Ram Prakash et al. Int. J. Res. Chem. Environ. Vol.3 Issue 4 October 2013(61-67) [61] International Journal of Research in Chemistry and Environment Vol. 3 Issue 4 October 2013(61-67) ISSN 2248-9649 Research Paper Removal of Hexavalent Chromium by Using Mangifera Indica Bark (Biosorption) Supriya Singh 1 , Tripathi Alka 1 , Srivastava S. K. 2 , *Ram Prakash 2 1 Department of Applied Sciences, Institute of Engineering & Technology, Lucknow- 226021, (U.P.), INDIA 2 Central Ground Water Board, MoWR, Govt of India, Bhujal Bhawan, Lucknow- 226021, (U.P.), INDIA Available online at: www.ijrce.org (Received 14 th August 2013, Accepted 25 th September 2013) Abstract: Presence of the toxic metal chromium (hexavalent) as pollutant in surface / ground water found at various locations is either due to the discharge of untreated chromium containing effluents or dumped solid wastage containing chromium salts which is followed by leaching into water bodies. The existence of this metal in hexavalent form is one of the most important environmental issues due to its health impacts on human. Adsorption is one of the effective techniques for chromium (VI) removal from wastewater. Here studies are carried out for chromium (VI) removal, by using biosorbent, which is prepared from Mangifera indica bark. The parameters investigated in this study are contact time, adsorbent dosage, temperature, variable initial chromium (VI) concentration and pH. The adsorption processes of chromium (VI) are tested with Linear, Langmuir and Freundlich isotherm models. Application of the Langmuir isotherm to the systems yielded maximum adsorption capacity of 19.64 mg/g at 30 o C in 50 mg/L Cr (VI) solution of pH- 7 and biosorbent dose of 1g/L. The adsorption of chromium (VI) was found to be maximum up to 80.2% at low values of pH – 2 having Cr (VI) concentration of 50 mg/L and adsorbent dose of 1g/L. The contact time of 60 min resulted to the 67% adsorption of metal in 5mg/L solution using adsorbent dose of 1g/L. Here FTIR spectra were also carried out to correlate the adsorption sites of biosorbent and hexavalent chromium. Keywords: Adsorption capacity, Chromium (VI), Mangifera indica bark, Linear, Freundlich & Langmuir isotherm. Introduction Presence of chromium (VI) in the surface and ground water is hazardous to the environment because of its high toxicity. Due to its high potentiality to contaminate drinking water sources [1] , possible human health risk occurs and it finally pollute our ecosystem. In recent years, increasing awareness of water pollution and its far reaching effects has prompted concerted efforts towards pollution abatement. Among the different heavy metals, chromium is a common and very toxic pollutant introduced into natural waters from a variety of industrial wastewaters [2] . The two major sources of contamination are tanneries (trivalent chromium), electroplating and metal finishing industries (hexavalent chromium). Chromium occurs most frequently as Cr (VI) or Cr (III) in aqueous solutions [3] . Both valency of chromium are potentially harmful but hexavalent chromium possesses a greater risk due to its water soluble nature and high penetrating power to enter into the living cells [3] , which leads to its carcinogenic properties. Hexavalent chromium, which is primarily present in the form of chromate CrO 4 -- and dichromate Cr 2 O 7 -- , has significantly higher levels of toxicity than the other valence states [4] . In general, chromium (VI) is removed from waste water by various methods such as chemical precipitation, electrochemical reduction, sulfide precipitation, cementation, ion-exchange, reverse osmosis, electro dialysis, solvent extraction, and evaporation, etc. [5] . However, these methods are cost intensive and are unaffordable for large scale treatment of wastewater which is rich in chromium (VI). Adsorption using activated carbon is an effective method for the treatment of industrial effluents contaminated with chromium (VI) and quite popular [6,7] . Other commercial adsorbents are recently reported to have been used in industries, although their versatility and adsorption capacity are generally less than those of activated carbon [8] . Conventional methods for removing Cr (VI) ions from industrial wastewater include reduction [9] , reduction followed by chemical precipitation [10] , adsorption on the