Surface Reaction of SnII on Goethite (α-FeOOH): Surface Complexation, Redox Reaction, Reductive Dissolution, Phase Transformation


Surface Reaction of SnII on Goethite (α-FeOOH): Surface Complexation, Redox Reaction, Reductive Dissolution, Phase Transformation

Dulnee, S.; Scheinost, A. C.

To elucidate the potential risk of 126Sn migration from nuclear waste repositories, we investigated the surface reactions of SnII on goethite as a function of pH and SnII 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 (HRTEM) and selected area electron diffraction (SAED). The results demonstrate the rapid and complete oxidation of SnII by goethite and formation of SnIV 1E and 2C surface complexes. The contribution of 2C complexes increasesd with Sn loading. The SnII oxidation leads to a quantitative release of FeII from goethite at low pH, and to the precipitation of magnetite at higher pH. Based on the XAS data, we developed a surface complexation model using the CD-MUSIC approach, with log K values of 15.5 ±1.4 for the 1E complex and 19.2 ±0.6 for the 2C complex. This model predicts Sn sorption across pH 2 to 12 and at two different Sn loadings (12.5 and 62.5 μmol/g).

Keywords: tin; EXAFS; goethite; sorption; redox; surface complexation; CD-MUSIC

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Publ.-Id: 20297