Surface Reaction of Sn^II on Goethite (α-FeOOH): Surface Complexation, Redox Reaction, Reductive Dissolution, and Phase Transformation

Abstract

To elucidate the potential risk of (126)Sn migration from nuclear waste repositories, we investigated the surface reactions of Sn(II) on goethite as a function of pH and Sn(II) loading under anoxic condition with O2 level < 2 ppmv. Tin redox state and surface structure were investigated by Sn K edge X-ray absorption spectroscopy (XAS), goethite phase transformations were investigated by high-resolution transmission electron microscopy and selected area electron diffraction. The results demonstrate the rapid and complete oxidation of Sn(II) by goethite and formation of Sn(IV) (1)E and (2)C surface complexes. The contribution of (2)C complexes increases with Sn loading. The Sn(II) oxidation leads to a quantitative release of Fe(II) from goethite at low pH, and to the precipitation of magnetite at higher pH. To predict Sn sorption, we applied surface complexation modeling using the charge distribution multisite complexation approach and the XAS-derived surface complexes. Log K values of 15.5 ± 1.4 for the (1)E complex and 19.2 ± 0.6 for the (2)C complex consistently predict Sn sorption across pH 2-12 and for two different Sn loadings and confirm the strong retention of Sn(II) even under anoxic conditions.

Goethite (α-FeOOH) nanopowders synthesized via a surfactant-assisted hydrothermal method: morphology, magnetic properties and conversion to rice-like α-Fe2O3 after annealing

“…Therefore, the rough edge seems like a kind of implication for the beginning of phase transition from α-FeOOH to α-Fe 2 O 3 , which could be confirmed by the results of XRD patterns and SEM images at 240ºC. 8 Fig. 5(a) gives the magnetic hysteresis loops of as-synthesized α-FeOOH powders obtained with different content of CTAB at 220ºC.…”

Fabrication of FeOOH hollow microboxes for purification of heavy metal-contaminated water

“…This high valence state of Fe endowed the FeOOH hollow structure with more unoccupied orbitals for linking with hydroxyl groups. 43 Furthermore, according to the results of the Boehm titration (Fig. S9, ESI †), a larger amount of protons were needed to change the pH value in case of the FeOOH microboxes, which clearly confirmed that a high content of hydroxyl groups was present on the surface of the hollow structures.…”

Deciphering the Distribution and Crystal-Chemical Environment of Arsenic, Lead, Silica, Phosphorus, Tin, and Zinc in a Porous Ferrihydrite Grain Using Transmission Electron Microscopy and Atom Probe Tomography

“…showed that Sn 4+ can replace up to 50% of the Fe 3+ sites in ferrihydrite. However, Sn 4+ is highly immobile due to the low solubility of cassiterite (SnO 2 ) and thus Sn 2+ dominates the aqueous geochemistry of Sn The latter cation oxidizes to Sn 4+ when interacting with surfaces of Fe-(hydr)­oxides (as observed for goethite and magnetite), which subsequently leads to the formation of adsorption complexes involving Sn 4+ -octahedra sharing edges or two corners with Fe 3+ -octahedra. , …”