The effects of dissolved and colloidal substances on flocculation of mechanical pulps

The effect of dissolved and colloidal substances (DCS) on chemical-induced flocculation of a bleached mechanical pulp was probed using the technique o f focused-beam reflectance measurement (FBRM), also known as scanning laser microscopy (SLM). Addition of DCS to washed fibres decreased the extent of aggregation induced by a cationic polyacrylamide (C-PAM) flocculant and co lloidal sodium montmorillonite (NaM) or anionic colloidal silica (ACS). The flocculation activity of the sodium montmorillonite or anionic colloidal s ilica was more sensitive to DCS addition than that of the cationic floccula nt. Addition of low MU: high charge-density cationic coagulants largely rev ersed the detrimental effects of the DCS and restored the flocculation indu ced by the C-PAM and the anionic colloidal silica. The DCS was separated in to a dissolved and a colloidal component, and the effect of these individua l constituents on the extent of aggregation induced by the C-PAM and the an ionic colloidal silica was examined.