Mechanism of enhanced crystallization of stannous sulfate by ultrasound-negative pressure synergy

Atmosphere evaporation crystallization of stannous sulfate (SnSO₄) is constrained by low efficiency. Although negative-pressure evaporation accelerates solvent removal, the resulting abrupt increase in supersaturation often triggers uncontrolled explosive nucleation, forming irregular agglomerates with broad particle size distributions. To address this issue, this study proposes a novel synergistic ultrasonic-negative pressure crystallization strategy. Under optimized conditions (80 °C, 40 kHz, 107 W, 0.03 MPa, 150 rpm), the synergistic process achieved an exceptional 88.6 %±1.6 % efficiency and produced rod-shaped crystals with a uniform unimodal particle size distribution (D₅₀ = 38.42 ± 0.27 μm). In-situ high-speed visualization revealed a unique transformation in bubble behavior under the synergistic field, negative pressure reduced the cavitation threshold, generating two distinct bubble populations-transient bubbles enhanced by negative pressure (boosting volumetric mass transfer) and stable oscillating bubbles (serving as heterogeneous nucleation sites). This study elucidates the effects of negative pressure coupled with ultrasonic on solution cavitation behavior and crystal growth, providing a theoretical foundation for controlled crystallization under negative-pressure and ultrasonic synergy.