Application of a kinetic model for studying of impurities effect on crystallization of NaCl, KBr, ADP and Sucrose solutions

The 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 supersaturation and impurity concentration. A mathematical model describing crystal growth rates from aqueous solution as a function of impurity concentration is presented. The model assumes that the step velocity decreases linearly with increasing surface coverage (θeq) by impurities adsorbed on the growing crystal, and a proportionally constant, α, is introduced to take into account the effectiveness factor of impurity. When α>1, the step velocity is stopped at θeq <1 (incomplete coverage of the active sites for adsorption). In the case of α=1, the velocity reaches zero just at θeq=1 (complete coverage) but approaches a limiting value. The Lungmuir adsorption isotherm is used to relate the relative step velocity with the impurity concentration in solution. The value of α is changed by stereo chemical factors and decreases as the supersaturation is increased. In experimental observations, with increasing amount of impurity concentration in solution, the step velocity decreases. Comparison between the experimental data and model predictions shows that the agreement between them is very good.

کلیدواژه ها:

impurity ، crystal growth rate ، impurity effectiveness factor ، supersaturation ، step velocity