Adsorption of fluoride from aqueous solution on magnesia-loaded fly ash cenospheres

A novel adsorbent, magnesia-loaded fly ash cenospheres (MLC), was prepared by wet impregnation of fly ash cenospheres with magnesium chloride solution. Its physicochemical properties were characterized by X-ray diffractometry, Fourier transform infrared spectrometry, scanning electron microscopy and X-ray fluorescence spectrometry. Adsorption experiments were conducted to test the effects of pH, adsorbent dosage, contact time, reaction temperature and coexisting anions on fluoride removal. The coexisting ions had a large impact on fluoride removal by MLC in order comprehensive > dihydric phosphate > nitrate > sulfate. The adsorption process fitted the Langmuir isotherm and the adsorption kinetics followed the pseudo-second-order rate equation. The values of Delta G degrees (318 K), Delta H degrees and Delta S degrees were -0.409 kJ mol(-1), 20.04 kJ mol(-1) and 63.80 Jmol(-1)K(-1), respectively. The maximum adsorption capacity of MLC was about 6.0 mg g(-1) in the solution with 100 mg L-1 of fluoride ions at pH 3.0 and 318 K. MLC is low cost and more effective for fluoride adsorption so as to be used widely in wastewater treatment. (C) 2011 Elsevier B.V. All rights reserved.