The effect of flocculant/microparticles retention programs on floc properties

The flocculation of an alkaline fine paper furnish by a cationic flocculant and combinations of a cationic flocculant with colloidal silica or bentonite microparticles was evaluated by scanning laser microscopy (SLM) to derive information on flee properties such as flee size and shear stability. It was found that both types of microparticles affect reflocculation, although colloidal silica forms flocs with higher shear resistance than bentonite. The shear resistance of flocs produced by colloidal silica could be maximized by adjustment of the flocculant dosage. The results of these studies are consistent with a colloidal silica bridging mechanism in which silica molecules form bridges between polymer segments on different particles.