关键词: 磷石膏, α-半水石膏, CaCl₂溶液, NaCl溶液

Abstract: 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%.

Key words: phosphogypsum, α-calcium sulfate hemihydrate, CaCl₂ solution, NaCl solution