Kinetic and thermodynamic study on adsorption of lead(II) ions in water over dithizone-immobilized coal bottom ash

Abstract

In this study, the activated coal bottom ash (Act-CBA) was first modified with dithizone in alkaline solution (Dtz-CBA) and then used for Pb(II) adsorption in water. The success of dithizone-immobilization on Act-CBA was confirmed by SEM-EDX (Scanning Electron Microscope-Energy Dispersive X-Ray), FTIR (Fourier-Transformed Infra Red), and XRD (X-Ray Diffraction) analyses. Adsorption study for Pb(II) in water with Act-CBA and Dtz-CBA included effects of solution pH, adsorption temperature, Pb(II) concentration, and contact time on the adsorption process to systematically determine kinetic and thermodynamic parameters for the adsorption. The results demonstrated that Langmuir isotherm model was the best fit one among them and that the maximum adsorption capacity was 21 mg g−1 at 283 K for Dtz-CBA. Furthermore, pseudo-second order kinetic model was the best to express the adsorption behavior of Pb(II) on Dtz-CBA. Standard Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes estimated from the adsorption isotherms taken at 283, 293, 303, and 313 K revealed that the adsorption process was spontaneous and endothermic under the present conditions, and had both physical and chemical interactions between Pb(II) and Dtz-CBA. The activation energy for the Pb(II) adsorption on Dtz-CBA (15 kJ mol−1) was much lower than that on Act-CBA (41 kJ mol−1) indicating that the dithizone-immobilization gave rise to easier and more rapid adsorption of Pb(II) on the adsorbent, which was useful for the purpose of practical applications.