MANUFACTURE OF CALCIUM SULPHATE ALPHAHEMIHYDRATE

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 hydrochloride acid as a coproduct. The preferred reaction temperature is at least 20 degrees centigrade above the transition temperature (about 70.degree.C.), e.g. at 95-100.degree.C. at atmospheric pressure. The product of the invention has particular utility in the manufacture of plaster board, wall blocks or as an inert filler.