The role of polymer adsorption kinetics in flocculation

The adsorption of polymeric flocculants on the surfaces of suspended solid particles is a non-equilibrium process. It is postulated that the process is controlled by an irreversible attachment between polymer molecules and solid particles. The frequency of such collisions determines the kinetics of adsorption and the distribution of adsorbed polymer on individual particle surfaces. A simplified model is presented in which polymer-particle collision frequencies determine the distribution of adsorbed polymer, and therefore, the adhesion efficiency of the particle-particle collisions that lead to flocculation. The implications of the model with regard to the effects of process variables, such as polymer molecular weight, particle size distribution, solids concentration and mixing conditions, are discussed at length. The critical importance of initial dispersion stability on polymer dosage requirements and overall process performance is demonstrated. The model provides considerable insight into the mechanisms involved in the use of progressive polymer addition to control adsorption and enhance flocculation efficiency. (C) 1999 Elsevier Science B.V. All rights reserved.