Abstract: 　Bayan Obo rare earth tailings are rich in various strategic resources such as thorium and rare earth elements. Hydrothermal leaching with hydrochloric acid is an important technical approach to realize resource recovery and environment friendly disposal.To systematically explore the leaching effect and intrinsic mechanism of the tailings in the hydrochloric acid hydrothermal system,and clarify the influence of different leaching times on the leaching behavior of valuable elements (espe cially thorium),a variety of characterization methods including Inductively Coupled Plasma Emission Spectroscopy (ICP),X ray Diffraction (XRD),Fourier Transform Infrared Spectroscopy (FT-IR),Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS),Thermogravimetry-Differential Scanning Calorimetry (TG-DSC) and Zeta potential analysis were a dopted in this study to systematically investigate the phase changes,element leaching rules and surface property evolution of the tailings during the hydrothermal leaching process.The experimental results show that under the conditions of liquid-solid ratio of 6∶1 mL/g,temperature of 90 ℃ and leaching time of 4 h,the leaching rates of Th,Ca,Fe,Pb,Mg,Mn,Al and PO3 4 reach 20.08%,39.63%,36.81%,52.75%,69.25%,59.94%,58.69% and 73.64%,respectively.Among them,the leaching rates of major rare earth elements with important industrial value such as Y,Pr and Nd all exceed 30%.After leaching,the total weight loss of the tailings decreases significantly from the initial 9.14% to 1.98%,the absolute value of the surface Zeta poten tial changes from -4.93±0.70 mV to -9.70±0.68 mV,the hydrophilicity is significantly enhanced,and the thermal stability and chemical stability are obviously improved.The study confirms that hydrochloric acid can selectively leach the easily soluble mineral phases on the surface of the tailings through the synergistic effects of interfacial corrosion,acidolysis reaction,ion ex change and preferential dissolution of defects,promoting the enrichment of high-stability components such as silica,fluorite and monazite in the solid phase.This study not only provides a theoretical basis and technical reference for the efficient recovery of valuable elements (especially thorium and rare earth elements) from Bayan Obo rare earth tailings,but also offers a feasible path for the environment-friendly storage of such tailings,which is of great significance for promoting the resource utilization of rare earth tailings and the construction of green mines.

Key words: rare earth tailings,hydrochloric acid,hydrothermal leaching,thorium,valuable element recovery,stability