Bubble behaviors in a lab-scale cyclonic-static micro-bubble flotation column

Bubble behaviors in the gas–liquid and lab-scale cyclonic-static micro-bubble flotation column (FCSMC) were investigated and optimized. By particle image velocimetry and charge-coupled device camera, bubble velocity and migration under low and high gas holdup conditions were measured. The particle image velocimetry measurement under low gas holdup shows that the swirling was significantly stronger than the rising in the near-axis area, and it declined as height increased. The central region contained high gas holdup and velocity. The bubble distribution under high gas holdup revealed that, in the column flotation unit, when water circulation rate (qw) increased, gas concentration moves toward the bottom. An excessively high qw drove gas downward and even caused the gas to be pulled into the pump. When aeration rate (qg) increased, the radial distribution improved but was not significant. If qg was excessive, the gas amount increased toward the top due to reflux when the rising bubbles met the free surface. Specifically, the greater bubble concentration in central region was observed under most test conditions. Additionally, an elongated ‘air column’ existed along the central axis and became more obvious with a high qw. The cyclonic inverted cone structure resulted in the gas gathering toward the center and the air column phenomena that deteriorate bubble mineralization. A non-uniform filling method was proposed to optimize the flow field. Filling with non-uniform sieve plates was proved to be more effective on bubble distribution equalization, air column inhabitation and non-axial velocity decreasing. These results provide the basis for structure optimization and process regulation of cyclonic-static micro-bubble flotation column. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.