A Method of Estimating Uranium Reduction Degree for In situ Leaching Uranium Mine Restoration

To address the challenge of evaluating groundwater remediation effectiveness after in situ Leaching (ISL) uranium mining, this study proposes a novel quantitative assessment method based on uranium isotopic fractionation (δ²³⁸U). Taking a long-term suspended CO₂+O₂ ISL mining area in northern China as the research subject, systematic monitoring of δ²³⁸U values, hydrochemical parameters, and uranium concentrations in groundwater samples was conducted, revealing key geochemical behaviors during natural remediation. Preliminary exploration found that the ²³⁸U/²³⁵U fractionation factor ε in the study area is (0.46±0.07)‰, with most monitoring wells showing significantly negative δ²³⁸U values (minimum −2.49‰), indicating the occurrence of U(VI) reduction as the dominant remediation mechanism. Further research demonstrates that δ²³⁸U exhibits a significant negative correlation with redox potential (Eh) and serves as a more reliable direct indicator of U(VI) reduction extent than Eh alone. However, high concentrations of carbonate complexes can inhibit the reduction process, resulting in less negative δ²³⁸U values at strongly reducing sites (Eh < 0 mV). This study confirms that δ²³⁸U can serve as an effective tracer for assessing the efficacy and stability of natural groundwater remediation in ISL mining areas, providing a scientific basis for setting remediation goals and optimizing technical strategies.