Efficient removal of Se-79 from highly acidic solution using SiO2 particles functionalised with iron hydroxide

• A novel adsorbent FeOOH@SiO 2 was successfully prepared and used for removal of Se(IV) and Se(VI). • FeOOH@SiO 2 shows powerful adsorption abilities for Se(IV) and Se(VI) in 3 mol/L HNO 3 system. • FeOOH@SiO 2 has excellent acid resistance, γ-irradiation and thermal stability. • Surface complexing process was proposed for Se(IV) and Se(VI) adsorption. Due to its high solubility, radioactivity and toxicity, the separation of selenium from spent fuel reprocessing waste and industrial wastewater has attracted much attention. In this study, a novel adsorbent FeOOH@SiO 2 with particle size of ∼100 μm was successfully prepared by loading FeOOH on micron-sized silica with emulsion methods. FeOOH@SiO 2 with good acid resistance, γ-irradiation and thermal stability exhibits excellent adsorption abilities for Se(IV) and Se(VI) including fast adsorption kinetics, great adsorption capacities (11.0 mg/g for Se(IV) and 6.04 mg/g for Se(VI)) and preferable adsorption selectivity. It is worth noting that FeOOH@SiO 2 can still remove nearly 90 % of Se(IV) and 80 % of Se(VI) even in 3 mol/L HNO 3 system. Combined with the observations from X-ray photoelectron spectroscopic characterization and surface potential measurement, the adsorption mechanism caused with electrostatic attraction and the formation of inner complexes for Se(IV), and reduction reaction and partial formation of outer complexes for Se(VI) can be deduced. After 4 adsorption–desorption cycles, FeOOH@SiO 2 still exhibits satisfactory reusability. Dynamic column experiments also demonstrated that FeOOH@SiO 2 exhibited excellent removal capabilities towards Se(IV) and Se(VI) from real water samples. The present work demonstrates that FeOOH@SiO 2 has great potential application for 79 Se removal in highly acidic nuclear waste.