ABSTRACT
I. Introduction ................................................................ 768 II. Stability of Suspensions in the Presence of
Surfactants, Polymers, and their Mixtures............... 769 A. Effect of Surfactants ........................................... 770 B. Effect of Polymers ............................................... 774 C. Multipolymer Flocculation.................................. 781 D. Mixed Polymer-Surfactant Systems.................. 783
III. Population Balance Model for Flocculation............... 788 A. Kinetics of Aggregation....................................... 789 B. Kinetics of Fragmentation.................................. 792 C. Collision Efficiency.............................................. 794
1. Salt-induced Coagulation ............................. 796 2. Systems involving Polymers......................... 797
D. Dynamics of Polymer Adsorption....................... 798 IV. Concluding Remarks................................................... 799 Acknowledgments................................................................ 800 References............................................................................ 800
I. INTRODUCTION
Flocculation and dispersion of colloidal suspensions are important unit operations in many industries such as pulp and papermaking [1], mineral and ceramics processing [2,3], and water treatment [4], to name a few. Flocculation plays a major role also in the fate and transport of contaminants in aquatic environments [5]. Polymers and polyelectrolytes, inorganics, and surfactants are commonly used either to flocculate or to disperse a suspension. Flocculation is a complex phenomenon that involves several steps or subprocesses occurring sequentially or concurrently. These include: (i) mixing of particles and polymers or surfactants in solution, (ii) adsorption of the polymer or the surfactant molecules on particle surfaces, (iii) reconformation of adsorbed chains on the surface, (iv) formation of aggregates due to salt, polymer, or surfactant, (v) breakage of flocs by shear, (vi) restructuring of flocs, (vii) reflocculation of broken flocs, (viii) desorption of polymer under high shear, and (ix) subsidence or sedimentation or creaming of flocs.
