Sporosarcina Pasteurii was chosen for the experiment to study the effect and mechanism of fine-grained uranium tailings reinforced by MICP. The biochemical characteristics of strains and microbial immobilization in uranium tailings were analyzed. The results showed that the CaCO3 production rate is positively correlated with the physiological activity of Sporosarcina Pasteurii and the concentration of calcium sources, and the higher the solution concentration of CaCl2, the lower the discharge rate of bacterial liquid from the sand column, but high concentration of CaCl2 solution will affect the uniform distribution and migration of bacteria in the uranium tailings. After 16 days, the direct shear was used to test the reinforcement effects of fine-grained uranium tailings by MICP. The cohesive force and the internal friction angle of fine-grained uranium tailings were increased by 140.1% and 46.7%. The production amount of CaCO3 is 138.89 kg/m3. The results showed that the MICP-reinforced technology can effectively improve the shear strength of the uranium tailings, and the experiment provides a new method for the reinforcement of the fine-grained uranium tailings dam.

The sand columns inoculated with the indigenous microorganism (Aspergillus niger) were used to investigate the effect of bioclogging during the radioactive effluent percolation. The hydraulic gradient, volumetric flow rate, and uranyl ions concentration were monitored over time. The sand columns were operated with continuous radioactive effluent of uranium tailings reservoir. After 68 days, the hydraulic conductivity of the sand columns decreased more than 72%, and the adsorption rate of uranyl ions by Aspergillus niger reached more than 90%. Environmental scanning electron microscope imaging confirmed the biofilm covering the surface of sand particles and connecting sand particles together, which resulted in a reduction of hydraulic conductivity. The results indicated that the propagation of Aspergillus niger can clog the seepage channel and effectively adsorb the uranyl ions of radioactive effluent in the porous media, which provides a suitable measure for controlling the migration of radioactive effluent of uranium tailings reservoir into the subsurface environment.

The soil–water characteristic curve (SWCC) is an essential parameter for studying the mechanical properties of unsaturated tailings, and it plays an important role in stability assessment and prediction of unsaturated tailings dams. In this paper, the matrix suction was measured indirectly by a filter paper-based method to investigate the effects of key factors (gradation, temperature, and initial dry density) on the soil–water characteristic curves of fine-grained tailings, and the Van Genuchten model was adopted to obtain the empirical equation of SWCC and to verify the accuracy of experimental results. The results showed the following: 1) the Van Genuchten model fits well the relationship between matric suction and volumetric moisture content of fine-grained tailings, indicating that experimental data determined by filter paper-based method is accurate and appropriate; 2) at the same volumetric moisture content, the matrix suction increased with decreasing average particle size, and the decrease in temperature will increase the matrix suction and water-holding capacity of fine-grained tailings, and the matrix suction of the tailings in summer is 38.3% lower than that in winter under the natural volumetric moisture content (14.0%); 3) when the saturation degree of fine-grained tailings is less than 60%, the greater the initial dry density, the better the water-holding capacity and matrix suction.

The stability of tailings dam will be affected by the internal erosion under unsteady seepage caused by heavy rainfall infiltration which changes the physical and mechanical properties of tailings. In this paper, the hydraulic sedimentary model was established to investigate the effects of dry beach slope on the sedimentary characteristics of tailings in upstream tailings dam, and the results indicated that the dry beach with a larger slope has a more obvious stratification of tailings. Additionally, the sand column model was built to investigate the effects of internal erosion on the physical and mechanical properties of sedimentary tailings under unsteady seepage, and the results indicated that the migration of fine-grained tailings was caused by internal erosion increases the permeability and reduces the shear strength of the tailings. After internal erosion of tailings under heavy rainfall in 50 years return period for 24 h, the average particle size of downstream tailings (sample DT), midstream tailings (sample MT), and upstream tailings (sample UT) increased by 6.4%, 12.0%, and 2.4%, respectively, the hydraulic conductivity of the samples DT, MT, and UT increased by 27.2%, 17.9%, and 15.3%, respectively, and the shear strength of each samples decreased by 20.9%, 15.1%, and 12.4%, respectively.