Efficient recovery of rare earth elements from rare earth tailings using Acidithiobacillus thiooxidans: Mechanisms...

The recovery of rare earth elements (REEs) from secondary resources is critical for resource sustainability and environmental protection. In this study, Acidithiobacillus thiooxidans (A. thiooxidans) was applied to bioleach REEs from rare earth tailings (RET). An average REEs extraction efficiency of 98.1% was achieved from 0.5% (w/v) RET within 14 days, outperforming many previously reported bioleaching systems. Variations in pH and scanning electron microscope (SEM) observations indicated that bioleaching was primarily driven by sulfur oxidation-induced acid dissolution. Analyses using three-dimensional excitation-emission matrix (3D-EEM) and Fourier transform infrared spectroscopy (FTIR) revealed that extracellular polymeric substances (EPS) secreted by A. thiooxidans were enriched in oxygen-containing functional groups, which facilitated the stabilization of dissolved REEs through complexation. Pearson correlation analysis further confirmed that acid dissolution was the dominant leaching mechanism, while EPS-mediated interactions played a secondary stabilizing role. Overall, this study demonstrates the feasibility of efficient REEs recovery from RET via bioleaching.