Adsorption of Chromium (VI) on Azadirachta Indica (Neem) Leaf Powder
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Adsorption of Chromium (VI) on Azadirachta Indica (Neem) Leaf Powder ARUNIMA SHARMA AND KRISHNA G. BHATTACHARYYA∗ Department of Chemistry, Gauhati University, Guwahati 781 014, Assam, India [email protected]
Received June 17, 2003; Revised August 20, 2004; Accepted September 23, 2004
Abstract. A novel adsorbent was developed from mature leaves of the Neem tree (Azadirachta Indica) for removing metal ions from water. The adsorbent, in the form of fine powder, was found to be very effective in removing chromium (VI) from aqueous solution. The adsorption was carried out in a batch process taking different concentrations of the metal ion in aqueous solution with variation in adsorbent amount, pH, agitation time and temperature. The suitability of the adsorbent was tested with Langmuir and Freundlich isotherms and with various equilibrium kinetic data. A small amount of the Neem Leaf Powder (NLP) (1.6 g dm−3 ) could remove as much as 87% of Cr (VI) in 300 min from a solution of concentration 14.1 mg dm−3 at 300 K. The optimum range of pH for the adsorption process was 4.5–7.5 and since the natural pH of the Cr (VI) solution was 5.5, no addition of acid or alkali was necessary for achieving maximum adsorption. The adsorption coefficients indicated a high potentiality for the NLP to be used as an adsorbent for removing Cr (VI) from water. Keywords: Neem Leaf Powder, Chromium (VI), Metal removal by adsorption
1.
Introduction
Adsorption onto solid adsorbents can effectively remove pollutants from both aqueous and gaseous streams and therefore has considerable environmental significance. Activated carbon, the most popular adsorbent, has been traditionally used for the removal of odor, taste, and colors, which are designated as trace pollutants. Its high adsorptive capacity and versatility have expanded its application to the treatment of numerous industrial waste streams. Other commercial adsorbents, having increased reversibility, have been recently reviewed (Thomas and Crittenden, 1998) and although their versatility and adsorption capacity are generally less than those of activated carbon, they are advantageous for certain applications. Such low cost adsorbents (Ho and McKay, 1999; Bailey et al., 1999) have found use in laboratory scale for treatment of various pollutants from water and wastewater. ∗ To
whom correspondence should be addressed.
The present work aims to develop a nonconventional adsorbent from the leaves of the Azadirachta Indica (Neem) tree to be used for toxic pollutants, such as Cr (VI) in aqueous medium. Chromium is a naturally occurring element found in rocks, animals, plants, soil, and in volcanic dust and gases. The most common forms of chromium present in the environment are chromium (0), chromium (III), and chromium (VI). Chromium (III) occurs naturally in the environment and is an essential nutrient that helps the use of sugar, protein, and fat by the body (ATSDR, 2001). Chromium (VI) and chromium (0) are generally produced by industrial processes. The metallic chromium [Cr (0)] is use
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