JPH0692631A - Production of hemihydrate gypsum - Google Patents

Abstract

PURPOSE:To provide a method for producing alpha type hemihydrate gypsum, continuous fibrous alpha type hemihydrate gypsum and beta type hemihydrate gypsum in which various uses with low energy consumption have been proposed. CONSTITUTION:This method for producing hemihydrate gypsum is composed of a step for heating sulfuric acid and a calcium compound. Continuous fibrous alphatype hemihydrate gypsum, a type hemihydrate gypsum or beta type hemihydrate gypsum is selectively obtained by regulating the amount of the calcium compound or further, as necessary, the amount of the acid so as to provide the molar ratio of (the theoretical amount of the produced hemihydrate gypsum)/(the amount of gypsum soluble in the reactional solution) within a prescribed range.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing hemihydrate gypsum, and more specifically, when a calcium compound and sulfuric acid are reacted under predetermined conditions, (theoretical amount of hemihydrate gypsum) / ( By adjusting the amount of calcium compound used so that the molar ratio of the amount of gypsum that can be dissolved in the reaction solution) falls within a predetermined range, and further by adjusting the amount of acid used as necessary, various usage methods are possible. The present invention relates to a method for selectively obtaining long-fiber α-type hemihydrate gypsum, α-type hemihydrate gypsum or β-type hemihydrate gypsum with low energy consumption.

[0002]

2. Description of the Related Art Recently, sulfuric acid has been used in large quantities for the purpose of imparting various properties to industrial products.
A large amount of waste sulfuric acid is by-produced and processed. Further, a flue gas desulfurization device in a thermal power plant or the like has a built-in oxidation process of sulfurous acid gas, from which sulfuric acid can be obtained. Therefore,
It can be said that the effective utilization technology of sulfuric acid produced as a by-product from various industries is a useful technology from the viewpoint of effective utilization of resources and environmental conservation (for example, Japanese Patent Laid-Open No. 52-71397 and Japanese Patent Publication No. 56-
41316).

[0003] Hemihydrate gypsum is known to have α-type and β-type forms. α-type hemihydrate gypsum can be made into long fibers, columnar shapes and agglomerates depending on hydrothermal conditions and additives, and by utilizing their respective shape characteristics, reinforcing fibers for molded organic polymers such as plastics. A wide range of applications have been proposed as hydration curable materials used for the production of light-weight gypsum hardened products and high-strength gypsum hardened products. However, producing hemihydrate gypsum from dihydrate gypsum means treating dihydrate gypsum hydrated and stabilized at a low temperature again under high temperature and high pressure conditions. Compared to the method of producing gypsum, the loss of production energy is inevitably high. Also,
Although several methods for producing α-type hemihydrate gypsum under normal pressure have been proposed, most of them obtain α-type hemihydrate gypsum by dissolving dihydrate gypsum in acid and controlling the production conditions. However, these are also disadvantageous in terms of total energy consumption compared to the method of directly obtaining hemihydrate gypsum by the reaction of sulfuric acid and calcium compound from the above-mentioned point. On the other hand, β-type hemihydrate gypsum is consumed in large quantities as a raw material for gypsum boards, etc., but part of it is a fired product of gypsum dihydrate obtained by flue gas desulfurization and waste sulfuric acid neutralization. Has been done. Therefore, in the production of β-type hemihydrate gypsum by the conventional method, energy consumption associated with the firing of dihydrate gypsum is unavoidable.

[0004]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a method for producing α-type hemihydrate gypsum and long-fiber α-type hemihydrate gypsum, which have been proposed for various uses, with a low energy consumption, and a conventional method of once dihydrate. A method of directly producing β-type hemihydrate gypsum, which was obtained by synthesizing gypsum and calcining it, and directly producing useful hemihydrate gypsum, from the flue gas desulfurization process and the waste sulfuric acid neutralization process To provide a way to do.

[0005]

That is, a method for producing hemihydrate gypsum according to the present invention is a method for producing hemihydrate gypsum, which comprises heating sulfuric acid and a calcium compound. The amount of calcium compound or, if necessary, the amount of acid used, is adjusted so that the molar ratio of (amount of production) / (amount of gypsum that can be dissolved in the reaction solution) falls within a predetermined range. It is characterized by selectively obtaining water gypsum, α-type hemihydrate gypsum or β-type hemihydrate gypsum.

[0006]

The operation of the hemihydrate gypsum according to the present invention will be described in detail below. The present inventors reacted sulfuric acid and a calcium compound while heating, when producing hemihydrate gypsum, as a result of various studies to selectively produce α-type and β-type hemihydrate gypsum, respectively, (Theoretical amount of hemihydrate gypsum) /
It has been found that the molar ratio of (amount of gypsum that can be dissolved in the reaction solution) determines the morphology of precipitated hemihydrate gypsum.

The amount of gypsum that can be dissolved in the reaction solution (hereinafter referred to as "solubility of gypsum") varies depending on the concentration of coexisting acid. As the acid for increasing the solubility of gypsum, any acid may be used as long as it does not form a salt having a solubility lower than that of calcium sulfate by reacting with a calcium compound and enhances the solubility of gypsum, for example, nitric acid or hydrochloric acid. And sulfuric acid can be used. The solubility of gypsum in hydrochloric acid or nitric acid aqueous solution is as shown in FIG. 1 at 100 ± 2 ° C.

When sulfuric acid and a calcium compound are reacted, hemihydrate gypsum and acid or water are produced. As a calcium compound, for example, using calcium nitrate and calcium chloride,

[Chemical 1] H ₂ SO ₄ + CaCl ₂ + 1 / 2H ₂ O → CaSO ₄ · 1 / 2H ₂ O ↓ + 2HCl

## STR2 ## is as _{H 2 SO 4 + Ca (NO} 3) 2 + 1 / 2H 2 0 → CaSO 4 · 1 / 2H 2 O ↓ + 2HNO 3. At this time, the concentration of the acid produced is determined by the amount of hemihydrate gypsum produced, that is, by the amount of sulfuric acid or calcium compound used in the reaction, and the reaction of sulfuric acid and calcium compound removes hemihydrate gypsum. It can be seen that the reaction to be generated is theoretically an equivalent reaction.

Therefore, in the above reaction, use of a calcium compound so that the molar ratio of (theoretical amount of gypsum hemihydrate) / (amount of gypsum soluble in the reaction solution = solubility of gypsum) falls within a predetermined range. It was discovered that the form of hemihydrate gypsum produced can be controlled by adjusting the amount, or further adjusting the amount of acid added as necessary. In other words, the present inventors prepared a mixed solution of heated sulfuric acid and various acids, and added amount of calcium compound added, theoretical amount of hemihydrate gypsum produced, addition of acid and solubility change of gypsum. As a result of detailed comparison and examination of morphological changes of hemihydrate gypsum, the ratio between the solubility of gypsum and the theoretical production amount of hemihydrate gypsum was 1
It has been found that α-type hemihydrate gypsum is selectively produced when it exceeds 1, and is less than 1.45, and β-type hemihydrate gypsum is produced when it is 1.45 or more.

The molar ratio of (theoretical amount of hemihydrate gypsum) / (amount of gypsum soluble in the reaction solution = solubility of gypsum) is 1.
Since a mixture of α-type hemihydrate gypsum and β-type hemihydrate gypsum is formed in the vicinity of 45 to 2, it is necessary to select the molar ratio according to the purpose.

In the present invention, as the acid for increasing the solubility of gypsum, an acid based on a known technique such as the above-mentioned nitric acid, hydrochloric acid, sulfuric acid or the like can be used, but also for acids other than these, At each temperature, the concentration of the acid and the solubility of gypsum at that concentration were measured, and as a result, if the effect of increasing the solubility of gypsum in this acid is recognized, it is easy to apply this acid to the present invention. By analogy.

In the present invention, the method of controlling the concentration of the reaction solution in the precipitation step was used to control the shape of the hemihydrate gypsum, which is a poorly soluble calcium compound. The present inventors have conducted extensive studies on a method for producing longer-fiber α-type hemihydrate gypsum, and as a result, the solubility of gypsum, here, the concentration of a calcium compound that reacts with sulfuric acid and, if necessary, the solubility of gypsum further. By adjusting and adding an acid that enhances, the molar ratio of (theoretical amount of hemihydrate gypsum) / (amount of gypsum that can be dissolved in the reaction solution = solubility of gypsum) exceeds 1 and is less than 1.3. It has been found that a long fiber α-type hemihydrate gypsum having a length of 500 μm or more can be easily produced.

It was confirmed that by bringing the molar ratio as close to 1 as possible, the fiber was further lengthened, and a long fiber α-type hemihydrate gypsum having a crystal length of about 1500 μm and an aspect ratio of 150 or more was obtained. Of.

The product having a molar ratio of 1.3 or more and less than 1.45 is a fibrous or lumpy α-type hemihydrate gypsum, but the fibrous product is less than 500 μm and has an aspect ratio. Most of the crystals were 100 or less, and the fibers were about the same as the fibrous α-type hemihydrate gypsum produced by the conventionally known method. Therefore, when producing α-type hemihydrate gypsum having a relatively short fiber length, or when producing agglomerated α-type hemihydrate gypsum, it is preferable to adjust the solubility of gypsum.

By the way, when a hemihydrate gypsum is produced by reacting sulfuric acid with a calcium compound in a heated state, when an acid is produced after the reaction, and when the acid is an acid which enhances the solubility of gypsum, There was a concern that the generated hemihydrate gypsum would dissolve. Therefore, in the conventional method, the addition of an acid that increases the amount of gypsum that can be dissolved in the reaction solution was a contradictory idea in order to increase the yield. However, the present inventors, on the assumption that the dissolution-precipitation process is greatly involved in the production reaction mechanism of gypsum, detailed research leading to the present invention,
As a result of the examination, when hemihydrate gypsum is produced by the reaction of sulfuric acid and a calcium compound while heating, even if an acid that increases the solubility of gypsum is added to the reaction system, it dissolves in the acid at each concentration. There is a limit to the amount of gypsum that can be obtained, and it is possible to avoid a decrease in yield by adjusting the amount of calcium compound and acid added so that hemihydrate gypsum is produced in excess of the amount of gypsum at each acid concentration. And
Furthermore, the solubility of gypsum is adjusted by adjusting the addition amount of the calcium compound so that the molar ratio of (theoretical amount of hemihydrate gypsum produced) / (amount of gypsum soluble in the reaction solution = solubility of gypsum) exceeds 1. However, since I can always manufacture a hemihydrate gypsum with a constant molar ratio, I realized that it is possible to increase the yield while adjusting the acid concentration to increase the solubility of gypsum. is there. Further, in any case, when producing gypsum from the reaction of a water-soluble calcium compound and sulfuric acid, by generating an acid at the same time with hemihydrate gypsum,
The dissolution of gypsum is a phenomenon that inevitably occurs, and we have come to the idea that it may be possible to adjust the morphology of hemihydrate gypsum by taking advantage of this state. Based on that assumption, as a result of repeated intensive research, control of the morphology of hemihydrate gypsum, which was not previously possible by reacting sulfuric acid and a calcium compound in a solution while heating, that is, α according to the present invention
It became possible to selectively produce type hemihydrate gypsum, long-fiber α-type hemihydrate gypsum, and β-type hemihydrate gypsum.

Generally, the lower limit temperature of the stable region of hemihydrate gypsum in pure water is 97 ° C. On the other hand, when an acid such as sulfuric acid, hydrochloric acid or nitric acid coexists, the lower limit temperature of the stable region lowers. Therefore, in the present invention using these acids, hemihydrate gypsum can be produced at a relatively low temperature of about 75 ° C. Becomes However, the rate of transition of hemihydrate gypsum to dihydrate gypsum,
Considering the process steps such as filtration and drying after manufacturing, 90
It is preferable to manufacture at a temperature of not less than ° C.

The temperature at which hemihydrate gypsum transforms into anhydrous gypsum depends on the water vapor pressure and is about 150 ° C. at atmospheric pressure. Also, considering the boiling phenomenon of the reaction solution, etc.
In the practice of the present invention at 0 ° C. or higher, it is preferable to use a hydrothermal synthesizer such as an autoclave, but needle-like α-type hemihydrate gypsum, α-type hemihydrate gypsum and β-type hemihydrate gypsum are selectively obtained directly. Needless to say, in this case, it is more preferable to carry out the treatment at a relatively low temperature under normal pressure conditions.

The calcium compound used in the present invention is not particularly limited, and any compound that reacts with sulfuric acid to form gypsum can be used.

[0019]

【Example】

Example 1 The amount of gypsum that can be dissolved in the reaction solution and the theoretical production amount of hemihydrate gypsum were adjusted to 1.05, and the addition amount of the calcium compound and the acid that enhances the solubility of gypsum was adjusted to obtain long fibers. An α-type hemihydrate gypsum was produced. The apparatus used was a 200 cm ³ three-necked flask equipped with a reflux tube and a thermometer. 0.0 to this
An aqueous solution containing 3 mol of sulfuric acid was added in an amount of 50 cm ^3, and the temperature was kept at 98 ° C using a mantle heater. Further, in order to prevent bumping, a small amount of boiling stone was put inside the three-necked flask. 50 cm ^{3 of} an aqueous solution of 98 ° C. containing 0.03 mol of calcium chloride was added as a calcium compound.
In addition, the synthesis reaction was performed by holding for 120 minutes. Further, 0.02 mol of hydrochloric acid was added to each of the sulfuric acid and calcium chloride aqueous solutions as an acid for increasing the solubility of gypsum. At this time, the theoretical amount of hemihydrate gypsum was 0.03 mol, the amount of hydrochloric acid generated by the reaction of sulfuric acid and calcium chloride was 0.06 mol, and the amount of hydrochloric acid present in the solution immediately after the reaction was 0.10 mol. Is. The amount of gypsum that could be dissolved in this reaction solution, that is, 100 cm ^{3 of} an aqueous solution containing 0.10 mol of hydrochloric acid was 0.0286 mol. Therefore, the molar ratio of the theoretical production amount of hemihydrate gypsum to the dissolved amount of gypsum was adjusted to 1.05. The hemihydrate gypsum deposited by the reaction was suction-filtered with a glass filter, washed with hot water and methanol, and then the water adhering to the surface of the crystal was dehydrated and fixed with acetone. This was dried at 45 ° C. to obtain hemihydrate gypsum. As a result of thermal analysis, this hemihydrate gypsum showed a remarkable exothermic peak near 200 ° C. as shown in FIG. A micrograph showing the crystal structure of the obtained long-fiber α-type hemihydrate gypsum is shown in FIG. As can be seen from this micrograph, the long fibers had a length of 1500 μm or more and an aspect ratio of 150 or more.

Example 2 The addition amount of a calcium compound and an acid for increasing the solubility of gypsum was adjusted so that the molar ratio of the amount of gypsum that can be dissolved in the reaction solution to the theoretical amount of gypsum hemihydrate was 1.36. , Α-type hemihydrate gypsum was produced. The apparatus used, the amount of aqueous solution added, the holding time and the temperature were the same as in Example 1. The amounts of sulfuric acid and calcium chloride added were each 0.045 mol. Further, 0.025 mol of hydrochloric acid was added to each of the sulfuric acid and calcium chloride aqueous solutions as an acid for increasing the solubility of gypsum. At this time, the theoretical amount of hemihydrate gypsum produced was 0.045 mol, the amount of hydrochloric acid produced by the reaction of sulfuric acid and calcium chloride was 0.9 mol, and the amount of hydrochloric acid present in the solution immediately after the reaction was 0.14 mol. Is. The amount of gypsum that could be dissolved in this reaction solution, that is, 100 cm ^{3 of} an aqueous solution containing 0.14 mol of hydrochloric acid, was 0.0332 mol. Therefore,
The molar ratio of the theoretical amount of hemihydrate gypsum to the amount of dissolved gypsum was adjusted to 1.36. The hemihydrate gypsum precipitated by the reaction is suction filtered with a glass filter,
After washing with hot water and methanol, water adhering to the surface of the crystal was dehydrated and fixed with acetone. This was dried at 45 ° C. to obtain hemihydrate gypsum. This hemihydrate gypsum, as a result of thermal analysis,
As shown in FIG. 2, since a remarkable exothermic peak was shown at around 200 ° C., it was confirmed to be α-type hemihydrate gypsum.

Example 3 The amount of gypsum that can be dissolved in the reaction solution and the theoretical amount of gypsum hemihydrate formed are adjusted to 1.48 by adjusting the amount of the calcium compound and the acid that enhances the solubility of gypsum. , Manufactured hemihydrate gypsum. The apparatus used, the amount of aqueous solution added, the holding time and the temperature were the same as in Example 1. The amounts of sulfuric acid and calcium chloride added were each 0.044 mol. Further, 0.016 mol of hydrochloric acid was added to each of the sulfuric acid and calcium chloride aqueous solutions as an acid for increasing the solubility of gypsum. At this time, the theoretical amount of hemihydrate gypsum is 0.04.
4 mol, the amount of hydrochloric acid produced by the reaction of sulfuric acid and calcium chloride is 0.088 mol, and the amount of hydrochloric acid present in the solution immediately after the reaction is 1.12 mol. This reaction solution, i.e.
Since the amount of gypsum that can be dissolved in 100 cm ^{3 of} an aqueous solution containing 12 mol of hydrochloric acid is 0.0297 mol / 100 cm ³ ,
The molar ratio of the theoretical amount of hemihydrate gypsum to the solubility of gypsum was adjusted to 1.48. The hemihydrate gypsum precipitated by the reaction is suction filtered with a glass filter,
After washing with hot water and methanol, water adhering to the surface of the crystal was dehydrated and fixed with acetone. This was dried at 45 ° C. to obtain hemihydrate gypsum. This hemihydrate gypsum, as a result of thermal analysis,
As shown in FIG. 2, it had an exothermic peak at around 200 ° C. and 340 ° C., and was confirmed to be a mixture of α-type hemihydrate gypsum and β-type hemihydrate gypsum.

Example 4 The addition amount of the calcium compound and the acid for increasing the solubility of gypsum was adjusted so that the ratio of the amount of gypsum that can be dissolved in the reaction solution to the theoretical amount of gypsum hemihydrate was 2.16. Mold hemihydrate gypsum was produced. The apparatus used, the amount of aqueous solution added, the holding time and the temperature were the same as in Example 1. The amounts of sulfuric acid and calcium chloride added were each 0.080 mol. Further, 0.010 mol of hydrochloric acid was added to each of the sulfuric acid and calcium chloride aqueous solutions as an acid for increasing the solubility of gypsum. At this time, the theoretical amount of hemihydrate gypsum produced is 0.08.
0 mol, the amount of hydrochloric acid produced by the reaction of sulfuric acid and calcium chloride is 0.16 mol, and the amount of hydrochloric acid present in the solution immediately after the reaction is 0.180 mol. This reaction solution, i.e.
The amount of gypsum that can be dissolved in 100 cm ^{3 of} an aqueous solution containing 180 mol of hydrochloric acid was 0.037 mol / 100 cm ³ . Therefore, the molar ratio of the theoretical amount of hemihydrate gypsum to the solubility of gypsum was adjusted to 2.16. The hemihydrate gypsum deposited by the reaction was suction-filtered with a glass filter, washed with hot water and methanol, and then the water adhering to the surface of the crystal was dehydrated and fixed with acetone. This was dried at 45 ° C. to obtain hemihydrate gypsum. As a result of thermal analysis, this hemihydrate gypsum was β-type hemihydrate gypsum showing an exothermic peak at around 340 ° C. as shown in FIG.

Example 5 Long-fiber α-type semi-prepared by adjusting only the amount of calcium compound added so that the molar ratio of the amount of gypsum that can be dissolved in the reaction solution to the theoretical amount of gypsum hemihydrate is 1.15. Water gypsum was produced.
The apparatus used, the amount of aqueous solution added, the holding time and the temperature were the same as in Example 1. The amounts of sulfuric acid and calcium chloride added were each 0.015 mol. In this case, since an acid that enhances the solubility of gypsum is not added, the amount of hemihydrate gypsum that can be dissolved in the solution is affected only by the concentration of the acid that is produced simultaneously with the hemihydrate gypsum. At this time, the theoretical amount of hemihydrate gypsum produced was 0.015 mol, the amount of hydrochloric acid produced by the reaction of sulfuric acid and calcium chloride was 0.030 mol, and the amount of hydrochloric acid present in the solution immediately after the reaction was 0.030 mol. Is. The reaction solution, that is, 100 containing 0.030 mol of hydrochloric acid
The amount of gypsum that can be dissolved in a cm ³ aqueous solution is 0.013 mol / 10
It was 0 cm ³ . Therefore, the molar ratio of the theoretical amount of hemihydrate gypsum to the solubility of gypsum was adjusted to 1.15. The hemihydrate gypsum deposited by the reaction was suction-filtered with a glass filter, washed with hot water and methanol, and then the water adhering to the surface of the crystal was dehydrated and fixed with acetone. This was dried at 45 ° C. to obtain hemihydrate gypsum. As a result of thermal analysis, this hemihydrate gypsum was α-type hemihydrate gypsum showing an exothermic peak at around 200 ° C. In addition, it was confirmed by a scanning electron microscope that the fiber was a long fiber having a length of 520 μm and an aspect ratio of about 130.

Example 6 Production of α-type hemihydrate gypsum by adjusting only the amount of calcium compound added so that the ratio of the amount of gypsum that can be dissolved in the reaction solution to the theoretical amount of hemihydrate gypsum produced was 1.33. did. The apparatus used, the amount of aqueous solution added, the holding time and the temperature were the same as in Example 1. The amounts of sulfuric acid and calcium chloride added were each 0.020 mol. In this case, since an acid that enhances the solubility of gypsum is not added, the amount of hemihydrate gypsum that can be dissolved in the solution is affected only by the concentration of the acid that is produced simultaneously with the hemihydrate gypsum. At this time, the theoretical amount of hemihydrate gypsum produced was 0.020 mol, the amount of hydrochloric acid produced by the reaction of sulfuric acid and calcium chloride was 0.040 mol, and the amount of hydrochloric acid present in the solution immediately after the reaction was 0.040 mol. Is. The amount of gypsum that can be dissolved in this reaction solution, that is, 100 cm ^{3 of} an aqueous solution containing 0.040 mol of hydrochloric acid is 0.015 mol / 100 cm ^3.
Met. Therefore, the molar ratio of the theoretical production amount of hemihydrate gypsum to the solubility of gypsum was adjusted to 1.33. The hemihydrate gypsum deposited by the reaction was suction-filtered with a glass filter, washed with hot water and methanol, and then the water adhering to the surface of the crystal was dehydrated and fixed with acetone. This was dried at 45 ° C. to obtain hemihydrate gypsum. As a result of thermal analysis, this hemihydrate gypsum was α-type hemihydrate gypsum showing an exothermic peak at around 200 ° C.

Example 7 Hemihydrate gypsum was produced by adjusting only the amount of calcium compound added so that the ratio of the amount of gypsum that can be dissolved in the reaction solution to the theoretical amount of hemihydrate gypsum was 1.74. The apparatus used, the amount of aqueous solution added, the holding time and the temperature were the same as in Example 1. The amounts of sulfuric acid and calcium chloride added were each 0.
It was 040 mol. In this case, since an acid that enhances the solubility of gypsum is not added, the amount of hemihydrate gypsum that can be dissolved in the solution is affected only by the concentration of the acid that is produced simultaneously with the hemihydrate gypsum. At this time, the theoretical amount of hemihydrate gypsum is 0.0
40 mol, the amount of hydrochloric acid produced by the reaction of sulfuric acid and calcium chloride is 0.080 mol, and the amount of hydrochloric acid present in the solution immediately after the reaction is 0.080 mol. The amount of gypsum that could be dissolved in this reaction solution, that is, 100 cm ^{3 of} an aqueous solution containing 0.080 mol of hydrochloric acid was 0.023 mol / 100 cm ³ . Therefore, the molar ratio of the theoretical production amount of hemihydrate gypsum to the solubility of gypsum was adjusted to 1.74. The hemihydrate gypsum deposited by the reaction was suction-filtered with a glass filter, washed with hot water and methanol, and then the water adhering to the surface of the crystal was dehydrated and fixed with acetone. This was dried at 45 ° C. to obtain hemihydrate gypsum. As a result of thermal analysis, this hemihydrate gypsum was found to be a mixture of α-type hemihydrate gypsum and β-type hemihydrate gypsum, having exothermic pieces at around 200 ° C and around 380 ° C.

Example 8 β-type hemihydrate gypsum was prepared by adjusting only the addition amount of the calcium compound so that the molar ratio of the amount of gypsum that can be dissolved in the reaction solution and the theoretical amount of hemihydrate gypsum is 2.24. Was manufactured. The apparatus used, the amount of aqueous solution added, the holding time and the temperature were the same as in Example 1. The amounts of sulfuric acid and calcium chloride added were each 0.08 mol. In this case, since an acid that enhances the solubility of gypsum is not added, the amount of hemihydrate gypsum that can be dissolved in the solution is affected only by the concentration of the acid that is produced simultaneously with the hemihydrate gypsum. At this time, since the theoretical production amount of hemihydrate gypsum is 0.08 mol / 100 cm ³ , the molar ratio of the theoretical production amount of hemihydrate gypsum to the solubility of gypsum was adjusted to 2.24. . The hemihydrate gypsum deposited by the reaction was suction-filtered with a glass filter, washed with hot water and methanol, and then the water adhering to the surface of the crystal was dehydrated and fixed with acetone. This was dried at 45 ° C. to obtain hemihydrate gypsum. As a result of thermal analysis, this hemihydrate gypsum was β-type hemihydrate gypsum.

[0027]

According to the method for producing hemihydrate gypsum of the present invention,
When reacting a calcium compound with sulfuric acid under prescribed conditions, the molar ratio of (theoretical amount of hemihydrate gypsum) / (amount of gypsum that can be dissolved in the reaction solution = solubility of gypsum) should be within the prescribed range. By adjusting the amount of the compound used, and further by adjusting the amount of the acid used as necessary, various utilization methods have been proposed for long-fiber α-type hemihydrate gypsum, α-type hemihydrate gypsum or β Mold hemihydrate gypsum can be selectively produced with low energy consumption.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the concentration of hydrochloric acid or nitric acid aqueous solution at 100 ± 2 ° C. and the solubility of gypsum.

FIG. 2 is a graph showing the thermal analysis results of hemihydrate gypsum obtained in the examples.

FIG. 3 is a micrograph of the long-fiber α-type hemihydrate gypsum obtained in Example 1.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ren Yasue 1-19-18 Omiya, Suginami-ku, Tokyo (72) Inventor Yoshiyuki Kojima 3-23-2 Tsukagoshi, Warabi-shi, Saitama Prefecture

Claims (1)

[Claims] 1. A method for producing hemihydrate gypsum, which comprises heating sulfuric acid and a calcium compound, wherein a molar ratio of (theoretical amount of hemihydrate gypsum) / (amount of gypsum that can be dissolved in a reaction solution). By adjusting the amount of the calcium compound or the acid to be used, if necessary, so that
A method for producing hemihydrate gypsum, which comprises selectively obtaining long-fiber α-type hemihydrate gypsum, α-type hemihydrate gypsum or β-type hemihydrate gypsum.