Wetting Technologies for High-Accuracy Sink-Float Separations in Water- Based Media
B. Hu*, 1, N. Fraunholz2, P. Rem1
Identifiers and Pagination:Year: 2010
First Page: 71
Last Page: 80
Publisher Id: TOWMJ-3-71
Article History:Received Date: 19/10/2009
Revision Received Date: 05/11/2009
Acceptance Date: 25/11/2009
Electronic publication date: 14/12/2010
Collection year: 2010
open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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.