Nonisothermal crystallization kinetics of potassium chloride produced by stirred crystallization

Abstract

The elucidation of the crystal nucleation and growth process can help control crystal size and quality. Here,the classical theory of primary nucleation was first used to study the homogeneous and heterogeneous nucleation mechanism of potassium chloride (KCl) crystallization. The growth kinetics in the presence of seed in KCl was then investigated. To understand the nucleation mechanism of KCl, the induction period of KCl was analyzed using classical nucleation theory to calculate the interfacial tension (γ) and various nucleation parameters, including the radius of the critical nucleus (r*), the critical free energy of the nucleus (ΔG*), and the molecular number of the critical nucleus (i*). The results showed a homogeneous nucleation mechanism at high supersaturation ratios (≥1.10) and a heterogeneous nucleation mechanism at low supersaturation ratios (<1.08). Meanwhile, the KCl crystal exhibited a continuous growth mechanism as inferred by the surface entropy factor (f) value. The SEM data demonstrated that the increase in crystallization temperature and supersaturation ratio could increase the average crystal size. The particle size-independent growth model is suitable for the growth process according to the relationship between crystal particle number density and particle size. In addition, the crystal nucleation and growth rates in stirred crystallization were calculated using the population balance equation, and then various kinetic parameters were estimated. The estimated parameters suggested an increase in growth with an increase in supersaturation ratio and stirring rate. Meanwhile, the impact of each parameter in the nucleation rate equation showed that the degree of influence is suspension density, supersaturation ratio, and finally, stirring rate.