AI Article Synopsis
- The transformation of ferrihydrite through photoinduced processes plays a crucial role in understanding the geochemical cycling of iron and trace elements in environments lacking oxygen.
- UV irradiation combined with sulfite leads to the formation of hydrated electrons, which enhance the reduction of ferrihydrite to Fe(II) and allow for the oxidation to more stable Fe(III) minerals.
- The concentration of sulfite is vital for determining the types and amounts of mineral products formed, with higher concentrations leading to a complete transformation to goethite and promoting the stabilization of cadmium in newly formed minerals.
Article Abstract
The photoinduced transformation of ferrihydrite is an important process that can predict the geochemical cycle of Fe in anoxic environments as well as the fate of trace elements bonded to Fe minerals. We report that the photooxidation of sulfite by UV irradiation produces hydrated electrons (super-reductants), which significantly promote ferrihydrite reduction to Fe(II), and SO (a moderate oxidant), enabling its further oxidation to more crystalline Fe(III) products. The experimental results show that the concentration of sulfite was key in influencing the rate and extent of surface-bound Fe(II) formation, which ultimately determined the distribution of individual products. For example, fitting of the Mössbauer spectroscopy data revealed that the relative abundances of mineral species after 8 h of treatment in the UV/sulfite systems were 41.9% lepidocrocite and 58.1% ferrihydrite at 2 mM SO; 41.8% goethite, 28.2% lepidocrocite, and 29.1% ferrihydrite at 5 mM SO; and 100% goethite at 10 mM SO. The combined results of the chemical speciation analysis and the Cd K-edge EXAFS characterization provided compelling evidence that Cd was firmly incorporated into the structure of newly formed minerals, particularly at high sulfite concentrations. These findings provide an understanding of the role of UV/sulfite in facilitating ferrihydrite transformation and promoting Cd stabilization in oxygen-deficit soils and aquatic environments.
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| http://dx.doi.org/10.1016/j.watres.2023.119607 | DOI Listing |
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