oxide particles and at least one powdery coating oxide selected from the group consisting of magnesium oxide, aluminum oxide, and silicon oxide at 0 ° C. to 100 ° C. for 1 minute or more without adding an additive And obtaining nickel oxide particles coated with the coating oxide, wherein the amount of the coating oxide added is calculated in terms of metal element and the nickel oxide particles and coating oxide. A method for coating nickel oxide particles , which is used for producing reduced nickel by reduction of nickel oxide , characterized in that the content is 0.02% by mass or more with respect to the total mass .   The method of claim 1, wherein the mixing is performed without preheating and heating.   The method according to claim 1, wherein the mixing is performed at room temperature. The method according to any one of claims 1 to 3 , wherein the mixing is performed by a V-type mixer or a concrete mixer. The method according to any one of claims 1 to 4 , wherein the nickel oxide particles have a diameter of 0.1 to 5 mm. The coating oxide has a size not larger than 45 [mu] m, method according to any one of claims 1-5. The amount of the coating oxide, in terms of metal elements, based on the total weight of the nickel oxide particles and the coating oxide, 0.03 to 0.10 wt%, more of claims 1 to 6 The method according to claim 1. The coating oxide is magnesium oxide, the method according to any one of claims 1-7. The coating oxide is aluminum oxide, the method according to any one of claims 1-7. The coating oxide is silicon oxide, the method according to any one of claims 1-7. Said nickel oxide particles, is formed on the surface of the particles, magnesium oxide, aluminum oxide, and composed of at least one selected from the group consisting of silicon oxide becomes and an oxide coating of claim 1-10 Coated nickel oxide particles produced by the method according to any one of the above and used for producing reduced nickel by reduction of nickel oxide. A nickel oxide particle coated with a coating oxide is formed by the method according to any one of claims 1 to 10 , and the coated nickel oxide particle is heated to a temperature that does not cause sintering at 750 ° C or higher. A method for producing reduced nickel, comprising a step of heating and supplying a reducing gas to the heated particles to reduce the nickel oxide, thereby producing reduced nickel. The method according to claim 12 , wherein the reducing gas is at least one selected from the group consisting of ammonia, hydrogen, carbon monoxide, or a natural gas or propane gas containing them. The method according to claim 12 or 13 , wherein the heating temperature is less than 950 ° C. The method according to claim 12 or 13 , wherein the heating temperature is 900 ° C or lower. The method according to any one of claims 12 to 15 , wherein the reduction is performed while fluidizing the particles with nitrogen gas.