Adsorption of Cr(VI) using activated neem leaves: kinetic studies
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Adsorption of Cr(VI) using activated neem leaves: kinetic studies B.V. Babu · S. Gupta
Received: 13 December 2006 / Revised: 16 July 2007 / Accepted: 17 September 2007 / Published online: 4 October 2007 © Springer Science+Business Media, LLC 2007
Abstract In the present study, adsorbent is prepared from neem leaves and used for Cr(VI) removal from aqueous solutions. Neem leaves are activated by giving heat treatment and with the use of concentrated hydrochloric acid (36.5 wt%). The activated neem leaves are further treated with 100 mmol of copper solution. Batch adsorption studies demonstrate that the adsorbent prepared from neem leaves has a significant capacity for adsorption of Cr(VI) from aqueous solution. The parameters investigated in this study include pH, contact time, initial Cr(VI) concentration and adsorbent dosage. The adsorption of Cr(VI) is found to be maximum (99%) at low values of pH in the range of 1-3. A small amount of the neem leaves adsorbent (10 g/l) could remove as much as 99% of Cr(VI) from a solution of initial concentration 50 mg/l. The adsorption process of Cr(VI) is tested with Langmuir isotherm model. Application of the Langmuir isotherm to the system yielded maximum adsorption capacity of 62.97 mg/g. The dimensionless equilibrium parameter, RL , signifies a favorable adsorption of Cr(VI) on neem leaves adsorbent and is found to be between 0.0155 and 0.888 (0 < RL < 1). The adsorption process follows second order kinetics and the corresponding rate constant is found to be 0.00137 g/(mg) (min). Keywords Adsorption · Batch studies · Neem leaves · Kinetics · Isotherms Abbreviations b Langmuir constant (l/mg) B.V. Babu () · S. Gupta Chemical Engineering Group, Birla Institute of Technology and Science (BITS), Pilani 333 031, Rajasthan, India e-mail: [email protected]
C0 initial concentration of Cr(VI) (mg/ml) Ce concentration of chromium at equilibrium (mg/ml) kad rate constant of the pseudo first-order adsorption process (min−1 ) k2 second-order rate constant (g/mg min) q amount of Cr(VI) adsorbed by the adsorbent (mg/g) qe amount of Cr(VI) adsorbed at equilibrium by the adsorbent (mg/g) qt amount of Cr(VI) adsorbed at time, t, by the adsorbent (mg/g) V initial volume of chromium solution (ml) W weight of the adsorbent (g)
1 Introduction Chromium exists in two stable oxidation states, Cr(III) and Cr(VI). The Cr(VI) state is of particular concern because this form is hazardous to health. Chromium is introduced into the natural bodies of water from industries like electroplating, leather tanning, cement industries, steel industries, and photography. Cr(VI) causes skin irritation resulting in ulcer formation. Over exposure to Cr(VI) leads to liver damage, pulmonary congestion and oedema (Raji and Anirudhan 1998). The current maximum contamination level (MCL) for total chromium in drinking water in the U.S.A. is stipulated by the Environmental Protection Agency (EPA) to be 100 µg/l (Lalvani et al. 1998). So the elimination of Cr(VI) from drinking water is of great concern. Various te
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