Gravity separation of concentrated bidisperse suspensions in inclined plate settlers

Abstract

Sedimentation rates of concentrated bidisperse suspensions containing light and heavy particles in inclined channels have been measured for two different fluid-particle systems. The first system consists of spherical polystyrene and polymethyl methacrylate beads in a salt solution and the second consists of spherical polystyrene and glass beads in a sucrose solution. Settling experiments have been conducted in two different rectangular channels of 4 × 6 cm and 3 × 8 cm cross sections. The angle of inclination was varied from 0° to 30° from the vertical. The initial concentration of the light and heavy particles in the suspension was varied from 8 to 20 vol%. The influence of the Boycott effect, due to inclination, and the fingering phenomena, due to lateral segregation, on the separation of the light and heavy particle species within the bidisperse zone was evaluated. The separation rate was found to be significantly influenced by the angle of inclination and the total initial concentration of the suspension. The Boycott effect due to the increasing angle of inclination compliments the separation due to the fingering phenomena up to a certain angle. This limiting angle, beyond which the performance degrades, is found to be a function of total solids concentration.