The 12 th Symposium on Analytical and Environmetal Problems, Szeged, 26 September 2005 245 COMPARATIVE RESEARCHES CONCERNING THE DECONTAMINATION OF WASTEWATER POLLUTED WITH HEXAVALENT CHROMIUM Marius Gheju * , Aurel Iovi * , Corneliu Bogatu ** * “Politehnica” University of Timisoara, Faculty of Industrial Chemistry and Environmental Engineering, Bd. V. Parvan Nr. 6, Et. 1, 1900, Timisoara, Romania, e-mail: mariusgheju@yahoo.com ** National R&D Institute for Industrial Ecology – ECOIND, PO Box 254 Of.1, P-ta Victoriei Nr.2, Et.2, 1900 Timisoara, Romania, e-mail: corneliu.bogatu@rectorat.utt.ro ABSTRACT The aim of this study was to determine the possibility of removing Cr(VI) from aqueous solutions by use of two locally abundant low cost materials: coal ash and scrap iron. The removal efficiency of hexavalent chromium by adsorption on coal ash was calculated and the optimum reaction conditions (ash concentration, mixing time, pH) were established. The adsorption data were then fitted to the Langmuir and Freundlich isotherms. The results show that coal ash is not a very strong adsorbent for this pollutant. The reduction of Cr(VI) by scrap iron was investigated in batch system with four different types of scrap iron. The effects of mass ratio Cr(VI) : scrap iron, iron shape, mixing speed and pH were investigated. The results showed that the reduction of Cr(VI) by scrap iron is possible, but depends to a large extent on acid concentration. INTRODUCTION Chromium exists in natural environments in two main oxidation states, Cr(VI) and Cr(III), that are characterized by different toxicity and chemical behavior [3, 17]. Hexavalent chromium is known to be toxic to humans, animals, plants and microorganisms [5, 6, 12, 18, 20]. Trivalent chromium, on the other hand, is less toxic and readily precipitates as Cr(OH) 3 [16] or as Fe x Cr 1-x (OH) 3 [1, 10] under alkaline or even slightly acidic conditions. The conventional process currently used to remove hexavalent chromium is its reduction to Cr(III) by chemical means (usually using Fe(II)) followed by precipitation [10]. In recent years alternative method for removal of metal ions uses the sorption by waste materials, both organic and inorganic [7, 15, 19]. Also, there has been great interest in using zerovalent iron for in situ reduction of redox active metals from contaminated groundwater [1, 2, 4, 11, 14]. The objective of the present investigation is to compare the efficiency of Cr(VI) removal from simulated aqueous contaminated samples by use of two locally abundant low cost materials: coal ash (adsorption) and scrap iron (reduction). MATERIALS and METHODS The coal ash used in all experiments was taken from Rovinari power plant. As source of zerovalent iron we have tested four different types of scrap iron resulted from the mechanic processing of steel: large spiral fibers, small spiral fibers, steel shavings and fine steel powder.