Consolidation and aggregate densification during gravity thickening

A continuous laboratory column system has been used to investigate the cons olidation behaviour of kaolin slurries flocculated by a nonionic flocculant under different conditions. Measurements of the steady-state bed density p rofile showed that higher agitation intensities during flocculation resulte d in lower bed densities. The relative importance of compression versus she ar for kaolin dewatering was determined by operating the steady-state colum n system at different bed heights above a mechanical rake. It was found tha t rake action, not compression, was the dominant dewatering mechanism. Samp les taken from the consolidating bed before and after the rake were analyse d by microscopy to determine the density-size relationship of the individua l aggregates. This showed that the dewatering induced by the rake action oc curred not only by removal of inter-aggregate liquor but also by densificat ion of the aggregates (i.e. removal of intra-aggregate liquor). Measurement s made on full-scale thickeners are also presented which demonstrate simila r behaviour. (C) 2000 Elsevier Science B.V. All rights reserved.