Journal of Hazardous Materials 165 (2009) 566–572 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Characterization of biosorption process of As(III) on green algae Ulothrix cylindricum Mustafa Tuzen a,∗ , Ahmet Sarı a , Durali Mendil a , Ozgur Dogan Uluozlu a , Mustafa Soylak b , Mehmet Dogan c a Department of Chemistry, Gaziosmanpasa University, 60250, Tokat, Turkey b Department of Chemistry, Erciyes University, 38039, kayseri, Turkey c Department of Chemistry, Hacettepe University, Ankara, Turkey article info Article history: Received 12 June 2008 Received in revised form 6 September 2008 Accepted 7 October 2008 Available online 14 October 2008 Keywords: U. Cylindricum Green algae Biosorption As(III) abstract Arsenic (As) is generally found as As(III) and As(V) in environmental samples. Toxicity of As(III) is higher than As(V). This paper presents the characteristics of As(III) biosorption from aqueous solution using the green algae (Ulothrix cylindricum) biomass as a function of pH, biomass dosage, contact time, and temperature. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were applied to describe the biosorption isotherm of As(III) by U. cylindricum biomass. The biosorption capacity of U. cylindricum biomass was found as 67.2mg/g. The metal ions were desorbed from U. cylindricum using 1 M HCl. The high stability of U. cylindricum permitted 10 times of adsorption–elution process along the studies with a slightly decrease about 16% in recovery of As(III) ions. The mean free energy value evaluated from the D–R model indicated that the biosorption of As(III) onto U. cylindricum biomass was taken place by chemical ion-exchange. The calculated thermodynamic parameters, G ◦ , H ◦ and S ◦ showed that the biosorption of As(III) onto U. cylindricum biomass was feasible, spontaneous and exothermic under examined conditions. Experimental data were also tested in terms of biosorption kinetics using pseudo- first-order and pseudo-second-order kinetic models. The results showed that the biosorption processes of As(III) followed well pseudo-second-order kinetics. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Heavy metal pollution is increasing throughout the world with the growth of industrial activities. Unlike organic pollutants, heavy metals are non-biodegradable and therefore, the removal of them is extremely important in terms of healthy of livings specimens [1,2]. Arsenic, a common element in nature, is a naturally occur- ring contaminant of drinking water and can be found in the earth’s crust, ground and marine water and in the organic world as well. It is mobilized through a combination of natural processes such as weathering reactions, biological activity and volcanic emissions [3,4] as well as through a range of anthropogenic activities such as gold mining, non-ferrous smelting, petroleum-refining, combus- tion of fossil fuel in power plants and the use of arsenical pesticides and herbicides [5,6]. Contaminated groundwater by arsenic is a well known environ- mental problem that can have severe human health implications. Chronic exposure to arsenic concentrations above 100ppb can ∗ Corresponding author. Tel.: +90 356 2521616; fax: +90 356 2521585. E-mail address: mtuzen@gop.edu.tr (M. Tuzen). cause vascular disorders, such as dermal pigments (Blackfoot dis- ease) and skin, liver and lung cancer [7,8]. An arsenic concentration of 10 g/L has been recommended by World Health Organization as a guideline value for drinking water [9]. Arsenic may exist in groundwater both in +3 and +5 oxi- dation states depending upon the prevalent redox conditions. As(III) is more toxic in biological systems than As(V) [10]. Sev- eral studies have demonstrated that arsenic removal can be achieved by various techniques, namely oxidation/precipitation [11,12], Fe-electrocoagulation/co-precipitation [13], alum coagu- lation/precipitation [14], lime softening, metal-oxide adsorption using packed beds of activated alumina [15,16], granular ferric hydroxide [17], iron-oxide coated sand [18], reverse osmosis and nanofiltration [19,20], ion-exchange resin [21,22], polymer ligand exchange [23], coagulation-microfiltration [24], etc. Most of these methods suffer from some drawbacks, such as high capital and operational cost or the disposal of the residual metal sludge, and are not suitable for small-scale industries. On the other hand, numer- ous biological materials have been tested for removal of toxic ions from aqueous solutions over the last two decades. However, only a limited number of studies have investigated the use of adsorbents obtained from biological sources, e.g., bio-char [25], methylated 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.10.020