Claims
- 1. Process for preparing calcium sulphate anhydrite crystals wherein calcium sulphate dihydrate is recrystallized at an elevating temperature in the presence of concentrated sulphuric acid comprising maintaining in the recrystallization zone a sulphuric acid concentration of 40-65% wt. calculated relative to the quantity of liquid phase in the recrystallization mixture and controlling the average particle size of the calcium sulphate anhydrite crystals by varying the temperature and residence time of the recrystallization mixture in the recrystallization zone so that the temperature is maintained between about 40.degree. C. and about 90.degree. C., and the residence time is from about 5 minutes to less than about 30 minutes,
- thereby producing calcium sulphate anhydrite crystals
- having an average particle size between about 0.5.mu. and
- about 3.mu., and
- wherein calcium sulphate anhydrite crystals of a given average particule size may be produced by varying the temperature in an inverse relationship to the acid concentration and wherein no anhydrite seed crystals are present in the reactor at the initiation of the recrystallization and wherein no anhydrite seed crystals are added to the recrystallization mixture.
- 2. Process for preparing calcium sulphate anhydrite crystals wherein calcium sulphate dihydrate is recrystallized at an elevated temperature in the presence of concentrated sulphuric acid comprising maintaining in the recrystallization zone a sulphuric acid concentration of 40-65% wt. calculated relative to the quantity of liquid phase in the recrystallization mixture and controlling the average particle size of the calcium sulphate anhydrite crystals by varying the temperature residence time of the recrystallization mixture in the recrystallization zone so that the temperature is maintained between about 20.degree. C. and about 45.degree. C., and the residence time is between about 30 minutes and about 3 hours,
- thereby producing calcium sulphate anhydrite crystals
- having an average particle size between about 10.mu. and about 20.mu., and
- wherein calcium sulphate anhydrite crystals of a given average particle size may be produced by varying the temperature in an inverse relationship to the acid concentration and wherein no anhydrite seed crystals are present in the reactor at the initiation of the recrystallization and wherein no anhydrite seed crystals are added to the recrystallization mixture.
- 3. Process according to claim 2 further including the step of obtaining calcium sulphate dihydrate in the preparation of phosphoric acid resulting from the digesting of phosphate ore with sulphuric acid.
- 4. Process according to claim 2 further including the step of separating calcium sulphate anhydrite from the mixture obtained in recrystallization and using the remaining dilute sulphuric acid for digesting phosphate ore.
Priority Claims (1)
Number |
Date |
Country |
Kind |
7812109 |
Dec 1978 |
NLX |
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Parent Case Info
This is a continuation, of application Ser. No. 103,153 filed Dec. 13, 1979, now abandoned.
US Referenced Citations (7)
Foreign Referenced Citations (4)
Number |
Date |
Country |
561205 |
May 1944 |
GBX |
848617 |
Sep 1960 |
GBX |
1101771 |
Jan 1968 |
GBX |
1103206 |
Feb 1968 |
GBX |
Non-Patent Literature Citations (2)
Entry |
Slack A. V., Phosphoric Acid, Marcel, Dekker Inc. NY NY 1968, vol. 1, Part II, pp. 545-548. |
Masterson et al., Chemical Principles, N. B. Saunders Co., Philadelphia, Pa. 1969, pp. 362-364. |
Continuations (1)
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Number |
Date |
Country |
Parent |
103153 |
Dec 1979 |
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