On the microprocesses air dispersion and particle-bubble attachment in flotation machines as well as consequences for the scale-up of macroprocesses

By means of considerations, experimental results as well as high-speed photographs it is shown that in flotation machines the zone of high local energy dissipation, i.e. the impeller stream, is the active region for the realization of the microprocesses bubble dispersion and particle-bubble attachment. Because of the pressure differences as well as the turbulent pressure fluctuations existing there, it is not unlikely that gas precipitation influences the attachment events substantially. Outside of the impeller stream, the local energy dissipation is so far reduced below the mean dissipation <(epsilon)over bar> = P/m that the preconditions for realizing these microprocesses, which are controlled by turbulence, are no more met. However, these phenomena call for further explanation. It seems to be very likely that the widespread and too simplistic ideas on the course of the particle-bubble attachment need substantial adjustments and/or completions. Moreover, the consequences which result from these findings for the hydrodynamic scale-up are discussed. (C) 1998 Elsevier Science B.V.