JPS62119116A - Production of lepidocrocite - Google Patents

Abstract

PURPOSE:To obtain lepidocrocite suitable for the production of magnetic iron oxide powder for a magnetic recording medium by adding the alkali aq. soln. of the prescribed amount to a ferrous chloride aq. soln. and thereafter ageing the mixture under the specified conditions and blowing O2-contg. gas therein and furthermore adding the alkali soln. and also blowing O2-contg. gas therein. CONSTITUTION:The alkali aq. soln. such as caustic alkali and NH3 is added to a ferrous chloride aq. soln. in 0.4-0.7 times of theoretical amount necessary for the formation of ferrous hydroxide. Then while stirring this processing liquid in the nonoxidizing atmosphere such as inert gas atmosphere, it is aged by keeping it for 20-120min under the conditions of 6.0-9.0 pH value and 10-50 deg.C temp. Thereafter the seed crystal of gamma-FeOOH (lepidocrocite) is formed by blowing O2-contg. gas to the processing liquid after the maturation. gamma-FeOOH forming reaction is completely finished by adding the above-mentioned alkali aq. soln. to the above-mentioned matured liquid formed with the seed crystal and also blowing O2-contg. gas therein. Thereby lepidocrocite is obtained which is small in grain size distribution and has excellent properties having stably the required various grain sizes.

Description

[Detailed description of the invention] (Industrial application field) The present invention is directed to lepidocrocite (γ-F' e OOH)
More specifically, the present invention relates to a method for producing lepidocrocite, which is suitable as a starting material when producing magnetic iron oxide powder for magnetic recording media such as audio tapes, video tapes, and magnetic cards.

(Prior Art and Problems to be Solved) Generally, magnetic iron oxide powder for magnetic recording media such as audio tapes, video tapes, magnetic carts, etc.

Using a-FeOOH (goethite) or Y-FeOOH (lepidocrocite) as a starting material, this is sequentially subjected to treatments such as calcination (dehydration, baking), reduction, and oxidation to produce acicular γ-Fe, o , (makuhemite), or Co-γ-Fe with cobalt deposited on the particle surface by cobalt modification treatment, 0. It is manufactured by obtaining In this case, the magnetic properties of the obtained magnetic iron oxide powder depend on the properties of the above-mentioned starting material, so in order to obtain magnetic iron oxide powder suitable for magnetic recording media, it is necessary to use a starting material with excellent properties. be.

In this respect, conventionally, lepidocrocite (γ-FeOOH)
The magnetic iron oxide powder prepared using . magnetic orientation, dispersion,
Although the squareness ratio and transfer characteristics are excellent, there is a problem of large particle size distribution, and the properties of the final product (coercive force,
This has the disadvantage of having an adverse effect on the reversal magnetic field strength distribution, etc.).

By the way, among the above starting materials, lepidocrocite is usually produced by the following synthetic reaction method.

First, ferrous chloride (Fe) obtained using pickling waste liquid etc.
CQ□) Add an alkaline aqueous solution such as caustic alkali or ammonia to the water Ifj liquid to neutralize it. On this occasion.

The molar ratio of hydroxyl group to iron (OI-I/Fe) is about 0.20~
An alkaline aqueous solution is mixed so that the concentration is 0.35.

Next, this is oxidized with a Mi-containing gas (air or oxygen) to produce seed crystals through a sheet reaction. The reaction temperature at this time is about 10-25°C. As the seed reaction approaches completion, the pH of the reaction solution decreases, and when the alkaline content is completely consumed and the reaction ends, the P I-I value will be approximately 3.2 to 3.8.
becomes.

After that, the temperature is raised to 30-50℃, and the pH value is about 3.5-4.
．． A growth reaction is carried out by blowing in an oxygen-containing gas and adding an alkaline aqueous solution so that the concentration of the alkali becomes 5.5.

As this growth reaction approaches completion, the reaction rate slows down,
PH value is high! Do 1. The reaction is terminated when the pH value reaches approximately 5.5, and needle-like lepidocrocite is obtained.

However, as mentioned above, with the above method, only lepidocrocite with a large particle size distribution can be obtained, which cannot be said to have good properties, and furthermore, it is difficult to control the average particle size, so it is not suitable for the purpose of use. However, there was a drawback that lepidocrocite having an arbitrary average particle size could not be provided.

For this reason, goethite (α-Fe○○H) is currently frequently used as a starting material for the production of magnetic iron oxide powder.

The present invention solves the drawbacks of the prior art and produces lepidocrocite, which has many advantages as described above, and has excellent properties such as a small particle size distribution and stably having various required particle sizes. The purpose of the present invention is to provide a method for producing docrosite.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, when a ferrous chloride aqueous solution and an alkali aqueous solution are mixed, lepidocrocytos]- is produced, but the uniformity of the crystal grain size is We found that controlling this will bring about good results in the production and growth of lepidocrocite seed crystals in the subsequent steps,
For this purpose, the key point is to provide a "ripening" step in which the mixed aqueous solution is maintained under specific conditions before the seed reaction.

The present invention will be explained in detail below based on examples.

The aging process in the present invention is carried out between the mixing process of adding an alkaline aqueous solution to the ferrous chloride aqueous solution and the seeding reaction process of oxidizing with an oxygen-containing gas and generating seed crystals of lepidocrocite through a seed reaction. The 1-' H value of the mixed aqueous solution is 6.0 to 9.0. Temperature is 10-50℃
Hold within the range of 20 to 120 minutes. Of course, since this is not a sheet reaction, it goes without saying that it is carried out in a non-oxidizing atmosphere such as an inert gas atmosphere, and is carried out with stirring.

The mixing and stirring state is 1. For example, the rotation speed of the stirring blade is 200 to 4.
It is sufficient to set it to 0 rpm.

It should be noted that if the holding time is less than 20 minutes, there is no effect of making the grain size of green last uniform.However, if the holding time is held for more than 120 minutes, the above effect cannot be expected any longer, so it is necessary to extend the treatment time. The holding time is within the range of 20 to 120 minutes, preferably 30 minutes to 100 minutes. Furthermore, if the pH value and temperature of the mixed aqueous solution are outside the above range, goethite may be generated or the acicularity of the particles may deteriorate, so it is necessary to carry out the process at a relatively low temperature and with a weak acid or a weak alkali within the above range.

In addition, by appropriately setting the P I-I value, temperature, and holding time, it is possible to control the crystal grain size of green last, and therefore, the solution concentration of ferrous chloride, which is the starting material, can be controlled. The average particle size of the lepidocrocite obtained can be controlled by selecting conditions such as the following.

The steps other than the aging step in the present invention are the same as conventional ones, and the conditions are not particularly limited.

However, the theoretical amount of alkali required to convert ferrous chloride to ferrous hydroxide is added separately in the seed reaction step and the growth step, but the amount added in the seed reaction step is determined to prevent the generation of goethite. In order to prevent this and obtain lepidocrocite particles with excellent acicularity, the amount needs to be 0.4 to 0.7 times the above theoretical amount.

(Example) Person 1j1- While stirring a ferrous chloride aqueous solution 25Q having a concentration of 0.97 mol/Q in a reactor maintained in a nitrogen gas atmosphere, the concentration was 0.97 mol/Q.
A 42Ω aqueous solution of 71 mol/12 thorium hydroxide was added, and the pH value was 7.6. The mixture was maintained at a temperature of 13°C for 60 minutes with stirring to ripen.

After this aging, air at 5 atm (gauge pressure) is supplied at 20 Q/m.
A seed reaction was carried out by blowing at a rate of 0.25 in to oxidize. During this time, the liquid temperature was controlled at 13°C.

After confirming the completion of the seed reaction by measuring the PH value (PII
=3.2), stop blowing air, blow nitrogen gas at 1.5 atm (gauge pressure) at a rate of 3 Q/min to create an inert atmosphere inside reactor 1, and raise the temperature to 48°C while stirring. did.

Thereafter, instead of nitrogen gas, air at 5 atm (gauge pressure) was blown at a rate of 3Ω/min, and a sodium hydroxide aqueous solution with a concentration of 1.6 mol/Q was added at a constant rate of 80ε/min to cause a growth reaction. I did it.

This growth reaction ended when the pH value rose to 5.5.

Big Catch Aim 1 While stirring 25Q of ferrous chloride aqueous solution with a concentration of 1.0 mol/Q in a reactor maintained in a nitrogen gas atmosphere,
Add mol/Q ammonia aqueous solution 41Q, pH value 7
．． 5. The mixture was maintained at a temperature of 13° C. for 60 minutes with stirring to ripen. After this aging, air at 5 atmospheres (gauge pressure) is added for 20 minutes.
A seed reaction was performed by blowing at a rate of Q/mib for oxidation. During this time, the liquid temperature was controlled at 13°C.

After confirming the completion of the seed reaction by measuring the PH value (PH=
3.4) Stop blowing air, blow nitrogen gas at 1.5 atm (gauge pressure) at a rate of 3Q7'+in to create an inert atmosphere inside the reactor, and raise the temperature to 45°C while stirring. .

Thereafter, instead of nitrogen gas, air at 5 atm (gauge pressure) was blown at a rate of 312/min, and an aqueous sodium hydroxide solution with a concentration of 1.6 mol/Q was added at a constant rate of 80 g/min to cause a growth reaction. I did it.

This growth reaction was terminated when the pH value rose to 5.5.

An offering mouth.

In Example 1, the mixed aqueous solution of ferrous chloride and sodium hydroxide was immediately subjected to the seed reaction step without being aged, and the same treatment was performed thereafter.

Comparative Example 2 In Example 2, the mixed aqueous solution of ferrous chloride and ammonia was immediately subjected to a seed reaction step without aging,
Thereafter, similar processing was performed.

Regarding each lepidochrosite obtained in the above four cases,
The particle size of the particles was measured using a silver electron microscope to obtain a particle size distribution. The results are shown in Table 1. The particle size distribution was expressed by the standard deviation value of the particle size distribution in the long axis direction of the acicular lepidocrocite particles, and the average particle size was expressed by the average value of the particle size distribution.

As is clear from Table 1, the particle size distribution of the obtained lepidocrocite is much smaller and more uniform in the case of the present invention example which has a ripening process compared to the comparative example. , indicating excellent properties. Also, this
The effect of aging can be expected to be the same regardless of the type of alkali (sodium hydroxide or ammonia), and even if the average particle size is small (Example 1) or large (Example 2), the effect of aging can be expected to be the same regardless of the type of alkali (sodium hydroxide or ammonia). is obtained.

(Effects of the Invention) As described in detail above, according to the present invention, in the synthesis reaction of lepidocrocite, an aging step under specific conditions is performed before the seed reaction, so that the lepidocrocite can have an arbitrary average particle size, and Acicular lepidocrocite with excellent properties and extremely small distribution can be stably produced, and therefore magnetic iron oxide powder with excellent properties can be produced.

Claims (1)

[Claims] After adding an alkaline aqueous solution such as caustic alkali or ammonia to the ferrous chloride aqueous solution, the pH value is 6. ．．
20 to 9.0 under the conditions of 0 to 9.0 and temperature 10 to 50°C
It was held for 120 minutes to ripen, then an oxygen-containing gas was blown in to generate γ-FeOOH seed crystals, and the alkali aqueous solution was added and an oxygen-containing gas was blown in to form γ-FeOOH.
A method for producing lepidocrocite, which comprises completing a FeOOH production reaction.