For researching the kinetics of unseeded batch crystallization process, the KNO₃-H₂O system was tested and the assumption that the kinetic characteristic after spontaneous nucleation is similar to that of seeded crystallization process was proposed. Responding to the assumption, a kinetic model related to transmittance, as a variable reflecting solid phase information, was established by optical method in order to reduce the relativity between model parameters and concentration data. Using the model, the secondary nucleation and crystal growth kinetics parameters of KNO₃ crystal were successfully estimated from the intermediate and final stages’ experimental data, and the values of parameters appeared to be in good agreement with those of seeded crystallization process published in literature. Based on it, a quantitative design method of seed load was subsequently put forward for seeded crystallization process, and the corresponding experiment also acquired perfect effect.

Key words: unseeded crystallization, kinetics modeling, transmittance, seed load, quantitative design