COLLOIDAL FILTRATION AND (SIMULTANEOUS) SEDIMENTATION OF ALUMINA AND SILICA SUSPENSIONS - INFLUENCE OF AGGREGATES

Colloidal filtration and (simultaneous) sedimentation is studied for suspensions of alumina particles and monodisperse silica spheres. A comparison is made between stable suspensions and systems which are aggregated due to salt addition (silica) or absence of a deflocculant (alumina). From separate sedimentation experiments we conclude that the stable silica settles as an ordered particle array, that the unstable silica sediments as separate aggregates, and that aggregated aluina behaves as a densifying network. The filtration results show that settling of aggregates during filtration changes the filtration kinetics in accordance with our model for simultaneous filtration and sedimentation. Further, aggregates in suspension are shown to have little influence on the silica compact microstructure, whereas they clearly increase porosity and permeability of the alumina compact. We also find that for all suspensions porosities of compacts prepared by sedimentation are clearly larger then porosities of filter compacts. Copyright © 1990, Wiley Blackwell. All rights reserved