© by PSP Volume 21 – No 8c. 2012 Fresenius Environmental Bulletin 2466 NICKEL REMOVAL FROM AQUEOUS SOLUTIONS UTILIZING GREEK NATURAL BENTONITE AND VERMICULITE Anna Bourliva 1, *, Kleopas Michailidis 1 , Constantine Sikalidis 2 , Anestis Filippidis 1 and Maria Betsiou 2 1 Department of Mineralogy-Petrology-Economic Geology, School of Geology, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece 2 Department of Chemical Engineering, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece ABSTRACT In the present study two natural Greek clays, ben- tonite from Milos island and vermiculite from Askos area, North Greece were used for Ni(II) removal from aqueous solutions. Batch adsorption studies were carried out with various initial Ni(II) concentrations, adsorbent dosages, pH, and contact time. The Ni(II) adsorption capacity increased with initial metal ion concentration, contact time, and solu- tion pH but decreased with an increase in the amount of the clay adsorbent. Overall the kinetic studies showed that the nickel adsorption process followed pseudo-second-order kinetics. The adsorption data gave good fits with Langmuir (r 2 >0,95) and Freundlich (r 2 >0,93) isotherms and yielded Langmuir monolayer capacities of 26.32 to 38.46 mg/g and Freundlich adsorption capacities of 2.95 to 3.05 mg (1−1/n) L 1/n /g for the natural bentonite and vermiculite, respec- tively. In summary, the results have established high poten- tial for both natural Greek clays to remove Ni(II) from aqueous medium. KEYWORDS: bentonite; vermiculite; adsorption; clay minerals; heavy metals. 1 INTRODUCTION Heavy metal ions have become an ecotoxicological hazard of prime interest and increasing significance, be- cause of their accumulation in living organisms [1]. Among heavy metals, nickel is one of the most utilized by western society in silver refineries, electroplating, zinc base cast- ing and storage battery industries [2]. The chronic toxicity of nickel to humans and the environment has been well documented [3]. Direct exposition to nickel causes derma- titis. Some nickel compounds, as carbonyl, are carcino- genic and are easily absorbed by skin. * Corresponding author It is essential to remove Ni(II) from industrial waste- water before being discharged. Hence, removal of nickel from water and wastewater assumes importance. The con- ventional methods for heavy metal removal from water and wastewater include oxidation, reduction, precipitation, mem- brane filtration, ion exchange and adsorption. Among all, adsorption is highly effective and economical. Though activated carbon is a well-known adsorbent for the removal of heavy metals from water and wastewater, its high cost limits its use as an adsorbent [4]. Recently, the use of natural clays for sorption or elim- ination of heavy metals in effluents has been object of study in a great deal of research due to its several eco- nomic advantages [5-7]. The cost of these adsorbents is relatively low when compared to other alternative adsorb- ents, including activated carbon, natural and synthetic zeolites, ion-exchange resins and other adsorbent materials. Clay minerals such as montmorillonite, vermiculite, illite and kaolinite are some natural materials that are being studied as heavy metal and even radioactive elements adsorbents [8-11]. Another advantage of using clay as an adsorbent is related to its intrinsic properties such as: great specific surface area, excellent physical and chemi- cal stability and several other structural and surface prop- erties [12]. In this work the adsorption capacity of Ni 2+ ions by these two natural Greek clays was studied. Bentonite is locally available and abundant in Greece. Additionally, ex- tensive zones of vermiculite have been found in Askos area, Northern Greece at the contacts of serpentinized ul- tramafic bodies and surrounding two-mica gneisses con- stituting a significant source of this industrial mineral in Greece [13]. 2 MATERIALS AND METHODS 2.1 Adsorbents characterization Two natural Greek clays, bentonite from Milos island (BN) and vermiculite from Askos area (V), North Greece were used in the present study. The natural bentonite was provided by the S&B Industrial Minerals S.A., Milos is-