Adsorption behaviour of calcined layered double hydroxides towards removal of fluoride from aqueous solution

Removal of fluoride from aqueous solution by calcined layered double hydroxides (CLDHs) was investigated in batch mode. The influences of calcined temperature, Mg/Al molar ratio of CLDHs, PH of aqueous solution, temperature and co-existing anions on the removal of fluoride have been discussed in detail. it was found that the LDHs with an Mg/Al ratio of 2 calcined at 500 degrees C had the highest capacity to remove fluoride and the maximum percentage removal of fluoride takes place at PH 6.0. The adsorption capacity of CLDHs decreases with a rise in temperature, indicating that the removal process is exothermic in nature. The data from isotherms fitted well to the linearly transformed Langmuir equation. The negative values of Delta G(0) and Delta H-0 calculated using the Langmuir constant, confirm the spontaneous and exothermic nature of the removal of fluoride.