Biochemical Engineering Journal 34 (2007) 69–75 Chromium(VI) removal by calcined bauxite Saroj S. Baral a,∗ , Surendra N. Das a , Pradip Rath b , Gautam R. Chaudhury a a Department of Environmental Management and Inorganic Chemicals, Regional Research Laboratory (CSIR), Bhubaneswar 751013, India b Department of Chemical Engineering, National Institute of Technology, Rourkela 769008, Orissa, India Received 11 April 2006; received in revised form 25 October 2006; accepted 23 November 2006 Abstract The present paper deals with the efficiency of treated bauxite to remove Cr(VI) from a synthetic solution. It includes adsorption of Cr(VI) as a function of contact time, particle size, adsorbent dosage, temperature and initial concentration of the synthetic solution. The treated bauxite (1 g/25 mL) is found to be capable of removing up to 98% of Cr(VI) from solution having low initial concentration (10 mg/L). The adsorption is highest at 45 ◦ C and rate of adsorption is very slow after 5 min. The adsorption isotherm follows both the Langmuir and Freundlich isotherm. The change in the lattice structure of adsorbent before and after calcinations was analyzed by XRD, FTIR and SEM analysis. The thermodynamic and kinetic parameter such as Gibbs free energy, isosteric heat of adsorption and rate constant were calculated. © 2006 Elsevier B.V. All rights reserved. Keywords: Calcined bauxite; Adsorption; Cr(VI) removal; Isotherm; Kinetics; XRD; FTIR; SEM 1. Introduction Cr(VI) is highly toxic in nature [1]. Wastes and effluents from chromite beneficiation, paints and pigments, chrome chem- icals, leather tanning, electro plating industries, etc. are the major sources of Cr(VI). Other industrial effluents contain- ing traces of Cr(VI) include mechanical workshops, glass, ceramic, photography and textile dyeing [2]. Cr(VI) causes diseases like non-healing skin ulcers, nasal septum rupture, allergic dermatitis, lung cancer and renal malfunctioning [3]. The permissible limit of Cr(VI) in potable water is 0.05 mg/L [4], but industrial and mining effluents can be discharged with 0.5 mg/L. Since most of the industrial and mine effluents contain higher than the permissible limit, treatment to reduce/remove the pollutant before discharge into the environment becomes inevitable. There are various methods to treat Cr(VI) contaminated water such as chemical treatment, adsorption, ion exchange, solvent extraction, reverse osmosis, foam floatation, etc. [5]. Among all those processes, adsorption is an economically feasible alter- nate [6]. A variety of materials have been used as adsorbent for Cr(VI) and a number of studies have been reported using adsor- ∗ Corresponding author. Tel.: +91 9861084217. E-mail address: ss baral2003@yahoo.co.in (S.S. Baral). bents like granular activated carbon [7], condensed tanning gel [6], soya cake [8], activated cow dung [9], tires and saw dust [10], activated sludge [11], sulphate-modified titania [12], activated red mud [13], ligno-cellular substrate [14], aminated polyacry- lonitrile fibers [15], fly ash [16], Fe-modified steam exploded wheat straw [5], rice husk based activated carbon [17], etc. Keeping in view the importance of treating Cr(VI) contam- inated water; the present study reports the feasibility of using a new low cost material, i.e., feed bauxite used for alumina extraction. The raw material is available in plenty in the country, especially Orissa and Andhra Pradesh at nominal cost. 2. Experimental 2.1. Material preparation and characterizations A stock synthetic standard solution (10 M) of potassium dichromate (E. Merck, GR grade) was used to prepare the adsor- bate solutions of required strength. The bauxite used in this study was collected from the captive mines of National Alu- minium Company, Pachpatmali, Koraput, Orissa. This bauxite is used as feed for extraction of alumina in their refinery situated nearby. The lumpy sample was crushed and ground to powder form and sieved through 125 m screen. The bauxite sample was pelletised to determine the chemical composition using 1369-703X/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.bej.2006.11.019