Kinetics and thermodynamics of aqueous copper adsorption by Ca-Al-Zn LDH and its calcined product

Abstract

T he Ca-Al-Zn layered double hydroxide (LDh) which synthesized by the co-precipitation method and its calcined product was used in the removal of Cu(II) from aqueous solutions. At optimum conditions, the calcined Ca-Al-Zn LDh product has a higher potential application in the cupreous ion's adsorption field (45.2mg/g) than the uncalcined LDH (38.8mg/g). Langmuir and Freundlich models were used to optimizing the adsorption process and pseudo-first and pseudo-second-order models were used to evaluating the adsorption kinetics of Cu(II) onto Ca-Al-Zn LDH and its calcined product. Langmuir model fitted the experimental data better than Freundlich model and the pseudo-first-order model is more sufficient to depict the adsorption kinetics. From thermodynamic studies; Gibbs free energy (∆G°), Enthalpy change (∆H°), and Entropy change (∆S°) revealed that the adsorption processes are spontaneous, endothermic, and randomness processes at the solid-solution interface during adsorption.