Kinetic and equilibrium study on uptake of iodide ion by calcined layered double hydroxides

Iodide contamination removed using calcined MgAl-CO3 layered double hydroxides (denoted as CLDH) was conducted in batch conditions. The equilibrium isotherms of uptake of iodide by CLDH were well fitted by the Langmuir equation, and thermodynamic parameters including Delta G(0), Delta H-0 and Delta S-0 were calculated from Langmuir constants. The negative value of Delta H-0 confirms the exothermic nature of adsorption. The negative values of Delta G(0) at 30, 40, 50 and 60 degrees C indicate the spontaneous nature of adsorption. The negative value of Delta S-0 suggests the decreased randomness at the solid/solution interface for the uptake of iodide on CLDH. The influences of initial iodide ion concentration, dosage of CLDH, temperature of iodide removal have been tested in kinetic, respectively. Three kinetic models were used to fit the experimental data, and it was found that the pseudo-second order kinetics model could be used to describe the uptake process appropriately. The value of E-a was calculated to be 100.3 kJ mol(-1), which suggests that the process of uptake iodide ion is controlled by the reaction rate of iodide ion with the CLDH rather than diffusion. The reconstruction of CLDH to I-LDHs due to uptake of iodide ion has been confirmed by X-ray diffraction patterns, FT-IR spectroscopy and TG-MS measurements.