Evaluation of Nucleation and Growth Kinetics of Li3PO4 Reactive Crystallization from Low-Concentration Lithium-Rich Brine

Li3PO4 is a promising raw material for the low-cost synthesis of high-performance LiFePO4. Reactive crystallization from low-concentration lithium-rich brine is a key process for the efficient preparation of high-quality Li3PO4 products. The effect of operating conditions (temperature/supersaturation/impurities/ultrasonic) on the induction time was investigated using a focused beam reflectance measurement. The evaluation of the primary nucleation, growth kinetics, and parameters for the extraction of Li3PO4 from low-concentration lithium-rich brine was conducted using an induction time method. The dominant mechanisms at different stages were inferred through online monitoring of the particle size distribution during the Li3PO4 crystallization process. Results show that induction time decreases with increasing operating conditions (temperature/supersaturation/ultrasonic frequency), indicating that their increases all promote nucleation. Impurities (NaCl/KCl) did not significantly affect the induction time, whereas Na2SO4 and Na2B4O7 significantly increased it, with Na2B4O7 showing the most notable effect. Classical nucleation theory was applied to determine kinetic parameters (nucleation activation energy/interfacial tension/contact angle/critical nucleus size/surface entropy factor). Results indicate that Li3PO4 mainly nucleates through heterogeneous nucleation, with a temperature increase weakening the role of heterogeneous nucleation. Fitted models indicate that Li3PO4 predominantly follows the secondary nucleation and spiral growth mechanism. Our findings are crucial for crystallization design and control in producing high-quality Li3PO4 from lithium-rich brines.