JPS5835936B2 - Method for producing α-type hemihydrate gypsum having needle-like crystals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing α-type hemihydrate gypsum having oblique crystals.

Gypsum has various crystal forms, and it has recently been discovered that α-type handwash gypsum, which has oblique crystals, can be used for special purposes, such as synthetic resin fillers and paper strength enhancers. It is attracting attention.

This α-type handwash gypsum is conventionally produced by heating a slurry of gypsum trihydrate and water under pressure in the presence of a crystallizing agent, or by heating a slurry of sulfite lime and water with air in the presence of a crystallizing agent. Alternatively, it is known to be manufactured by a method of supplying oxygen and heating under pressure.

However, this method requires a long reaction time, and it is difficult to set conditions such as temperature and pressure and to select a crystal modifier for industrial implementation.

In particular, those having needle-shaped crystals have the disadvantage that the slurry of water and gypsum becomes gel-like during the reaction, making industrial operations such as stirring and separation operations impossible as a practical matter.

The present invention Nagisa et al. investigated various methods for producing α-type hemihydrate gypsum having oblique crystals in a short time and industrially advantageously, and found that a specific metal ion was present in a specific ratio in the reaction slurry. The present invention was completed based on the knowledge that the reaction proceeded extremely well and α-type hemihydrate gypsum having excellent needle-like crystals could be obtained by this method.

That is, the gist of the present invention is to heat-treat a water slurry of trihydrate gypsum under pressure, or to heat-treat a water slurry of sulfite lime under pressure and supplying air or oxygen to produce α-type handwash gypsum. When manufacturing, at least one salt selected from inorganic acid salts of chromium, cerium, titanium, zinc, rhodium, potassium, palladium, and niobium is added in an amount of 0.001 to 1.0% by weight based on gypsum or sulfite lime.
The present invention relates to a method for producing α-type hemihydrate gypsum having needle-like crystals.

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

Examples of the trihydrate applied in the present invention include:
Examples include natural gypsum, acid/acid by-product gypsum, and by-product gypsum from the flue gas desulfurization process.

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

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

The slurry prepared in this way usually has a size of 1 to 8!
Heat treatment is performed under pressure of AG, and the heating temperature is, for example, 1
10 to 150°C, preferably 120 to 130°C,
Processing time is usually 5 to 180 minutes, preferably 5 to 120 minutes.
It takes about a minute.

This heat treatment is usually carried out under stirring in a pressure-resistant container such as an autoclave.

In the present invention, the presence of specific metal ions in the slurry is an essential condition during the above-mentioned heat treatment.

That is, at least one selected from inorganic acid salts of chromium, cerium, titanium, zinc, rhodium, potassium, palladium, and niobium is present as a crystal modifier.

It is important that the amount of metal ions present in this case is in the range of 0.001 to 1.0% by weight, preferably in the range of o, ooi to 0.1% by weight.

If the amount added is outside the above range, the crystal growth rate will be slow and the needle-like crystals will be short, making it impossible to obtain high-quality needle-like crystals.

In the present invention, specific examples of the inorganic acid salt include sulfates such as chromium sulfate, chromium chloride, cerium sulfate, titanium sulfate, titanium chloride, zinc sulfate, rhodium chloride, potassium sulfate, palladium nitrate, and niobium nitrate; Examples include inorganic acid salts such as hydrochloride or nitrate.

Further, in the present invention, it is preferable to use these inorganic acid salts without using them together with known crystallizing modifiers such as organic acid salts.

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 pressurizer heat treatment is carried out in exactly the same manner as described above when using trihydrate gypsum as the raw material, except that air or oxygen is supplied to oxidize the sulfite lime to trihydrate gypsum.

α-type hemihydrate gypsum with needle-like crystals generated by heat treatment is filtered and washed according to conventional methods.
Drying is carried out at a temperature of 150° C. for 1 to 3 hours.

In addition, if necessary, the product can be made into a product by performing post-processing such as calcination treatment to convert it into anhydrite. By including it in the lime slurry, α-type hemihydrate gypsum having needle-like crystals can be produced industrially and advantageously in a short time.

Next, the present invention will be explained in detail using examples.

Example A slurry was prepared from 2511 gypsum trihydrate powder and 225 g of water, the compounds shown in Table 1 were added thereto, and the mixture was heated at 120'C in a 500 yd glass autoclave with stirring at 50 Or, p, m rotation. The reaction was carried out at −2.0% G for 15 minutes.

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

The gypsum crystals thus obtained were subjected to differential thermal analysis and observed using an optical microscope.

The results were as shown in Table 1.

Claims (1)

[Claims] 1 Heat-treat the water slurry of gypsum trihydrate under pressure, or
Alternatively, when producing α-type hemihydrate gypsum by heating a water slurry of sulfite lime under pressure and supplying air or oxygen, chromium, cerium, titanium, zinc,
α-type semi-silicon having acicular crystals characterized by the presence of at least one salt selected from inorganic acid salts of rhodium, potassium, palladium and niobium in an amount of 0.001 to 1.0% by weight based on gypsum or sulfite lime. Method of manufacturing hydrogypsum.