Suspension of apatite particles in a self-aerated Denver laboratory flotation cell

Minerals & Metallurgical Processing , 2009, Vol. 26, No. 2, pp. 74-78

Lima, O.A.; Marques, C.V.P.; Leal Filho, L.S.

ABSTRACT:

Effective solids suspension is a necessary precondition for particle collection, and solids suspension is largely dependent on the hydrodynamics of the flotation cell. This study attempted to correlate the status of the suspension of apatite particles of different sizes in a Denver laboratory flotation cell versus the impeller rotational speed (N) adopted to operate the machine. The latter variable (N) influences the impeller capacity to lift the particles from the bottom of the tank and also to disperse them throughout the volume of the vessel. Such an impeller capacity can be characterized by the critical impeller speed for the accomplishment of solids off-bottom suspension (N_z) and also by the velocity of the radial water flow discharged by the impeller (U) divided by the particle terminal settling velocity (U_s). This way, the status of the suspension of apatite particles inside the flotation cell can be characterized by one of three categories: “segregation” (N/N₂ < 0.60 and U_s/U > 0.08); “suspension” (0.60 ≤ N/N₂ < 1 and 0.06 < U_s/U < 0.10); and “dragging” (N/N₂ ≥ 1 and U_s/U ≤ 0.03). The range of impeller rotational speed (N), which was able to suspend the finest particles (D_p = 90 µm), was unable to suspend the coarsest particles (D_p = 254 µm). Conversely, the high value of N (N > 1,300 rpm), which is adequate to suspend the coarsest particles, may promote the entrainment of the finest particles to the froth layer.