COLLOID PARTICLE FLOCCULATION BY WATER-SOLUBLE POLYMERS

This is a review paper of the research work carried out by the group of laboratories in the "Action de Recherches Coordonnees": floculation with water-soluble polymers. The work dealt with model colloids (silica or latex) and (most often) acrylamide polymers. The main parameters governing i) adsorption of these polymers onto the surface of the colloids, ii) the amount of polymers needed for getting optimal floculation (minimum of turbidity for the supernatant liquid) and iii) the floculation kinetics, were studied. These parameters determine the relative contribution of the two main floculation mechanisms, i.e. charge neutralization and interparticular bridging. The structure of the aggregates (flocs) may be observed directly in favorable cases, by transmission electron microscopy after flash congelation. Small angle neutron scattering has been extensively used and lead to nice analysis of the floc structure, chiefly when the situation is not far from equilibrium conditions. Aggregation models have also been used to quantitatively analyze the cluster compacity, through their fractal dimension. The pertinent models for each situation can be selected, using the study of floc size distribution. It may be shown that it is not obviously necessary to introduce the polymers in these models.