Preparation of α-hemihydrous gypsum from CaCl2 and MgCl2 and their composite solution
In order to improve the utilization rate and added value of phosphogypsum,α-hemihydrate gypsum was prepared from phosphogypsum by atmospheric hydrothermal synthesis method.The effects of CaCl2,MgCl2 and their composite solu-tions on the dehydration rate,phase composition and microcrystal morphology of α-hemihydrate gypsum prepared by atmo-spheric hydrothermal preparation of phosphogypsum were studied.It was found that phosphogypsum could be dehydrated and recrystallized to form α-hemihydrate gypsum in CaCl2 solution,MgCl2 solution and CaCl2-MgCl2 composite solution at 95℃.In CaCl2 solution and MgCl2 solution,the formation rate of α-hemihydrate gypsum accelerated with the increase of salt solution concentration,in which phosphogypsum could be completely reacted into α-hemihydrate gypsum after reaction of 35% CaCl2 solution for 4 h or 25% MgCl2 solution for 1 h.In the CaCl2-MgCl2 composite solution,the dehydration and con-version rate of phosphogypsum gradually accelerated with the increase of the concentration of MgCl2 solution.When the mass fraction of CaCl2 was≤19% and the mass fraction of MgCl2 was≥11%,the hydrothermal reaction of phosphogypsum for 1 h could form α-hemihydrate gypsum with relatively complete particle distribution.
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