Process for the production of neutral synthetic anhydrite

摘要

Neutral synthetic anhydrite is obtained from calcium sulphate contaminated with sulphuric acid, a by-product in the continuous production of hydrofluoric acid from calcium fluoride and sulphuric acid, by neutralizing the sulphuric acid with a basic calcium compound in the absence of moisture at a temperature between 100 DEG C. and 150 DEG C. The basic calcium compound may be the oxide, hydroxide or carbonate. The reaction mixture may be ground to a particle size not greater than 2 mm., and the neutral anhydrite may be ground to 170 mesh (U.S. standard screen). Before storing, the neutral anhydrite should be cooled to below 100 DEG C.