6 - Sedimentation and thickening

Abstract

This chapter discusses the basic principles of batch and continuous settling, and applies it to the analysis of the operation of industrial thickeners. The solids content of a slurry can be increased using sedimentation techniques. The natural tendency of the solids to settle under the influence of gravity is exploited to remove some of the water from the slurry. When the particles that make up the slurry are small, the settling is quite slow and special techniques are required to achieve a separation. Because of the slow rates of settling that are commonly encountered, comparatively large equipment is required. Thickening is an important process for the partial dewatering of comparatively dense slurries. Essentially, the slurry is allowed to settle under gravity but the particles are so close together that they hinder each other during settling, and they tend to settle as a mass rather than individually. The rate of settling is a fundamental characteristic of the slurry, which must be determined experimentally for each slurry under appropriate conditions of flocculation, in order to design and size an appropriate thickener.