Modeling of Cd(II) Sorption on Mixed Oxide

Abstract

Mixed oxide of iron and silicon (0.75M Fe(OH)₃:0.25M SiO₂) was synthesized and characterized by various techniques like surface area analysis, point of zero charge (PZC), energy dispersive X-rays (EDX) spectroscopy, Thermogravimetric and differential thermal analysis (TGDTA), Fourier transform infrared spectroscopy (FTIR) and X-rays diffraction (XRD) analysis. The uptake of Cd²⁺ ions on mixed oxide increased with pH, temperature and metal ion concentration. Sorption data have been interpreted in terms of both Langmuir and Freundlich models. The Xm values at pH 7 are found to be almost twice as compared to pH 5. The values of both ∆H and ∆S were found to be positive indicating that the sorption process was endothermic and accompanied by the dehydration of Cd²⁺. Further, the negative value of ∆G confirms the spontaneity of the reaction. The ion exchange mechanism was suggested to take place for each Cd²⁺ ions at pH 5, whereas ion exchange was found coupled with non specific adsorption of metal cations at pH 7.