JPS5945740B2 - Nickel oxide coating method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for coating nickel oxide.

More particularly, the present invention relates to a method of coating nickel oxide particles with magnesium oxide.

When reducing nickel oxide to obtain high nickel grade L>reduced nickel, the reduction reaction 9 progresses slowly at low temperatures, and progresses quickly at high temperatures.

However, even in the case where the reduction reaction Q progresses, problems such as adhesion agglomeration between reduced nickel particles and adhesion of reduced nickel particles to the furnace wall cannot be avoided, and the reduction of nickel oxide cannot be avoided industrially. This makes it difficult to implement.

In order to solve this problem regarding adhesion between particles as well as adhesion to the furnace wall, a number of solutions have been proposed.

One is based on the correlation between reduction temperature and particle size distribution.
The goal was to optimize the reduction rate and rate while minimizing particle mechanical problems.

It has also been proposed to coexist with inert particles and use them as a mechanical buffer phase to avoid the problem of adhesion between metal surfaces.

However, the presence of large amounts of inert particles has been shown to be necessary to achieve effective anti-fouling.

Further, such a method causes problems such as segregation of inert particles and scattering during fluidized reduction, and furthermore requires a sorting step to remove the inert particles afterwards, making handling complicated.

Furthermore, it is known (Canadian Patent No. 869,475) to attempt to solve the adhesion problem by using small amounts of very fine inert particles and high purity nickel oxide.

However, the Canadian patent requires the use of high-purity nickel oxide and also includes the use of hydrogen as a reducing agent, which is economically disadvantageous and inevitably complicates the process.

On the other hand, Japanese Patent Publication No. 55-9932 proposes forming an anti-agglomeration coating on nickel oxide particles in order to overcome the problem of adhesion.

The method comprises the addition of particles of non-ferrous metal oxides (e.g. nickel oxide, cobalt oxide) with a sulfur content of 0.005 to 0.5% and a small amount (in both cases) of calcium oxide, magnesia or a compound which can be thermally decomposed to these oxides. forming a moving bed of the non-ferrous metal oxide particles and contacting the bed with a reducing atmosphere at a temperature sufficient to reduce the non-ferrous metal oxide particles, the anti-agglomeration coating being formed under the reducing conditions. .

However, even in the method described in Japanese Patent Publication No. 55-9932, the sulfur content in the coated nonferrous metal oxide is 0°0.
05 to 0.5%, so when fluidized reduction is performed by injecting fuel oil, the reduction rate decreases because decomposition of the fuel oil is inhibited by sulfur; However, under these conditions, the adhesion of the coating layer is insufficient and the coverage rate is also poor (desulfurization tends to be incomplete; 111 Reduction is performed using coated nickel oxide with a high sulfur content. In this case, the nickel particles become brittle and a large amount of dust is generated.However, there is still room for improvement.

Under these circumstances, the present inventors conducted various studies to further improve the known method, and as a result, discovered a new method for coating nickel oxide particles.

Therefore, the main object of the present invention is to provide a method for coating nickel oxide particles.

Another object of the present invention is to provide coated nickel oxide particles that can effectively avoid the problems of adhesion between nickel oxide particles and adhesion to the furnace wall during nickel oxide Q reduction.

The above and other objects and features of the present invention will become more apparent from the following description.

That is, the present invention includes the step of blowing a solution of a soluble magnesium compound into a fluidized bed of nickel oxide or its precursor at a high temperature of 1000° C. or higher, and burning magnesium oxide onto the surface of the nickel oxide particles. , relates to a method for coating nickel oxide particles with magnesium oxide with extremely low sulfur content.

The term "sintering" used in the method of the present invention refers to the phenomenon in which magnesium metal in an atomized state is deposited on nickel oxide particles like a type of vapor deposition and is baked under ambient high temperature conditions. do.

The nickel oxide particles used in the present invention may be obtained by any method, and examples include fluidized roasted nickel sulfide products and rotary moving bed roasted nickel sulfide products.

Further, in the present invention, the nickel oxide precursor means something that can be converted into nickel oxide by thermal decomposition or the like, and includes, for example, a product after a primary desulfurization treatment during desulfurization of nickel sulfide.

It is desirable that the coating material used in the present invention satisfies the following conditions.

(a) It should be inexpensive; (b) it should be able to uniformly cover the entire nickel oxide surface when used in a small amount; (c) it should be easily available, harmless, and pose no danger in handling. (d) It is easy to handle and the coating operation is easy, and the process of coating the fruit is not complicated; (e)
(f) not be easily removed by friction, heat, etc.;
and (ω) It shall be harmless when used as part of the reduced nickel.

Soluble salts of magnesium, aluminum, calcium and the like satisfy these conditions.

Among these, the use of soluble salts of magnesium is most preferred.

This is because magnesium is superior to other substances in terms of anti-adhesive properties, solubility, availability, economy, etc.

Soluble magnesium compounds include magnesium sulfate,
Examples include magnesium thiosulfate, magnesium nitrate, magnesium chloride, and magnesium acetate.

However, based on the above conditions, magnesium chloride, magnesium nitrate, etc. are excellent soluble magnesium compounds, but they are preferable in the present invention because they generate harmful gases such as chlorine gas and nitrogen oxides that cannot be exhausted as they are when thermally decomposed. It's not a thing.

Further, when the method of the present invention is carried out in combination with an exhaust gas desulfurization process, it is undesirable because it contaminates the sulfuric acid produced in the process, and it is also unsuitable because it causes corrosion of the furnace flue and the like.

There is no particular limit to the concentration of the soluble magnesium solution, but if the concentration is low, a large amount of solution must be used, which is undesirable as it will require cooling the furnace (and if the concentration is high, it may be difficult to use in terms of solubility). Moreover, it is economically disadvantageous as it leads to loss of magnesium compounds.

Therefore, it is advantageous and preferable to use it in a range of 10 to 25% by weight.

The ratio of soluble magnesium to nickel oxide is preferably in the range of 0.2 to 0.3% by weight of nickel oxide, expressed as the weight of magnesium baked onto the nickel oxide.

Thereby, as shown in Example 4, it is possible to sufficiently prevent adhesion between particles, agglomeration, and adhesion on the furnace wall during reduction of nickel oxide.

Although it is possible to carry out magnesium coatings above the upper limit of the above range, especially when using sulfur-containing compounds,
Desulfurization is difficult, and the use of large amounts of magnesium compounds is economically disadvantageous.

The coating method of the present invention is desirably carried out so that the sulfur content is 0.005% by weight or less and the magnesium content is 0.2 to 0.3% by weight for the entire magnesium oxide-coated nickel oxide. It is necessary that the temperature during bonding be 1000° C. or higher.

If the temperature is less than 1000° C., disadvantages such as decreased magnesium yield, poor desulfurization, and poor magnesium sintering are seen, which is not preferable.

In the present invention, either a batch type or a continuous type fluidized bed furnace may be used (or any type of fluidized bed furnace may be used).

The soluble magnesium compound can be used alone or as a mixture of two or more compounds, and the solution is preferably an aqueous solution because it is most economical and easy to handle.

Hereinafter, the method of the present invention will be explained with reference to the attached drawings with reference to preferred specific examples, but the present invention is not limited thereto in any way.

First, FIG. 1 schematically shows a process of oxidizing and roasting nickel sulfide in a fluidized roasting furnace to obtain nickel oxide with a low sulfur content.

In the oxidative roasting of nickel sulfide, desulfurization operations are usually carried out twice.

This is because primary roasting (primary desulfurization) alone has poor desulfurization efficiency and poor nickel oxide productivity. (
This is because a secondary desulfurization operation is essential.

Nickel sulfide is supplied from the upper part of the primary roasting furnace 1, and the tuyere at the lower part of the furnace is also supplied, and oxidation roasting (
primary desulfurization).

The nickel sulfide that has undergone the primary desulfurization treatment is then sent to the secondary roasting furnace 2 and treated in the same manner as in the primary roasting furnace, and finally a nickel oxide product cooled in the cooler 3 is obtained.

The gas discharged from the primary and secondary roasting furnaces 1 and 2 is led to the flue 5 above each roasting furnace, and is desulfurized in the flue gas desulfurization device 4 provided in the flue and then released. .

Sulfuric acid is produced in this desulfurization step.

In the first aspect of the present invention, the secondary roasting and magnesium oxide coating are performed simultaneously in the secondary roasting stage (the first
(see figure).

Therefore, the nickel oxide source in this embodiment is the nickel oxide precursor after the primary desulfurization treatment.

2 of nickel sulfide under high temperature conditions of 1000℃ or more
By blowing, for example, an aqueous magnesium sulfate solution into the second roasting furnace 2, a magnesium oxide layer can be uniformly formed on the surface of the nickel oxide particles.

According to this embodiment, there is no need to prepare a new reactor for forming the magnesium oxide coating, and the high-temperature reactor from the primary reactor 1 can be used as is in the coating process, so the yield of magnesium is extremely high. Furthermore, since the coating treatment can be performed during the oxidative roasting of nickel sulfide, it is possible to save energy and to obtain magnesium oxide-coated nickel oxide having an extremely low sulfur content.

During the oxidative roasting of nickel sulfide, sulfur dioxide gas is generated, so cooling and cleaning of the gas and production of sulfuric acid are usually carried out as exhaust gas treatment.

Therefore, when coating nickel oxide at the same time as oxidative roasting of nickel sulfide, it is advantageous to use sulfur-containing magnesium sulfate, magnesium thiosulfate, etc. as a coating agent. Using the obtained waste acid and manufactured sulfuric acid, it is possible to dissolve inexpensive magnesium oxide in it to create magnesium sulfate, which allows for cost savings and product cost reduction, as well as waste acid treatment at the same time. It can be done and is extremely advantageous.

On the other hand, it is also possible to form a magnesium oxide coating by spraying a soluble magnesium compound solution to cool the high-temperature nickel oxide after the secondary desulfurization treatment when it is put into a cooler. is insufficient, and the desulfurization rate is also poor.

Furthermore, a method of impregnating with a magnesium solution while cold and then exposing to high temperature and baking is also considered.

However, in this case as well, the coverage is insufficient and favorable results cannot be obtained.

Another embodiment uses nickel oxide itself.

FIG. 2 shows an example of this embodiment. Nickel oxide is placed in a roasting furnace 10 under a high temperature condition of 1000° C. or higher, and an appropriate amount of magnesium salt solution is blown into the roasting furnace 10 to burn the magnesium oxide onto the surface of the nickel oxide particles.

In this case, the nickel oxide may be dropped by gravity from the upper part of the furnace, or may be mechanically blown into the furnace wall.

The magnesium salt solution is blown into the furnace wall near the hearth.

Further, in order to maintain the furnace temperature at 1000° C. or higher, fuel oil or fuel gas is introduced from the furnace wall near the hearth.

The coated nickel oxide is led to a cooler 11, where it is cooled and then taken out.

The exhaust gas from the torrefaction furnace 10 and the cooler is led to a flue in the upper part thereof, treated in an exhaust gas cooling and cleaning device 12 provided there, and then discharged.

Thus, according to the coating method of the present invention, magnesium oxide can be baked onto nickel oxide particles with a yield of 90% or more, and the coated nickel oxide particles obtained by this process are free from adhesion agglomerates between particles during reduction. It does not cause any oxidation or adhesion to the furnace wall.

Furthermore, compared to conventional methods in which nickel oxide is reduced by mixing with silica, magnesia, dolomite, etc., there is no need to use a coating agent, and it is easier to separate additives such as silica, magnesia from reduced nickel. Since it does not require any manipulation, it is economically advantageous, and it is also easy to handle, which has many advantages.

Further, since the coated nickel oxide obtained by the coating method of the present invention can be transferred to the subsequent reduction step as it is in a high temperature state, preheating for reduction is not required, and energy can be saved.

Next, the method of the present invention will be explained in more detail with reference to Examples.

Example 1 During oxidative roasting of nickel sulfide, a 25% solution of magnesium sulfate (at room temperature) was blown into the secondary roasting furnace to coat nickel oxide with 1-edge magnesium oxide.

Magnesium sulfate solution is 5 parts per 100 parts of nickel oxide.
．． The total amount was 76.

The temperature was 1030°C.

The particle size distribution and chemical composition of the magnesium oxide-coated nickel oxide obtained at this time are shown in Tables 1 and 2, respectively.

The yield of magnesium is as high as 92.7%,
The sulfur content was also extremely low as shown in Table 2.

As a result of analyzing the obtained magnesium oxide-coated nickel oxide particles using an X-ray microanalyzer, it was found that magnesium oxide was coated on the surface of the nickel oxide particles to a thickness of approximately 4 microns, and no segregation of magnesium, sulfur, etc. was observed. Ta.

(See Figure 3) Analysis of the magnesium oxide-coated nickel oxide particles using an X-ray microanalyzer was performed by embedding the particles in an appropriate resin, polishing the particles, and then subjecting them to line analysis.

Magnesium char) A is shown in the lower part of FIG. 3, and a magnesium peak is seen on the end face of nickel oxide (near the solid line α in FIG. 3).

On the other hand, β indicates the chart of nickel, and the observed unevenness is due to non-uniformity of the surface of the nickel particles, and the depressions indicate the presence of holes or depressions in the nickel particles.

The right side of the solid line α corresponds to the resin part as a matrix,
The left side corresponds to magnesium oxide coated nickel oxide particles.

As a result of reducing this magnesium oxide-coated nickel oxide in a fluidized-bed reduction furnace at 900° C., high-grade reduced nickel with a reduction degree of 88% or more was stably obtained without adhesion and agglomeration.

Example 2 By the same method as in Example 1, nickel oxide was coated with magnesium oxide at a temperature of 1020°C.

Tables 3 and 4 show the particle size distribution and chemical components of the magnesium oxide-coated nickel oxide particles obtained at this time.

The yield of magnesium was 98%.

Example 3 As illustrated in Fig. 2, when nickel oxide was charged into a fluidized furnace and the fluidized bed temperature was maintained at 840'C and 900°C, a magnesium sulfate solution was blown into the fluidized bed to form a magnesium oxide coating. I did it.

Table 5 shows the 8% Mg3 of the nickel oxide used.

Table 6 shows the Mg 3.8% and magnesium yield of the magnesium oxide-coated nickel oxide obtained at this time.

As understood from Table 6, since the temperature is lower than 1000°C, the sulfur content is high and the yield of magnesium is also very poor.

Example 4 According to a method similar to Example 1, nickel oxide was coated with magnesium oxide at a temperature of 1030°C.

The yield of magnesium when the amount of magnesium sulfate solution added to nickel oxide was changed as shown in Table 7, 8%, Mg%, and the obtained nickel oxide at 900 ° C.
Table 7 shows the presence or absence of adhesion of nickel particles to each other when reduced by

[Brief explanation of drawings]

FIG. 1 is a flowchart schematically showing the oxidative roasting process of nickel sulfide, FIG. 2 is a process diagram showing one embodiment of the method of the present invention, and FIG. Fig. 2 is a chart showing the results of line analysis of a cross section of nickel oxide particles coated with an X-ray microanalyzer.

Claims (1)

[Claims] 1. A step of blowing a solution of a soluble magnesium compound into a fluidized bed of nickel oxide or its precursor at a high temperature of 1000° C. or higher to burn magnesium oxide onto the surface of the nickel oxide particles. with extremely low sulfur content, including
A method of coating nickel oxide particles with magnesium oxide. 2. The method according to claim 1, wherein the soluble magnesium is magnesium sulfate, magnesium thiosulfate, magnesium chloride, magnesium nitrate or magnesium acetate. 3. The method of claim 2, wherein the nickel oxide precursor is a product obtained after a primary desulfurization treatment of nickel sulfide. 4. Claim 3, wherein the injection of the soluble magnesium solution is performed in the secondary desulfurization step of nickel sulfide.
The method described in section.