Application of a Kinetic Model for Studying Impurities Effect on Crystallization of NaCl, KBr, ADP and Sucrose Solutions

Addition of impurities has an important role on the kinetic crystallization. Therefore, influence of impurities on the crystallization kinetics of NaCl, KBr, ADP and Sucrose solutions was investigated in a fluidized bed crystallizer. The growth and dissolution rates were related to the super saturation and impurity concentration. A strong mathematical model is applied to describe crystal growth rates within aqueous solutions as a function of impurity concentration. The model tries to relate the step velocity to the useful parameters such as the surface coverage (?eq), as well as the effectiveness factor of impurity, ?. When ? > 1, the step velocity is stopped at ?eq < 1 (incomplete coverage of the active sites for adsorption). In the case of ?=1, the velocity reaches zero just at ?eq=1 (complete coverage) but approaches a limiting value. The value of ? is changed by stereo chemical factors and decreases as the supersaturation is increased. The Langmuir adsorption isotherm is used to relate the relative step velocity with the impurity concentration in solution. Experimental results show that increasing the amount of impurity concentration leads to a decrease in the step velocity. Experimental data and model predictions have been compared to show that the agreement between them is very good. The obtained results are suitable for designing and quality control of the crystallization processes in chemical industries.