Copyright © 2013 by Modern Scientific Press Company, Florida, USA International Journal of Modern Chemistry, 2013, 4(3): 167-179 International Journal of Modern Chemistry Journal homepage: www.ModernScientificPress.com/Journals/IJMChem.aspx ISSN: 2165-0128 Florida, USA Article Removal of Chromium(VI) and Nickel(II) Ions from Aqueous Solutions Using Sunflower (Helianthus annus) Leaves as Adsorbent A. U. Augustine 1, *, J. N. Egila 2 1 Department of Chemistry, Federal University Lafia, Nasarawa State, Nigeria 2 Department of Chemistry, University of Jos, Plateau State, Nigeria * Author to whom correspondence should be addressed; E-Mail: abelloves@yahoo.com; Tel.: 08032062900. Article history: Received 8 May 2013, Received in revised form 11 June 2013, Accepted 15 June 2013 Published 25 June 2013. Abstract: The use of sunflower (Helianthus annus) leaves as adsorbent for the removal of Cr(VI) and Ni(II) ions from aqueous solutions was carried out using batch adsorption experiments. The percentage sorption of Cr(VI) ion decreased with increase in pH, and the optimum sorption efficiency was at pH 2 (92.90 %) and that of Ni(II) ions increased with increase in pH of the solution with optimum percentage removal at pH 6 (75.47 %). There was higher removal of metal ions at the initial stage, which latter decreased with increase in absorbent dosage. The optimum percentage sorptions of metal ions were observed at 1.00 g (95.00 %) and 1.25 g (76.78 %) for Cr(VI) and Ni(II) respectively. The optimum sorption efficiencies were observed at 35 min of contact time with the values of 94.20 % and 75.14 % for Cr(VI) and Ni(II) ions respectively. The percentage removal for Cr(VI) and Ni(II) ions by the adsorbent decreased with increase in initial metal ion concentration. The maximum adsorption capacity for Cr(VI) and Ni(II) were 25 mg/g and 12.6 mg/g respectively. Also, the adsorption data of the metal ions Cr(VI) and Ni(II) fitted well for both Freundlich and Langmuir adsorption isotherms. Keywords: Helianthus annus; sunflower; leave; adsorbent; chromium; nickel; removal.