An extended model for the estimation of flocculation efficiency factors in multicomponent flocculant systems

A model for the flocculation efficiency in flocculant systems consisting of up to three components (a low molecular weight (MW) cationic polymer, a high MW cationic polymer and an anionic particle sol) is presented. The model is based on the classical bridging mechanism, Extensions have been carried out to take into account the addition of low MW polymers making surface sites inaccessible for bridging polymers, the flocculation induced by the addition of anionic microparticles, and the conformation of the adsorbed high MW polymer layer. According to this model, the collision efficiency is a function of the degree of surface coverage of the suspended particles by low MW polymer, the degree of surface coverage by high MW polymer, and the addition of a third component which interacts with adsorbed high MW cationic polymers. In the experimental work, the model was tested by determining adsorption isotherms, by flocculation experiments on suspensions of cellulosic fibres and by experiments on a pilot paper machine. The model was found to give a good qualitative description of the experimental results.