In Situ Acidic Leaching Behavior and Clogging Mitigation Strategies for Sandstone-Hosted Uranium Deposits in Inner Mongolian Basin, China

To elucidate formation clogging mechanisms during the acidic in situ leaching (ISL) of a sandstone-hosted uranium deposit in Inner Mongolia, this study combines mineralogical characterization, permeability tests, leaching experiments, and field trials. The low-carbonate ore (0.73% CaCO3 equivalent) consists predominantly of quartz, feldspar, and clay minerals, with insoluble U(IV) contributing 60.36% of the total uranium. Core permeability under acid exposure evolved through three distinct stages: an initial gradual decline driven by gypsum precipitation, followed by a fluctuating increase due to mineral dissolution, and culminating in a final decline and stabilization induced by feldspar illitization and fine-particle migration. Laboratory column leaching identified 10 g·L−1 H2SO4 as the optimal leaching agent, yielding a residue-based uranium recovery of 95.43% at a low acid consumption of 9.10 kg per tonne of ore. Field trials confirmed that the accumulation of Ca2+, Al3+, Fe3+, and SO42− triggers the precipitation of Al(OH)3, Fe(OH)3, and gypsum, leading to severe formation clogging and pump failure. To mitigate this, a 7-day injection-production switching strategy is proposed to acidify the near-wellbore zone to pH < 2, effectively dissolving precipitates and restoring formation permeability. These findings provide practical guidance for optimizing acidic ISL operations in low-carbonate, clay-rich sandstone-hosted uranium deposits.