Mathematical modeling of polymer-induced flocculation by charge neutralization

摘要

A detailed mathematical model for flocculation of colloidal suspensions in presence of salts and polymers is described and validated.In former case,the classical DLVO theory,which accounts for relevant variables such as pH and salt cocnentration,is incorporated into a geometrically sectioned discrete population balance model.For processes involving polymers,flocculation via simple charge neutralization is modeled suing a modified DLVO theory in which the effect of adsorbed polymer layers on van der Waals attraction is included.The fractal dimension of aggregates is obtained by dynamic scaling of experimental data for time evolution of mean aggregate size.The particle surface potential is assumed to be approximatley equal to the zeta potential.The model predictions are in clsoe agreement with experimental results for flocculation of colloidal hematite suspensions in the presence of KCl and polyacryoic acid at different concentrations.In particular,given values of model parameters,e.g.,Hamaker constant,fractal dimension,surface potential,and thickness of adsorbed polymer layer,the model can realistically describe the kinetics of floccualtion by a simple charge neutralization mechanism and track the evolution of floc size distribution.Representative examples of sensitivity of the floccualtion mdoel to perturbations in surface potential and fractal dimension and to modification in the DLVO theory for polymer-coated particles are included.