JPS5834410B2 - Shinjiyou Alpha Agata Hansu Isetsu Kono Seizouhou - Google Patents

Description

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

Gypsum has various crystal structures, but α-type hemihydrate gypsum is superior in terms of strength. In particular, acicular α-type hemihydrate gypsum is used for special purposes, such as paper strength in filling parts for synthetic resins. It is known that it is suitable for use in fields such as enhancers.

As a method for producing this acicular α-type hemihydrate gypsum, a method is known in which a slurry of trihydrate gypsum and water is heat-treated under pressure in the presence of a suitable crystallizing agent.

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

In view of the above circumstances, the present inventors have conducted various studies on industrially advantageous production methods for acicular α-type hemihydrate gypsum, and have found that when using a combination of specific crystal modifiers, Furthermore, the present invention was completed based on the knowledge that acicular α-type hemihydrate gypsum can be obtained without the slurry exhibiting gelation.

That is, the gist of the present invention is that when producing α-type hemihydrate by heat-treating a slurry consisting of gypsum trihydrate and water under pressure, (1) a sodium salt of citric acid, tartaric acid, or fumaric acid is and (2) at least one compound selected from sulfates of aluminum, iron, or nickel (excluding the combination of sodium citrate and nickel sulfate) as a modifier. The invention relates to a method for producing acicular α-type hemihydrate gypsum.

To explain the present invention in detail, examples of the trihydrate gypsum applied in the present invention include natural gypsum, flue gas desulfurization gypsum, and the like.

These gypsums are usually ground to a uniform size of about 50 to 80 microns, and then mixed with water to form a gypsum slurry.

The amount of water at this time is usually selected from a range of 2 to 100 times the weight of gypsum, preferably 3 to 100 times the weight of gypsum.

The slurry prepared in this way is usually stirred in a pressure-resistant container such as an autoclave at a rate of 1 to 8 Kf/crt.
Heat treated under pressure of 1 G.

The heat treatment temperature is usually 110 to 150°C, preferably 120 to 130°C, and the treatment time is about 1 to 3 hours, preferably about 1 to 2 hours.

In the present invention, acicular α-type hemihydrate gypsum is obtained by performing the above-mentioned heat treatment in the presence of a specific combination of crystal modifiers.

The present invention uses a sodium salt of citric acid, tartaric acid, or fumaric acid together with a sulfate of aluminum, iron, or nickel (excluding the combination of sodium citrate and nickel sulfate) as a crystallizing agent. be.

Preferred combinations of these modifiers include sodium citrate and aluminum sulfate, sodium citrate and iron sulfate (particularly ferrous sulfate), and sodium tartrate and nickel sulfate.

In the case of a combination of sodium citrate and nickel sulfate, the crystals become columnar, and the desired acicular α-type hemihydrate gypsum cannot be obtained.

The amount of each of these crystal modifiers added to the gypsum was 0.
It is 1 to 5.0 weight thick, preferably 0.5 to 2.0 weight thick, and it is preferable that the combined proportions are approximately the same.

These modifiers may be added to the gypsum trihydrate in advance, or may be added after the slurry is prepared.

The acicular α-type hemihydrate gypsum produced by the heat treatment is filtered and washed in a conventional manner.

After washing, it is usually dried at a temperature of 90 to 150° C. for 1 to 3 hours, and if necessary, subjected to polishing treatment or the like to be manufactured into a product.

According to the present invention, by using a specific crystal modifier in combination, it is possible to obtain acicular α-type hemihydrate gypsum in a short time and without exhibiting the gelation phenomenon of gypsum slurry. So its industrial value is a dog.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example The modifier shown in Table 1 was added to a slurry consisting of 25S' of trihydrate gypsum powder and 225TJI of water, and the mixture was stirred at 500 rpm in a 500-glass autoclave.
The reaction was carried out for 2 hours at 130° C. and 2.6 Kg/crAG.

After the reaction was completed, the mixture was heated at 97'C and dried with hot air at 95C for 1 hour.

The crystal structure of the gypsum crystal 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.

Further, during production, the gypsum slurry did not gel, stirring was performed well throughout, and the subsequent f-filtering operation was carried out smoothly.

Comparative Example In the example, the same procedure as in the example was carried out except that sodium citrate or nickel sulfate was used alone as a modifier. Gypsum hemihydrate is plate-shaped, and
When nickel sulfate was used alone, the α-type hemihydrate gypsum obtained was acicular, but the gypsum slurry gelled during the reaction, making stirring and separation operations difficult.

Claims (1)

[Claims] 1. A slurry made of gypsum trihydrate and water is heated under pressure at 110~
When producing α-type hemihydrate gypsum by heat treatment at 150°C, (1) at least one compound selected from sodium salts of citric acid, tartaric acid, or fumaric acid and (2) sulfate of aluminum, iron, or nickel. The acicular α-type semi-semi-acid material is characterized in that at least one compound selected from the following is present in the slurry as a crystal modifier (excluding the combination of citric acid and nickel sulfate). Method of manufacturing hydrogypsum.