Clay-iron oxide magnetic composites for the adsorption of contaminants in water

In this work, the adsorption features of clays with the magnetic properties of iron oxides have been combined in a composite to produce a magnetic adsorbent. These magnetic composites can be used as adsorbent for contaminants in water and can be subsequently removed from the medium by a simple magnetic process. The bentonite-iron oxide magnetic composites have been prepared with weight ratios of 2:1, 1.5:1, and 1:1 and characterized by powder X-ray diffraction (XRD), thermogravimetric analysis (TG), magnetization measurements, chemical analyses, temperature-programmed reduction (TPR), N-2 adsorption-desorption isotherms, Mossbauer spectroscopy, and scanning electron microscopy (SEM). The results suggest that the main magnetic phase present is maghemite (gamma-Fe2O3). A magnetization enhancement can be produced by treatment with H-2 at 600 degreesC to reduce maghemite to magnetite. Nitrogen adsorption isotherms showed that the surface area and microporosity increased from 7 m(2) g(-1) (V-micropores = 0.003 cm(3) g(-1)) for the pure bentonite to 55 m(2) g(-1) (V-micropores = 0.009 cm(3) g(-1)) for the composite clay/iron oxide (2:1). The adsorption isotherms of metal ions Ni2+, Cu2+, Cd2+, and Zn2+ from aqueous solution onto the composites also showed that the presence of iron oxide produced an increase on the adsorption capacity of the bentonite. (C) 2002 Elsevier Science B.V. All rights reserved.