Experiments and Simulations for Reactive Crystallization of Li3PO4 from Low Concentration Li-Rich Brine

Li3PO4 is an ideal precursor for synthesizing high-performance LiFePO4, as it simultaneously provides lithium and phosphorus sources. Extremely low solubility of Li3PO4 enables efficient lithium recovery from low-concentration Li-rich brine by reactive crystallization. A focused beam reflectance measurement (FBRM) system was employed to monitor the key optimization parameters for Li3PO4 crystallization, supersolubility, and metastable zone widths (MSZWs). The optimized process parameters were determined by systematically investigating the effects of operating conditions. Additionally, prediction of supersolubility and MSZWs was accomplished with theoretical models. Results demonstrate that both supersolubility and MSZWs exhibit a pronounced negative correlation with temperature. Supersolubility decreased sharply when LiCl concentration exceeded 5 mol·L−1 or Na3PO4 concentration surpassed 0.8 mol·L−1. Conversely, it increased exponentially with Na3PO4 feeding rate. The effect of impurity (NaCl/KCl) was non-monotonic, initially increasing and then decreasing supersolubility and MSZWs. Among these, Na2B4O7 most significantly enhanced both parameters, followed by Na2SO4. The supersolubility data were well-fitted by an empirical equation (R2 > 0.99). For MSZWs prediction, the self-consistent Nývlt-like model (R2 > 0.9883) and the modified Sangwal’s model (R2 > 0.994) achieved superior performance. Collectively, these findings establish a theoretical basis for optimizing lithium recovery via Li3PO4 crystallization, facilitating more efficient and sustainable production of high-purity lithium products.