Mechanism of action of Fe(III) on antimony release under anoxic acidic conditions

Oxidative dissolution of stibnite (Sb₂S₃) is the primary process that controls the release of antimony (Sb) from rock and ore into the soil and water environment and affects its transport and transformation. Fe(III) in acid mine wastewater is a widespread natural oxidant in the mine environment. However, the role of Fe(III) on the oxidative dissolution of Sb₂S₃ and Sb release is unknown. By simulating a dark anoxic and acidic mine groundwater environment, this study conducted Fe(III) concentration to Sb₂S₃ surface area ratio (I) controlled Sb₂S₃ oxidative dissolution kinetics experiments, and combined the dissolved state composition and solid phase characterization means of S-Sb-Fe redox products to reveal the mechanism of Fe(III) action on Sb release. The results show that the oxidative dissolution of Sb₂S₃ under the action of Fe(III) is an acid-producing process, and the larger the I value is, the more obvious the promotion effect of Fe(III) on Sb release. Under anoxic conditions, Fe(III) undergoes redox with Sb₂S₃, and the main products are Sb(V), S(0) and Fe(II). After the reaction, S(0) and Fe₂O₃ were detected on the mineral surface, which hindered the continuation of the oxidative dissolution reaction of Sb₂S₃. At a certain value of I, both the low concentration of Fe(III) and the increase of dissolved oxygen (DO) will reduce the attachment of S(0) on the mineral surface and promote the increase of Sb release; the Cl⁻ in solution will promote the dissolution release of Sb₂S₃ through the coordination complexation effect. The interaction between Fe(III) and Sb₂S₃ under anoxic acidic conditions controls the release of Sb, which can provide an important theoretical basis for prevention and control of groundwater Sb contamination after mine pit closure.