Crystallization kinetics of the borax decahydrate

摘要

The growth and dissolution rates of borax decahydrate have been measured as a function of supersaturation for various particle sizes at different temperature ranges of 13 and 50 ℃ in a laboratory-scale fiuidized bed crystallizer. The values of mass transfer coefficient, K, reaction rate constant, k_r and reaction rate order, r were determined. The relative importances of diffusion and integration resistance were described by new terms named integration and diffusion concentration fraction. It was found that the overall growth rate of borax decahydrate is mainly controlled by integration (reaction) steps. It was also estimated that the dissolution region of borax decahydrate, apart from other materials, is controlled by diffusion and surface reaction. Increasing the temperature and particle size cause an increase in the values of kinetic parameters (K_g, K_r and K). The activation energies of overall, reaction and mass transfer steps were determined as 18.07, 18.79 and 8.26kJmol~(-1), respectively.