THE FLOCCULATION OF KAOLIN SUSPENSIONS WITH ANIONIC POLYACRYLAMIDES OF VARYING MOLAR MASS AND ANIONIC CHARACTER

Standard kaolin suspensions were flocculated using anionic polyacrylamides of varying molar mass and charge density. Flocculant performance was assessed by determining the extent of polymer adsorption, the subsidence rates of the flocculated suspensions, the residual turbidities of the supernatant, the mobilities of the particles and floc size. The sol concentration was kept constant at 20 g kaolin dm-3 in 10-3mol dm-3NaCl solution; the pH was varied from 3 to 10. Subsidence rates increased with dosage and molar mass, and followed the trend in polymer adsorption. The subsidence rates are less than cationic polyacrylamides of the same molar mass and charge density, and maximum values are reached at much lower dosages. The polymer charge, which is of the same sign as the clay particles, does not counteract the molecular lengths in determining the capability of flocculation by polymer bridging, although the flocs formed had an open structure in contrast to those formed by cationic polyacrylamides. Above pH 7 the polymer could not counteract the increasing self-repulsion of the clay particles with resulting inadequate flocculation. © 1990.