| Summary: | An extensive review and discussion relating to surface properties of solids in aqueous media, sedimentation and flocculation of suspensions are presented. Attention is given to the properties of polymeric flocculant solutions and to factors affecting the behaviour of flocculated suspensions. The effects of prolonged stirring on the viscosities of polymer flocculant solutions have been investigated. It is shown that a slight decrease in viscosity with prolonged stirring occurs even at moderate stirring rates. The viscosity decrease is attributed to molecular degradation which is strongly affected by the ionic nature of both flocculant and medium. The research was mainly devoted to the study of the properties of suspensions flocculated by different agitation methods. The methods employed included inverting and rotating cylinders, mechanical stirrers and agitation by plunger and cyclone. Experimental apparatus and technique are described by which settling rate, sediment volume, clarity of supernatant liquid and compressive strength of sediment may be conveniently measured. The following exponential relationship was found to exist between the compressive strength, a, and the solids volume fraction, c, of flocculated sediment: n(c-c z) o = a. e where the constants a, n and c were dependent on the type of agitation and flocculant dosage. The properties of flocculated suspensions are shown to be considerably affected by the type of agitation used. It appears that the suitability of an agitation method is dependent on the requirements of subsequent processes.
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