On the optimization of hydrodynamics in fine particle flotation

Abstract

There is absolutely no question that a key role for an effective fine particle flotation plays the achievement of sufficiently high flotation velocities by means of large collision rates between the value mineral particles and bubbles in the strongly turbulent rotor (impeller) stream of the flotation machines. Therefore, a large ratio ε R m / ν F n has to be aimed at ( ε R is the local energy dissipation rate in the impeller stream; ν F is the kinematic viscosity of the fluid phase), i.e. ε R should be as large and ν F as small as possible. On the one hand, for that it is important to use an impeller–stator system having a large power number and an intensive internal slurry recirculation. On the other hand, a satisfactory dispersion state and thus advantageous rheological properties (low apparent viscosity) of the slurry must be aimed at. The latter effects a substantial reduction of the turbulence damping and with that not only an increase of ε R in the impeller stream but also a decrease of its volume contraction. Furthermore, an adequate control of the entrainment into the froth lamellae plays a role in optimization.