Novel Ce(III) based Ce-oxide/Fe₃O₄ composite for high-efficiency removal of Sb(V) and Sb(III) from wastewater at wide pH range

The pollution of antimony (Sb) in water environment has threatened human health and ecological safety. Fe-Ce adsorbents have been considered as superior materials for Sb removal. However, poor stability and high sensitivity to pH variations limited their application. Herein, a novel Ce(III) based Ce-oxide/Fe₃O₄ composite (Fe₃O₄− [Ce(III)]_{x = 1.0}) was greenly prepared for adsorption of Sb(V) and Sb(III) from wastewater. Compared with Ce(IV), Ce(III) based Ce-oxide/Fe₃O₄ composite had better adsorption properties for both Sb(V) and Sb(III). Fe₃O₄− [Ce(III)]_{x = 1.0} effectively removed Sb(V) and Sb(III) at wide pH range (2.0–9.0), and the maximum adsorption capacities were 106.69 and 91.16 mg/g, respectively. Fe₃O₄− [Ce(III)]_{x = 1.0} not only had strong magnetism, but also removed 91.25% of Sb(V) and 81.47% of Sb(III) after seven adsorption-desorption cycles. Coexisting ions had little impact on removal of Sb(V) and Sb(III) via Fe₃O₄− [Ce(III)]_{x = 1.0}. Various characterization analyses suggested that Ce(III) was crucial to the adsorption processes. The main mechanisms for Sb adsorption included the formations of Fe-O-Sb and Ce-O-Sb complexes, ligand exchange, electrostatic attraction, and hydrogen bonding. Remarkably, the main contributors to Sb(V) and Sb(III) removal were respectively the outer=sphere complex (Fe-O-Sb(V)) and inner-sphere complexes (Ce-O-Sb(III/V) and Fe-O-Sb(III)), showing discrepancies of adsorption mechanisms between Sb(V) and Sb(III). Finally, two actual Sb-containing waters treated with FE₃O₄-{Ce(III)_x=1.0 both met the Sb discharge standard, highlighting its potential application value.