Compressibility and channel formation in sedimenting systems

Channelling and compression in batch and continuous gravity sedimentation systems have been investigated using an electrical impedance imaging technique. The accuracy of such a system is shown to be a function of a number of variables, in particular particle morphology. Not all materials were found to be suitable to this form of imaging. Three primary materials, aragonite, calcite and talc were used, each exhibited random channelling, i.e. channel formation was not due to the presence of foreign bodies or externally induced. Channels in this type of channelling form within a zone which grows and propagates upwards into a suspension. Through visual observations this region has been sub-divided into hard and soft zones. Superposition of zone propagation on characteristic (loci of concentration) plots has yielded information on the conditions required for channel formation and growth and has led to a revised set of conclusions on the nature of random channelling. [Continues.]