Modeling flocculation of colloidal mineral suspensions using population balances

02 March 2004 | 14:42 Code : 3629 Geoscience events
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Flocculation as well as dispersion of mineral suspensions has become increasingly important in mineral processing as we have to deal ...
Flocculation as well as dispersion of mineral suspensions has become increasingly important in mineral processing as we have to deal with fine and ultrafine particles. Population balance models for flocculation of such suspensions are discussed in this paper. Models ranging from those based on pure aggregation and fragmentation to those based on simultaneous aggregation–fragmentation are presented in detail. The two important parameters in the population balance model are the collision frequency factor and the collision efficiency factor. Differences among collision frequency models for impermeable and permeable aggregates are described. The main drawback of existing flocculation models is the disregard of forces between mineral particle surfaces. The collision efficiency is usually assumed to be unity or employed as a fitting parameter in a majority of the models. An approach for incorporating the influence of surface forces in the presence of salts and polymers is outlined. Another important lacuna of flocculation models is the assumption of homogeneous flow structure or uniform fluid velocity gradient in stirred flocculation tanks. Short-cut procedures adopted in the literature to address heterogeneous fluid flow structure are summarized. It is also stressed that an integrated approach be followed to tackle practically relevant issues such as selective flocculation of mineral mixtures, dual polymer flocculation, dynamics of polymer/surfactant adsorption, polymer–surfactant interactions, surface precipitation of dissolved species and presence of air bubbles in the suspension. P. Somasundaran

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