Shear-induced flocculation: The evolution of floc structure and the shape of the size distribution at steady state |
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Affiliation: | 1. College of Agriculture, Ibaraki University, Chuo 3-21-1, Ami-machi, Inashiki-gun, Ibaraki 300-0393, Japan;2. Research and Development, Earth Environmental Service Co., Ltd., Higashikanagawa 2-33-1, Kanagawa-ku, Yokohama-shi, Kanagawa 221-0044, Japan;1. CSIRO Mineral Resources, Waterford, Western Australia, Australia;2. Complex Systems Group, Department of Mathematics and Statistics, University of Western Australia, Australia;3. CSIRO Mineral Resources, Kensington, Western Australia, Australia |
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Abstract: | The flocculation of polystyrene particles in a stirred tank was studied at various shear rates (63–129 s−1) and aluminum sulfate, Al2(SO4)3 16H2O, flocculant concentrations. The competition between coagulation and fragmentation during shear-induced flocculation determined the equilibrium or steady state particle (floc) structure and size distribution. The evolution of the floc structure with time was monitored by image analysis of digitized floc images. The average floc structure became less open or irregular as the floc size distribution attained steady state as a result of shear-induced breakage/restructuring. At high alum (flocculant) concentrations, the steady state floc size distribution appeared to be self-preserving with respect to shear rate. In contrast, at lower flocculant concentrations, the steady state floc size distribution narrowed with increasing shear rate as the large tail of the distribution was pushed to smaller particle sizes by shear-induced fragmentation. |
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