JPS6364923A - Production of goethite - Google Patents

Abstract

PURPOSE:To produce dense goethite having particulate shape of strip, uniform axial ratio, narrow particle size distribution and improved dispersibility, oxidizing ferrous carbonate formed from an aqueous solution of ferrous salt to give goethite and heat-treating the goethite in an aqueous solution. CONSTITUTION:An aqueous solution of ferrous salt (e.g. aqueous solution of ferrous chloride, etc.) is treated with a carbonate (e.g. sodium carbonate, etc.) at <=70 deg.C (preferably 30-60 deg.C) to form ferrous carbonate and an oxygen- containing gas is introduced to the reaction mixture to form goethite. Then the goethite suspension in a slurry state is heat-treated at 70-250 deg.C (preferably 100-180 deg.C) to give dense goethite having improved particulate shape, dispersibility, etc., and strip shape.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an improvement in a method for producing goethite particles, and more specifically, to improving a method for producing goethite particles. It relates to a manufacturing method.

(Prior Art) Goethite (α-iron peroxyhydroxide) is widely used as a raw material for yellow pigments and red pigments, and as a raw material for magnetic materials such as magnetite, γ-iron oxide, and metallic iron.

In the case of pigments, magnetic materials, etc., it is very important that they have high dispersibility, including their particle shape, when turning them into paints.

The quality of dispersibility in making paint is influenced by the particle shape, particle size distribution, dispersibility, etc. of the goethite that is the raw material. When pigments, magnetic materials, etc. are manufactured by using these materials, the dispersibility becomes poor when they are made into paints.

Therefore, as goethite used as a raw material for pigments, magnetic materials, etc., it is desirable to have good dispersibility, well-uniformed particle size, and a narrow particle size distribution.

Furthermore, in applications of magnetic materials, it is desirable to use materials that do not cause agglomeration, sintering, etc. during heat treatments such as reduction and oxidation of goethite.

In addition, magnetic materials, especially magnetic materials for magnetic recording media such as magnetic tapes and floppy disks, include acicular γ-iron oxide,
Metallic iron is often used, but with the demand for higher density recording, perpendicular magnetic recording has been developed in place of the conventional in-plane magnetic recording, and the particle shape of the magnetic material has also changed to perpendicular magnetic. There is also a need to develop a recording method suitable for the recording method.

Many methods have already been proposed for the production of goethite, but most of them are aimed at producing acicular goethite, and the goethite obtained by these methods has pigments, magnetic properties, etc. Although it is often used as a raw material for materials such as wood, it is generally needle-shaped with an axial ratio of 10 or more, the particle size is irregular, and its dispersibility is not very good.

The synthesis methods of goethite known so far are summarized as follows.

1 Add a large amount of alkali hydroxide to the ferrous salt aqueous solution to adjust the pH.
11 or more and oxidizing the produced ferrous hydroxide to obtain goethite (for example, JP-A-56-155509, JP-A-56-169132 @).

2 A method of obtaining goethite by neutralizing Fe ions in an aqueous solution of ferrous salt with an alkali of equal or less concentration and oxidizing ferrous hydroxide at a pH of 8.5 or less (for example, JP-A-53
-73497).

3 Add excess carbonate to the ferrous salt aqueous solution and adjust the pH to 9 to 1.
A method for obtaining spindle-shaped goethite by oxidizing iron carbonate at
No. 307, Japanese Unexamined Patent Publication No. 60-138002).

4 Add a caustic alkaline solution such as caustic soda to the ferrous salt aqueous solution to generate ferrous hydroxide at a temperature of 50°C or less,
A method of converting ferrous carbonate into ferrous carbonate by adding acidic carbonate such as ammonium bicarbonate at a temperature of 45 to 70°C, and then converting ferrous carbonate into goethite by aerating oxygen-containing gas
65499, and JP-A-49-42597, JP-A-49-42598, and JP-A-49-42599).

Ferric hydroxide is prepared by adding a ferric salt solution to an alkaline aqueous solution at a temperature of 530°C or less, and after aging, 120-2
Method for obtaining rice-grain-like goethite by hydrothermal treatment at a temperature of 50°C (JP-A-58-49693, JP-A-58-496)
No. 94, Japanese Patent Publication No. 53-28158, etc.).

In method 1.2 above, twins may be mixed into goethite,
Dispersibility may be low due to crystals sticking together.

In particular, in method 1, improvement in particle size distribution is desired. 3
Although the particle size distribution and dispersibility were good in the method, the particles were spindle-shaped and, according to observation using an electron microscope (TEM), were slightly lacking in density.

The goethite obtained by methods 4 and 5 does not have sufficiently good dispersibility and there is room for improvement.

Furthermore, method 4 requires a ferric salt, which is more expensive than a ferrous salt, and has the problem that the particle size distribution of goethite is wide. In addition, the method No. 5 has problems such as a large axial ratio (nearly a fine needle-like shape) and a wide particle size distribution even at °C.

With these methods, it is difficult to obtain goethite that satisfies the particle shape, particle size distribution, and dispersibility.

(Problems to be Solved by the Invention) The purpose of the present invention is to produce particles with a rectangular shape, uniform axial ratio (ratio of major axis to minor axis), narrow particle size distribution width, and dense particles with good dispersibility. The purpose of the present invention is to provide a method for producing goethite.

(Means for Solving the Problems) The object of the present invention can be achieved by generating iron carbonate from an aqueous ferrous salt solution and heat-treating goethite obtained by oxidizing the iron carbonate in the aqueous solution. It was discovered and completed.

That is, the present invention produces goethite by adding carbonate to a ferrous salt aqueous solution at a temperature of 70° C. or lower to generate ferrous carbonate, and then supplying oxygen or an oxygen-containing gas to carry out an oxidation reaction. Then, the slurry-like goethite suspension was
This is a method for producing goethite characterized by performing heat treatment at a temperature within the range of 0 to 250°C. In particular, this is a method of adjusting the shape of goethite (hereinafter referred to as shaping treatment) by heating the slurry-like goethite suspension in the latter stage.

In the present invention, ferrous sulfate, ferrous nitrate, ferrous chloride, etc. are used as the ferrous salt, and the ferrous salt is generally used as an aqueous solution by dissolving it in water. The appropriate concentration of the ferrous salt is 0.03 to 1 mot/.

Furthermore, as is known so far, an aqueous solution of ferrous salt contains Cr, Ni, Co, Cu, Mg,
It is also possible to add a small amount of water-soluble salts such as Ca, such as nitrates and sulfates, and the amount added is Me/Fe (atomic ratio: Me is Cr, Ni, Co, Cu, Mg).
%Ca etc.) is suitably 0.001 to 0.1.

The carbonate is not particularly limited as long as it produces ferric carbonate, but sodium or ammonia carbonates and carbonates such as carbonate, sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate are preferred. used.

The appropriate amount of carbonate to be used is 1 to 5 equivalents, preferably 1.5 to 3.5 equivalents, relative to ferrous ion.

The temperature when adding the carbonate is 70°C or less, preferably 1
A temperature of 0 to 70°C is appropriate; as the temperature increases, the axial ratio increases, which tends to adversely affect the particle size distribution ~ 10 Supply of oxygen or oxygen-containing gas is generally performed by adding carbonate to produce ferrous carbonate. This is done by blowing directly into the slurry. Air is conveniently used as oxygen-containing gas.

Oxygen-containing gas affects the size of the particles produced in relation to the oxidation rate of Fe+2; if the oxidation rate of Fe+2 is too fast, the particles tend to become minute, and if the oxidation rate is too slow, the particles tend to become long and large. It is desirable to appropriately control the particle size to a desired size by adjusting the amount.

The temperature when converting ferrous carbonate to goethite by supplying an oxygen-containing gas is preferably 20 to 70°C, preferably 30 to 60°C, in order to produce particles with a well-balanced shape. . If the temperature is too high or too low, dispersibility will be poor and the particle size distribution will tend to be wide. Furthermore, the magnetic properties tend to deteriorate.

In the present invention, after supplying an oxygen-containing gas to produce goethite, the slurry-like goethite suspension is heat-treated to improve the particle shape of the goethite, resulting in dense strip-like goethite.

Heat treatment of goethite suspension takes a long time if the temperature is low, and α-Fezes may be generated if the temperature is too high, so the temperature is 70 to 250 °C, preferably 100 to 18 °C.
It is preferable to carry out the heating in the range of 0°C. The heating time can range from 1 hour to 24 hours to achieve the objective.

The pH of the slurry suspension during the heat treatment can be 7.5 or higher. However, in the range of pH 7.5 to pH 11, it is better to maintain the temperature at 110° C. or higher, so the use of an autoclave is recommended. In this case, the goethite slurry may be in a state containing carbonate as it is in the reaction solution, or
There is no problem with slurry made by washing the goethite with phlegm and then adding the green onion to the water again.

On the other hand, increase the pH by adding alkali hydroxide, etc.
If the temperature is 12 or higher, use an autoclave at 150°C.
In the above case, even if heat treatment is performed at a temperature of about 110° C. or 80° C. without using an autoclave, by utilizing the boiling point increase at normal pressure, a sufficient effect can be obtained.

The goethite obtained by the method of the present invention has a narrow particle size distribution because of its well-aligned axial ratio, has good dispersibility, and is strip-shaped and dense, so it can be used as a raw material for magnetic materials, etc. In this case, you can expect improved characteristics.

(Example) Example 1 Put 25 tons of water into a reaction tank with an internal volume of 30 tons, dissolve sodium carbonate (Nat COs ) 2 K9, and add nitrogen (N
t) The solution was deoxidized by gas.

After that, ferrous chloride (FeCl2・n H2
5 tons of an aqueous solution in which 1.5 kg of O) was dissolved was gradually added to the reaction tank at 50° C. and aged until it became a uniform slurry.

Thereafter, air was blown into the reaction tank at 50° C. to perform air oxidation to synthesize spindle-shaped goethite.

Next, this goethite is thoroughly washed with water, the slurry concentration is 1 to 4%, and sodium hydroxide (Na
OH) aqueous solution was added to bring the whole to a 6N-NaOH concentration, transferred to an autoclave, and heat-treated at 150 to 160°C for 2 hours.

Figure 2 shows an electron micrograph of goethite before heat treatment.
The product after heat treatment is shown in FIG. Both photos were taken under the same conditions, and the magnification of the photos is 60,000x.

It can be seen that the shape of the goethite has been changed from a spindle shape to a strip shape, and the black color of the goethite after heating has become stronger, indicating that it has become denser.

Example 2 The raw material goethite of Example 1 was not treated with NaOH (, 3M
-Nai COs concentration and autoclave Example 1
The same heat treatment was performed.

As in the case of fruit flow side 1, the goethite had been shaped and had become strip-shaped and dense.

Example 3 After washing the raw goethite of Example 1 with water, it was transferred in a slurry form to an autoclave without adding any additives, and heat-treated under the same conditions as in Example 1.

The obtained goethite had a rectangular shape and was well shaped.

Example 4 The same raw material goethite as in Example 1 was separated, the alkali concentration of the suspension was adjusted to 6 N NaOH, and then heated at 110°C under normal pressure.
Heat treatment was performed for 20 hours.

An electron micrograph (60,000x magnification) of the obtained goethite is shown in FIG. In this case as well, it can be seen that the game site has a neat rectangular shape and is detailed.

Example 5 Water was added to the reaction species, and sodium carbonate (Naz
CO3) 19.9 Ky was dissolved and deoxidized with N2 gas. Then ferrous chloride (FeC4・n Hz
O) Dissolve 9 in 24.9 and add Fe to Fe using Fe powder.
was added at 50° C., and the slurry was aged until the ferrous carbonate slurry became sufficiently uniform.

Thereafter, air was blown into the slurry at 40° C. to oxidize it to obtain spindle-shaped goethite.

Example 1 and colleagues then added sodium hydroxide (NaOH
) An aqueous solution was added to prepare a slurry made into 6N-NaOH, and heat treatment was performed at 80° C. for 20 hours in a stainless steel container under normal pressure.

The goethite had been sufficiently shaped into a rectangular shape.

Table 1 shows the results of measuring the average particle diameter, axial ratio, coefficient of variation, and particle size distribution range of goethite before and after heat treatment in Examples 1 to 5.

Table 1 From this table, it can be seen that the particle size distribution of the raw goethite (before treatment) is about the same as that of the goethite after shaping, and is in a very good condition.

Furthermore, when comparing Figure 2 with Figures 1 and 3, it can be seen that in the electron micrographs taken under the same conditions, the color of the particles after shaping has become darker, indicating that the density of goethite has improved due to heat treatment. I know what you're doing.

(Effects of the Invention) According to the present invention, the narrow particle size distribution width and good dispersibility, which are the characteristics of goethite made from iron carbonate, and the characteristics of goethite, which is produced under highly alkaline conditions, are crystallized. It is possible to produce goethite that has two properties: good density.

Furthermore, the alkali hydroxide used in a highly alkaline environment can be used repeatedly after passing through the goethite, and is a highly economical method from the viewpoint of raw materials.

The goethite obtained by the present invention is rectangular and has a uniform particle shape, so it can be used for various purposes.In particular, as a magnetic material, it has good density, so it can be used only in conventional in-plane magnetic recording methods. First, it is applicable to perpendicular magnetic recording systems.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph (60,000 times magnification) illustrating the particle structure of goethite that was subjected to the shaping treatment in the autoclave shown in Example 1. Figure 2 shows Examples 1 to 4.
This is an electron micrograph (60,000x magnification) illustrating the particle structure of the raw material goethite used in the process. FIG. 3 is an electron micrograph (60,000x magnification) illustrating the grain structure of goethite in Example 4, which was heat-treated under normal pressure. Agent Patent Attorney Tatsuo Chanoki’] 1st %@*, II

Claims (1)

[Claims] After adding carbonate to a ferrous salt aqueous solution at a temperature of 70°C or less to generate ferrous carbonate, an oxidation reaction is performed to generate spindle-shaped goethite and a slurry-like goethite suspension. A method for producing goethite, characterized by carrying out heat treatment at a temperature within the range of 70 to 250°C.