Modelling PCC flocculation by bridging mechanism using population balances : Effect of polymer characteristics on flocculation

Abstract

A population balance model for flocculation of PCC particles with polyelectrolytes of very high molecular weight, medium charge density and different degree of branching is presented. The model considers simultaneously aggregation, breakage and flocs restructuring to describe the PCC flocculation by bridging mechanism. The maximum collision efficiency factor, a parameter related with the fragmentation rate and a time constant for flocs restructuring have been taken as fitting parameters. These fitting parameters are optimized to get the best fit between experimental data obtained by LDS in a previous study and the modelled results. The optimized parameters were correlated with flocculant concentration, flocs structure and polymer branching. The correlations obtained show well the effects of flocculant concentration, flocs structure and polymer structure on the flocculation kinetics and flocs restructuring which are translated in the model parameters. Moreover, the flocs break up due to polymer degradation was introduced in the model by decreasing, with time, the maximum collision efficiency factor. It was shown that this effect can be neglected since the improvement in the results is too small relatively to the high increase of the computational time required to perform the simulation