JPS6251899B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing yellow iron oxide (α-FeOOH) used in magnetic materials, pigments, and the like. More specifically, the present invention relates to a method for producing fine needle-like yellow iron oxide, which is suitable as a raw material for producing magnetic materials.

Generally, the particle shape of magnetic iron oxide or magnetic iron powder produced by reducing yellow iron oxide (α-FeOOH) or oxidizing the reduction depends on the yellow iron oxide that is the starting material. Therefore, in order to obtain high-grade magnetic iron oxide or magnetic iron powder, the properties of yellow iron oxide are extremely important.

In recent years, with the development and higher performance of magnetic recording equipment, there has been a demand for higher performance magnetic powder used in magnetic tapes and the like.

Generally, in order to improve the magnetic properties of magnetic powder, it is necessary to make the particles uniform in particle size and in the form of fine needles with a large axial ratio (major axis/width). As mentioned above,
Since the particle shape depends on the yellow iron oxide that is the raw material for its production, there is a demand for yellow iron oxide with uniform particle size and fine needle-like shape.

Conventionally, as a method for producing yellow iron oxide, there is a method of adding an alkali to a ferrous salt solution such as ferrous sulfate to form ferrous hydroxide, which is then oxidized. It is known that the oxidation reaction of ferrous hydroxide is greatly affected by the amount of alkali added, pH, etc., and Fe ₃ O ₄ is likely to be generated when the PH is close to neutral.

For this reason, conventional methods for producing yellow iron oxide are broadly divided into two methods: acidic and strongly alkaline methods.

In other words, in the acidic production method, the reaction is usually carried out while controlling the pH while adding an alkali to the ferrous salt solution, but this reaction is caused by the α-FeOOH produced at the beginning of the reaction or added as a nuclide.
α-FeOOH is grown on top. Therefore, in order to obtain fine needle-like particles, α-FeOOH
It is necessary to appropriately control the growth of the reaction, and the reaction conditions are extremely limited (Japanese Patent Publication No. 48-22915, etc.).

In addition, as one of this acidic production methods, calcium hydroxide or magnesium hydroxide is added to the ferrous salt solution.
A method has been proposed in which 0.5 to 0.9 equivalents of iron are added to carry out the oxidation reaction, but since the above-mentioned alkali is poorly soluble in water, it is difficult to handle it on a large scale. 36635 Publication).

On the other hand, the strong alkaline production method is an excellent method for producing fine acicular yellow iron oxide used as a raw material for magnetic iron oxide, etc., but the amount of alkali required to produce ferrous hydroxide is far greater than the amount of alkali required to produce ferrous hydroxide. It has the disadvantage of requiring a large amount of alkali.
5610, Special Publication No. 13298, etc.). Nowadays, when resource conservation is discouraged and alkalis such as sodium hydroxide and ammonia have become expensive, there is a need for an economical method for producing fine acicular yellow iron oxide that consumes less alkali.

In view of the above-mentioned circumstances, the present inventors have conducted extensive research into a method for producing fine needle-like yellow iron oxide. The present invention was completed after discovering that it is greatly influenced by the ratio and the coexistence ratio of total iron and sulfate radicals (SO ₄ ^2- ).

In other words, when ferrous hydroxide (molar amount) ≦ ferrous sulfate (molar amount), the amount of sulfate radicals present does not have a large effect, but when ferrous hydroxide (molar amount) > ferrous sulfate In the case of (mole amount), the coexistence ratio of total iron and sulfate radicals has a large influence, and this book was based on the knowledge that when they exist in an appropriate ratio, acicular yellow iron oxide with uniform particle size can be obtained. This led to the invention.

The present invention uses ferrous hydroxide and ferrous sulfate in a ratio of 2:1.
Introducing an oxygen-containing gas at a temperature below 60°C into a suspended aqueous solution of ferrous hydroxide containing a molar ratio of ~4:1 and total iron and sulfate radicals in a molar ratio of 3:2 to 5:1. The present invention provides a method for producing yellow iron oxide, which is characterized by:

In the present invention, the coexistence ratio of ferrous hydroxide and ferrous sulfate is extremely important. In other words, if the coexistence ratio exceeds a molar ratio of 4:1, no matter how much the quantitative ratio of sulfate radicals and the reaction rate are adjusted, the contamination of Fe ₃ O ₄ cannot be avoided, resulting in needle-like particles with uniform particle size. Yellow iron oxide cannot be obtained. On the other hand, if the ratio of ferrous hydroxide is small, the productivity of yellow iron oxide will decrease, and the economic efficiency will be lost, which is contrary to the purpose of the present invention.

Therefore, it is necessary to adjust the coexistence ratio (molar ratio) of ferrous hydroxide and ferrous sulfate to 2:1 to 4:1.

When the coexistence ratio of ferrous hydroxide and ferrous sulfate is in the above range, the amount of sulfate radicals present is also important.
A suitable molar ratio of total iron to sulfate is 3:2 to 5:1, preferably 2:1 to 4:1.

If the abundance ratio of sulfate radicals is out of the above range, Fe ₂ O ₄ tends to be mixed in, resulting in needle-like collapse and non-uniform particle size.

In the present invention, the usual method of adding 2/3 to 4/5 equivalents of alkali to a ferrous sulfate solution and then oxidizing the produced ferrous hydroxide cannot be used.
This is because in this case, the coexistence ratio of total iron and sulfate radicals is 1:1, and contamination of Fe ₃ O ₄ is unavoidable.

Therefore, in the present invention, it is necessary to separately prepare ferrous hydroxide and mix it with ferrous sulfate.

In the present invention, an alkali is added to the reaction mother liquor containing ferrous sulfate obtained by separating the yellow iron oxide produced after the completion of the reaction, and the produced ferrous hydroxide is separated and recovered for use in the next reaction. can be suitably applied as a method for preparing ferrous hydroxide.

Next, the reaction temperature is 60℃ or less, preferably 20℃~
It is 50℃. At temperatures above 60°C, Fe ₃ O ₄ is mixed in, making it impossible to obtain fine acicular particles with uniform particle size.

There are no particular restrictions on the alkali used when preparing ferrous hydroxide, but sodium hydroxide or potassium hydroxide is preferred from the viewpoint of ease of handling.

The concentration of the reaction solution is also not particularly limited, but it is preferably 0.2 to 1.0 mol Fe/in view of the viscosity of the solution.

There are no restrictions on the composition of the oxygen-containing gas, and it is economically advantageous to use air.

The yellow iron oxide pigment of the present invention obtained under the above conditions has a fine needle-like particle shape with uniform particle size,
Suitably used as a raw material for magnetic iron oxide or magnetic iron powder.

Further, the yellow iron oxide of the present invention is a clear yellow α-FeOOH with uniform particle size and is very useful as a pigment.

In addition, there is no PH control during reaction or other complicated operations, no excessive alkali is required, and unreacted ferrous sulfate can be recovered and processed in a suitable manner.
This is an extremely economical and advantageous method for producing yellow iron oxide as it can be reused.

Hereinafter, the present invention will be explained using examples.

In Examples and Reference Examples, all parts indicate parts by weight.

Example 1 (a) An aqueous solution in which 278 parts of ferrous sulfate heptahydrate (FeSO ₄ 7H ₂ O) was dissolved in 3000 parts of water, and 80 parts of sodium hydroxide (NaOH) was dissolved in 1000 parts of water. was added with vigorous stirring.

The thus obtained Fe(OH) ₂ suspension was centrifuged in a nitrogen gas atmosphere, and 365 parts of wet
Got the cake.

This wet cake contains 90 parts of Fe(OH) ₂ and
Contains 11.9 parts _{of Na2SO4} .

(b) 83.4 parts of FeSO ₄ 7H ₂ O and Fe(OH) ₂ obtained in section (a)
of wet cake was dispersed in 2000 parts of water.
(This reaction solution is Fe(OH) ₂ /FeSO ₄ = 3.3/1
(molar ratio), and Fe ²⁺ /S ₄ ^2- = 3.4/1 (molar ratio). ) The oxidation reaction was carried out at a temperature of 40°C for 6 hours by blowing air (50/hr) with vigorous stirring. (The reaction slurry has a yellowish color and the pH is 3.2.
It was hot.

A yellow powder was obtained by filtering, washing with water, and drying.

X-ray analysis showed that this powder had a structure of α-FeOOH, and no FeSO ₄ was detected.

Also, when observed with an electron microscope, the length is 0.3 to 0.4
The particles had a needle-like shape with a width of about 0.04 μ and a uniform particle size.

FIG. 1 shows an electron micrograph at a magnification of 20,000 of the yellow iron oxide obtained in this example.

Reference Example 1 361.4 parts of FeSO ₄ .7H ₂ O was dissolved in 1500 parts of water, and an aqueous solution of 80 parts of NaOH dissolved in 500 parts of water was added thereto with vigorous stirring. (This reaction solution is Fe
(OH) ₂ /FeSO ₄ =3.3/1 (molar ratio), Fe ²⁺ /
SO ₄ ^2- = 1/1 (molar ratio). ) The oxidation reaction was carried out at a temperature of 40°C for 6 hours by blowing air (500/hr) with vigorous stirring. (The reaction slurry has a slightly dark yellowish-brown color, and the pH is 3.3.
It was hot. ) After over-washing and drying, a yellow powder was obtained.

From the electron micrograph, this powder has a length of 0.2 to 0.6
They were acicular and columnar particles with irregular μ particle size.

Figure 2 shows an electron micrograph of the yellow iron oxide obtained in this reference example at a magnification of 20,000.

Reference Example 2 440 parts of Fe(OH) ₂ wet cake obtained in the same manner as in Section (a) of Example 1 (108 parts of Fe(OH) ₂ and 14 parts of Na ₂ SO _4
55.6 parts of _FeSO4.7H2O were dispersed in 2000 parts of water. (This reaction solution is Fe(OH) ₂ /FeSO ₄ =
6/1 (molar ratio), and Fe ²⁺ /SO ₄ ^2- = 4.7/1 (molar ratio).

When the oxidation reaction was carried out at 40℃ by blowing air (500/hr) with vigorous stirring, the reaction slurry turned dark black and Fe ₃ O ₄ was produced, and yellow iron oxide (α-FeOOH) could not be obtained. Ta.

Example 2 370 parts of Fe(OH) ₂ wet cake (containing 90 parts of Fe(OH) ₂ ) obtained in the same manner as in Example 1(a) and
Disperse 139 parts of FeSO ₄ 7H ₂ O in 2000 parts of water, and blow air (400/
hr), oxidation reaction was carried out for 5 hours, the reaction slurry was filtered under reduced pressure, and the obtained wet cake of yellow powder was dispersed and washed twice with 1000 parts of water and dried.

This yellow powder was α-FeOOH with a uniform particle size and a needle-like shape with a length of 0.4 to 0.5 μm and a width of about 0.05 μm.

Example 3 _FeSO4 .
An aqueous solution prepared by dissolving 139 parts of 7H ₂ O and 80 parts of NaOH in 500 parts of water was added with vigorous stirring.

The thus obtained Fe(OH) ₂ suspension was centrifuged in a nitrogen gas atmosphere to obtain 380 parts of a wet cake containing about 90 parts of Fe(OH) ₂ .

Using this Fe(OH) ₂ wet cake, an oxidation reaction was carried out under the same conditions as in Example 1(b), and as in Example 1, fine needle-like α-FeOOH with uniform particle size was obtained.
I got it.

[Brief explanation of the drawing]

Figure 1 shows an electron micrograph (magnification: 20,000 times) of the yellow iron oxide obtained in Example 1 of the present invention.
The figure shows an electron micrograph (magnification: 20,000 times) of yellow iron oxide obtained in Reference Example 1.

Claims (1)

[Claims] 1. Ferrous hydroxide and ferrous sulfate in a ratio of 2:1 to 4:1.
Contains a molar ratio of , and total iron and sulfate (SO ₄ ^2- )
Yellow iron oxide (α-
Production method of FeOOH). 2. The method according to claim 1, in which an alkali is added to the reaction mother liquor from which the produced yellow iron oxide is separated, and ferrous sulfate is precipitated as ferrous hydroxide, which is separated and recovered and used for the reaction. . 3. The method according to claim 2, wherein sodium hydroxide or potassium hydroxide is used as the alkali. 4. The method according to any one of claims 1 to 3, wherein the molar ratio of total iron to sulfate is 2:1 to 4:1. 5. The method according to any one of claims 1 to 4, in which air is used as the oxygen-containing gas.