Abstract:

The leaching solution readily migrates through high-permeability zones within the aquitard at in-situ leaching (ISL) uranium mining sites, leading to the diffusion of uranium and other contaminants into surrounding groundwater, which has become a critical bottleneck restricting the development of in-situ leaching uranium mining technology. Microbially induced calcium carbonate precipitation (MICP) exhibits effective cementation and permeability reduction in rock and soil. It can be used to seal high-permeability zones within the aquitard, but its standalone application often results in unsatisfactory sealing performance. Therefore, this study applies mesoporous silica (MS) synergistically with MICP to grout permeable sandstone from uranium mining areas and investigates its cementation and water-stopping performance. Through single-factor experiments, the effects of reaction time, grouting cycles, initial bacterial concentration (OD₆₀₀, the optical density measured at a wavelength of 600 nm), urea/Ca²⁺ molar ratio, and initial pH on the amount of calcium carbonate precipitation and the seepage reduction rate were analyzed. The sandstone before and after cementation was characterized using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and Fourier transform infrared spectroscopy (FTIR), to reveal the mechanisms of permeability reduction by MICP-MS. The results show that the addition of MS increased both the calcium carbonate content and the seepage reduction rate of the cemented sandstone. With an MS addition amount of 4%, an initial bacterial OD₆₀₀ of 1.2, a urea/Ca²⁺ ratio of 1.5:1.0, and an initial pH of 7, after five grouting cycles, the MICP-MS treatment achieved a seepage reduction rate of 90.72%. Microscopic analysis revealed that MS is rich in various functional groups and acts as nucleation sites adsorbing Ca²⁺, which promotes the precipitation of calcium carbonate. Moreover, MS and calcium carbonate can form an MS-CaCO₃ composite cement that jointly fills pores and reduces the permeability coefficient of sandstone, effectively preventing the diffusion and migration of the leaching solution. These results provide reliable technical support for the green and sustainable development of in-situ leaching uranium mining.

Key words: microbially induced carbonate precipitation, mesoporous silica, permeability reduction, in-situ leaching uranium mining, aquitard