Exogenous organic acids drive efficient bioleaching of rare earth tailings by Acidithiobacillus thiooxidans: Process optimization and interfacial mechanism

The green recovery of rare earth elements (REEs) from rare earth tailings is crucial for resource recycling and mine ecological remediation. To address the low REEs leaching efficiency of a single Acidithiobacillus thiooxidans strain, this study evaluated the combined regulatory effects of four exogenous organic acids on REEs bioleaching, and elucidated the mechanisms via multiscale characterization and CatBoost machine learning model. The results showed that gluconic acid markedly enhanced REE leaching, raising the 8 day extraction efficiencies of La, Dy, and Y by 6.7–45%, 4–41%, and 12–32%, respectively, relative to the control across the tested dosages. Acetic acid exhibited an obvious inhibitory effect on leaching. Oxalic acid and citric acid showed concentration-dependent promotional effects with obvious threshold characteristics. XPS and BET analyses confirmed that the leaching system underwent dynamic structural evolution, and the complexation of organic acids with REEs and the surface coating of microbial extracellular polymers jointly regulated the leaching process. Pearson correlation and CatBoost model (R 2 =0.985) further revealed the intrinsic relationship between organic acid concentration, reaction time and leaching efficiency, providing theoretical support and technical reference for the green and efficient recovery of REEs from tailings.