Experimental Investigation into the Bubble-Particle Aggregate Rising Dynamics of Coarse Particle Fluidized Bed Flotation

The rising and upward transport of bubble-particle aggregates in the freeboard region of coarse particle fluidized bed flotation is essential for efficient coarse mineral recovery. Yet, the aggregate rising dynamics remain insufficiently quantified. In this study, a custom-built optical platform coupled with image analysis was applied to systematically investigate the microscopic morphology and macroscopic terminal rising velocity of aggregates in the freeboard region across varying particle loadings (ζ), upward flow velocities (Ref), particle sizes (Dp), and bubble sizes (Db). Results demonstrate that increasing ζ induces an “increase-decrease-rebound-stabilization” transition in aggregate aspect ratio (E), attributable to bubble stiffness variations. Concurrently, terminal rising velocity (UT,ag) exhibits an inverse S-shaped decay with increasing ζ, but rises alongside larger Db and elevated Ref, which is primarily attributed to the flow separation point advancement due to particle spreading, sharp pressure drag augmentation, and net buoyancy attenuation. Additionally, Larger Db values provide enhanced net buoyancy compensation, whereas high Ref conditions accelerate aggregates through velocity superposition effects and increased drag force contributions. Furthermore, a predictive model for UT,ag and an inverse drag force equation were developed based on a “velocity vector decoupling-flow regime nonlinear weighting-physical constraint enforcement” modeling strategy. Finally, a flow regime map for the rising bubble-particle aggregate was established alongside a predictive criterion for critical loading, offering a robust theoretical foundation for optimizing coarse particle fluidized bed flotation.