Journal of Hazardous Materials B139 (2007) 167–174 Equilibrium and kinetic adsorption study of a cationic dye by a natural adsorbent—Silkworm pupa B. Noroozi b , G.A. Sorial a,∗ , H. Bahrami b , M. Arami b a Department of Civil and Environmental Engineering, University of Cincinnati, P.O. Box 210071, Cincinnati, OH 45221-0071, United States b Textile Engineering Department, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran Received 11 April 2006; received in revised form 6 June 2006; accepted 7 June 2006 Available online 10 June 2006 Abstract In this work the use of silkworm pupa, which is the waste of silk spinning industries has been investigated as an adsorbent for the removal of C.I. Basic Blue 41. The amino acid nature of the pupa provided a reasonable capability for dye removal. Equilibrium adsorption isotherms and kinetics were investigated. The adsorption equilibrium data were analyzed by using various adsorption isotherm models and the results have shown that adsorption behavior of the dye could be described reasonably well by either Langmuir or Freundlich models. The characteristic parameters for each isotherm have been determined. The monolayer adsorption capacity was determined to be 555 mg/g. Kinetic studies indicated that the adsorption follows pseudo-second-order kinetics with a rate constant of 0.0434 and 0.0572 g/min mg for initial dye concentration of 200 mg/l at 20 and 40 ◦ C, respectively. Kinetic studies showed that film diffusion and intra-particle diffusion were simultaneously operating during the adsorption process. The rate constant for intra-particle diffusion was estimated to be 1.985 mg/g min 0.5 . © 2006 Elsevier B.V. All rights reserved. Keywords: Adsorption isotherm; Adsorption kinetics; Basic Blue 41; Silkworm pupa 1. Introduction Chemical contamination of water by a wide range of pollu- tants is a serious environmental problem due to their potential human toxicity. The textile industry uses large volumes of water in wet processing operations and, thereby, generates substantial quantities of wastewater containing large amounts of dissolved dyestuffs and other products, such as dispersing agents, dye bath carriers, salts, emulsifiers, levelling agents and heavy metals [1,2]. Dyes are synthetic aromatic compounds which are embod- ied with various functional groups. Some dyes are reported to cause allergy, dermatitis, skin irritation, cancer, and mutations in humans. Thus, the removal of dyes from effluents before they are mixed up with unpolluted natural water bodies is important [3]. Today there are more than 10,000 dyes available commer- cially [4]. The annual production of dyes worldwide is around 7 × 10 5 t, 5–10% of which is discharged into waste streams by ∗ Corresponding author. Tel.: +1 513556 2987; fax: +1 513556 2599. E-mail address: George.Sorial@uc.edu (G.A. Sorial). textile industries. The majority of these dyes are of synthetic origin and toxic in nature with suspected carcinogenic and geno- toxic effects [5]. Textile wastewaters offer considerable resistance to biodegra- dation due to presence of the dyestuffs which have a complex chemical structure and are resistant to light, heat and oxidation agents. The colored dye effluents are considered to be highly toxic to the aquatic life and affect the symbiotic process by dis- turbing natural equilibrium by reducing photosynthetic activity due to the colorization of the water [6]. Biological treatment processes such as aerated lagoons and conventional activated sludge processes are frequently used to treat textile effluents. These processes are efficient in the removal of suspended solids but largely ineffective in removing dyes from wastewater [7]. Removal of dyes from effluents in an economic fashion remains a major problem for textile industries. The need of treating textile wastewaters by a tertiary treatment, mostly for residual dye removal is required [1]. Physico-chemical processes are generally used to treat dyes laden wastewater. These processes include flocculation, electro-flotation, precipitation, electro-kinetic coagulation, ion exchange, membrane filtration, electrochemical destruction, 0304-3894/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2006.06.021