Removal of selenite by zero-valent iron combined with ultrasound: Se(IV) concentration changes, Se(VI) generation, and reaction mechanism

• Zero-valent iron combined with ultrasound can effectively remove Se(IV).
• Reaction mechanism of Se(IV) with ZVI in presence of ultrasound was investigated.
• The primary reaction products of ZVI and Se(IV) were Se0, ferrihydrite, and Fe2O3.

In this paper, the performance and application of zero-valent iron (ZVI) assisted by ultrasonic irradiation for the removal of selenite (Se(IV)) in wastewater was evaluated and reaction mechanism of Se(IV) with ZVI in such systems was investigated. A series of batch experiments were conducted to determine the effects of ultrasound power, pH, ZVI concentration, N2 and air on Se(IV) removal. ZVI before and after reaction with Se(IV) was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Results indicated that ultrasound can lead to a significant synergy in the removal of Se(IV) by ZVI because ultrasound can promote the generation of OH and accelerate the advanced Fenton process. The primary reaction products of ZVI and Se(IV) were Se0, ferrihydrite, and Fe2O3.