Effect of bubble trailing vortex on coal slime motion in flotation

•Relative height of low-velocity region fitted well with Re of a correlation coefficient 0.931.•Separation angle showed a good mathematical relationship to the fluid flow velocity with a correlation coefficient of 0.991.•Horizontal forces acting on the coal particle was analyzed to support the particle trajectory around the trailing vortex region. Understanding the coal slime motion around the trailing vortex is an important precursor for predicting the entrainment probability of the bubble trailing vortex in coal flotation. Using a particle image velocimetry (PIV) system, we investigated the length of low-velocity region and the separation behavior of liquid from the cylinder surface under different fluid flow velocities. As the average fluid flow velocity increased, the height of the low-velocity region firstly increased and then gradually decreased, while the separation angle firstly decreased rapidly and then be almost constant at 94.2°. The relative height of low-velocity region and the separation angle fitted well with the fluid flow velocity, respectively. The trajectory of the coal particle having a diameter of 0.1875 mm moved around the cylinder was explored via a high-speed camera system. The coal particle first moved against the cylinder surface and then entered the trailing vortex region, where the centrifugal force and dynamic pressure provided sufficient energy. After a similar circular motion, the coal particle left the region relying on the dynamic pressure. Our results can provide a valuable insight into the development of technology for cleaner mineral flotation.