Regularities in pressure filtration of fine and colloidal suspensions

Abstract

A number of interesting and potentially useful regularities have been observed in high pressure batch filtration of fine and colloidal suspensions carried out to equilibrium under a wide variety of physical and chemical process conditions. Two such regularities are described here. The first regular behavior, demonstrated by a large number of colloidal suspensions, can be represented by the Pareto profile, which relates filtration rate with solid content of filter cake at equilibrium. The profile is found to be a strong function of material fineness but is seemingly independent of physical and chemical process conditions. Since it can be treated as a constrained performance benchmark for the filtration of a suspension, it is germane for evaluating the filtration process in terms of two of its more important process measures, namely, kinetics and maximum extent of dewatering that is achievable. The Pareto regularity reflects the fact that in general it is not feasible to improve both measures simultaneously in a batch filtration which is driven to equilibrium, and any process modification may improve one measure but invariably at the expense of the other. The second regular behavior, namely, self-similarity in pressure filtration is demonstrated for filtration of wide variety of varying materials and process conditions. Simple transformation and scaling of slurry filtration data with critical solid volume fraction and critical time at the transition from cake formation stage to cake consolidation stage translate the filtration curves into a form which are remarkably self-similar. This self-preserving behavior is demonstrated for a wide variety of experimental data under varying physical and chemical process conditions for different colloidal systems. Some implications of the regularities are discussed.