Abstract
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°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 Δ G 0 and Δ H o calculated using the Langmuir constant, confirm the spontaneous and exothermic nature of the removal of fluoride.
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