MANUFACTURE OF CALCIUM SULPHATE ALPHA-HEMIHYDRATE

摘要

A process for the manufacture of calcium sulphate alpha-hemihydrate which comprises the step of interacting an aqueous solution of calcium chloride and a source of sulphate or bisulphate ions in an aqueous system at a temperature above the calcium sulphate hemihydrate/gypsum transition temperature under the reaction conditions. The preferred reagents are the waste calcium chloride/sodium chloride effluent of the ammonia soda process and sulphuric acid (e.g. impure sulphuric acid effluent) to give hydrochloric acid as a co-product. The preferred reaction temperature is at least 20 DEG C. above the transition temperature (about 70 DEG C), e.g. at 95 DEG -100 DEG C at atmospheric pressure.