JPS61106420A - Preparation of acicular goethite - Google Patents

Abstract

PURPOSE:To obtain superior acicular goethite having a sharp distribution of crystal particle size contg. no branched crystal by adding a water-soluble Zn compd. to a ferric salt and alkali hydroxide in the presence of water to obtain slurry of ferric hydroxide by the reaction between the above described reactants, and again the obtd. slurry. CONSTITUTION:A ferric salt such as ferric chloride, etc. is dissolved in pure water together with a water-soluble Zn compd. (e.g. ZnSO4) in an amt. of 2-10atom% Zn per one Fe atom. Obtd. aq. soln. is added to aq. alkali (e.g. NaOH) to cause reaction at <=50 deg.C to obtain a slurry contg. colloidal ferric hydroxide, which is aged at 20-90 deg.C for 2-3hr, then washed with water, filtered, and dried. By this method, acicular goethite contg. no conglomerated particles, consisting of fine crystals being suitable as a raw material for prepd. a magnetic recording medium is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing acicular goethite, which is suitable as a raw material for producing magnetic powder.

[Conventional technology]

Conventionally, goethite has been produced by (1) adding an equivalent amount or more of an alkaline solution to a ferrous salt solution to obtain a slurry of ferrous hydroxide, and adding oxygen to the slurry of ferrous hydroxide, with or without adding an alkali carbonate; How to blow gas.

(2) A so-called hydrothermal synthesis method in which ferric hydroxide colloid produced from a ferric salt solution is hydrothermally treated; (3) ferric hydroxide is produced from a ferric salt and this liquid is aged; There are known methods for synthesizing gamesite.

[Problem that the invention seeks to solve]

However, in method 1) of blowing oxygen-containing gas.

Branched crystals of goethite often occur, and the grain size distribution is wide. In the hydrothermal synthesis method (2), since the synthesis is carried out at a high temperature of 100°C or higher, α-Fe203 crystals are often generated, and there are many goethite aggregates.
It is also complicated to operate.

In addition, the method (3) of aging a liquid (slurry) containing colloid of ferric hydroxide requires a long period of aging,
Also, the shape of the game site is unstable and not solid.

The present invention provides a method for producing acicular goethite that can improve the drawbacks of the prior art. The purpose of the present invention is to
In particular, there are no dendritic branched crystals.

The present invention provides acicular goethite with excellent acicularity, sharp particle size distribution, no agglomeration of individual particles, and fine crystal grains suitable as a raw material for manufacturing magnetic recording media.

[Means for solving problems]

The present invention claims that the above object can be achieved by improving the method for producing goethite from a slurry of ferric hydroxide produced by reacting a ferric salt and an alkali hydroxide in the presence of water. Based on discovery.

The present invention provides a method for producing goethite from a slurry of ferric hydroxide produced by reacting a ferric salt and an alkali hydroxide in the presence of water. The present invention relates to a method for producing acicular goethite, which is characterized by adding a small amount of a water-soluble zinc compound and reacting at a temperature of 50° C. or lower when reacting in the presence of water.

According to the present invention, it is possible to obtain the desired goethite without performing hydrothermal synthesis or adding an alkali carbonate, and the drawbacks of the method (3) can be improved. .

In the present invention, the ferric salt is ferric chloride.

Examples include ferric nitrate and ferric sulfate.

Ferric salts are generally used as aqueous solutions. In addition, alkali hydroxides include sodium hydroxide, potassium hydroxide,
Lithium hydroxide, cesium hydroxide, etc. are used, and alkali hydroxide is also preferably used in the form of an aqueous solution. The temperature at which the ferric salt aqueous solution and the alkali hydroxide aqueous solution are reacted to produce ferric hydroxide is higher than 50°C.

Since the particles become longer than 0.5 μm, it is necessary to keep the temperature at 50° C. or lower. The lower the temperature when generating ferric hydroxide, the smaller the goethite particles tend to be, but it is not economical to lower the temperature to an extremely low temperature, so it is usually below 50°C, especially between 0 and 40°C. Temperature is preferably employed.

The water-soluble zinc compound added when producing ferric hydroxide is not particularly limited as long as it is water-soluble, but zinc sulfate, zinc chloride, zinc nitrate, etc. are generally preferably used.

The amount of water-soluble zinc compound added is preferably such that the number of zinc atoms is 2 to 10 atoms, preferably 4 to 8 atoms, relative to iron atoms. If the amount of water-soluble zinc compound added is extremely small, the acicularity of goethite will be poor, the acicular ratio (axial ratio) will be small, and the shape will be unstable, resulting in aging of the slurry of ferric hydroxide. It takes a long time to create a game site. Further, as the amount of the water-soluble zinc compound added increases, the acicular ratio improves, but if the amount is too large, agglomeration of particles may occur. The water-soluble zinc compound may be added after being dissolved in water, or may be added without being dissolved, or may be used after being dissolved together with a ferric salt.

When the slurry of ferric hydroxide produced by adding a water-soluble zinc compound is aged, the desired acicular goethite is produced. The aging temperature is 20 to 90°C, preferably 30 to 70°C, but it is preferably slightly higher than the temperature at which ferric hydroxide is produced, generally about 20°C or more higher. The aging time may be about 2 to 6 hours, but generally about 4 to 6 hours is sufficient. Aging may be carried out under stirring or simply by standing still. If the ripening temperature is too low or too high.

Furthermore, if the aging time is too short, goethite with poor needle-like properties is likely to be produced or reproducibility may be poor.

Acicular goethite produced by ripening can be recovered by conventionally known normal operations such as washing with water and filtration.

This can be done by operations such as drying.

Example 1 Ferric chloride [FeCA3.6H20) 3000 S'
and zinc sulfate (ZnSO4-7H20) 96f were dissolved in pure water to make 60t, and the solution was cooled to 8°C. This solution was added to 120 tons of pure water with sodium hydroxide (NaOH:
Sodium hydroxide in which 145005' was dissolved and cooled to 8℃
Ferric hydroxide containing zinc hydroxide was gradually added to the dillium aqueous solution at 10°C, and the slurry temperature was raised to 50°C.
℃ and left for 5 hours to ripen and generate goethite.

Next, remove the supernatant, wash the precipitate with water, and filter.

After drying, acicular goethite particles were obtained.

The obtained particles were observed using a transmission electron microscope ('rKM). The average long axis of 30 particles in a TEM photograph is 0.25μ
m, the short axis was 0.036 μm, the axial ratio was 7, and the shape of each particle was a well-aligned needle crystal, with no aggregation of each particle observed. Also, the specific surface area is 507? ? ”/1.

Examples 2 to 4 Acicular goethite particles were obtained in the same manner as in Example 1, except that the amount of zinc sulfate added was changed to the amount listed in Table 1.

Example 5 Acicular goethite particles were obtained in the same manner as in Example 1, except that zinc sulfate in Example 1 was replaced with zinc chloride.

Examples 6-7 Example 1 except that zinc sulfate in Example 1 was replaced with zinc chloride, and ferric chloride was replaced with ferric sulfate (Example 6) and ferric nitrate (Example 7). Acicular goethite particles were obtained in the same manner as above.

Example 8 Example 1 except that the temperature when producing ferric hydroxide containing zinc hydroxide in Example 1 was changed from 10°C to 50°C.
Acicular goethite particles were obtained in the same manner as above.

The particles obtained in Examples 2 to 8 were measured in the same manner as in Example 1, and the results are shown in Table 1. Further, the goethite particles obtained in each Example including Example 1 had a narrow particle size distribution width and were sharp, well-aligned acicular crystals, and no aggregation of one particle was observed.

Comparative example 1 Example 1 except that zinc sulfate was not added.

Goethite particles were obtained in the same manner as in Example 1.

The obtained goethite particles had a small particle size and a small axial ratio, and crystallization was not promoted. The results of measuring the particles in the same manner as in Example 1 are shown in Table 1. Comparative Example 2 The zinc sulfate in Example 1 was replaced with zinc chloride, and the temperature at which ferric hydroxide containing zinc hydroxide was generated was changed. 10℃ to 30℃
An attempt was made to obtain goethite particles in the same manner as in Example 1 except that the temperature was changed to 0.degree. C., but acicular goethite particles were not obtained.

〔Effect of the invention〕

According to the present invention, there is no need for hydrothermal treatment or addition of alkali carbonate, and the fine goethite particles have no dendritic branched crystals, have a sharp particle size distribution, and have excellent acicular properties without agglomeration. particles are obtained.

Claims (3)

[Claims] (1) In a method for producing goethite from a slurry of ferric hydroxide produced by reacting a ferric salt and an alkali hydroxide in the presence of water, the ferric salt and the alkali hydroxide are A method for producing acicular goethite, which comprises adding a small amount of a water-soluble zinc compound and reacting at a temperature of 50° C. or lower when reacting in the presence of water. (2) Claim 1 in which the amount of water-soluble zinc compound added is 2 to 10 atomic % based on iron atoms in terms of zinc atoms.
The method for producing acicular goethite described in Section 1. (3) A method for producing acicular goethite according to claim 1, wherein a slurry of ferric hydroxide is aged to produce goethite.