Antimony(V) Incorporation into Schwertmannite: Critical Insights on Antimony Retention in Acidic Environments

This study examines incorporation of Sb(V) into schwertmannite-an Fe(III) oxyhydroxysulfate mineral that can be an important Sb host phase in acidic environments. Schwertmannite was synthesized from solutions containing a range of Sb(V)/Fe(III) ratios, and the resulting solids were investigated using geochemical analysis, powder X-ray diffraction (XRD), dissolution kinetic experiments, and extended X-ray absorption fine structure (EXAFS) spectroscopy. Shell-fitting and wavelet transform analyses of Sb K-edge EXAFS data, together with congruent Sb and Fe release during schwertmannite dissolution, indicate that schwertmannite incorporates Sb(V) via heterovalent substitution for Fe(III). Elemental analysis combined with XRD and Fe K-edge EXAFS spectroscopy shows that schwertmannite can incorporate Sb(V) via this mechanism at up to about 8 mol % substitution when formed from solutions having Sb/Fe ratios <= 0.04 (higher ratios inhibit schwertmannite formation). Incorporation of Sb(V) into schwertmannite involves formation of edge and double-corner sharing linkages between (SbO6)-O-V and Fe-III(O,OH)(6) octahedra which strongly stabilize schwertmannite against dissolution. This implies that Sb(V)-coprecipitated schwertmannite may represent a potential long-term sink for Sb in acidic environments.

Automated summary

This study investigates the incorporation of Sb(V) into schwertmannite and finds that heterovalent substitution for Fe(III) is the mechanism of Sb(V) incorporation. Schwertmannite can stabilize Sb(V) through the formation of edge and double-corner sharing linkages. This suggests that Sb(V)-coprecipitated schwertmannite may serve as a long-term sink for Sb in acidic environments.