CA1117271A

CA1117271A - Spherical gypsum and process for production of same

Info

Publication number: CA1117271A
Application number: CA000280321A
Authority: CA
Inventors: Mitsuo Hashimoto; Masaru Inoue; Toshiyuki Takyu; Shinho Shiho; Masami Takasaki
Original assignee: Idemitsu Kosan Co Ltd
Current assignee: Idemitsu Kosan Co Ltd
Priority date: 1976-11-29
Filing date: 1977-06-10
Publication date: 1982-02-02
Also published as: SE7706274L; JPS5817132B2; JPS5366895A; FR2372120A1; DE2728213A1; GB1536097A; FR2372120B1; IT1115860B

Abstract

ABSTRACT OF THE DISCLOSURE

Spherical gypsum formed from substantially fibrous gypsum intertwining with one another, and a process for producing such spherical gypsum by subjecting 0.5 to 80% by weight of .beta.-type hemihydrate gypsum or 5 to 80% by weight of dihydrate gypsum or 5 to 80% by weight of the mixture thereof to a hydrothermal reaction in an acid medium, each proportion being based on the weight of the acid medium.

Description

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BACKGROIJWD OF THE INVENTION
1. Field of the Invention The present invention relates to spherical gypsum and a process for production of the same. More particularly, it is concerned with spherical gypsum formed from fibrous gypsum and a process for production of the same.

2. Description of the Prior Art It is well known that gypsum occurs in a wide variety of forms. In the course of our investigations to develop a fibrous and lightweight gypsum product, we have succeeded in producing spherical gypsum formed from fibrous gypsum inter-twining with one another.
The spherical gypsum of the present invention is dis-tinctly different in form from conventional minute granular gypsum and fibrous gypsum, having the characteristics in that the bulk density is small, and thus the spherical gypsum of the present invention is expected to have many new industrial applications.

SUMMARY OF THE INVENTION

An object of the present invention is to provide spherical gypsum formed from substantially fibrous gypsum and a process or production of the same.

BRIEF DESCRIPTION OF THE DR~WINGS
.,_ _ .. .. _ ...... _ . __ _ Figures 1 and 2 illustrate the microscopic view of the spherical gypsums obtained by the process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
. __ . . . . .
Microscopic analysis reveals that the spherical gypsum of the present invention is in the form of a "close-cropped head"

1 or an "aegagropila" as shown in Figures l and 2. With regard to the mechanism according to which the spherical gypsum of the present invention is formed, it is considered that fibrous crystals grow from a gypsum used as a starting material and intertwined with one another, irregularly and three-dimensionally, in the same reaction sys-tem to form an agglomerate, thereby showing the substantially spherical form. On the surface of the agglomerate, there are observed a number of "whiskers 1I due to the fibrous crystals and its appearance is like a 'Iclose-cropped head" or an "aegagropila" as described above. Thisdifference in appearance is considered to be caused by the kinds of the gypsum used as a starting material, etc.
The spherical gypsum of the present invention is classified in the three groups: ~-type hemihydrate gypsum, di-hydrate gypsum and anhydrite gypsum according to the composition thereof. In any case, its bulk density is O.Ol to 0.8 g/cm3 and on the average, as much as O.l g/cm . On the other hand, while the diameter of the spherical gypsum varies with the production conditions thereof, it is usually O.OOl to lO
millimeters and on the average, 0.3 millimeters.
The spherical gypsum of the present invention is white and has the advantages in that it is subject to less crystal breakage as compared with fibrous one, and in that it is uniform in quality and lightweight. Furthe~more, this spherical gypsum is less soluble in water and has excellent dispersibility in water and heat insulating properties, and in addition, it is non-combustible and has excellent heat resis-tance.
Hereinafter a process for production of the spherical gypsum of the present invention ~ill be explained.
This spherical gypsum can be produced hy a hydrothermal 1 reaction of ~-type hemihydrate gypsum or dihydrate gypsum or the mixture thereof in an acid medium. Gypsums used as starting materials are, as described above, ~-type hemihydrate gypsum, dihydrate gypsum and a mixture thereof; any materials composed mainly of these compounds can be used. These gypsums are mixed with an acid medium in the following ratios to form slurries:
in the case of ~-type hemihydrate gypsum, 0.5 to 80% by weight, preferably 5 to 50% by weight; in the case of dihydrate gypsum, 5 -to 80~ by weight, preferably 20 to 50% by ~eight; and in the t~ case of the mixture thereof, 5 to 80~ by weight, preferably 20 to 50~ by weight, each being based on the weight of the acid medium. When the amount of dihydrate gypsum or the mixture is less than 20~ by weight, both spherical and fibrous gypsums are produced.
Acid mediums which can be used in the present invention, are organic acids such as formic acid, acetic acid, maleic acid and the like, and inorganic acids such as phosphoric acid, hydrochloric acid, nitric acid, sulfuric acid and the like.
These acid mediums are used as aqueous solutions containing these acid components in proportions of 5 to 80% by volume.
The hydro~hermal reaction is usually carried out at a temperature of the reflux temperature of the reaction medium at ordinary pressure, and it is also possible to effect the reaction under pressure. The reaction time is usually more than 1 hour, preferably 3 to 5 hours.
By effecting the hydrothermal reaction of the gypsum under the above described conditions, the objective spherical gypsum can be obtained.
Then the solid-liquid separation of the resulting reaction mixture is carried out, if desired, and the liquid 1 thus obtained is reused as a reaction medium. This solid-liquid separation is preferably effected while the mixture was still hot. On the other hand, a solid matter havin~ a medium content ~medium/solid x 100) of less than ~0~ is subjected to heat processing: that is, the solid matter is dried at 50 to 80C for 1 to 3 hours and if desired, calcined at 400 to 1,000C for 0.5 to 3 hours. The former step gives ~-type hemihydrate gypsum and the latter step gives anhydrite gypsum.
The method of the present invention provides spherical gypsum having the above described characteristics~ In addition, it is possible to feed the gypsum as a starting material in an amount of up to 80 parts by weight per 1~0 parts by weight of the reaction medium, and to effectively conduct the reaction in a high slurry Concentration, which is advantageous from the commercial standpoint. Furthermore, the present invention has the advantage in that the solid-liquid separation after the reaction is easy.
The gyps~m product of the present invention can be used as a filler, a lightweight non-combustible aggregate, an insulation material, a heat insulating material, a sound absorbing material, a core material, an adsorbent, a carrier, a filter medium, a soil conditioner, non-woven fabric, abrasive, pottery, plaster, fertilizer, gardening material, buffer agent, detergent, catalyst, explosive, coating material, pesticide, etc.
The present invention will be explained in more detail by reference to the following examples.

To 6 liters of a 20~ by volume aqueous solution of acetic acid was added 0.6 kg of ~-type hemihydrate gypsum, which `7~

1 were mixed to form a slurry. This slurry was subjected to a hydrothermal reaction by heating under reflux for 4 hours at a temperature of 104C and ordlnary pressure while stirring by the use of a propeller type of agitating blade.
After the hydrothermal reaction, the solid~ uid separation of the resulting mixture was conducted by the use of a centrifugal separator to recover the reaction solvent for reuse. The solid matter thus obtained was dried at 60C ~`
for 3 hours in a hot-air drying chamber to remove the solvent attached thereto, and thus ~-type hemihydrate gypsum was obtained.
The microscopic analysis of the gypsum products obtained above revealed that they were generally uniform spheres in the form of a "close-cropped head" as shown in Figure 1. The diameter of the sphere was about 0.3 millimeters and its bulk density was 0.07 g/cm3. This dry gypsum was then calcined at 500C for 3 hours in an electric furnace, and thus spherical II-type anhydrite gypsum having stable crystal structure was obtained. This spherical II-type anhydrite gypsum was ;
about 0.3 millimeters in diameter and generally uniform, and it was 0.06 g/cm3 in bulk density and very`lightweight.

~XAMPLE 2 To 6 liters of a 20~ by volume aqueous solution of acetic acid was added 1.2 kg of dihydrate gypsum, which were mixed to form a slurry. This slurry was subjected to a hydro-thermal reaction by heating under xeflux for 4 hours at a temperature of 104C and ordinary pressure by the use of a propeller type of agitating blade.

After the hydrothermal reaction, the solid-liquid separation of the resulting mixture was conducted by the use of a centrifugal separator while it was hot, to recover the reaction solvent for reuse. The solid matter thus obtained was dried at 60C for 3 hours in a hot-air drying chamber to remove the solvent at~ached thereto, and thus ~-type hemihydrate gypsum was obtained.
The microscopic analysis of the gypsum products thus obtained revealed that they were spheres in the form of an "aegagropila" as shown in Figure 2~ The diameter of this sphere was about 0.3 millimeters and the bulk density was 0.13 g/cm3. This dry gypsum was then calcined at 500C for

3 hours in an electric furnace, and thus spherical II-type anhydrite gypsum having stable crystal structure was obtained~
This anhydrite gypsum was about 0.3 millimeters in diameter and 0.13 g/cm3 in bulk density.

.. .. .
To 6 liters of a 20% by volume aqueous solution o~
acetic acid was added 1.8 kg of dihydrate gypsum, which were mixed to form a slurry. This slurry was processed in the same manner as in Example 1 to obtain spherical ~-type hemihydrate gypsum and II-type anhydrite gypsum.
The microscopic analysis revealed that the spherical gypsum obtained above was in the ~orm o~ an "aegagropila"
as shown in Figure 2. Any of these ~-type hemihydrate gypsum and II-type anhydrite gypsum were about 0.3 millimeters in diameter and about 0.06 g/cm3 in bulk density.

-To 6 liters of a 10% by volume aqueous solution of sulfuric acid was added 1 kg o~ ~-type hemihydrate gypsum, which were mixed to form a slurry. This slurry was processed in the 1 same manner as in Example 1 to obtain spherical ~-type hemihydrate gypsum and II-type anhydrite gypsum.
Any of these ~-type hemihydrate gypsum and II--type anhydrite gypsum were about 0.3 millimeters in diameter and about 0.08 g/cm3 in bulk density.

To 6 liters of a 20% by volume aqueous solution of acetic acid were added 0.6 kg of ~-type hemihydrate gypsum and 1.2 kg of dihydrate gypsum, which were mixed to form a slurry. This slurry was processed in the same manner as in Example 1 to obtain spherical a-type hemihydrate gypsum and II-type anhydrite gypsum.
The microscopic analysis revealed that most of the spherical gypsum obtained above occurred in the form of 'laegagropila" in which minute fibers intertwined with une another and covered the surface of "close-cropped head" and some of the spherical gypsums occurred in the form of "close-cropped head" as observed in Example 1 and in the form of "aegagropila" as observed in Example 2.
Any of these ~-type hemihydrate gypsum and II-type anhydrite gypsum were about 0.5 millimeters in diameter and about 0.07 g/cm3.

.. ,.. _ :
The procedure of Example 5 was repeated with the exception that the amount of dihydrate gypsum was 1.8 kg and thus ~-type hemihydrate gypsum and II-type anhydrite gypsum were obtained.
The results of the microscopic analysis of the spheri-cal gypsum obtained above were the same as those in Example 5.

,, ~rrJ~ J~

1 Any of ~-type hemihydrate gypsum and II-type anhydrite gypsum were about 1.2 millimeters in diameter and about 0.11 g/cm3 in bulk density.

The procedure of Example 5 was repeated with the exception that the amount of the ~-type hemihydrate gypsum was 1.8 kg and thus -type hemihydrate gypsum and II-type anhydrite gypsum were obtaindd.

The microscopic analysis revealed that most oE the spherical gypsum obtained above occurred in the form of "close-cropped head", and some of them occurred in the form of "aegagropila" and the one in which the both intertwined with each other. The spherical ~-type hemihydrate gypsum and II-type anhydrite gypsum were about 0.1 millimeter in diameter and about 0.3 g/cm in bulk densityO

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for producing spherical gypsum which comprises subjecting a material selected from the group consist-ing of B-type hemihydrate gypsum, dihydrate gypsum and a mixture of B-type hemihydrate gypsum and dihydrate gypsum, to a hydro-thermal reaction in an acid medium containing an organic or an inorganic acid in a proportion of about 5 percent to about 80 percent by volume of said medium, wherein the hydrothermal reaction is carried out at about the reflux temperature of said medium and at about ordinary pressure or slightly greater than ordinary pressure, and the amount of B-type hemi-hydrate gypsum is from about 0.5 percent to about 80 percent by weight based on the weight of the acid medium, the amount of di-hydrate gypsum or the mixture of B-type hemihydrate gypsum and dihydrate gypsum is from about 5 percent to about 80 percent by weight based on the weight of the acid medium.

2. A process as claimed in claim 1 wherein said material is B-type hemihydrate gypsum and is present from about S percent to about 50 percent by weight based on the weight of said acid medium.

3. A process as claimed in claim 1 wherein said material is dihydrate gypsum and is present from about 20 percent to about 50 percent by weight based on the weight of said acid medium.

4. A process as claimed in claim 1 wherein said material is a mixture of B-type hemihydrate gypsum and dihydrate gypsum and is present from about 20 percent to about 50 percent by weight based on the weight of said acid medium.

5. A process as claimed in claim 1 wherein said acid is selected from the group consisting of formic acid, acetic acid, maleic acid, phosphoric acid, hydrochloric acid, nitric acid and sulfuric acid.

6. A process as claimed in claim 1 wherein said reaction is carried out for more than 1 hour.

7. A process as claimed in claim 6 wherein said reaction time is from about 3 to about 5 hours.

8. A process as claimed in claim 1 further including the step of solid-liquid separation of the resultant reaction mixture.

9. A process as claimed in claim 8 further including the step of heat treating the resultant solids.

10. A process as claimed in claim 9 wherein said solids are dried at about 50°C to about 80°C for about 1 to about 3 hours.

11. A process as claimed in claim 10 further including the step of calcining the resultant product at about 400°C to about 1000°C for about 0.5 to about 3 hours.

12. A process as claimed in claim 1, 8 or 9 wherein said hydrothermal reaction is carried out with agitation.

13. Spherical gypsum having a bulk density of about 0.01 to about 0.8 g/cm3, a diameter of about 0.001 to 10 milli-meters and formed from substantially fibrous gypsum, wherein said gypsum is selected from the group consisting of .alpha.-type hemi-hydrate gypsum and anhydrite gypsum.

14. A process as claimed in claim 3, 10 or 11 wherein said hydrothermal reaction is carried out with agitation.