science JOURNALS

AMERICAN JOURNAL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
© 2014, Science Huβ, http://www.scihub.org/AJSIR
ISSN: 2153-649X, doi:10.5251/ajsir.2014.5.4.134.138
Uptake of chromium (vi) on activated Delonix regia leaves and bark:the
binary isotherm and kinetics.
Saratu Mamman and Tayelolu Olosunla
Department of Chemistry, University of Abuja, PMB 117, Abuja-Nigeria
mammansarah@yahoo.com and sunlagabt@yahoo.com

ABSTRACT
The activated Delonix regia leaves (DRL) and tree bark (DRB) were used as biosorbents for the
removal of Chromium(VI) from aqueous solutions. The biosorption studies were carried out using
each biosorbent singly and the combination of the two in equimolar proportions, respectively.
Biosorption experiments were performed as a function of pH, contact time, particle size,
biosorbent dosage, temperature, initial concentration of the biosorbate. Optimum removal of
chromium (VI) was obtained at pH 2 after two hours. Kinetics data fitted satisfactorily to the
pseudo-first-order rate equation for all the biosorbents, suggesting that the biosorption process is
chemisorption. The equilibrium data were tested for Langmuir and Freundlich models, and the
Freundlich model fitted better for all the biosorbents with correlation coefficient (R2) values in the
range of 0.997 - 0.999. Thermodynamic parameters such as Gibbs free energy, enthalpy and
entropy evaluated from experimental data, revealed that uptake of Chromium (VI) was
endothermic at 25 0C. The results show that a larger proportion of Chromium (VI) was adsorbed
when the binary (DRBL) form of the biosorbents was used as compared to the individual
biosorbents.
KeyWords: Uptake, Kinetics, Isotherm, Chromium (VI), Delonix regia