Influence of Aluminum on Morphologies and Crystallization Kinetics of Hemihydrate Calcium Sulfate in the Hemihydrate Process of Phosphoric Acid Production

The influence of aluminum on morphologies and crystallization kinetics of hemihydrate calcium sulfate (HH) in the hemihydrate process of phosphoric acid production was investigated. X-ray diffraction analyses showed that Al3+ ions can be adsorbed onto the crystal surface and incorporated into the crystal lattice. The crystal growth rate first increases and then decreases due to the dual role of Al3+ ions in a mixed suspension mixed product removal (MSMPR) crystallizer. For the first time, the effect of Al3+ ions on nucleation kinetics of HH at 93 °C was investigated by focused-beam reflectance measurement (FBRM). The results indicate that Al3+ ions retard the nucleation by increasing the interfacial tension values (γ).