Reactive Transport Modeling of Uranium In-Situ Leaching: Geochemical Validation and Analysis of Controls on Uranium Recovery

Global energy demand is projected to continue increasing in the coming decades. Nuclear energy is expected to remain an important component of future energy because of its ability to provide electricity with low greenhouse gas emissions. Saudi Arabia possesses uranium resources and, under Vision 2030, aims to expand mineral development to support economic diversification and long-term resource utilization. As uranium is the primary fuel for nuclear energy, efficient uranium extraction methods are increasingly important. In-situ leaching (ISL) has become the dominant uranium mining method because it enables uranium recovery with lower surface disturbance than conventional mining methods. However, uranium recovery during ISL is governed by coupled geochemical reactions and transport processes, making recovery behavior difficult to predict and limiting confidence in identifying the parameters that control recovery. This study investigates uranium ISL using a combined geochemical and hydrologic modeling approach with emphasis on consistency across scales. A two-stage modeling strategy was developed. The first stage focused on geochemical validation through thermodynamic, kinetic, and one-dimensional reactive transport modeling. Uranium dissolution, oxidation, and transport behavior were validated against published experimental studies to establish confidence in the geochemical framework. The second stage extended the validated geochemical framework into a two-dimensional reactive transport simulation representing a sandstone-hosted uranium deposit under acidic and oxidizing leaching conditions. Sensitivity analysis was then performed to identify the parameters controlling uranium recovery. The results show consistent chemical control across all modeling scales. Thermodynamic validation reproduced the dependence of uranium solubility on acidity, while kinetic validation reproduced oxidation-driven uranium dissolution. The one-dimensional validation captured the coupling between reaction and transport observed in laboratory experiments. At the reservoir scale, the model reproduced acid front, uranium breakthrough, peak production, declining production, and progressive ore depletion. Sensitivity analysis showed that uranium recovery is governed primarily by geochemical processes. Acid concentration was identified as the dominant control on recovery. The uraninite reaction rate constant, reactive surface area, and injection rate formed a comparable middle group, and porosity had the smallest effect. This study demonstrates that geochemical validation and reactive transport simulation can be used to predict uranium recovery and identify the operational and geochemical controls governing ISL performance.