Classification and breakage of flocs in hydrocyclones

The availability of small diameter (10-50 mm) hydrocyclones allows classification and clarification of aqueous slurries containing fine particles (down to similar to 2 mu m in size). However, in some applications it is necessary to treat ultra-fine sub-micron particles that have been purposely aggregated to increase their apparent size in order to make centrifugal separation feasible. For some time the possibility of processing of slurries containing aggregates (eg ceramics, minerals, pharmaceuticals, fine chemicals, biomaterials, etc) has been considered doubtful since it was presumed that shear forces within the hydrocyclone would tend to render such operations ineffective by breaking up the aggregates. The complex mechanisms involved in the separation of aggregates have not allowed a clear understanding of the breakage-separation process, and no model has been available that considers the breakage and separation of particles simultaneously. This paper demonstrates the feasibility of processing dilute suspensions of aggregates using small diameter hydrocyclones by presenting a critical assessment of previous work, and new experimental measurements employing in-situ particle size, density and mass flow measurements for the process streams coupled with robust data reconciliation procedures. A model to describe the breakage-separation phenomenon is proposed and tested. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.