| The calcined LDH has been demonstrated to reconsititute their original layered structure in the presence of appropriate anions. In the light of this so-called "memory effect", removal of chloride from aqueous solution was studied on calcined Mg-Al-C03 LDH. The influences of CLDH structures, adsorbent dose, initial chloride concentration, and temperature on removal of chloride have been investigated, respectively. The maximum adsorption capacity was obtained at a calcined temperature of 500℃, Mg/Al ratio of 4 within 6h. The residual chloride was found to be 3mg/L with an initial concentration of 100mg/L. The second-order kinetics was observed for the adsorption process which follows the Freundlich-type and Langmuir-typeadsorption isotherm. Thermodynamic parameters such as △G~0, △H~0 △S~0 were calculated from Langmuir isotherm. The negative value of △H~0 confirms the exothermic nature of adsorption. The negative value of △G~0 indicates the spontaneous nature of adsorption. The negative values of △S~0 suggest the decreased randomness at the solid/solution interface for the adsorption of fluoride on CLDH, because of the CLDH reconsititute their original layered structure. The rate constants and activation energy of adsorption were also calculated from temperature tests. An E_a value of 43.8kJ/mol indicates that this process is not diffusion-determining, but reaction-determining. The explanation of adsorption phenomenon has been supported by X-ray diffraction and FT-IR results.
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