Technical Note Calcined tetrabutylammonium kaolinite and montmorillonite and adsorption of Fe(II), Co(II) and Ni(II) from solution Krishna G. Bhattacharyya a, ⁎, Susmita Sen Gupta b a Department of Chemistry, Gauhati University, Guwahati 781014, Assam, India b Department of Chemistry, B N College, Dhubri 783324, Assam, India abstract article info Article history: Received 20 December 2008 Received in revised form 5 August 2009 Accepted 6 August 2009 Available online 12 August 2009 Keywords: Kaolinite Montmorillonite Fe(III), Co(II) and Ni(II) Adsorption Kinetics Kaolinite and montmorillonite were modified with tetrabutylammonium (TBA) bromide, followed by calcination. The structural changes were monitored with XRD, FTIR, surface area and cation exchange capacity measurements. The modified clay minerals were used for adsorption of Fe(III), Co(II) and Ni(II) ions from aqueous solution under different conditions of pH, time and temperature. The uptake of the metal ions took place by a second order kinetics. The modified montmorillonite had a higher adsorption capacity than the corresponding kaolinite. The Langmuir monolayer capacities for the modified kaolinite and montmorillonite were Fe(III): 9.3 mg g -1 and 22.6 mg g -1 ; Co(II): 9.0 mg g -1 and 22.3 mg g -1 ; and Ni(II): 8.4 mg g -1 and 19.7 mg g -1 . The modified kaolinite interacted with Co(II) in an endothermic manner, but all the other interactions were exothermic. The decrease of the Gibbs energy in all the cases indicated spontaneous adsorption. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Water is particularly vulnerable to contamination from discharge of wastewaters by various industries. The tremendous increase in the use of heavy metals over the past few decades has inevitably resulted in an increased flux of metallic substances into the aquatic environment. Adsorption is a promising technique for regulating mobility of chemical species and their geochemical cycles in the environment. A variety of conventional and non-conventional adsorbents have been tried to remove different metal ions from aqueous solutions. A few examples are removal of Pb(II) on slag (Dimitrova, 2002), Cd(II), Zn(II) on red mud (Gupta and Sharma, 2002), Pb(II), Cr(VI) on fly ash (Gupta and Ali, 2004), Zn(II), Cd(II) on low-grade phosphate (Kandah, 2004), As(III) on treated sand (Gupta et al., 2005), Cu(II) (Gupta et al., 2006) and Pb (II) (Gupta and Rastogi, 2008) on Spirogyra species, etc. Being an important constituent of soil, the clay minerals take up various contaminants from water as it flows over soil or penetrates underground. The surface properties of the clay minerals can be modified by replacing the inorganic interlayer cations by quaternary ammonium ions (Kukkadapu and Boyd, 1995; Lagaly et al., 2006). Intercalation of TMA (tetramethylammonium), TMP (tetramethylpho- sphonium) and PTMA (phenyl trimethylammonium) ions into mont- morillonite (Stevens and Anderson, 1996; Lawrence et al., 1998; Lagaly et al., 2006) has been found to infer significant changes in the adsorption properties. Preparation of N, N′-didodecyl-N, N′-tetramethylethane diammonium (DEDMA) montmorillonite has also been reported (Akcay et al., 2006). Li and Bowman (2001) prepared hexadecyl trimethylammonium-kaolinite for removal of inorganic oxyanions, namely, nitrate, arsenate and chromate. Adsorption of heavy metal ions on organo-clays is comparatively limited. Changes in adsorption properties of kaolinite and montmorillonite modified with tetrabuty- lammonium ions have been previously reported with respect to Pb(II) adsorption (Sen Gupta and Bhattacharyya, 2005), Cd(II) (Sen Gupta and Bhattacharyya, 2006), and Cu(II) adsorption (Bhattacharyya and Sen Gupta, 2006). 2. Experimental 2.1. Preparation of TBA-kaolinite (K1) and montmorillonite (M1) Kaolinite, KGa-1b, and montmorillonite, SWy-2, used for the experiments were obtained from Source Clay Minerals Repository, University of Missouri-Columbia, USA. TBA-kaolinite (K1) and mont- morillonite (M1) were prepared by reaction with tetrabutylammonium bromide, (C 4 H 9 ) 4 N + Br - (CDH, Mumbai, India) (Mortland et al., 1986). 2.2. Preparation of aqueous solutions of the metal ions Stock solutions containing 1000 mg of metal ions per litre were prepared by dissolving appropriate amount of Fe(NO 3 ) 3 ·9H 2 O (E. Merck, Mumbai, India), Co(NO 3 ) 2 ·6H 2 O (E. Merck, Mumbai, India) and Ni(NO 3 ) 2 ·6H 2 O (Qualigens, Mumbai, India) in twice Applied Clay Science 46 (2009) 216–221 ⁎ Corresponding author. Tel.: +91 361 2571529; fax: +91 361 2570599. E-mail address: krishna2604@sify.com (K.G. Bhattacharyya). 0169-1317/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2009.08.006 Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay