摘要： The accuracy of sink-float separations in water-based media such as Magnetic Density Separation is
compromised by tiny air-bubbles attached to the surface of hydrophobic materials in the feed. Separations of plastics
mixtures with accuracy better than 10 kg/m3 require a total elimination of air-bubbles by pre-wetting the surface of the
feed particles with a thin film of water. Theoretical and experimental results are compared for pre-wetting processes based
on condensation from the gas phase and direct liquid-solid contact for both shredded waste and virgin polymers. The tests
show that the wettability of most polymers improve slightly by steaming for about 1 minute, but the best wetting results
are obtained with immersion in boiling tap water. The success of wetting in boiling water can be explained by the
deposition of a thin layer of calcium carbonate. Shredded plastics are easier to be wetted than virgin polymers, probably
because a relatively rougher surface is caused by the shredder process. A new wetting process to eliminate air bubbles was
developed on the basis of these results, which carries a minimal amount of heat and water with the feed to the MDS
process liquid.
