Effect of Organic Acid-Modified Mesoporous Alumina toward Fluoride Ions Removal from Water

Mesoporous alumina (MA) was prepared via the sol-gel process at 40 degrees C/48 h followed by calcinations at 550 degrees C/5 h, in the absence of organic acids and in the presence of malic, tartaric, and citric acids (sample IDs: A-550, AM-550, AT-550, and AC-550, respectively). For fluoride ion adsorption on MA, the effects of different parameters such as contact time, concentration of adsorbate (F- ions), pH, temperature, and competing ions were studied. The adsorption kinetics of fluoride ions followed the pseudo-second-order model. The prepared MA showed the maximum F- ions adsorption capacity of 47.2, 49, 51.2, and 62.5 mg g(-1) for the samples A-550, AM-550, AT-550, and AC-550, respectively. The adsorption efficiency of MA followed the order AC-550 > AT-550 > AM-550 > A-550, corroborating to their BET surface area and pore volume. The competing anions (PO43-, Cl- and SO42-) have a slight effect of reducing the F- ions adsoption in the order of PO43- > SO42- > Cl-. For interpretation of adsorption isotherms, both Langmuir and Freundlich models were used. The F- ions adsorption efficiency remained almost the same up to 3 cycles of the regenerated MA.