Patent ID: 7700066

Claim:
A process for preparing α-calcium sulfate hemihydrate with high purity which comprises the following steps: a) adding aqueous solutions containing sulfate ions and calcium ions to calcium chloride solution with a range of concentration; c) reacting the mixture of a) at a range of temperature for an appropriate time; c) filtering and washing the reaction products of b) with a rinsing solvent to isolate the solid and liquid phases and remove the water or impurity; d) collecting and drying the solid phase to obtain α-calcium sulfate hemihydrate with high purity; wherein the relationship between the range of the concentration of calcium chloride (X, molarity) and the range of the reaction temperature (Y, ° C.) is shown as the following formula: −0.4x 5 +7.33x 4 −52.83x 3 +187.17x 2 −328.27x+316<y<1.2x 5 −22x 4 +158.5x 3 −561.5x 2 +984.8x−588 (2<X<5); wherein the temperature in b) is not provided by microwave and the sulfate ions and calcium ions in a) was not provided by calcium sulfate; and wherein the sulfate ions of step a) is selected from the group consisting of potassium sulfate, sodium sulfate and magnesium sulfate.