Study on effect of crystallizer on preparation of anhydrous calcium sulfate from phosphogypsum
The production of phosphogypsum(PG)is large,and its resource utilization is difficult,which seriously affects the development of phosphorus chemical industry.In order to improve the added value of PG application,anhydrous CaSO4 with high whiteness was prepared by normal pressure salt solution method with PG as raw material,NaCl and EDTA-2Na as crystallization agents.The effect of crystal transition agent on the preparation of anhydrous CaSO4 was studied by SEM,XRD,FT-IR and particle size analyzer.The results showed that when the mass fraction of NaCl was 15%and the mass frac-tion of EDTA-2Na was 0.5%,the dehydration time of PG crystal water was shortened from 120 min to 40 min,and the dehy-dration effect was remarkable.At the same time,the particle size distribution of anhydrous CaSO4 crystal was uniform,the particle surface was complete,the D50 was 5.26 µm,the whiteness was 92.5%,and the P2O5 content was only 0.045%.It was mainly because non-lattice Na+ reduced the activity of water in the system,and promoted the dehydration,crystallization and impurity removal of PG.The coordination ion layer formed by the coordination between carboxyl groups in EDTA-2Na and Ca2+ on the surface of gypsum crystal could regulate the growth of anhydrous CaSO4 crystal and modify the crystal face.
phosphogypsumcrystal modifieranhydrous CaSO4normal pressure salt solution method
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