Aggregation processes serve a critical role in many industrial and environmental strategies. Better understanding and controlling colloidal aggregation can significantly enhance solid-liquid separation processes and thus serve a wide range of industries such as paper manufacturing, water treatment and minerals recovery.
In polyelectrolyte induced colloidal/particle flocculation, the flocculant efficiency is normally adversely affected by the increased ionic strength of colloidal suspension such as the water enclosed system in papermaking. However, the effect of salt on flocculation induced by polyelectrolytes should be double-sided based on the DLVO theory. In addition, when the time scales between the equilibrated polymer adsorption and particle flocculation become comparable, the effect of polymer adsorption kinetics on flocculation becomes more important. Therefore, the current study investigates the precipitated calcium carbonate (PCC) filler flocculation induced by the cationic polyacrylamide (CPAM) under various ionic strengths. The early stage flocculation under all conditions was shown within the non-equilibrium polymer adsorption regimes. The maximum amount of polymer adsorbed on PCC without salt was more than three times of that expected from the simple flat monolayer adsorption of polymer coils. However, the increased ionic strength led to the decreased amount of adsorbed polymer. Nevertheless, the synergy from the appropriate combination of adsorbed CPAM and salt demonstrated to promote the PCC aggregation more efficiently than the same quantity of their individual components. The correlation between polymer adsorption kinetics and flocculation kinetics under different salt concentration are studied to better understand the flocculation mechanism.