Buletinul tiinţific al Universităţii “Politehnica” din Timisoara, ROMÂNIA Seria CHIMIE I INGINERIA MEDIULUI Chem. Bull. "POLITEHNICA" Univ. (Timioara) Volume 54(68), 1, 2009 13 Cobalt (II) Removal from Aqueous Solutions by Adsorption on Modified Peat Moss C. Caramalău, L. Bulgariu, M. Macoveanu Technical University “Gheorghe Asachi” of Iai, Faculty of Chemical Engineering and Environmental Protection, Department of Environmental Engineering and Management, Bd. D. Mangeron, 71A, 700050, Iai, Romania Phone: (0232) 271759, Fax: (0232) 271759, E-Mail: lbulg@ch.tuiasi.ro, http://www.ch.tuiasi.ro Abstract: The adsorption behaviour of cobalt (II) from aqueous solutions on un-treated and treated peat moss was investigated. The treatments suppose the mixing of peat moss with 0.2 mol/L aqueous solution of HNO 3 and NaOH, respectively. The influence of initial solution pH, peat moss dose, initial cobalt (II) concentration and contact time, was studied in batch experiments. The optimum results were obtained at pH = 6.0 (acetate buffer), an adsorbent dose of 5 g/L and an initial concentration of 240 mg Co(II)/L. The experimental results have show that in case of peat moss treated with NaOH, the adsorption capacity increase with 15 % and the contact time necessary for to attain the equilibrium decrease until 15 min. In case of peat moss treated with HNO 3 , the adsorption capacity slowly decrease and the contact time required for to attain the equilibrium has almost the same value as un-treated peat. The adsorption process of cobalt (II) on un-treated and treated peat moss was tested with Langmuir isotherm model and the isotherm constants were deduced from this. Keywords: peat moss, cobalt (II) ions, adsorption, chemical treatments, isotherm 1. Introduction Environmental contamination with metal ions represents a potential treat to human, animals and plants. The metal ions do not undergo biodegradation and many of them are soluble in aqueous solutions, therefore become more available for living systems and accumulate in the environment [1]. Cobalt (II) compounds are essential in many industries. Their applications in nuclear power plants, metallurgy, mining, pigments, paints and electronic are only few examples where the presence of cobalt in waste waters represents a major environmental problem [2, 3]. Conventional methods for removing dissolved metal ions fro aqueous media include chemical precipitation, chemical oxidation and reduction, ion exchange and activated carbon adsorption [3-5]. However, these processes have significant disadvantages, such as incomplete removal of metal ions, high quantities of toxic sludge, required additional reagents and have high operation cost. In recent years, considerable attention has been received the utilization of adsorption technique, in which the adsorbents are natural material or industrial and agricultural wastes, to passively remove of metal ions from aqueous effluents. Thus, the utilization of peat [6-8], living and death biomass [9-11] or clay and related minerals [12- 14] offers an efficient and cost-effective alternative compared to traditional chemical and physical remediation and decontamination techniques. A large number of studies from literature related the performances of different such adsorbents for the removal of different metal ions under various experimental conditions. In most of these is showed that such natural or waste products can be good adsorbents for metal ions and some of them have excellent ion-exchange properties. The adsorbent used in this study is peat moss (from Poiana Stampei, Romania). This a complex material, obtained by partial degradation of vegetables, and where the major constituents are cellulose, lignin and humic substances [15]. Due to these constituents, the peat moss has in its structure different polar groups (such as carboxylic, phenolic, alcoholic, etheric, etc.) which can chemical bind metal ions from aqueous solutions. In ours previous studies [16, 17], it has that cobalt (II) can be successfully removed from aqueous solutions (> 97 %) when its initial concentration is lower than 100 mg/L. For a higher initial metal ion concentration the cobalt removal percents drastically decrease, and the adsorption process is not efficient any more. In order to improve the adsorption capacity of peat moss for cobalt, simple chemical treatments were used. These treatments suppose the mixing of peat moss with 0.2 mol/L aqueous solutions of HNO 3 and NaOH, respectively. An increasing of adsorption capacity for cobalt (II) with less 15 % and a decreasing of contact time necessary for to attain the equilibrium until 15 min was obtained, when the peat moss was treated with NaOH solution. The main advantage of this procedure is that the increasing of adsorption capacity of peat moss is done without to be used additional expensive additives. In this study, the batch experiments were conducted in order to investigate the adsorption of cobalt (II) ions from aqueous solutions on un-treated and treated peat moss.