Journal of Hazardous Materials 143 (2007) 8–16 The removal of Cu(II) and Co(II) from aqueous solutions using cross-linked chitosan—Evaluation by the factorial design methodology Antonio R. Cestari a,∗ , Eunice F.S. Vieira a , Iataanderson A. de Oliveira a , Roy E. Bruns b a Laboratory of Materials and Calorimetry, Departamento de Qu´ ımica/CCET, Universidade Federal de Sergipe, CEP 49100-000 S ˜ ao Crist ´ ov˜ ao, Sergipe, Brazil b Universidade Estadual de Campinas, Instituto de Qu´ ımica, CP 6154, 13083-970 Campinas, S ˜ ao Paulo, Brazil Received 31 May 2006; received in revised form 27 July 2006; accepted 28 August 2006 Available online 1 September 2006 Abstract A2 3 factorial design was employed to evaluate the quantitative removal of Cu(II) and Co(II) on glutaraldehyde-cross-linked chitosan from kinetic isotherms, using chitosan masses of 100 and 300 mg and temperatures of 25 and 35 ◦ C. The adsorption parameters were analyzed statistically using modeling polynomial equations and a cumulative normal probability plot. The results indicated the higher quantitative pref- erence of the chitosan for Cu(II) in relation to Co(II). Increasing the chitosan mass decreases the adsorption/mass ratio (mol g -1 ) for both metals. The principal effect of the temperature did not show statistical importance. The adsorption thermodynamic parameters, namely  ads H,  ads G and  ads S, were determined. Exothermic and endothermic results were found in relation to a specific factorial design experiment. A comparison of  ads H values was made in relation to some metal–adsorbent interactions in literature. It is suggested that the adsorption thermo- dynamic parameters are determined by the influence of the principal and interactive experimental parameters and not by the temperature changes alone. © 2006 Elsevier B.V. All rights reserved. Keywords: Removal of metals; Chitosan; Adsorption thermodynamics; Chemometrics 1. Introduction Metals from aqueous and non-aqueous solutions have become increasingly important in many industries, including battery and power storage, coatings, electroplating, and power industries. Traditional metal elimination are often of limited effectiveness in order to decrease allowable levels specified by regulatory agencies [1]. These metals inevitably make their way into plant discharge streams in at least dilute concentra- tions, despite application of remediation technologies [2]. The limitations and cost of traditional treatment methods has led researchers to search for alternative treatments. One promising area of development has been adsorption. Activated carbon is the most common adsorbent due to its effectiveness, versatility, and good capacity for the adsorption ∗ Corresponding author. Tel.: +55 79 32126656; fax: +55 79 32126684. E-mail address: cestari@ufs.br (A.R. Cestari). of metals, dyes and other organic compounds. However, it suffers from a number of disadvantages, mainly its high cost on large- scale uses [3]. This has led many workers to search for the use of cheap and efficient alternative adsorbent materials such as the biopolymers chitin and chitosan [4]. Chitin is a biodegradable and nontoxic polysaccharide widely spread among marine and terrestrial invertebrates and fungi [3,4]. It is usually obtained from waste materials of the sea food-processing industry, mainly shells of crab, shrimp, prawn and krill. Its isolation calls for chemical treatments to eliminate natural contaminants, such as inorganics, proteins, lipids and pigments. By treating crude chitin with aqueous 40–50% sodium hydroxide in the 383–388 K range chitosan is obtained. Chitin and chitosan are closely related since both are linear polysaccharides containing 2-acetamido-2-deoxy- d-glucopyranose and 2-amino-2-deoxy-d-glucopyranose units joined by (1 → 4) glycosidic bonds [5]. The chemical and physical properties of these polymers are different in nature 0304-3894/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2006.08.063