INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 4, No 3, 2013 © Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN 0976 – 4402 Received on September 2013 Published on November 2013 250 Freundlich, Langmuir adsorption isotherms and kinetics for the removal of malachite green from aqueous solutions using agricultural waste rice straw Jagdish Singh, Gagndeep Kaur Department of Biotechnology, Mata Gujri College Fatehgarh Sahib Punjab, India jagdish122@rediffmail.com doi: 10.6088/ijes.2013040300004 ABSTRACT Malachite (N-methylated diamino triphenyl methane), a green menace, is extensively being used as dye for colouring silk, leather and paper. It is carcinogenic and catalyzes allergic problems. In this work agricultural waste rice straw as adsorbent was employed to remove Malachite green from aqueous solutions. Effects of pH, concentration of the dye, temperature and adsorbent dosage was determined for maximum removal of dye. Equilibrium isotherms for the adsorption of the dye were well fitted to the Freundlich and the Langmuir isotherm models. Thermodynamic parameters, Gibb’s free energy (∆G◦), change in enthalpy (∆H◦) and change in entropy (∆S◦) have revealed spontaneous and endothermic nature of adsorption process. Kinetic measurements established that the adsorption of Malachite green over rice straw follows first-order kinetics Keywords: Adsorption, Malachite green, Isotherm, Kinetics, Dye 1. Introduction Leather, textile, paper and pulp industries discharge a large quantity of highly coloured effluent containing dyes into nearby rivers or land without any treatment because conventional treatment methods are very expensive. Small amount of dye present in water (< 1 mg/L), is highly visible and consequently undesirable (Sun and Yung 2003). Based on the chromophore group, 20 to 30 different groups of dyes are effective pollutant so removal of color from effluents is one of the major environmental problems. Different investigations are focused on effectiveness of low cost adsorbents like pearl mille husk, neam leaf powder, coconut husk, wheat straw, sewage sludge, perlite, maize cobs, wood, peat, natural adsorbent, banana pith and chitin (Poots et al. 1976; Poots et al.1978; Lin et al.1987; Nawar and Doma 1989;Low and Lee 1990; Nassar and Guendi 1991; Namasivayam and Kanchana 1993; Annadurai and Krishnan 1996; Walker and Weatherly 1998; Selverani 2000; Dogan et al. 2000;Robinson et al. 2002; Olereo et al.,2003; Verma and Mishra 2006;) for effluent treatment for various application. The dye under investigation, Malachite green is used to colour silk, leather and paper. It is water-soluble and found as contaminant in industrial effluents. Clinical and experimental observations reported so far reveal that malachite green is a multi-organ toxin. Malachite green is highly cytotoxic to mammalian cells (Fessard et al. 1999) and carcinogenic to liver, thyroid and other organs in animals (Rao 1995; Rao and Fernandes 1996; Doerge et al. 1998; Mahudawala et al. 1999; Sundarrajan et al. 2000). Incidences of tumours in lungs, breast and ovary have also been reported from rats exposed to malachite green (Werth and Bioteaux 1958). Because of its hazardous health effects, the present study is devoted to its removal from the wastewater using adsorption technique. The study has been carried out under effect of different variables, like temperature, pH, adsorbent dose and adsorbent concentration for the development of convenient and economically viable process for malachite green removal using a waste material rice straw as potential adsorbent.