Equilibrium Study of Heavy Metals Adsorption on Kaolin

Abstract

The adsorption of Cu(II), Cd(II), and Zn(II) from one- and two-component systems, on the raw and Na-form of kaolin, was investigated under batch conditions. The transformation of the raw kaolin into its Na-form causes surface-to-surface arrangement of crystals, which led to quantitatively similar but certainly different metal ion isotherm curves. Subsequently, the identified homogeneous Langmuirian adsorption on raw kaolin changed after sodium saturation into a heterogonous one. The Langmuir constants obtained from one-component systems were used to test the applicability of the new isotherm equation for modeling of the two-component equilibrium on raw kaolin. This model yielded quantification of the relative amounts of binding sites on the kaolin, showing partial specificity of the adsorbent to the individual metal ions. The validity of the model was confirmed by the alignment between the modeled equilibrium surface and 225 experimental points obtained for two different experimental sets.