Process for the preparation of calcium sulphate anhydrite and calcium sulphate anhydrite obtained by this process

摘要

A process for preparing calcium sulphate anhydrite from calcium sulphate dihydrate so that the calcium sulphate anhydrite crystals will have a predetermined average particle size. The process is conducted by recrystallizing the calcium sulphate dihydrate at moderate temperatures in the presence of sulphuric acid having a concentration of 40-65% wt. calculated relative to the quantity of liquid phase in the recrystallization mixture. The particle size of the final product is controlled by varying the temperature and residence time of the recrystallization mixture in recrystallization zone and by varying the temperature in an inverse relationship to the acid concentration.P P Calcium sulphate anhydrite crystals having an average particle size between about 0.5 and about 3 micron are produced by maintaining the temperature between about 40 C. and 90 C. and the residence time from about 5 minutes to less than about 30 minutes. Average particle sizes in the range of about 10 to about 20 micron are produced by maintaining the temperature in the range of about 20 C. and about 45 C. and the residence time between about 30 minutes and 3 hours. PPAnhydrite seed crystals are not supplied in the reactor at the initiation of the recrystallization nor are added to the recrystallization mixture.