Kinetics Study on the Liquid Entrapment and Melt Transport of Static and Falling-Film Melt Crystallization

Experiments were carried out to study the kinetics of crystal growth and the sweating process in two kinds of melt crystallization modes: static melt crystallization (SMC) and falling-film melt crystallization (FFMC). The system utilized in this paper was hyperpure phosphoric acid with water and trace amounts of metal ions as impurities. The kinetic experimental data of crystal growth, liquid entrapment, and the melt-transport process were well fitted by power function equations (R-2 > 0.947). The fractal and porous media theories were introduced to improve the model of melt transport and explain the difference between the two modes. The separation efficiencies of SMC and FFMC on different ion impurities were Compared. The SMC mode separated calcium and ferrum ions with higher efficiency than the FFMC mode, while the FFMC mode separated sodium and magnesium ions better than the SMC mode. A combined operation mode was suggested to prepare hyperpure phosphoric acid in industrial applications.