Investigation on evolution characteristic of dynamic pore and reactive transport of leaching solute in uranium-bearing sandstone during in-situ alkaline leaching mining: An in-situ LF-NMR leaching experiment

In-situ uranium leaching involves complex physicochemical interactions critically influencing reservoir permeability and leaching efficiency. This study investigated microstructural changes in uranium-bearing sandstone during alkaline leaching mining through integrated column leaching experiments, real-time multi-pore geometry structure and leaching solution morphology was motored using online low-field nuclear magnetic resonance (LF-NMR), and uranium-bearing sandstone component and leaching agent was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF). The uranium-bearing sandstone predominantly comprises micropores (T 2 < 2.5 ms), mesopores (2.5 ms < T 2 < 100 ms), and macropores (T 2 > 100 ms), with the pore system mainly composed of quartz, clinochlore, kaoline, and orthoclase. The results demonstrate that permeability reduction of 48.6% (from 0.976 to 0.502 mD), with total pore porosity increase of 2.44% was primarily driven by a substantial micropore reduction of 5.98%. A significant micropore clogging was induced by precipitation of secondary minerals (CaSO 4 , Mg(OH) 2 , and silica colloids) during late-stage leaching (156–363 PV). An innovative empirical relation model for microporosity and permeability was established, and enhanced the prediction accuracy of permeability evolution. These insights reveal that micropore dynamically influence permeability evolution and uranium recovery efficiency, which benefits the technology optimization in alkaline leaching mining.