Journal of Hazardous Materials 144 (2007) 464–469 Solid phase extraction of chromium(VI) from aqueous solutions by adsorption of its ion-association complex with cetyltrimethylammoniumbromide on an alumina column N. Rajesh a,∗ , B. Deepthi b , Archana Subramaniam b a Department of Chemistry, Birla Institute of Technology and Science, Pilani 333031, India b Department of Chemical Engineering, Birla Institute of Technology and Science, Pilani 333031, India Received 30 August 2006; received in revised form 16 October 2006; accepted 17 October 2006 Available online 26 October 2006 Abstract A simple approach has been developed for the solid phase extraction of chromium(VI) based on the adsorption of its ion-association complex with cetyltrimethylammoniumbromide (CTABr) on an alumina column. The effect of various parameters such as acidity, stability of the column, sample volume, effect of diverse ions, etc. have been studied in detail. The adsorbed complex could be eluted using sodium hydroxide and the concentration of chromium has been established using visible spectrophotometry after complexation with diphenyl carbazide. The calibration graph was linear in the range 0–0.5 g mL -1 chromium(VI) with a detection limit of 5 gL -1 . A highest preconcentration factor of 25 could be obtained for 250 mL sample volume. The data from the column studies were also studied using the Thomas model of adsorption. The experimental results obtained were correlated with the proposed model of adsorption. The Thomas rate constant k was found to be 0.0025 L/min mg and the maximum adsorption capacity q o was found to be 0.36 mg Cr/g alumina at an initial chromium(VI) concentration of 1 mg L -1 . The validity of the method has been checked by applying it to study the recovery of chromium in spiked water samples and electroplating wastewater. © 2006 Elsevier B.V. All rights reserved. Keywords: Chromium(VI); Cetyltrimethylammoniumbromide; Alumina; Solid phase extraction; Thomas model 1. Introduction The considerable emphasis on the removal of toxic metal ions led to the development of a variety of analytical methodolo- gies. Hence, there has been considerable growth in the analytical chemistry of various metal ions. Chromium is not an exception to this. Among the stable oxidation states of chromium, Cr(III) is an essential dietary mineral in low doses, whereas Cr(VI) is carcinogenic [1]. In view of the toxic nature of chromium(VI), development of methods in order to establish their levels in the environment and industrial quality control are quite significant. Solid phase extraction has been explored for the preconcentration of many metal ions [2–5]. A variety of adsorbents have been used for the preconcentration of chromium [6–13]. ∗ Corresponding author. E-mail address: rajesh@bits-pilani.ac.in (N. Rajesh). A survey of the literature for the preconcentration of chromium(VI) reveals that solid phase extraction is one of the versatile methods. The major advantage of solid phase extrac- tion is the high selectivity and enrichment factor that could be achieved in this method. Among the various adsorbents, silica and alumina have been extensively studied for the adsorption of chromium. In this paper, a simple methodology is proposed for the solid phase extraction of chromium based on the adsorption of its ion-association complex with cetyltrimethylammonium- bromide on a basic alumina column. The adsorbed complex could be easily eluted using sodium hydroxide and the recovery of chromium was established using visible spectrophotometry after complexation with diphenyl carbazide. The effects of vari- ous experimental parameters such as sample volume, volume of eluent, flow rate, effect of diverse ions, etc. were studied in detail. The data from the column studies were fitted with the Thomas model of adsorption. The validity of the proposed method was checked by applying it to the determination of chromium in spiked water samples and electroplating wastewater. 0304-3894/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2006.10.059