Mechanistic competition between chemical dissolution and physical mass transfer in sandstone uranium leaching:...

In-situ leaching of sandstone-type uranium deposits is frequently constrained by permeability impairment due to pore throat clogging. This issue not only hinders uranium recovery efficiency but also escalates the environmental risk of radioactive nuclide mobilization into surrounding aquifers. Currently, the relative contributions of chemical dissolution limitations and pore-permeability evolution to leaching efficiency remain poorly understood and lack a systematic quantitative evaluation. Herein, a multi-scale experimental framework comparing powder and column leaching was constructed. By introducing a physical mass-transfer efficiency factor (β) and integrating Visual MINTEQ thermodynamic simulations, the mechanisms of precipitation-induced clogging during water-rock interactions were systematically analyzed. Results demonstrate significant variability in the capacity of different lixiviants to mitigate mass-transfer resistance. Citric acid exhibited the highest efficiency, whereas EDDS demonstrated the lowest. Inorganic salt systems, while primarily driven by chemical oxidation, are prone to the precipitation of amorphous colloids (e.g., iron hydroxides). This triggers pore throat clogging and inhibits permeability enhancement, thereby increasing the risk of radioactive nuclide sequestration in the subsurface. Low-molecular-weight organic acids synergistically integrate pore-permeability optimization with efficient chemical complexation, enabling effective mobilization of radioactive nuclides. However, oxalic acid systems are susceptible to localized clogging due to secondary calcium oxalate precipitation. While synthetic chelating agents exhibit strong targeted extraction capacity, they struggle to degrade the rigid quartz-rich mineral framework, leading to significant reductions in leaching efficiency due to physical blockage. These findings provide a theoretical basis for elucidating the pore-clogging mechanisms governed by water-rock interactions and offer scientific guidance for optimizing ISL processes to maximize uranium recovery.