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), N2 adsorption–desorption isotherms, Mössbauer spectroscopy, and scanning electron microscopy (SEM). The results suggest that the main magnetic phase present is maghemite (γ-Fe2O3). A magnetization enhancement can be produced by treatment with H2 at 600 °C to reduce maghemite to magnetite. Nitrogen adsorption isotherms showed that the surface area and microporosity increased from 7 m2 g−1 (Vmicropores=0.003 cm3 g−1) for the pure bentonite to 55 m2 g−1 (Vmicropores=0.009 cm3 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.