Flocculation and dewatering of kaolin suspensions in the presence of polyacrylamide and surfactants

Flocculation, as a result of the interaction between non-ionic polyacrylamide polymer (PAM-N) and kaolin surface in aqueous suspension, has been discussed both in the absence and in the presence of surfactants namely, cationic cetyl trimethyl ammonium bromide (CTAB), anionic sodium dodecyl sulphate (SDS) and non-ionic TX 100. The results of separation properties have been discussed in the light of kaolin surface charge, PAM-N and surfactant adsorption,including conformation of the adsorbed polymer and properties of solution due to mutual interaction of polymer and surfactants. The kaolin settling rate improves by more than twentyfold through flocculation by PAM-N. Flocculation also reduces the specific resistance to filtration (SRF) from 7.8 x 10(11) to 1.1 x 10(11) m/kg. The high molecular weight polymer, however, entraps excess water in the flocs resulting in very high cake moisture content. Pretreatment with either of the surfactants reduces the adsorption of nonionic PAM due to blocking of some surface sites by surfactant molecules. The polymer under these circumstances assumes different conformation favouring conditions for better flocculation by bridging and increases settling rate. Though flocculation of the surfactant pretreated kaolin does not reduce SRF, the cake moisture is reduced substantially. Addition of PAWN from a mixture with surfactants leads to increase in PAWN adsorption on kaolin, but it decreases settling rate as well as moisture content of the filter cake without any change in the SRF value. (C) 2002 Elsevier Science B.V. All rights reserved.