Light Promotes the Immobilization of U(VI) by Ferrihydrite

Abstract

The environmental behaviors of uranium closely depend on its interaction with natural minerals. Ferrihydrite widely distributed in nature is considered as one main natural media that is able to change the geochemical behaviors of various elements. However, the semiconductor properties of ferrihydrite and its impacts on the environmental fate of elements are sometimes ignored. The present study systematically clarified the photocatalysis of U(VI) on ferrihydrite under anaerobic and aerobic conditions, respectively. Ferrihydrite showed excellent photoelectric response. Under anaerobic conditions, U(VI) was converted to U(IV) by light-irradiated ferrihydrite, in the form of UO2+x (x < 0.25), where •O2− was the dominant reactive reductive species. At pH 5.0, ~50% of U(VI) was removed after light irradiation for 2 h, while 100% U(VI) was eliminated at pH 6.0. The presence of methanol accelerated the reduction of U(VI). Under aerobic conditions, the light illumination on ferrihydrite also led to an obvious but slower removal of U(VI). The removal of U(VI) increased from ~25% to 70% as the pH increased from 5.0 to 6.0. The generation of H2O2 under aerobic conditions led to the formation of UO4•xH2O precipitates on ferrihydrite. Therefore, it is proved that light irradiation on ferrihydrite significantly changed the species of U(VI) and promoted the removal of uranium both under anaerobic and aerobic conditions.

Atrazine degradation through a heterogeneous dual-effect process using Fe–TiO2-allophane catalysts under sunlight

“…3 b and Table 2 present the Tauc-plot patterns of the different catalysts and the calculated band gap values, respectively. The Fe-allophane catalyst band gap was 1.71 eV, which is similar to the value reported for ferrihydrite [ 66 ]. Concerning the TiO 2 -allophane catalysts, band gap values between 3.24 eV and 3.29 eV were obtained, which are typical of anatase structures [ 42 , 67 ].…”

“…In the case of Fe-allophane catalyst, 34 % of ATZ degradation was achieved in the PC process after 360 min of reaction time, due to the photocatalytic properties of iron oxide present in the allophane structure. As highlighted earlier, the Fe-allophane catalyst displays a poorly ordered iron oxide phase, similar to the ferrihydrite-like materials [ 13 , 38 ], reported as a semiconductor material able to oxide pollutants under sunlight [ 66 ]. This result agrees with the previously discussed band-gap value (1.71 eV) and the ability of Fe-allophane to adsorb the light across a broad wavelength range.…”

Adsorption Behavior of U(VI) and Re(VII) on Iron Sulfide Nanoparticles Modified with Titanate Nanotubes: Mechanism and Performance Insights

“…A variety of methods have been proposed to treat U(VI) and Re(VII) from effluents, including ion exchange, [11] adsorption, [12] chemical precipitation, [13] liquid membrane, [14] and solvent extraction. [15] Compared with these methods, the adsorption method stands out with several advantages of convenience, efficiency, and economy.…”