Recycling coir pith, an agricultural solid waste, for the removal of procion orange from wastewater D. Kavitha * , C. Namasivayam Environmental Chemistry Division, Department of Environmental Sciences, Bharathiar University, Coimbatore-641 046, India Received 16 October 2005; received in revised form 17 December 2005; accepted 31 January 2006 Available online 2 May 2006 Abstract Batch adsorption experiments were carried out for the removal of procion orange from its aqueous solution using coir pith carbon. This study examines adsorption kinetic parameters on coir pith carbon. The effect of process parameters like contact time, concentration of dye, temper- ature and pH on the extent of procion orange adsorption from solution has been investigated. In order to develop an effective and accurate design model for removal of dye, adsorption kinetics and equilibrium data are essential basic requirements. Kinetic study showed that the adsorption of dye on coir pith carbon was a gradual process. Lagergren first-order, second-order, Bangham’s and intra-particle diffusion model were used to fit the experimental data. Results of the kinetic studies show that the adsorption reaction is second-order kinetic model with respect to dye solution concentration. Equilibrium isotherms were analyzed by Langmuir, Freundlich, DubnineRadushkevich, and Tempkin isotherms. The adsorption equilibrium data obeyed Langmuir, DubnineRadushkevich, and Tempkin isotherms. The adsorption capacity was found to be 2.6 mg/g of car- bon. Increase of temperature increased adsorption. Acidic pH was favorable for the adsorption of dye. Studies on pH effect and desorption show that chemisorption seems to play a major role in the adsorption process. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Adsorption; Procion orange; Coir pith carbon; Isotherms; Kinetics; Temperature study 1. Introduction Removal of color from wastewater is a most challenging and perplexing problem. The colored wastewaters from these industries are harmful to the aquatic life in rivers and lakes due to reduced light penetration and the presence of highly toxic metal complex dyes. Dyes can cause allergic dermatitis, skin irritation, cancer, mutation, etc. Most of the industries like textile, leather, plastics, paper, food, cosmetics, etc., use dyes and pigments to color their products. Although the exact num- ber and amount of dyes produced in the world is not known, it is estimated to be more than 100,000 with over 7  10 5 tons of dye-stuff produced annually [1e3]. A large number of reactive dyes are azo compounds that are linked by an azo bridge [4]. Even the presence of very low concentrations of dyes (less than 1 mg/L) in the effluent is highly visible and is considered undesirable [5]. In addition, since reactive dyes are highly soluble in water, their removal from effluent is difficult by conventional physicochemical and biological treatment methods [6,7]. Photocatalytic degradation of reactive dye using sunlight/ ZNO [8], by ozonation [9] and in a bubble-column reactor [10], electrochemical process by manganese mineral [11], coagulation [12], ozone membrane separation [13], anaerobic decolourisation [14], advanced oxidation with UV/H 2 O 2 and adsorption on GAC [15], granulated iron hydroxide and its oxidative regeneration for adsorption of reactive dyes have also been investigated [16]. Wastewaters from dyeing industries are released into nearby land or rivers without any treatment because the con- ventional treatment methods are not cost effective in the Indian context. On the other hand, low-cost technologies do * Corresponding author. Hallym University, Department of Environmental Sciences and Biotechnology, 1 Okchon-dong, Chuncheon, Gangwon-do 200- 702, Republic of Korea. Tel.: þ82 33 248 2165; fax: þ82 33 241 1536. E-mail address: srikavi1@gmail.com (D. Kavitha). 0143-7208/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.dyepig.2006.01.040 Dyes and Pigments 74 (2007) 237e248 www.elsevier.com/locate/dyepig