Modeling of Cd(II) sorption on mixed oxide

Mixed oxide of iron and silicon (0.75m fe(oh)3:0.25m sio 2) 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 δh and δs were found to be positive indicating that the sorption process was endothermic and accompanied by the dehydration of cd2+. further,the negative value of δg 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.