Studies on f locculation and dewatering of kaolin suspensions by anionic polyacrylamide f locculant in the presence of some surfactants L. Besra a, * , D.K. Sengupta a , S.K. Roy b , P. Ay c a Regional Research Laboratory, Council of Scientific and Industrial Research (CSIR), Bhubaneswar 751 013, Orissa, India b Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur 721 302, WB, India c Lehrstuhl Aufbereitungstechnik, Brandenburgische Technische Universitaet, Cottbus 03044, Germany Received 29 May 2001; received in revised form 20 August 2001; accepted 29 August 2001 Abstract 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. C opt. floc c C l /2). Pretreatment of kaolin with all three surfactants form bigger flocs 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 flocs 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. C min. SRF c 0.25C l ). 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 0301-7516/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0301-7516(01)00081-3 * Corresponding author. Tel.: +91-674-481-635; fax: +91-674-581-637. E-mail address: ldbesra@rrlbhu.res.in (L. Besra). www.elsevier.com/locate/ijminpro Int. J. Miner. Process. 66 (2002) 1–28