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| Summary: In this study, the performance of cationic polyacrylamide (KPAM)/bentonite flocculation system on retention of precipitated calcium carbonate (PCC) and dewatering process of fibre-PCC suspension was investigated. As a result of study, the increase in mixing speed caused to decrease in PCC retention and drainage of suspension. It was due to the fact that the delamination of bentonite at higher hydrodynamic forces and transfer of KPAM to bentonite resulted in detachment of PCC aggregates from the fibre surfaces. It was found that the PCC retention increased with increasing bentonite addition and however, at higher KPAM addition, retention decreased because the excess KPAM adsorbed to bentonite resulting in the stabilization of bentonite and decreased its ability to form bridge between PCC particles and fibres. Additionally, dewatering was improved when KPAM and bentonite addition increased.It was also found that with increasing charged carboxyl groups on the fibre surface via CMC modification promoted PCC retention but that is significantly affected with KPAM and bentonite concentration in the suspension and surface modification degree of fibre. On the other hand, the CMC modification of fibre slightly decreased dewatering properties of fibre-PCC suspension. However, it is also showed that that was easily compensated with increasing chemical concentrations. Key Words: Microparticle flocculation system, retention, dewatering, KPAM, Bentonite
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