Effects of low-frequency ultrasound on enhancing the recovery of secondary copper resources via column flotation and corresponding numerical simulation

• Novel unilateral-ultrasound flotation column enables efficient Cu-S separation in tailings. • Ultrasound enhances Cu recovery (+13.63%) and efficiency (+1.09%) without grade compromise. • 20 kHz ultrasound optimizes bubble dynamics via cavitation and acoustic streaming effects. • Feed-zone ultrasound placement maximizes energy utilization and stabilizes particle trajectories. • COMSOL simulation reveals ultrasound-induced acoustic fields and flow restructuring. To address the challenges of low bubble-particle collision efficiency, particle agglomeration, turbulent flow fields, and issues related to mineral surface oxidation layers and slime coatings inherent in traditional flotation columns, this study established a COMSOL Multiphysics-based numerical model incorporating coupled pressure acoustics, acoustic streaming, and fluid dynamics multiphysics. Copper-sulfur separation experiments were concurrently conducted using a laboratory-scale unilateral ultrasonic flotation column. Numerical simulations and experimental results revealed that an ultrasonic frequency of 20 kHz significantly enhanced both cavitation effects and localized acoustic streaming compared to 40 kHz. This improvement increased concentrate recovery from 51.51% to 65.14% while maintaining concentrate grade, consequently raising Beneficiation efficiency from 4.42% to 5.51%. Strategic placement of the ultrasonic vibrator plate near the feed inlet demonstrated superior efficacy, effectively stabilizing the flow field and optimizing the processing of incoming mineral particles relative to alternative positions. Furthermore, ultrasonic treatment promoted flow field homogenization. Collectively, these findings serve as a critical theoretical foundation and provide robust experimental support for optimizing frequency selection and vibrator plate positioning in ultrasonically enhanced flotation column technology.