Phosphate adsorption on hydroxyl-iron-lanthanum doped activated carbon fiber

Rare earth, typical lanthanum, has attracted significant attention due to its high phosphate adsorption capability, but the high price and scarcity of the resources hinder its practical application. In this study, Lanthanum(III) was mixed with Iron(III) to obtain the composite metallic (hydr)oxide which are doped onto activated carbon fiber (ACF), named as ACF-LaFe, for phosphate adsorption. Single-factor and response surface methodology (RSM) were used to optimize the preparation. The phosphate adsorption capacity of ACF-LaFe was calculated to be 29.44 mg/g, which is much higher than that of ACF-LaOH or ACF-HFO in our previous reports. Adsorption kinetics and isothermal adsorption studies showed that the pseudo-first-order model and the Langmuir isotherm fitted the experimental data quite well, indicating that the phosphate adsorption onto ACF-LaFe should be monolayer and chemical adsorption with the surface reaction. The phosphate adsorption mechanism was investigated by means of pH study, scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR). Ionic competition study showed that the presence of concomitant anions had profounder adverse effect on phosphate adsorption onto ACF-LaFe with the order of F- > SO42- > NO3- > Cl-. The present study demonstrated that ACF-LaFe would achieve the dual aims of high phosphate removal and low running cost. (C) 2012 Elsevier B.V. All rights reserved.