Analysis of the removal of lead(II) from aqueous solutions by adsorption onto insolubilized humic acid: temperature and pH dependence

The removal of Pb(II) from aqueous solution by adsorption onto insolubilized humic acid (IHA) in single component system at different temperatures and different pH, and at constant ionic strength has been investigated. The experimental data have been analyzed using the Langmiur, Freundlich, and Redlich-Peterson isotherm models. In order to determine the best fit isotherm for each system, the experimental data has been fit to Langmiur and Redlich-Peterson models, while the worst correlation was obtained for the Freundlich model. The results, which were analyzed by the three models, showed temperature and pH dependence. The derived adsorption constants (log a(L)) and their temperature dependencies from Langmuir isotherm have been used to calculate the corresponding thermodynamic quantities such as the free energy of adsorption, heat and entropy of adsorption. The thermodynamic data indicate that Pb(II) adsorption onto IHA is entropically driven and characterized by physical adsorption. (C) 2004 Elsevier B.V. All rights reserved.