Patent ID: 8529863

Claim:
A process for continuously modifying dihydrate gypsum, said process comprising: (a) a hemihydration step of subjecting dihydrate gypsum as a starting raw material to wet calcination or dry calcination that converts the dihydrate gypsum into hemihydrate gypsum, (b) a charging step of feeding a slurry comprising the hemihydrate gypsum formed in the step (a) having pH in a range of 7.0 ±2.0 to an aqueous slurry in a recrystallization reaction tank, (c) a recrystallization step of hydrating and recrystallizing the hemihydrate gypsum into modified dihydrate gypsum of a crystalline form different from the dihydrate gypsum as the raw material, and (d) a discharge step of discharging a portion of the modified dihydrate gypsum from the recrystallization reaction tank, wherein: at least the steps (b) to (d) are conducted continuously or intermittently, a feed rate of the hemihydrate gypsum in the charging step (b) and a discharge rate of the modified dihydrate gypsum in the discharge step (d) are each not more than 20% of a total amount of gypsum in the recrystallization reaction tank per hour, and in the recrystallization step (c), the aqueous slurry in the recrystallization reaction tank is maintained at a constant temperature under stirring so that the aqueous slurry becomes uniform and that no solid-liquid separation occurs.