Study on the Chemical Dissolution Behavior of Clay Minerals Under CO2+O2 In Situ Leaching Conditions for Uranium Recovery

The accumulation of dissolved species during the in situ leaching (ISL) of uranium can lead to ore-layer blockage and reduced production capacity. Clay minerals, including montmorillonite, chlorite, kaolinite, and illite, are the primary cementing and filling materials in sandstone-hosted uranium deposits in China. However, previous studies have predominantly focused on the leaching behavior of uranium minerals, while systematic investigations into the dissolution mechanism of clay minerals under CO2+O2 conditions remain scarce. In this study, laboratory dissolution experiments, scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS), computed tomography (CT) scanning, and field verification were conducted to systematically investigate the dissolution behavior of major clay minerals and their contribution to ore-layer blockage under CO2+O2 leaching conditions. The results indicate the following: (1) Montmorillonite exhibited the most significant dissolution, with granular deposits rich in Ca and Si formed on its surface, which were inferred to be Ca-Si-rich precipitates. (2) Obvious changes in both microstructure and macroscopic physical properties of clay minerals were observed before and after leaching, with porosity decreasing by approximately 12.96% and permeability decreasing by approximately 10.16%. (3) Field verification revealed that the scale in the ore layer, filter cloth blockage, and resin surface caking were primarily composed of silica gel and hydroxide/carbonate precipitates of Al, Ca, and Fe, which are closely related to the dissolution and leaching of clay minerals. This study confirms that montmorillonite is the main source of clogging substances, and long-term closed circulation of injection and extraction leads to the accumulation of precipitates, exerting a significant impact on the uranium-leaching system. The findings provide a theoretical basis for anti-clogging and permeability enhancement in CO2+O2 ISL operations.