Efficient removal of antimonate and antimonite by a novel lanthanum-manganese binary oxide: Performance and mechanism

Antimony is a highly toxic pollutant and its removal from water gains increasing attention. To effectively remove both Sb(III) and Sb(V), a novel lanthanum-manganese binary oxide (L₁M₂BO) adsorbent was synthesized by a simple oxidation coupled with precipitation method. The as-prepared L₁M₂BO was detailedly characterized by the XRD, SEM, TEM, BET, FTIR and XPS techniques. It is amorphous and irregular in shape, with a particle size of 50-100 nm and a specific surface area of 180.4 m²/g. A remarkable synergistic effect between the lanthanum hydroxide and Mn oxide in improving antimony adsorption is shown. The maximum adsorption capacities of Sb(III) and Sb(V) are 364.6 mg/g and 131.1 mg/g at pH 7.0, respectively, which outcompete most of reported adsorbents. The adsorption behaviors of antimony fitted well the pseudo-second-order kinetic and Freundlich models. The adsorption mechanism of Sb(V) involves mainly the replacement of surface metal hydroxyl and forming inner-sphere complex. While the Sb(III) removal is a more complicated process, containing both Sb(III) adsorption and oxidation to Sb(V). Furthermore, the spent L₁M₂BO sorbent can be regenerated and reused. The L₁M₂BO could be used as an attractive adsorbent for antimony removal, owing to its easily fabrication, high effectiveness and reusability.