Studies on flocculation and dewatering of kaolin suspensions by anionic polyacrylamide flocculant in the presence of some surfactants

This paper reports the results of studies on flocculation and dewatering of kaolin suspensions by anionic polyacrylamide (PAM-A) flocculant in the presence of surfactants. They were namely anionic Sodium Dodecyl Sulphate (SDS), cationic Cetyl Trimethyl Ammonium Bromide (CTAB) and a non-ionic surfactant of polyoxyethylenic ether with trade name Triton X-100. The adsorption of PAM-A on kaolin is governed by a combination of both physisorption and chemisorption. The optimum flocculation concentration of PAM-A for fresh kaolin as well as surfactant-pretreated kaolin corresponds to about 50% coverage of the surface (i.e. Gamma(opt.floc) approximate to Gamma(infinity)/2). Pretreatment of kaolin with all three surfactants form bigger floes with PAM-A. The highest settling rate and the minimum specific resistance of the cake to filtration (SRF) are obtained by flocculating the SDS-pretreated kaolin. The floes thus formed are suitable for filtration and reduce SRF substantially. The PAM-A concentration corresponding to the minimum SRF in all the cases is sufficiently lower than that required for optimum flocculation, and the adsorption density is about 25% of the plateau adsorption density (i.e. Gamma(min. SRF) approximate to 0.25Gamma(infinity)). The influence of simultaneous addition of PAM-A and surfactants from their mixtures on flocculation and dewatering of kaolin suspension is dependent on the nature of mutual interaction of PAM-A and surfactant. Simultaneous addition of PAM-A with either SDS or TX 100 increases settling rate, whereas it decreases when added from its mixture with CTAB. The cake moisture content when both polymer and surfactants are present is governed more by the effect of polymer than the surfactant. (C) 2002 Elsevier Science B.V. All rights reserved.