Adsorptive Removal of Arsenic by Mesoporous Iron Oxide in Aquatic Systems

In an effort to explore the potential for the removal of arsenic from water, mesoporous iron oxide (MI) was prepared using a sonochemical method. The surface area and average pore size of the MI sample were determined using a Brunauer Emmett Teller (BET) analysis to be 269 m2/g and 6.9 nm, respectively. Kinetic experiments revealed that more than 90% of the As(III) and As(V) were adsorbed onto the MI sample within 5 min at 0.1 g/L of MI dosage. The Langmuir equation model suited As(V), whereas As(III) related better to the Freundlich equation model due to different adsorption mechanisms. The predominant mechanism of As(V) adsorption onto MI is thought to be the electrostatic force between As(V) and MI, whereas As(III) in the solution bound to the adsorbed As(III) on the MI in a way consistent with van der Waals attraction. The removal rate of As(III) and As(V) has the highest adsorption efficiency in the pH 5–9 range. The adsorption of As(III) and As(V) was little affected by ionic strength, however the presence of H4SiO40 and PO43− significantly reduced the arsenic adsorption capacity. Furthermore, the adsorption and regeneration efficiency of MI was maintained at around 100% for given adsorption–regeneration cycles.