Efficient removal of fluoride by hierarchical Ce-Fe bimetal oxides adsorbent: Thermodynamics, kinetics and mechanism

Ce-Fe bimetal oxides with hierarchical pore structure were successfully prepared by a facile approach and used as efficient adsorbent for fluoride removal. The existence of Fe(III) and Ce(IV) in the as-obtained adsorbent was determined by XRD, XPS and HRTEM. The BET surface area of the optimized adsorbent is 164.9 m(2)/g, and the corresponding hierarchical pore size centers at 1.68, 3.41 and 9.54 nm. Batch fluoride adsorption experiments were carried out to investigate the influence of various factors such as adsorbent dosage, contact time, initial solution pH and co-existing anions on the fluoride adsorption. Results show that the maximum adsorption capacity of the optimized adsorbent is as high as 60.97 mg/g. Furthermore, it shows high adsorption capacity over a wide range of pH from 2.9 to 10.1. The adsorption kinetic is well described by the pseudo-second-order model and the fluoride adsorption on the adsorbent agrees well with the Langmuir model. The effects of co-existing anions on the fluoride sorption followed the decreasing order of CO32- > HCO3- > SO42- > NO3- > Cl-, which was found to be closely correlated with the charge-radius ratio values (z/r) of the anions. Fluoride adsorption on the Ce-Fe bimetal oxides could be attributed to ion exchange between fluoride and Ce-OH groups. (C) 2015 Elsevier B.V. All rights reserved.