Colloids and Surfaces A: Physicochem. Eng. Aspects 279 (2006) 28–33 Removal of phenylamine and catechol by adsorptive micellar flocculation Thiago D’Orsi Almeida a,b,1 , Federico I. Talens-Alesson a,∗ a Scheme, University of Nottingham, UK b Mott MacDonald, Cambridge, UK Received 23 July 2005; received in revised form 15 November 2005; accepted 16 December 2005 Available online 23 January 2006 Abstract The surfactant/water partition ratios for phenylamine in the flocculates formed during adsorptive micellar flocculation (AMF) are found to be around four to five times higher than the ratios reported in the literature for micelle enhanced ultra filtration. Binding ratios phenylamine/surfactant may be as high a 0.25. This suggests that highly soluble organic compounds present in acidic form in aqueous solution are strong candidates for removal by adsorptive micellar flocculation. At concentrations of phenylamine 0.0128M or higher, micelles may not aggregate into large easily filtered flocs if the concentration of Al 3+ is less than 0.024 M, but into small colloidal aggregates in the size range of hundreds of nanometers. It is still possible to remove significant amounts of phenylamine and surfactant by a sequence of filtration of coarse solids and filtration through 200 nm pore membranes. The high efficiency of the smaller, less hydrophobic particles in capturing phenylamine, with binding ratios phenylamine/SDS of 0.35 and higher, strongly supports the view that hydrophobicity cannot be taken as the main reason why micellar flocculates capture contaminants. Cate- chol shows binding ratios up to 0.15, well above binding ratios up to 0.1 for phenol. That, being other properties similar, strong complexant catechol adsorbs much better than phenol, reinforces the view that superficial complexation with Al 3+ is a key mechanism in adsorptive micellar flocculation. © 2005 Elsevier B.V. All rights reserved. Keywords: Adsorptive micellar flocculation; Phenylamine; Catechol; Phenol; Laurylsulphate; Water treatment 1. Introduction For the last 25 years research on the potential of surfactant-mediated separation methods for water treatment has taken place. Topics investigated have included hemimicel- lar/admicellar systems (adsolubilisation) and micellar solutions, the latter in combination with membrane filtration apparatuses (micelle enhanced ultra filtration, MEUF) and phase change devices like changes in temperature to change the hydrophyllic- lipophillic balance of surfactants (cloud point separation). One such technique is adsorptive micellar flocculation. This tech- nique is based on the flocculation of micelles of some anionic surfactants (laurylsulphate and -olefinsulphonate) in the pres- ence of Al 3+ [1,2]. The flocculation process allows the adsorp- tion onto the flocculate of complexes between the flocculant cation and organic species present in solution. This gives the ∗ Correspondence to: Talenco Consulting, Psge Canti 8, 2-2, 08005 Barcelona, Spain. E-mail address: fi.talens-alesson@foreste.com (F.I. Talens-Alesson). 1 Present address: Mott MacDonald, Dememter House, Station Road, Cambridge CB1 2RS, UK. technique some similarities with precipitation–coagulation tech- niques, in which insoluble compounds between organic species and either Al 3+ or Fe 3+ form and their particles are subsequently aggregated by additional amounts of coagulant [3,4], or such compounds are deposited on the surface of solid particles already available [5] or the organic compounds are adsorbed on nascent aluminum hydroxide [6]. 1.1. Interactions organic compound—flocculant cation Because the solution is moderately acidic due to the presence of Al 3+ with pH usually between 3 and 3.5, most compounds investigated so far may be present in anionic form like pes- ticide 2,4-D (pK a 2.85) or in neutral form like phenol (pK a 9.89). However, even in the case of compounds present in the solution as non-dissociated like phenol complexation may take place [7,8]. High local concentration of cations must be expected around the micelles during the flocculation: molar ratios bound Al 3+ to micellar surfactant may be as high as 0.3 [1,9,10]. The results of complex formation under pH conditions similar to those in AMF indicate that at high Al 3+ concentrations the stoichiometries are aberrant (e.g. Benzoic:Al 3+ 1:9) [3,7].A 0927-7757/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2005.12.029