Abstract
A continuous laboratory column system has been used to investigate the consolidation behaviour of kaolin slurries flocculated by a nonionic flocculant under different conditions. Measurements of the steady-state bed density profile showed that higher agitation intensities during flocculation resulted in lower bed densities. The relative importance of compression versus shear for kaolin dewatering was determined by operating the steady-state column system at different bed heights above a mechanical rake. It was found that rake action, not compression, was the dominant dewatering mechanism. Samples taken from the consolidating bed before and after the rake were analysed by microscopy to determine the density–size relationship of the individual aggregates. This showed that the dewatering induced by the rake action occurred not only by removal of inter-aggregate liquor but also by densification of the aggregates (i.e. removal of intra-aggregate liquor). Measurements made on full-scale thickeners are also presented which demonstrate similar behaviour.
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