Synthesis of novel adsorbent S-SiO2@Fe3O4 based on strong bonding of S-O-Se for selenium removal in water

Industrial activities always result in out of limits of selenium [Se(IV) and Se(VI)] in aqueous, which seriously threatens human health. The sulfur loaded magnetic microspheres (SLMM) were successfully prepared by in-situ synthesis method and authenticated by XRD, SEM-EDS, TEM, BET, Raman, FT-IR, TG and VSM. The Se(IV) and Se(VI) adsorption by SLMM could adapt to a wide range of pH values (pH=2–10). Langmuir model indicated that the adsorption processes as a monolayer with homogeneous binding energy. The adsorption capacity for Se(IV) and Se(VI) by SLMM were 25.77 and 9.25 mg/g (25 °C) and declined with temperature increase. Thermodynamics demonstrated that the adsorption process was chemisorption with spontaneous exothermic properties. The adsorption rates were mainly controlled by mass transfer and chemisorption. The removal mechanism can be interpreted by the bonding of elemental sulfur and reduction of Fe(II) through Raman spectrum, HPLC-HG-AFS and XPS analysis. DFT (Density functional theory) calculations further revealed that the sulfur was inclined to bond with oxygen atom of Se(IV) with the most negative adsorption energy (Ead = −115.522 kJ/mol). In addition to sulfate and phosphate, SLMM had good anti-interference ability to other studied common anions in water. The used SLMM was identified with the good stabilization of selenium and the low possibility of secondary pollution caused by sulfur spills by leaching test. Our work disclosed the strong interaction between elemental sulfur and selenium and also provided a new-type adsorbent for selenium removal in aqueous for the first time.