Removal of perchlorate contaminants by calcined Zn/Al layered double hydroxides: Equilibrium, kinetics, and column studies

The adsorption properties of calcined layered double hydroxide (denoted as CLDH) for perchlorate (ClO4−) pollutant from aqueous solution were examined in batch and column model. The influences of chemical composition of adsorbents, adsorbent dose, and co-existing anions on the perchlorate removal in batch model have been investigated. The maximum uptake capacity was obtained at a calcined temperature of 500 °C with Zn/Al ratio of 2. The Freundlich isotherm and Langmuir isotherm were used to fit the data of equilibrium experiments. The removal of perchlorate ion is best represented by the Freundlich curve than that of the Langmuir. Free energy (ΔG0 = − 1.4 kJ/mol), calculated from Freundlich constants, indicated the spontaneity of the uptake process. The adsorption process was found to be endothermic and followed the modified multiplex kinetic model. The calculated values of Ea1 and Ea2 are 11.66 and 30.13 kJ/mol respectively, indicating that the rapid step of the uptake process is controlled by diffusion, and the slow step is controlled by the reaction of perchlorate with the CLDH rather than by diffusion. The effect of flow rate on the column behavior was also studied. Increasing the residence time in the column could enhance the sorption capacity of the bed and its efficiency.