Magnetic gamma-Fe2O3/Fe-doped hydroxyapatite nanostructures as high-efficiency cadmium adsorbents

Nowadays, water pollution by industrial waste water that contains heavy metal elements, such as Cd, has become an urgent concern to be solved. In this work, magnetic gamma-Fe2O3/Fe-doped hydroxyapatite (HAP) nanostructures are realized as Cd(II) adsorbents with outstanding adsorption performance. The Vibrating Sample Magnetometer (VSM) analysis and magnetic separation experiments reveal that gamma-Fe2O3/Fe-doped HAP nanostructures can be effectively separated by external magnet. Compared with pure HAP, the gamma-Fe2O3/Fe-doped HAP nanostructures show higher adsorbed concentration and adsorption rate. The maximum adsorbed concentration at the equilibrium is 258 mg g(-1) (under initial concentration of 500 mg L-1, temperature = 25 degrees C and pH = 5.0), which is higher than values reported for most of HAP-based adsorbents. The adsorption data could be well fitted by the Freundlich model, and the adsorption kinetic follows the pseudo-second-order model. Furthermore, the study of adsorption mechanism reveals that both ion-exchange and electrostatic interaction are involved in process of Cd(II) adsorption.