Hydrodynamics and separation regimes in a cyclonic-static microbubble flotation column

摘要

A cyclonic-static microbubble flotation column (FCSMC) operates under multiple flow regimes, which significantly improves recovery and selectivity. To understand the flow behavior and separation in an FCSMC, unsteady gas-fluid flow numerical simulations are performed. The computational fluid dynamics model is validated against the particle image velocimetry measurements applied to a lab-scale FCSMC. Hydrodynamic features and qualitative mineralization characteristics are studied. Global analysis reveals that an FCSMC operates under plug flow, swirling flow, and jet and pipe flow regimes along the pulp flow direction, through which the flow velocity, gas holdup, and turbulence gradually increase. This gradual intensification should overcome the mineral's decreased floatability over time. Local hydrodynamic and separation analyses indicate that the gas and liquid in the column unit move axially in opposite directions with very-low velocities, which results in countercurrent collisions, a low recovery capacity and high selectivity. In the cyclone unit, both phases rotate clockwise with high tangential, low radial, and axial velocities. Both axial and radial velocities of the gas and liquid have different magnitudes and opposite directions, which indicates the countercurrent collisions in the axial and radial directions. The density-based separation of tailings and surface flotation of middling takes place in this zone. In the pipe unit, the flow velocity, gas holdup, and turbulence are the highest of the entire FCSMC. Minerals with the lowest floatability are recovered in this zone, but the selectivity is low. Overall, the presence of multiple flow regimes allows the integration of multiple mineralization steps in one column and provides conditions for overcoming the decreased mineral floatability over flotation time, improving both mineralization and selectivity.