Microbial reduction of low-crystallinity tripuhyite (FeSbO₄): Implications for Sb(V) cycling in contaminated...

Tripuhyite (FeSbO₄) is an important antimony (Sb)-bearing mineral that controls Sb mobility in contaminated environments, yet its structural stability during microbial reduction remains unresolved. Understanding how FeSbO₄ behaves under anoxic conditions is therefore necessary to predict natural Sb cycling. This study examined how an anaerobic microbial community interacts with FeSbO₄ and alters its structural and redox behavior. Across all conditions, FeSbO₄ released measurable Sb(V), demonstrating that the mineral undergoes partial dissolution in anoxic environment even without microbial activity. However, when extensive microbial Fe(III) reduction occurred in the presence of the electron shuttle anthraquinone-2,6-disulfonate (AQDS), the released Sb was re-immobilized. This indicates that microbial reduction processes modulate Sb mobility. Microbial community analysis showed the enrichment of acetate-utilizing Fe(III)-reducing bacteria as key drivers of Fe reduction. Although secondary Fe minerals were not detected, X-ray absorption fine structure measurements and scanning electron microscopy images revealed the formation of an Sb(III)-bearing phase consistent with valentinite (Sb₂O₃) in the AQDS-amended treatment. This transformation suggests that AQDS not only enhances Fe(III) reduction but is also linked to Sb(V) reduction, and facilitates the immobilization of reduced Sb(III) as Sb₂O₃. Overall, this work provides the first evidence that FeSbO₄ is susceptible to microbially mediated redox transformations, and that these processes can significantly alter the mobility and speciation of Sb in reducing environments.