Flocculation Kinetics of Precipitated Calcium Carbonate and Its Response to Addition of Various Polymers and Salts

Precipitated calcium carbonate has proved to be economical filler in paper industry due to its technical compatibility, high availability and low price. An optimum amount of filler is important as an excess amount of fillers weaken paper strength by decreasing the fiber–fiber bonded area. In this study, the kinetics of aggregation of industrially applied precipitated calcium carbonate (PCC) were studied by measuring the  particle size distribution, zeta potential, and their response to various flocculants, dispersants and salts. Aggregate diameters (as measured by dynamic light scattering) increased with time but anionic dispersants suppressed agglomeration.  Simple electrolytes suppress agglomeration, while cationic polyelectrolytes caused flocculation. A model based on population balances and incorporating orthokinetic and perikinetic flocculation and also the effect of charge neutralization according to the DLVO theory was developed. The calculations from the model are in good agreement with observations of agglomerate size evolution. The model further enabled predictions of turbulence levels necessary to keep the PCC particles in a dispersed state under different conditions.