Nucleation metastable zone and induction time analysis of Li₂CO₃ in reactive crystallization: Effects of process parameters and impurities

Metastable zone widths (MSZWs) and induction time (t_ind) are critical parameters in the optimization of solution crystallization processes. The crystallization of Li₂CO₃ from brines currently suffers from poor yield control due to limited understanding of how process parameters MSZWs and t_ind. Hence, the aim of this work is to investigate the effect of operating parameters on the MSZWs and t_ind of Li₂CO₃ crystallization. A laser monitoring system is utilized to measure the MSZWs and t_ind during Li₂CO₃ crystallization. Three semiempirical models are introduced to predict the MSZWs, among which the self-consistent Nývlt-like model (R² > 0.9784) and Sangwal's model (R² > 0.9736) demonstrate superior predictive accuracy. The effect of impurity (NaCl/KCl/Na₂SO₄) and ultrasound on the MSZWs are investigated. Compared to pure water solutions, the presence of NaCl reduced the MSZWs by 18.97 %, while KCl showed minimal impact by 3.52 %. In contrast, Na₂SO₄ and mixed NaCl-KCl-Na₂SO₄ impurities expanded the MSZWs by 32.56 % and 44.88 %, respectively. Ultrasound irradiation reduced the MSZWs, reaching maximal efficacy (34.58 % decrease from 0 to 80 W) at 333.15 K. Furthermore, two different nucleation mechanisms are identified, heterogenous nucleation at low supersaturation (S < 2.11) and homogeneous nucleation at high supersaturation (S > 2.30). By calculating the solid-liquid interface energy (γ) it can be found that γ decreasing from 1.19 × 10⁻¹⁸ to 1.11 × 10⁻¹⁸ J·m⁻² as temperature increased (298-313 K). These findings provide a fundamental data for optimizing Li₂CO₃ crystallization, particularly the application of ultrasound and impurity control.