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 l ocal energy dissipation, i.e. the impeller stream, is the active regio n for the realization of the microprocesses bubble dispersion and part icle-bubble attachment. Because of the pressure differences as well as the turbulent pressure fluctuations existing there, it is not unlikel y that gas precipitation influences the attachment events substantiall y. 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 contro lled by turbulence, are no more met. However, these phenomena call for further explanation. It seems to be very likely that the widespread a nd too simplistic ideas on the course of the particle-bubble attachmen t need substantial adjustments and/or completions. Moreover, the conse quences which result from these findings for the hydrodynamic scale-up are discussed. (C) 1998 Elsevier Science B.V.