Ultrasound-enhanced crystallization of sodium stannate: Mechanisms of nucleation and growth control

The conventional crystallization technology for sodium stannate (Na2SnO3·3H2O) exhibits low efficiency, prolonged processing time, high energy consumption, and non-uniform crystal size distribution, which severely hinders the high-quality development of the sodium stannate industry. To address these challenges, ultrasonic technology was introduced into the crystallization process. The effects of various operating parameters under ultrasonic conditions on the yield, solid-solution transformation time, and crystal size distribution of sodium stannate were investigated, elucidating the crystallization behavior of sodium stannate solutions under ultrasonic fields. Furthermore, by analyzing the effects of ultrasound on key parameters such as the metastable zone width (MSZW), critical nucleation energy, and critical nucleation radius, the mechanism by which ultrasound enhances the crystallization of sodium stannate was clarified. Compared to conventional methods, ultrasonic-assisted crystallization significantly increased the sodium stannate crystallization yield from 3.7 to 7.2 g, reduced the solid-solution transformation time from 10 to 5 min, decreased the average crystal size (D50) from 102.3 ± 0.1 to 35.2 ± 0.1 μm, and narrowed the crystal size distribution from 11-563 μm to 5–224 μm. Ultrasound promoted homogeneous nucleation by reducing the MSZW, critical nucleation radius and free energy, thereby enhancing primary nucleation. Moreover, the microjet and mechanical effects generated by ultrasonic cavitation effectively reduced crystal agglomeration, enhanced the fragmentation of large crystal particles, and promoted secondary nucleation. This study successfully achieved the preparation of sodium stannate products with high yields and uniform crystal size, providing important theoretical insights for improving the sodium stannate crystallization process.