Removal of benzoate anions from aqueous solution using Mg-Al layered double hydroxides

The uptake of benzoate anions from aqueous solutions by calcined and uncalcined layered double hydroxides (LDHs) is reported. Adsorption (or sorption) isotherms have been determined at 25degreesC in the 0 to 100 mmol dm(-3) concentration range. The results showed that the calcined LDH sorbs 40 to 85% of the benzoate in solution in the concentration range usually found in industrial wastewater, and that the sorption capacity of this material is about 4 times greater than that observed for the parent LDH. The study of the sorption kinetics for the calcined material showed that it is a relatively slow process, which can be attributed to the fast regeneration of the calcined LDH with intercalated hydroxyl anions, followed by a slow process of anion exchange by benzoate. Collected solids after sorption present basal spacing close to 7.6 Angstrom, characteristic of intercalated hydroxyl anions or carbonate, suggesting a horizontal arrangement of benzoate in the interlayer.