Promoting the Mechanism of Oxygen Vacancy-Enriched γ-Fe2O3 Nanorods on the Immobilization of Gaseous Arsenic in Stimulated Flue Gas

Iron-bearing minerals have been reported to be sinks for arsenic, and oxygen vacancies in α-Fe2O3 can reduce the bioavailability of arsenic in soil and sediments and further contribute to arsenic immobilization. The mechanism of oxygen vacancies to promote gaseous arsenic immobilization by γ-Fe2O3 during coal combustion remains to be comprehensively investigated. The oxygen vacancy-enriched γ-Fe2O3 nanorod (Ovan γ-Fe2O3) was synthesized by regulating the synthesis conditions through NaBH4 reduction reaction and low-temperature calcination of lepidocrocite. The synthesized Ovan γ-Fe2O3 was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and it showed excellent gaseous As2O3 immobilization capacity (9.14 mg/g at 600 °C and 12.76 mg/g at 900 °C), much higher than the commercial γ-Fe2O3 under the stimulated flue gas (SFG) conditions. This sorbent also endured long-term gaseous As2O3 adsorption without penetration at 600 °C for 2 h (47.70 mg/g). Electron spin resonance (ESR) spectra proved that there were more oxygen vacancies (OVs) on Ovan γ-Fe2O3 than on the commercial γ-Fe2O3, which provided more arsenic immobilization sites, and it generated more extra OVs under 600 °C SFG. X-ray photoelectron spectroscopy (XPS) demonstrated that the immobilized arsenic compounds on the surface of the γ-Fe2O3 were transformed from As(III) to As(V), indicating that the oxygen vacancies promoted the oxidation of As2O3 to As2O5 with lower toxicity. The Ovan γ-Fe2O3 performed a strong thermal stability, long time endurance, and excellent immobilization capacity, making it a promising candidate for industrial use in high temperature flue gas.