Adsorption of Cobalt(II) from Aqueous Solutions by Fe3O4/Bentonite Nanocomposite

Fe3O4 and Fe3O4/bentonite were prepared by chemical co-precipitation method. They were characterized by X-ray powder diffraction (XRD), Fourier infrared spectroscopy (FTIR), and transmission electron microscope (TEM). Adsorption of cobalt(II) on the bentonite, Fe3O4, and Fe3O4/bentonite nanocomposite was studied. The results indicated that the metal oxides mainly occurred in the form of spinel structure of Fe3O4 and the presence of Fe3O4 significantly affect the surface area and pore structure of the bentonite. The specific surface area (Brunauer-Emmett-Teller (BET) method) of bentonite, Fe3O4, and Fe3O4/bentonite were determined to be 34.44, 98.44, and 140.5 m(2) g(-1), respectively. TEM image of Fe3O4/bentonite shows the particle diameter at 10 nm. The maximum adsorption capacity of cobalt(II) by Fe3O4/bentonite nanocomposite was determined to be 18.76 mg g(-1). The adsorption strongly depends on pH, where the removal efficiency increases as the pH turns to alkaline range (pH 9). The results suggest that higher adsorption capacity of composite than bentonite is attributed to the presence of Fe3O4. The adsorption process follows pseudo-second-order kinetics. The equilibrium data was analyzed by Langmuir model showing high correlation coefficient. The thermodynamic study of adsorption process showed that the adsorption of Co(II) onto Fe3O4 /bentonite was carried out spontaneously.