Kinetics of cadmium(II) uptake by mixed maghemite-magnetite nanoparticles.

In the present study, batch adsorption experiments involving the adsorption of Cd(II) ions from aqueous solutions have been carried out using mixed maghemite-magnetite as adsorbent. The uptake capacity of Cd(II) ions by mixed maghemite-magnetite increased with an increase in the pH of the adsorbate solution. An increase in adsorbent dosage increased Cd(II) removal but decreased adsorption capacity and it was found to follow the pseudo-second-order model. Cd removal from a solution containing 1.5 mg/L initial concentration of Cd(II) decreased from 1.9 to 1.3 mg/g upon increasing the temperature from 10 to 50 °C. Cadmium adsorption may be partly diffusion controlled and partly due to electrostatic effect along with specific adsorption involving the adsorption of Cd(++) and CdOH(+) on mixed maghemite-magnetite nanoparticles in the alkaline pH range. X-ray photoelectron spectroscopy (XPS) surveys confirmed that Cd(2+) ions may undergo oxidation-reduction reactions upon exposure to mixed maghemite-magnetite, or may be fixed by complexation to oxygen atoms in the oxyhydroxy groups at the surface of the iron oxide nanoparticles. After Cd(II) adsorption by the maghemite-magnetite mixture, the percent maghemite decreased from 74.8 to 68.5%.