Exploring the role of extracellular polymeric substances in the antimony leaching of tailings by Acidithiobacillus ferrooxidans

The concentration of Sb bearing tailings in water located in abandoned antimony mines was found to be a big problem, as they contaminate other water resources and entire food chain. Microorganisms were found to be key in tailing leaching and reaction speeding in the presence of extracellular polymeric substances (EPS) produced by bacteria. Herein, we investigated the pattern of the Sb leaching from Sb bearing tailings using Acidithiobacillus ferrooxidans, and analyzed the mechanism of EPS in the leaching process of Sb. To completely and deeply understand the functions of EPS in the bioleaching of antimony tailings, the generation behavior of EPS produced by Acidithiobacillus ferrooxidans (A. ferrooxidans) during bioleaching was characterized by three-dimensional excitation-emission matrix (3D-EEM). Meanwhile, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) were used to show the changes of EPS functional groups before and after leaching. Compared with the functional groups in EPS produced by A. ferrooxidans before leaching, the content of hydroxyl and amino groups that reduce high-valent metals to low-valent metals in EPS decreases after leaching, and the carbonyl content increases, corresponding to the ratio of trivalent antimony increased, indicating that EPS could reduce the risk of pentavalent antimony to trivalent one. At the same time, with biological scanning electron microscopy and energy spectrum scanning, the observation of EPS on the mineral surface showed that Sb was adsorbed in the EPS, and the XPS of Sb was fine. Spectral analysis showed that the Sb adsorbed in EPS contained both Sb(III) and Sb(V). Besides, for revealing the influence of EPS in the leaching process of Sb from tailings, this work provided an in-depth understanding of the mechanism of Sb released from tailings under the action of A. ferrooxidans and further provides a basis for the biogeochemical cycle of Sb.