Mechanische Verfahrenstechnik und Aufbereitung

Ultrasound supported Flotation

Froth flotation can be intensified by applying ultrasound at different stages of the process, leading to improved separation behaviour. The ultrasound-induced effects are primarily caused by the phenomenon of cavitation. The alternate sonic pressures generates vapour bubbles that grow and implode with high velocities, thereby applying high pressures, high shear stress and high temperatures. Effective cavitation, i.e. a locally and temporally concentration of energy, only appears in case of inharmonically oscillating bubbles, having diameters smaller than the called resonance diameter.
Further parameters, that influence the cavitation are:

  • Ultrasound frequency: The cavitation threshold and rises the necessary energy with increasing frecency while the bubble diameter decreases. The latter directly affects the heat transfer between bubble and surrounding liquid.
  • Ultrasound intensity depending on oscillation amplitude: Cavitation increases with rising intensity, limited by the decoupling of ultrasound transducer and liquid in the presence of too many cavitation bubbles.
  • Temperature: Close to the boiling point of a lot cavitation bubbles are generated simultaneously, which dampen the ultrasound propaganation and energy. Temperatures optimal for cavitation depend on the liquid.
  • External pressure: Increasing pressure raises the energy necessary for reaching the cavitation threshold, lesding to intensified implosions.
  • Particle surfaces: The cavitation requires the solid-liquid interface as a seed for bubble generation. Therefore cavitation is facilitated by increasing hydrophobic properties of the particle surface.

Ultrasound supported flotation has been used to improve the fine coal flotation and cleaning of PHC and PAH contaminated soil.

References

H.Z. Kuyumcu und S. Özkan:Investigations of effects of ultrasonic waves on various phases of froth flotation, Proceedings of XXIII. International Mineral Processing Congress, Vol. 1, ISBN 975-7946-27, Istanbul 2006, S. 598-603

H.Z. Kuyumcu und S. Özkan: The Influence of Ultrasonics on Coal Flotation, Aufbereitungs Technik 47 (2006), Nr. 1-2, S. 23-33

H.Z. Kuyumcu und J. Rosenkranz: Investigation of the Effect of Ultrasound on the Froth Flotation of Fine Soil contaminated with PHC and PAH. Proceedings of XI. International Mineral Processing Symposium, Ankara 2008, S. 881 - 889