International Research Journal of Environment Sciences________________________________ ISSN 2319–1414 Vol. 2(2), 30-37, February (2013) Int. Res. J. Environment Sci. International Science Congress Association 30 Trivalent Chromium removal from Aqueous solution using Raw Natural Mixed Clay from BURKINA FASO Pare Samuel 1 , Persson Ingmar 2 , Guel Boubié 3 , and Lundberg Daniel 2 1 Laboratoire de Chimie organique, Structure et réactivité, U.F.R.-S.E.A–Université de Ouagadougou, Ouagadougou 03, BURKINA FASO 2 Department of Chemistry, Swedish University of Agricultural Sciences, Uppsala, SWEDEN 3 Laboratoire de Chimie Physique et d’Electrochimie, U.F.R.-S.E.A–Université de Ouagadougou, Ouagadougou 03, BURKINA FASO Available online at: www.isca.in Received 10 th January 2013, revised 20 th January 2013, accepted 10 th February 2013 Abstract Acid-Base properties of the raw mixed clay TOU from Burkina Faso, were study as well as the potential of the sample, in removing of chromium(III). The interactions of chromium(III) cation with the natural mixed clay minerals were examined using extended X-ray absorption fine structure (EXAFS) spectroscopy. Chemical elementary composition study of the mixed clay revealed presence of Silicon, Aluminum and Iron as mains elements. Qualitative mineralogical characterization of the clay by X-Ray diffraction, point out quartz and 7Å Halloysite as the dominating component in the sample. pH pzc of the clays, as determined by potentiometric titrations, was 8.21. Cr 3+ adsorption on clay started at pH below pHpzc indicating inner-sphere complexes formation. More than 95% of chromium(III) is achieved at pH greater than 7. Chromium(III) forms a tetramer hydrolysis complex on the mineral surface with Cr–O bond and Cr· · ·Cr distances of 2.487, 3.087 and 3.636 Å, respectively, which is indicative of a chain structure with edge sharing CrO 6 octahedra. Keywords: Chromium (III), Natural mixed clays, Potentiometric titration, pHpzc, EXAFS Introduction Studies conducted in Burkina Faso reveal high level of particular heavy metal in streams and soil, mainly due to anthropogenic activities such as mining society’s effluents, agricultural activities, discharge from industrial plants and sewage works 1,2,3 . Chromium(III) is among the most common heavy metal pollutants found in Burkina Faso 2, 4 , mainly from tannery effluent 3 . Investigations have been made worldwide on available and environmental friendly material as adsorbent such as Chitosan 5, 6 , Activated P. Lentiscus Leave 7 , Acid Acrylic Resin 8 , clays 9 . Clays are known for their ability to effectively removed heavy metal by specific adsorption and cation exchange 9 . Large quantities of clay are available and are extracted and used in Burkina Faso for traditional potters, ceramic and individual brick 10-13 . Recently, some studies 11,14,15 , investigated on the potential of natural mixed clays used for heavy metal removal from aqueous solutions. The most important parameters controlling heavy metal adsorption and their distribution between clay and water are clay type, metal speciation, metal concentration, soil pH, solid:solution mass ratio, contact time 9,16,17,18,19 . Of all these factors, pH is considered the ‘master variable’ controlling ion exchange, dissolution/precipitation, reduction/oxidation, adsorption and complexation reactions 20 . Cations adsorption, are more effective at high pH. In this study, natural clay from Burkina Faso, TOU, acidic and basic properties were determined by potentiometric titration. Elementary composition of elements of sodium or heavier of the clay samples were investigated using the energy dispersive spectrometer (EDS) detector of scanning electron microscopy (SEM) instrument, Hitachi TM-1000, as well as qualitatively characterization of the clay mineralogical composition by powder X-ray diffraction. Dependence of chromium(III) uptake on pH by the clay were study. Investigations on the local structural environment of chromium(III) sorbed on silica using EXAFS have been reported 21 . Their results showed formation of monodentate chromium (III) surface complex on silica with Cr–Si distance of 3.39Å for the sorbed chromium while formation of polynuclear chromium hydroxide octahedra was discerned on the surface. It has been found that on the natural mixed alkaline clay, chromium(III) forms a polynuclear hydrolysis complex on the mineral surface with Cr–O bond and Cr· ·Cr distances of 2.00 and 3.03 Å respectively 22 . In this work, EXAFS (extended X-ray absorption fine structure) spectroscopy was applied to characterize sorbed chromium (III) on the clay surfaces without any pre-treatment, at pH 3.3. The main advantages of EXAFS are that the nearest neighbour distances around the absorbing element are observed and all states of aggregation can be studied with high precision in the distances even in very dilute samples with metals sorbed on mineral or clay surfaces 22 .