DIRECT FORMATION OF alpha -CALCIUM SULFATE HEMIHYDRATE UNDER ATMOSPHERIC PRESSURE

摘要

The invention relates to a process for the direct preparation of alpha -calcium sulfate hemihydrate by converting an organic calcium salt with a sulfate compound in an aqueous system at a temperature exceeding the alpha -calcium sulfate hemihydrate/calcium sulfate dihydrate transition temperature. In spite of the fact that said transition temperature has not been essentially decreased on account of the presence of the ions different from the calcium and sulfate ions it has been possible to obtain alpha -calcium sulfate hemihydrate in a high yield at a temperature, which is hardly higher than the hemihydrate/dihydrate transition temperature, for instance less than 1 DEG C. In view of the above it is possible to cary out the reaction below the boiling point of the solution or suspension of the organic calcium salt and the sulfate compound i.e. it is possible to perform the reaction at atmospheric pressure which is considered benificial from a technological point of view. Examples of organic calcium salts are calcium lactate, calcium acetate, calcium gluconate and calcium citrate.