Expression behaviour of fine particle suspensions and the consolidated cake strength

Abstract

The high-level expression of suspensions up to 50 bar is concerned with the recovery of finest particles, e.g. submicron particles. A so-called Press-Shear-Cell was designed, constructed and tested to measure the most important filtration process parameters. In a first filtration stage, a compressible filter cake builds up from a fine particle suspension. The following cake consolidation is applied to reduce the liquid amount in the small pores of the particle packing. To describe the two-stage expression process of fine sludge, a new dynamic model is introduced. In contrast to the common Tiller–Shirato model, which assumes constant average material properties of particle pressure p s, packing density ε s and permeability k inside the cake during constant pressure expression, the new dynamic expression model considers the time and local variation of these material properties. Furthermore, the wall friction resistance is taken into account with the wall friction angle ϕ W and the lateral pressure ratio λ of the cake. The pressure-dependent constitutive functions of kaolin and titanium dioxide filter cakes are shown. Yield loci in a water saturated particle packing were in situ measured with comparatively high normal loads of 100–1000 kPa.