Chloride adsorption on aminobenzoate intercalated layered double hydroxides: Kinetic, thermodynamic and equilibrium studies

MgAl layered double hydroxides (MgAl-LDHs) directly intercalated with aminobenzoate ions were synthesized by conventional calcination-rehydration method. The kinetic, thermodynamic and equilibrium studies on the chloride adsorption of the as-fabricated LDHs were performed by batch experiment technique. Besides, the microstructures of as-obtained MgAl-LDHs were observed by X-ray diffraction and FT-IR spectra. The results indicate that the chloride adsorption on the MgAl-LDHs is significantly affected by the initial pH value, LDHs dosage and contact time. Langmuir isotherm can provide a better fit for the experimental data of Cl- adsorption on the MgAl-LDHs than Freundich isotherm. The negative values of Gibbs free energy change (Delta G(0)) and standard enthalpy change (Delta H-0) for the process calculated using Langmuir constants are obtained, confirming the spontaneous and exothermic nature of the chloride adsorption process. In addition, the quasi -second order kinetic model is well suitable to describe the chloride adsorption process. The anion exchange in the interlayer of MgAl-LDHs is contributed to the Cl- adsorption, which has been demonstrated by the microstructure observation.