Polymer flocculation of calcite: Relating the aggregate size to the settling rate

The initial hindered settling velocities of flocculated calcite suspensions have been related to the mean aggregate sizes and solid fraction under a range of flocculation conditions that are similar to those occurring within a mineral processing thickener. Calcite particles were flocculated in turbulent pipe flow and the aggregates sized with an in situ probe (Lasentec FBRM). The flocculated suspension then flowed into vertical column used to measure the hindered settling velocity. This allowed the investigation of key flocculation parameters - the flocculant dosage, the primary particle size, the suspension solid fraction and the fluid shear rate. The hindered settling velocity was related to the mean aggregate size using a relationship based on Richardson and Zaki's extension of Stokes' law. The effect of aggregate porosity was incorporated using fractal geometry, allowing the estimation of the fractal dimension (2.4) from experimental data. It is an important step toward the development of a link between the size of aggregates produced by flocculation, and their settling and dewatering characteristics. This is also an essential step in the development of robust process models describing the performance of gravity thickeners which are widely used throughout the minerals and other industries. (c) 2006 American Institute of Chemical Engineers.