Proceedings of 2 nd Slovenian-Croatian Symopsium on Zeolites 82 ADSORPTION OF TOXIC METALS BY IRON (III) MODIFIED CLINOPTILOLITES Aleksandra Daković 1 , Sonja Milićević 1 , Milan Kragović 1 , Živko Sekulić 1 , Jovica Stojanović 1 , Jelena Perić 2 , Marina Trgo 2 , Nediljka Vukojević Medvidović 2 , Ivona Nuić 2 1 Institute for Tehnology of Nuclear and Other Mineral Raw Materials, Franche d' Epere 86, P.O. Box 390, 11000 Belgrade, Serbia 2 Faculty of Chemistry and Technology, University of Split, Teslina 10, Croatia E-mail: a.dakovic@itnms.ac.rs INTRODUCTION The contamination of water resources with toxic metals (copper, zinc, cadmium, lead, chromium, nickel, mercury, etc.) can cause serious problems to human beings, animals and plants. In the recent years, the levels of these toxic metals in surface waters have been increasing due to the pollution caused by industrial wastewaters discharges. Wastewaters from mining operations, electroplating plants, power-generating plants, electronic appliance factories and tanneries contain several toxic metals [1, 2]. Various treatment methods such as ion exchange, ultrafiltration, adsorption, coagulation-precipitation, etc. have been proposed for removal of toxic metals from waters. Among others, one of the most effective method for the removal of toxic metals from waters is their adsorption by low cost adsorbent materials [3-5]. Zeolites, crystalline aluminosilicates with defined structures that consist of a framework formed by tetrahedral of SiO 4 and AlO 4 , have been widely used in toxic metals adsorption experiments. Recently, iron-overexchanged clinoptilolite (Clino-Fe) was tested for removal of Mn 2+ ions from drinking water and in Cu 2+ ions adsorption from KCl solutions at different pH values [6, 7]. It was reported that Clino-Fe system had much higher adsorption capacity for Mn 2+ and Cu 2 ’ ions than unmodified clinoptilolite. In this paper, the natural zeolitic tuff with high content of clinoptilolite was modified with different amounts of iron (III) ions, and the obtained materials were tested for adsorption of copper, zinc and nickel. EXPERIMENTAL Natural zeolitic tuff from the Zlatokop deposit (Vranjska Banja, Serbia) was used as the starting material. The mineralogical composition of the natural zeolitic tuff was primarily clinoptilolite (minimum 85%) with small amounts of feldspar, quartz and pyrite determined by X-ray powder diffraction analysis (XRPD). Raw zeolitic tuff was sieved to yield particles below 43 m. The cation exchange capacity (CEC) of the starting material was 146 mmolM + /100g measured by 1M NH 4 Cl method. Iron (III) modified clinoptilolites were obtained by treatment of the starting material with three different concentrations of iron (III) chloride (Fe 3+ was added in amounts of 0.6, 1.5 and 2 CEC of the starting zeolitic tuff), using the following procedure: 100 g of the natural zeolitic tuff and 50 mL of each FeCl 3 solution were mixed, as well as, the pH of the mixture was adjusted to 10.0 using 0.1M NaOH [8]. The suspensions were stirred in laboratory mixer at 60ºC for 180 min. After the reaction time, the suspensions were rinsed with distilled water until Cl - ions were no longer detected and dried at 60ºC. The products were denoted as