Scientific Research and Essays

  • Abbreviation: Sci. Res. Essays
  • Language: English
  • ISSN: 1992-2248
  • DOI: 10.5897/SRE
  • Start Year: 2006
  • Published Articles: 2752

Full Length Research Paper

Biosorption of Cd2+ and Pb2+ ions onto mango stone and cocoa pod waste: Kinetic and equilibrium studies

Olu-owolabi, B. I.1, Oputu, O. U.2*, Adebowale, K. O.1, Ogunsolu, O.1 and Olujimi, O. O.3        
  1Department of chemistry, University of Ibadan. Nigeria. 2Department of Chemistry, Faculty of Applied Sciences, Cape Peninsula University of Technology, P.O. Box 1906, Cape Town, South Africa. 3Department of Chemistry and Chemical Technology, Walter Sisulu University, Mthatha Campus, Mthatha Eastern Cape, South Africa.
Email: [email protected]

  •  Accepted: 13 March 2012
  •  Published: 30 April 2012

Abstract

Mango stone (DMS) and cocoa pod (CPC), two agricultural waste materials evaluated for the removal of toxic cadmium ion Cd2+ and Pb2+ ions from aqueous media in batch adsorption mode. Adsorption variables such as the nature and composition of electrolyte, pH, adsorbent dose and equilibration time were optimized for the maximum accumulation of the metals to the biosorbents. The optimum contact time of 15 min for Cd2+ and 40 min for Pb2+ were found to be independent of the adsorbent in use but on the metal been adsorbed. The presence of alkali electrolyte ions Na+ and K+ reduced the uptake of Cd2+ and Pb2+ as these electrolytes ions competed and reduced the available adsorption sites for heavy metal removal, the effect been more pronounced in DMS than with CPC. Kinetic data obtained in this study fitted satisfactorily to the pseudo-second-order rate equation (R2 >0.995). Other tested kinetic models however proved useful for describing the adsorption mechanisms at different points in the biosorption process. The Langmuir, Freundlich, Dubinin- Radushkevich (D-R) and Temkin models were applied to describe the isotherms in the study. Based on the assumptions of these equilibrium models and the results obtained, an attempt was made at describing the surface adsorption characteristics of the biosorbents relative to the metals in question. Biosorption capacity of both biomasses for both metals compared well with those of earlier workers.

 

Key words: Adsorption, kinetics, equilibrium, isotherms, cocoa pods, mango stone.