Eng. Life Sci. 2013, 00, No. 00, 1–11 1 Rajdeep Chakravarty 1 Md. Motiar R. Khan 1 Akhil R. Das 2 Arun K. Guha 1 1 Department of Biological Chemistry, Indian Association for the Cultivation of Science, Kolkata, India 2 Polymer Science Unit, Indian Association for the Cultivation of Science, Kolkata, India Research Article Biosorptive removal of chromium by husk of Lathyrus sativus: Evaluation of the binding mechanism, kinetic and equilibrium study The adsorption of tri- and hexavalent chromium by the husk of Lathyrus sativus (HLS), which is an agro-waste has been investigated to find a potential solution to environmental pollution. The pH-dependent adsorption process finds the op- timum values for trivalent and hexavalent chromium ions at about pH 5.0 and pH 2.0, respectively. The process is very fast initially and attains an equilibrium within 90 min following pseudo second-order rate kinetics. Equilibrium adsorption data can best elucidated by the Langmuir–Freundlich dual model (r 2 = 0.998) in comparison with other isotherm models examined indicating that both physi- and chemisorption are components of the binding mechanism of chromium ions on HLS. The results show that one gram of HLS can adsorb 24.6 mg Cr 3+ and 44.5 mg Cr 6+ . Fourier transform infrared data and functional group modification experi- ments indicate that –NH 2 , -COOH, -OH, -PO 4 3− groups of the biomass interact chemically with the chromium ions. SEM-energy dispersive X-ray analysis and X-ray diffraction spectrum analysis were used to further assess the morphological changes and the mechanisms of chromium ion interaction with HLS. The analysis signified that the biosorption process involved surface morphological changes, complexation and an ion exchange mechanism. The amorphous nature of HLS facilitating metal biosorption was indicated by the X-ray diffraction analysis. Keywords: Biosorption / Chromium / Lathyrus sativus / SEM-EDXA / XRD  Additional supporting information may be found in the online version of this article at the publisher’s web-site Received: March 26, 2012; revised: August 30, 2012; accepted: September 18, 2012 DOI: 10.1002/elsc.201200044 1 Introduction Heavy metals are imposing large impact on environmental pol- lution as they are toxic and nonbiodegradable. A heavy metal chromium is used in different industries and known to be toxic to most of the living organism [1]. Of the two stable oxidation states, the trivalent chromium is mildly toxic whereas hexavalent chromium is highly toxic, carcinogenic, and mutagenic in na- ture. Considering the biochemical effects [2], the Environmental Protection Agency has set up the limit of 5 mg/L and 0.5 mg/L of Cr(III) and Cr(VI), respectively, [3] in the effluent prior to discharge into waterbodies. The traditional methods such as Correspondence: Dr. Rajdeep Chakravarty (rajdeep.chakravarty @rediffmail.com), Department of Biological Chemistry, Indian As- sociation for the Cultivation of Science, 2A & B, Raja S.C. Mullick Road, Kolkata-700 032, India. Abbreviations: EDX, energy dispersive X-ray; FTIR, Fourier transform infrared; HLS, husk of Lathyrus sativus; SEM, scanning electron micro- scope; XRD, X-ray diffraction ultrafiltration, reverse osmosis, chemical precipitation, or ion exchange [2] suffer from some limitations which involve cost effectivity, inadequate removal or production of huge amount of sludge, etc. The biosorption/bioaccumulation [4–6] methodol- ogy involving metal ion removal from wastewater by adsorption on biological materials has recently attracted considerable atten- tion due to potentiality of decreasing metal ion concentration lower than the permissible limit, low operating cost, surface area availability, metal ions selectivity for adsorption, the possibility of material regeneration, and nongeneration of toxic sludge as compared with the conventional methods. A number of studies dealing with chromium removal were carried out using naturally available biomaterials including microbial biomass [2, 3, 7–10]. Additional correspondence: Prof. Arun K. Guha, Department of Biological Chemistry, Indian Association for the Cultivation of Sci- ence, 2A & B, Raja S.C. Mullick Road, Kolkata-700 032, India. E-mail: bcakg@iacs.res.in Current address: Rajdeep Chakravarty, Department of Chemistry, Regent Education and Research Foundation, Barrackpore, Kolkata, 700 121, India C  2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.els-journal.com