A technique for continuous crystallization of high-quality ammonium polyvanadate: Crystallization mechanism and simulation of deflector tube baffle crystallizer

This study introduces a novel technology for continuous vanadium precipitation, aiming to resolve issues such as poor stack density, small particle size, and irregular morphology of ammonium polyvanadate in traditional intermittent processes. In this research, we optimized the process parameters for continuous vanadium precipitation and investigated the mechanism of continuous ammonium polyvanadate crystallization using the focused beam reflectometer measurement. Results showed that small, flaky ammonium polyvanadate particles initially formed between 0 and 12 min. These particles subsequently interlayered and aggregated, resulting in larger particles from 13 to 23 min. By 24 to 60 min, a dynamic equilibrium was reached in crystal growth, aggregation, de-embedding, and fragmentation. Kinetic analyses demonstrated that increasing the reaction temperature shifted crystal growth from surface reaction control to diffusion control. At higher temperatures, explosive nucleation of ammonium polyvanadate, crystal fragmentation, and dissolution occurred. By integrating the crystallization mechanism, we produced dense ellipsoidal ammonium polyvanadate particles with a stacking density of 0.772 g/cm3 and an average size of 107.04 mu m under optimal conditions, achieving a vanadium precipitation rate exceeding 99.0%. Simulation results confirmed that the deflector tube baffle crystallizer enabled continuous crystallization of ammonium polyvanadate, ensuring an average residence time of over 10 min for particles of 50 and 100 mu m, facilitating their growth to at least 100 mu m. This research provides data and theoretical support for the industrial application of continuous vanadium precipitation.