US Patent 7700066 Process for preparing alpha calcium sulfate hemihydrate

The invention provides a process for preparing α-calcium sulfate hemihydrate which comprises the following steps: adding aqueous solutions containing sulfate ions and calcium ions to calcium chloride solution with a range of concentration; reacting the mixture of a) at a range of temperature for an appropriate time; filtering and washing the reaction products of b) with a rising solvent to isolate the solid and liquid phases; and 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 (y) and the range of the reaction temperature (x) is shown as the following formula: −0.4x5+7.33x4−52.83x3+187.17x2−328.27x+316<y<1.2x5−22x4+158.5x3−561.5x2+984.8x−588 (2<X<5).