Preparation of α-calcium sulfate hemihydrate from phosphogypsum in hydrothermal electrolyte solutions under atmospheric pressure has been a promising way of effective utilization of phosphogypsum. In this paper preparation of α-calcium sulfate hemihydrate from phosphogypsum in Ca-Na-Cl solutions at 95℃was studied.Reaction time and solid products identification in 18.8% NaCl solution

24% CaCl2 and CaCl2+NaCl solutions were investigated through morphologic observation

water of crystalization determination and phase analysis methods.The results showed that NaCl solution was not favorable as the dehydration reaction medium of phosphogypsum though reaction time was only 20 min

because the dehydration product was α-calcium sulfate hemihydrate containing omangwaite (Na2Ca5(SO4)6·3H2O)which had no hydration property of gypsum.In 24% CaCl2 solution α-calcium sulfate hemihydrate phase could be obtained at reaction time of 240 min

reaction time was reduced obviously with increasing NaCl content in Ca-Na-Cl solution

but it was accompanied by increase of Na2O content and irregular uncompleted crystal shapes in the reaction product.Therefore

Ca-Na-Cl solution could be a suitable medium for dehydration reaction of phosphogypsum to form α-calcium sulfate hemihydrate in hydrothermal electrolyte solution under atmospheric pressure.Meanwhile NaCl content should be limited to 2%.