Kinetics, Isotherms, and Thermodynamics of Hg(II) Biosorption ontoCarica papaya

Abstract

ABSTRACT Carica papaya, a novel sorbent, was evaluated for sorption of Hg(II) from synthetic aqueous solutions using various pseudo-second order kinetic models as well as equilibrium sorption models. Batch kinetic and equilibrium experiments were carried out for the sorption of Hg(II) onto C. papaya at pH 6.5 and solid to liquid ratio (s/l) 1.0 g L−1. The kinetic data were fitted to second order models of Sobkowsk and Czerwinski, Ritchie, Blanchard, Ho and McKay, whereas Langmuir, Freundlich, and Redlich-Peterson models were used for the equilibrium data. A comparative study on both linear and nonlinear regression showed that the Sobkowsk and Czerwinski and Ritchie's second order model were the same. Ho and McKay's pseudo-second order model fitted well to the experimental data when compared with the other second order kinetic expressions. Langmuir isotherm parameters obtained from the four Langmuir linear equations by using linear method were dissimilar, but were the same when nonlinear method was used. Additionally, various thermodynamic parameters, such as ΔG 0, ΔH 0, and ΔS 0, were calculated. The negative values of Gibbs free energy (ΔG 0) and ΔH 0 confirmed the intrinsic nature of biosorption process and exothermic, respectively. The negative value of ΔS 0 showed the decreased randomness at the solid-solution interface during biosorption. KEYWORDS: adsorptionisothermskineticsmathematical modelingnonlinearthermodynamics ACKNOWLEDGMENTS The authors (S.B., B.J.) thank Dr. (Mrs.) K. H. Mody, Group Leader of Marine Environment, Central Salt and Marine Chemicals Research Institute (CSMCRI), for her constant encouragement and support throughout this work.