Effects of the Impurities on the Habit of Gypsum in Wet-Process Phosphoric Acid

There is a poor understanding of the effect of impurities in phosphate rock on the crystal habit of gypsum during wet-process phosphoric acid production. The present work studies the effects of Al 3+, SiF 6 2-, and F - on the habit of gypsum in an MSMPR crystallizer. It is found that the gypsum crystal shape changes little in the presence of Al 3+ alone. In the presence of both Al 3+ and F -, the shape of the gypsum crystal changes greatly and forms sphere-shaped aggregates instead of the elongated needles formed in the presence of Al 3+ . In the presence of F -, Al 3+, and SiF 6 2- ions, the gypsum crystal shape is similar to that in the presence of both F - and Al 3+ ions. In addition, the effects of Al 3+, SiF 6 2-, and F - on the crystallization kinetics of gypsum are also investigated.