Adsorptive removal of phosphate from aqueous solutions using activated carbon loaded with Fe(III) oxide

An composite adsorbent for the removal of phosphate from aqueous solutions was synthesized by loading iron oxide onto activated carbon. The adsorbent can be separated from the medium by a simple magnetic procedure owing to the magnetic properties of the iron oxides. The properties of the composite were investigated by nitrogen adsorption, scanning electron microscopy and X-ray diffraction. The adsorption of phosphate ions by the composite adsorbent and the activated carbon was compared in batch experiments. The composite adsorbent showed fast adsorption rates and high adsorption capacities and its adsorptive performance for phosphate ions was dependent on the pH value, iron content and anion concentration. The adsorption capacities of phosphate ions at pH 3.0 were 98.39 mg/g for iron oxide/activated carbon composite and 78.90 mg/g for activated carbon. The adsorptive isotherms for phosphate ions with activated carbon and the composite adsorbent all match the Freundlich model better than the Langmuir model. The adsorption kinetic data could be well described by the Lagergren pseudo-second-order kinetic equation. The adsorption by the composite adsorbent is endothermic for phosphate ions.