JPS5848491B2 - Method for producing acicular α-type hemihydrate gypsum - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing acicular α-type hand plaster.

Gypsum has various crystal structures. α-type hemihydrate gypsum is excellent in terms of strength, and acicular α-type hemihydrate gypsum is particularly suitable for use in special applications, such as fillers for synthetic resins and paper strength enhancers. It is known that there are

This acicular α-type gypsum hemihydrate can be produced by heating a slurry of gypsum dihydrate and water under pressure in the presence of a suitable crystallizing agent, or by heating a slurry of sulfite lime and water. A method of carrying out pressure heat treatment in the presence of an appropriate crystallizing agent (by supplying air or oxygen) is known.

However, in the conventionally known method, the reaction ζ takes a long time and the slurry tends to become gel-like during the reaction.
Therefore, in industrial implementation, it has the disadvantage of causing various troubles in stirring, separation operations, etc.

In view of the above circumstances, the inventors of the present invention have conducted various studies on industrially advantageous manufacturing methods for acicular α-type hand wash plaster.
The inventors completed the invention by obtaining the knowledge that sufficiently grown, high-quality acicular α-type gypsum can be obtained in a short period of time without causing the slurry to gel.

That is, the gist of the present invention is to heat-treat an aqueous slurry of gypsum dihydrate under pressure, or to heat-treat an aqueous slurry of sulfite lime under pressure while supplying air or oxygen to form α-type hemihydrate. When manufacturing gypsum, trivalent iron,
A compound selected from inorganic acid salts of aluminum, divalent nickel and manganese is added to gypsum or sulfite lime at a concentration of 0.
A method for producing acicular α-type hemihydrate gypsum, characterized in that it has a weight of 001 to 1.0 and is used alone as a crystal modifier.

The present invention will be explained in detail mainly in the case where trihydrate gypsum is used as a raw material.

Examples of dihydrate gypsum that can be used in the present invention include natural gypsum, phosphoric acid by-product gypsum, flue gas desulfurization gypsum, and the like.

These gypsums are usually pulverized uniformly to about 50 μm to 80% and then mixed with water to form a gypsum slurry.

The slurry concentration at this time is usually 1 to 10% by weight.

The slurry prepared in this way is usually heat-treated under pressure of 1 to 8 kg/iG while stirring using a pressure-resistant container such as an autoclave.

The heat treatment temperature is usually 110-150°C, preferably 120-130°C, and the treatment time is 5-180 minutes.
Preferably, it is about 5 to 120 minutes.

In the present invention, high-quality acicular α-type hemihydrate gypsum is obtained by performing the above-described heat treatment in the presence of a specific amount of a specific compound as a crystal modifier.

The modifier of the present invention is a compound selected from inorganic acid salts of trivalent iron, aluminum, divalent nickel, and manganese, and these are used alone as the modifier.

The amount of crystallizing agent compound used is 0.001 to 1.
It is important to select from the range of 0 weight φ, preferably 0.001 to 0.1 weight. If the amount used is larger than the above range, acicular α-type hemihydrate gypsum cannot be obtained, and on the contrary, it is too small. Gypsum hemihydrate that grows with gypsum does not form α-type.

Specific examples of the crystal modifier compounds include, for example, dichloromethane sulfuric acid
Sulfates such as iron, ferric chloride, aluminum sulfate, nickel sulfate, nickel chloride, nickel nitrate, manganese nitrate,
Hydrochlorides or nitrates, and in particular inorganic acid salts of ferric ions, are preferably used from the viewpoint of reaction rate and workability.

In this case, the usage amount of the inorganic acid salt of ferric ion is set to the above-mentioned preferred usage amount, that is, 0.001 to 0.
．． The effect is even more pronounced when the weight is increased by one weight.

Next, the case where lime sulfite is used as a raw material will be explained.

As the raw material sulfite lime, sulfite lime which is produced as a by-product when sulfur dioxide gas is treated by the wet gypsum lime method is usually used.

The heat treatment under pressure is carried out in exactly the same manner as in the case where dihydrate gypsum is used as the raw material, except that air or oxygen is supplied in order to acidify lime sulfite to trihydrate gypsum.

The acicular α-type hemihydrate gypsum grown from the heat treatment is filtered and washed according to a conventional method.

After washing, it is usually dried at a temperature of 90 to 150° C. for 1 to 3 hours, and, if necessary, subjected to post-treatments such as polishing or firing to convert it into anhydrite.

According to the present invention, by using a specific compound as a crystallizing agent, acicular α-type hemihydrate gypsum can be obtained in a short time and without exhibiting the gelation phenomenon of gypsum slurry. , its industrial value is a dog.

The present invention will be explained in more detail below from Example C.

Example 1 The compounds shown in Table 1 were added as modifiers to a slurry consisting of trihydrate gypsum powder 2 Q'i and water 2259, and the mixture was heated for 500 r.
2. at 120° C. with stirring at 50 O rpm in a nl glass autoclave. 0 kg/dG
The reaction was carried out for 15 minutes under the following conditions.

After the reaction was completed, the mixture was filtered in a heat oven at 97°C and dried with hot air at 95°C for 1 hour.

The crystal structure of the gypsum crystals thus obtained was subjected to differential thermal analysis, and the crystal shape was observed using an optical microscope, and the results shown in Table 1 were obtained.

As is clear from the above table, high-quality acicular α-type hemihydrate gypsum can only be obtained when the crystallizing agent of the present invention is used within the specific amount range specified by the present invention; If it is outside the range defined by the present invention, even if the crystal modifier of the present invention is used, high-quality acicular α-type hemihydrate gypsum cannot be obtained.

In the case of nickel sulfate (NISO4), if the amount used was outside the range of the present invention, the gypsum slurry would gel during the reaction, and the stirring and separation operations could not be performed satisfactorily.

Example 2 A reaction was carried out in the same manner as in Example 1 except that the compounds shown in Table 2 were used as crystal modifiers.

Claims (1)

[Claims] 1. A water slurry of gypsum dihydrate is subjected to pressure treatment and heat treatment, or
Alternatively, α-type hemihydrate gypsum is produced by heating a water slurry of sulfite lime under pressure and supplying air or oxygen.In this case, trivalent iron, aluminum, divalent nickel and manganese are Acicular α characterized in that a compound selected from inorganic acid salts is used alone as a crystal modifier in an amount of 0.001 to 1.0 weight more than gypsum or lime sulfite.
Method for manufacturing type hemihydrate gypsum. 2. The manufacturing method according to claim 1, wherein the crystal modifier compound is an inorganic acid salt of trivalent iron. 3 The amount of crystallizing agent compound used is 0.001 to 0 relative to gypsum.
．． Claim 1 characterized in that the weight is 1 weight φ.
Manufacturing method described in section.