JPH10167731A - Method for producing composite iron oxide fine particles - Google Patents

Abstract

[PROBLEMS] To provide a method for easily reducing residual chlorine in composite iron oxide fine particles. [PROBLEMS] A step of spraying a raw material liquid comprising a mixed aqueous solution containing at least iron chloride and manganese chloride. A step of directly applying heat of a combustion flame to the sprayed raw material droplets to cause an oxidation reaction and generating composite iron oxide fine particles by vapor phase growth, and a gas flow containing the generated composite iron oxide fine particles,
Passing the mixture through a solid-gas separator at a temperature exceeding the rechlorination temperature of manganese and not more than 600 ° C. to separate the composite iron oxide fine particles from the gas stream in a solid-gas state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing composite iron oxide fine particles used as a raw material for soft ferrite.

[0002]

2. Description of the Related Art A mixed solution of an aqueous solution of iron chloride and an aqueous solution of manganese chloride, or a raw material solution obtained by mixing an aqueous solution of one or more of metal chlorides of zinc, nickel and copper with the mixture is sprayed, and the heat of the combustion flame is applied. Various researches and developments have been made on the production of composite iron oxide fine particles by a spray roasting method in which thermal decomposition is performed or a vapor phase growth method in which the method is improved. Each of these methods is a method in which the powder after the reaction is transported in the same direction as the gas in cocurrent, and after cooling, is separated from the gas to obtain a composite iron oxide.

According to these methods, a desired composite oxide can be obtained even if the raw material contains a component which is highly volatile and hardly oxidized like zinc chloride. However, it is difficult to control the quality, and there is a problem in the stability of the composition such as a low yield of zinc. To solve this problem, Japanese Patent Application Laid-Open No. 4-260601 discloses 300-45.
It is disclosed that the stability of the composition is improved by setting the temperature as low as 0 ° C. and performing the separation and recovery from the gas at only one place. JP-A-6-293521 discloses that zinc chloride in a product is reduced by rapidly cooling to 400 ° C. or less within 5 seconds of reaction by spray roasting.

However, in these cases, no consideration is given to residual chlorine due to manganese chloride. That is, in the example of JP-A-6-293521, 1.7% by weight of manganese chloride remained in the composite oxide.
On the other hand, Japanese Patent Application Laid-Open No. 6-144838 discloses an example in which the chlorine residue can be considerably reduced to 0.04% by weight. After that, it is a complicated process in which the intermediate product obtained there is put in a rotary kiln and treated at a two-stage temperature for 40 minutes, and it is expected that there will be difficulties in terms of engineering and cost for practical use. .

[0005] These prior arts have been studied in accordance with the basic idea of reducing the burden on the solid-gas separation by lowering the solid-gas separation temperature. If it is exposed inside, condensation of hydrochloric acid occurs, which is a serious problem, and the fact is that cooling is performed with great effort.

[0006]

The present inventors have previously proposed a method for producing composite iron oxide fine particles by vapor phase growth (Japanese Patent Laid-Open No. 7-335023). According to this method, there is no concern about the yield of zinc, and it is possible to produce uniform fine iron oxide particles having good magnetic properties and a large particle size. The present invention particularly improves this method, and an object of the present invention is to provide a method for easily reducing the residual chlorine in the obtained composite iron oxide fine particles.

[0007]

In order to achieve this object, the present inventor first examined the form of chlorine. In other words, by measuring the chlorine concentration by chemically analyzing the composite iron oxide fine particles of the product, the amount of residual chlorine can be known, but in the case of the vapor phase growth method, there is no need for special measures such as rapid cooling. Originally, residual chlorine is as small as 1 to 3% by weight.
Line analysis could not identify the form of chlorine. Using the fact that residual chlorine can be removed by washing with pure water, we analyzed the washing liquid and measured the change in the composition of the composite iron oxide fine particles before and after washing, and determined that the form of chlorine was all manganese chloride. .

[0008] Regarding the location of the manganese chloride, the residual chlorine can be easily removed by washing with water. Therefore, it is presumed that the manganese chloride is not taken in the fine particles but exists on the surface of the fine particles. In normal spray roasting, unreacted substances are often left inside the particles except for volatile components such as zinc chloride, but in the vapor phase growth method, unreacted substances are left inside the particles if the conditions are met. Does not penetrate, and is condensed and deposited on the surface of the fine particles during the cooling process. Therefore, it is not known whether the manganese chloride existing on the surface is an unreacted substance or a substance obtained by rechlorinating the surface of the fine particles with hydrochloric acid gas generated by the reaction, so that only measures by trial and error can be taken.

Next, the present inventors investigated the reaction equilibrium between manganese chloride and oxide to identify the origin of manganese chloride. MnCl ₂ + H ₂ O + Fe ₂ O ₃ = MnFe ₂ O ₄ +2
HCl MnCl ₂ in the gas phase and solid
The equilibrium constant Kp was calculated from the change in free energy due to the reaction at each temperature in the range of 200 to 1000 ° C. in steps of 50 ° C. for the two cases of the liquid phase. Further, using this equilibrium constant, a calculation for confirming the direction in which the reaction proceeds in an actual atmosphere was similarly performed at each temperature. At the same time, a calculation was made to calculate the dew point of the manganese chloride vapor in that atmosphere back from the vapor pressure.

FIG. 1 shows the results of these calculations in which the horizontal axis represents temperature,
The vertical axis shows the equilibrium water vapor partial pressure plotted. Table 1 shows the preconditions for this calculation. If the equilibrium water vapor partial pressure is smaller than the actual water vapor partial pressure, the reaction proceeds to the oxidation side, and if it is higher, the reaction proceeds to the chloride side. Also,
If the ratio is about several times, it is necessary to consider where the equilibrium is settled or what the actual non-equilibrium state will be. However, if the ratio is two digits or more, the result can be expected. That is, the behavior of manganese can be simulated by interpreting this graph along the actual temperature history.

In this graph, the actual partial pressure of water vapor indicated by the horizontal dotted line is 0.44 atm under this condition. However, since it is the result of spraying the aqueous solution, naturally there must be some water vapor. Since it is not conceivable to operate such processes at high pressure, the partial pressure of steam naturally falls within a narrow range. Moreover, since the vertical axis is a logarithmic scale,
Even if the conditions are considerably changed, the position of the horizontal dotted line hardly changes.

The dew point of manganese chloride, indicated by the vertical dashed line in this graph, is 744 ° C. under these conditions, above which manganese chloride can completely evaporate to a gas. The curve of the equilibrium water vapor partial pressure when manganese chloride is a gas is orders of magnitude smaller than the actual water vapor partial pressure even at a temperature of 744 ° C. or higher, indicating that manganese is easily oxidized by the vapor phase growth method. Therefore, there should be no unreacted manganese, and the residual chlorine is considered to be due to the rechlorination reaction.

Next, the rate of the rechlorination reaction in the cooling process was examined. If the manganese chloride vapor disappears due to oxidation, the dew point of the manganese chloride naturally declines, but at this temperature much lower than the boiling point, considering the re-chlorination reaction, it is formed at the moment of salification. Is a solid-liquid phase. When manganese chloride is in the solid / liquid phase, the curve of equilibrium water vapor partial pressure rises sharply with decreasing temperature and rises to 460 ° C.
At the actual water vapor partial pressure. When the temperature becomes lower than 460 ° C., the equilibrium water vapor partial pressure immediately increases by an order of magnitude, and it can be understood that the rechlorination reaction proceeds rapidly.

The present invention has been completed on the basis of the result of the simulation, and the atmosphere temperature of the portion where the composite iron oxide fine particles generated by the vapor phase growth method are separated from the gas stream is adjusted to the manganese content in the manganese ferrite. This is a method of keeping the temperature at which the equilibrium does not proceed to the chloride side. According to this method, it has become possible to obtain high-quality composite iron oxide fine particles having little residual chlorine.

When a ceramic filter is used as the solid-gas separator, the backwashing pulse air enters the system and directly contacts the collected fine particles, so that the temperature is naturally controlled. This method can be reliably applied by preheating to at least the acid dew point or more, and if possible, to the same temperature as that of the solid-gas separator.

That is, the present invention provides a step of spraying a raw material solution comprising a mixed aqueous solution containing at least iron chloride and manganese chloride, and directly applying heat of a combustion flame to the sprayed raw material droplets to cause an oxidation reaction. A step of generating composite iron oxide fine particles by vapor phase growth, and a step of forming a gas stream containing the generated composite iron oxide fine particles at a temperature exceeding the re-chlorination temperature of manganese,
Passing the mixture through a solid-gas separator at a temperature of 0 ° C. or less to separate the composite iron oxide fine particles from the gas stream in a solid-gas state. Chloride, and can contain one or more selected from the group of copper chloride, furthermore, when a ceramic filter is used for the solid-gas separator, the pulse air for backwashing of the solid-gas separator is used. It is desirable to preheat to an acid dew point or higher and 200 ° C. or lower.

[0017]

[Table 1]

[0018]

FIG. 2 is a flow chart of a composite iron oxide production process by a vapor phase growth method to which the present invention is applied.
Hereinafter, the process will be described with reference to FIG. Fuel gas and combustion air are supplied to the burner 1 and burn in the reaction furnace 2 to form a combustion flame. A raw material liquid obtained by mixing hydrochloric acid with an aqueous solution containing metal chlorides of iron chloride and manganese chloride, zinc chloride, nickel chloride, and copper chloride is sprayed from inside the combustion flame. This allows
Water evaporates in a reducing atmosphere in the presence of hydrogen chloride, and water of crystallization of chloride is released to form anhydrous chloride crystals, which are not oxidized. Then, the anhydrous chloride crystal sublimates sequentially inside the combustion flame. At this time, the furnace temperature needs to have a region of about 800 ° C. or more in order to completely evaporate manganese chloride.

When the anhydrous chloride enters the outer oxidizing atmosphere, it undergoes an oxidation reaction with oxygen and water vapor and grows in a vapor phase to produce composite iron oxide fine particles. Dilution cooling air is blown into a flow composed of the combustion gas containing the composite iron oxide fine particles and the reaction product gas, and is led to the ceramic filter 3. Pulse air is blown into the ceramic filter 3 from the pulse air preheater 4 to be separated into solid and gas. The composite iron oxide fine particles are recovered by the double damper 5, and the hydrochloric acid is recovered by the hydrochloric acid recovery tower 6.

In this case, if the composite iron oxide fine particles are conveyed to the mixed gas flow and flow into the solid-gas separator, they are left to cool naturally without any forced cooling, so that the solid-gas separated gas Temperature drops to below 600 ° C. It is possible to operate the gas-solid separator at a higher temperature by keeping the temperature, etc., but special equipment is required for the equipment, which leads to higher equipment costs and pressure depending on the method of solid-gas separation. Since the loss increases and the load on the blower increases, the upper limit temperature is desirably 600 ° C. On the other hand, the lower limit temperature is a temperature exceeding a temperature at which manganese is rechlorinated in order to obtain good fine particles having a small amount of residual chlorine.
And

Solid-gas separators are generally used, such as electric dust collectors, cyclones and ceramic filters.
Any material that can withstand high temperatures can be used. Here, a ceramic filter is used, and the backwash pulse air is desirably used after being preheated to an acid dew point or higher so as not to cause condensation of hydrochloric acid in the filter housing.
However, the upper limit is practically 200 ° C. In theory it is desirable to preheat to higher temperatures, but above 200 ° C,
This is because the pulse air valve becomes very expensive. It is preferable to make the pulse air piping longer in the filter housing so that the temperature at which the particles actually come into contact with the particles is brought close to the ambient temperature. The composite iron oxide fine particles removed by the backwash are discharged from the lower part of the filter housing through the double damper to the outside of the system, and escape from the environment exposed to the hydrochloric acid vapor. On the other hand, the waste gas that has passed through the filter is released to the atmosphere via a hydrochloric acid recovery device.

FIG. 3 shows the residual chlorine of the composite iron oxide fine particles collected by widely changing the temperature of the solid-gas separator while keeping the reaction conditions almost constant in this process, with the vertical axis representing the residual chlorine. Blotted values are plotted with the ambient temperature on the horizontal axis. Although there is some variation due to differences in the average exposure time in the gas-solid
At temperatures above ℃, the amount of residual chlorine is 0.4% by weight or less in all cases, and the results are significantly different from those at lower temperatures. That is, it indicates that the accuracy of the simulation performed based on the equilibrium water vapor partial pressure was high.

As described above, according to the present invention, the residual chlorine is remarkably reduced to 0.4% by weight as compared with the prior art, so that the load in the residual chlorine removing process is remarkably reduced. Then, by employing the above-described process, uniform composite iron oxide fine particles having a desired particle size and a composition almost as expected can be obtained.

[0024]

EXAMPLES Table 2 shows a summary of Examples and Comparative Examples of the present invention. Further, the conditions in the reaction section of the example given here are the same as the preconditions for the calculation shown in Table 1. In the following Examples and Comparative Examples, the rechlorination temperature of manganese is 460 ° C.

[0025]

[Table 2] (Example 1) In this example, the flue from the reaction section to the ceramic filter was left to cool naturally, and the average exposure time from when the fine particles were captured by the filter to when it was removed was 22 seconds. . In this example, the preheating temperature of the pulse air was 170 ° C., and the ambient temperature of the collecting section was 490 ° C. Analysis of the composite iron oxide fine particles obtained at this time showed a residual chlorine concentration of 0.22% by weight, which was the lowest among a series of results under the reaction conditions. Example 2 Example 2 is the same as Example 1, except that the average exposure time is 1 minute and 40 seconds. In this example, the preheating temperature of the pulsed air was 190 ° C., and the ambient temperature of the collecting section was 541 ° C. Even if the exposure time was prolonged, the rechlorination reaction did not proceed because the temperature was sufficiently high, and the analysis result of the composite iron oxide fine particles obtained at this time was a residual chlorine concentration of 0.25% by weight. Comparative Example 1 In this comparative example, the flue outer surface from the reaction section to the ceramic filter was forcibly cooled with air, and the average exposure time was 22 seconds. In this example, the preheating temperature of the pulse air is 170 ° C., and the ambient temperature of the collecting section is 41 ° C.
8 ° C. This temperature is a temperature at which the reaction equilibrium proceeds to the chloride side, and the analysis result of the composite iron oxide fine particles obtained at this time was a residual chlorine concentration of 1.13% by weight. (Comparative Example 2) This is an example similar to Comparative Example 1, except that the average exposure time is 1 minute and 40 seconds. In this example, the preheating temperature of the pulse air was 170 ° C., and the ambient temperature of the trapping section was 432 ° C. Although the ambient temperature is slightly higher than Comparative Example 1,
Due to the long exposure time, re-chlorination proceeded more. The analysis result of the composite iron oxide fine particles obtained at this time was a residual chlorine concentration of 1.87% by weight. (Comparative Example 3) Same as Example 1, with an average exposure time of 2
This is an example of using pulse air at room temperature without preheating for 2 seconds. In this example, since cold bals air frequently enters, the ambient temperature of the collecting section is likely to decrease, and the temperature is 458 ° C.
Met. It is speculated that the temperature may have dropped, but the results of analysis of the composite iron oxide fine particles obtained at this time were twice as high as those in the case where pulse air was preheated at a residual chlorine concentration of 0.57% by weight. The salification reaction was in progress.

[0026]

According to the method of the present invention, when the composite iron oxide fine particles containing manganese produced by the vapor phase growth method are separated from the gas stream, rechlorination of the manganese oxide can be minimized. In addition, in order to carry out the method of the present invention, in many cases, only forced cooling in the flue, which has been performed so far, needs to be stopped, and the process can be simplified without significantly increasing equipment costs. Product quality can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing the equilibrium steam partial pressure of a solid / liquid phase of manganese chloride and the equilibrium steam partial pressure of a gas phase of manganese chloride, together with the actual steam partial pressure and the dew point of manganese chloride vapor.

FIG. 2 is a flowchart of a composite iron oxide production process by a vapor phase growth method applied to the present invention.

FIG. 3 is a graph in which the vertical axis indicates the residual chlorine of the composite iron oxide fine particles collected by changing the temperature of the solid-gas separator, and the horizontal axis indicates the ambient temperature in the solid-gas separator.

[Explanation of symbols]

 1 burner, 2 reactor, 3 ceramic filter, 4 pulse air preheater, 5 double damper, 6 chlorine recovery tower

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshiki Shibuya 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Steel Pipe Mining Co., Ltd. (72) Inventor Tatsuo Inoue 1-26 Shimoodanaka, Nakahara-ku, Kawasaki-shi 72) Inventor Hiroshi Sakaguchi 1-1-7 Komaba, Urawa City, Saitama Prefecture

Claims (3)

[Claims] 1. A step of spraying a raw material liquid comprising a mixed aqueous solution containing at least iron chloride and manganese chloride, and directly applying heat of a combustion flame to the sprayed raw material droplets to cause an oxidation reaction and vapor phase growth. A step of generating composite iron oxide fine particles, and passing a gas stream containing the generated composite iron oxide fine particles through a solid-gas separator at a temperature exceeding the re-chlorination temperature of manganese and not more than 600 ° C. to remove the composite iron oxide fine particles from the gas stream A method for producing composite iron oxide fine particles, comprising a step of solid-gas separation. 2. The production of composite iron oxide fine particles according to claim 1, wherein the mixed aqueous solution further contains one or more selected from the group consisting of zinc chloride, nickel chloride and copper chloride. Method. 3. The solid-gas separator is provided with a ceramic filter, and the backwash pulse air of the solid-gas separator has an acid dew point of 20 or more.
A method for producing composite iron oxide fine particles preheated to 0 ° C. or lower.