Abstract: This study addresses the issue of uranium-contaminated groundwater in decommissioned in-situ leaching uranium mining areas. Nano-hydroxyapatite (HAP) was synthesized using the gel method, and its ability to remove U(Ⅵ) was investigated by studying the effects of factors such as reaction time, initial U(Ⅵ) mass concentration, reaction temperature, and interfering ions. The reaction kinetics and thermodynamic behavior of HAP in U(Ⅵ) removal were also explored. The results before and after U(Ⅵ) removal by HAP were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), to elucidate the mechanism of U(Ⅵ) removal by HAP. Finally, the effectiveness of HAP for the remediation of real groundwater from decommissioned in situ uranium mining areas was evaluated. The results showed that in an acidic U(Ⅵ) solution (pH=3.0), adsorption equilibrium was reached within 120 min, with a U(Ⅵ) removal rate of 96.87% and a maximum adsorption capacity of 40.36 mg/g. In a neutral U(Ⅵ) solution (pH=7.0), adsorption equilibrium was achieved within 360 minutes, with a U(Ⅵ) removal rate of 96.04%, demonstrating excellent adsorption performance. The influence of various interfering ions on U(Ⅵ) removal by HAP was also investigated. At pH=3.0, Al³⁺ ions inhibited U(Ⅵ) removal, while at pH=7.0, \mathrmHCO_3^- ions had an inhibitory effect, whereas \mathrmPO_4^3- ions facilitated U(Ⅵ) removal. The mechanisms of U(Ⅵ) removal by HAP also varied under different pH conditions: at pH=3.0, the removal mechanism was mainly based on HAP dissolution-precipitation, surface complexation, and ion exchange; at pH=7.0, surface complexation and ion exchange dominated. HAP also demonstrated excellent performance in the treatment of real uranium-contaminated groundwater. Under acidic conditions (ρ₀=10.05 mg/L, pH=2.86), the U(Ⅵ) removal rate reached 87.5%. In a CO₂+O₂ neutral environment (ρ₀=10.3 mg/L, pH=7.58), the removal rate increased to 94.5%. In conclusion, HAP shows strong adsorption capacity for U(Ⅵ) and good environmental adaptability, making it a promising material for the remediation of uranium-contaminated groundwater in decommissioned in-situ leaching uranium mining areas.