Impact of Zn substitution on Fe(II)-induced ferrihydrite transformation pathways

Ferrihydrite transformations in flooded paddy soils: rates, pathways, and product spatial distributions

“…The relative favourability of goethite or lepidocrocite formation from Fe( ii )-catalysed ferrihydrite transformation is heavily influenced by the interaction of dissolved Fe( ii ), mineral-sorbed Fe( ii ), mineral-bound Fe( iii ), and other ions in the system, by mechanisms that are still debated. 21,23,37,42,43,45,49,51,60 Lepidocrocite is the favoured product when surface-associated concentrations of Fe( ii ) are lower, because more surface-associated Fe( ii ) ions enable more electron transfer reactions that convert lepidocrocite to goethite. 21,37,42 However, sorption of ligands on product mineral surfaces may prevent clear correlation between the amount of Fe( ii ) surface adsorption and abundance of transformation products in an experimental system.…”

“…35,37,40,41 The rates and products depend strongly on the ratio of Fe( ii ) to ferrihydrite. 21,37,42–46 Moreover, previous studies have measured effects on the rates and products of Fe( ii )-catalysed ferrihydrite transformation caused by diverse dissolved or sorbed metal ions, 20,23,47,48 structurally incorporated cations, 9,17,19,23,49,50 dissolved, sorbed or structurally incorporated inorganic anions, 19,21,22,51–54 co-precipitated or sorbed organic compounds, 17,18,55–57 cultivated bacteria, 56,58,59 as well as varying pH, 34,37,60 temperature, 36,51,60 and ferrihydrite-to-solution ratio. 44 These studies suggest that soil components may reduce electron flow from sorbed Fe( ii ), for example, by competition with Fe( ii ) for ferrihydrite surface sorption sites, or that soil components may be toxic to soil microbes, reducing the rate of mineral transformation.…”

Pb-Bearing Ferrihydrite Bioreduction and Secondary-Mineral Precipitation during Fe Redox Cycling

“…At the end of RP1 and RP2, no total Pb and bioavailable Pb were detected in the aqueous phase. Yan et al [48] have shown a transient release of zinc to the solution during the transformations of zinc-ferrihydrite that is induced by Fe(II). The results suggest that the Pb was either adsorbed (e.g., onto the surface, the structural defects, and the nanopores of biogenic minerals), was structurally incorporated into the biogenic minerals, or was occluded in the aggregate of biogenic minerals at the end of the incubation periods.…”

“…Rate and extent of bioreduction during RP1. Metal-bearing Fh bioreduction has been widely studied to decipher the impact of substituted metals on the reduction processes [48][49][50]. The nature and concentration of the metals modify the Fh particles' physicochemical properties, which disrupts the bioreduction process, compared to metal-free Fh.…”

Electron Transfer, Atom Exchange, and Transformation of Iron Minerals in Soils: The Influence of Soil Organic Matter

“…Reaction of aqueous Fe­(II) [Fe­(II) aq ] with Fe­(III) oxides is a dynamic and complex redox-driven process that triggers a cascade of reactions, including (1) sorption of Fe­(II) aq to the oxides, (2) electron transfer between sorbed Fe­(II) and structural Fe­(III), , (3) reductive dissolution coupled with oxidative growth and atom exchange, − and (4) in some cases, transformation to secondary minerals. , Fe­(II)–Fe­(III) electron transfer and atom exchange have been documented for ferrihydrite, lepdocrocite, magnetite, goethite, and even the most thermodynamically stable Fe oxide, hematite, upon exposure to Fe­(II) aq . ,− For several more stable Fe oxides, including goethite and hematite, Fe electron transfer and atom exchange can proceed without any obvious nucleation of a new mineral phase, − although changes in crystallite size or particle morphology of goethite and hematite are often noted following reaction with Fe­(II) by X-ray diffraction (XRD) or transmission electron microscopy (TEM)/scanning electron microscopy (SEM) analysis. ,, By contrast, after reaction with Fe­(II) aq , thermodynamically unstable Fe oxides (e.g., ferrihydrite and lepidocrocite) undergo obvious secondary mineral reactions. ,,, For instance, in anoxic environments at circumneutral pH, even micromolar concentrations of Fe­(II) can accelerate the transformation of ferrihydrite into more stable mineral forms such as goethite and magnetite. ,− Consequently, the implications of Fe­(II) aq –Fe­(III) oxide reactions for Fe cycling and the environmental behaviors of nutrients, containments, and OM may depend greatly on a soil’s specific mineral composition in addition to the amount of exposure to Fe­(II) aq .…”