Modeling of Copper(II), Cadmium(II), and Lead(II) Adsorption on Red Mud

Abstract The adsorption of toxic heavy metal cations, i.e., Cu(II), Cd(II), and Pb(II), on red muds has been modeled with the aid of a modified Langmuir approach assuming single-site adsorption and of a double-site binding model incorporating the effect of pH. For equilibrium concentrations of metal solutions between 0.03 and 5.8 mmol.dm −3 and equilibrium pH between 4.4 and 5.6, adsorption equilibrium constants corresponding to single- and double-site binding were found by linear and nonlinear least-squares approximation, respectively, and the double-site model was shown to conform better to experimental data. The contributions of the monomeric and dimeric hydroxo-complexes of Cu(II) to total copper adsorption at a fixed pH were also investigated. The Langmuir parameters of adsorption were found with the aid of the linearized Langmuir isotherm. This work aims to clarify heavy metal adsorption behavior on composite sorbents consisting of hydrated oxides.