During in situ leaching of ionic rare earth ore, the pore structure of the orebody changes due to the chemical replacement reaction between the leaching agent and the rare earth ore. To explore the influence of leaching agents on the pore structure of ionic rare earth ore during the leaching process, magnesium sulfate solutions with different concentrations and pH are used as leaching agents in this paper. An experimental method of indoor simulated column leaching, a Zetaprobe potential analyzer, and an NM-60 rock microstructure analyzer to measure parameters, including surface zeta potential, T2 map, and the pore structure of rare-earth ore particles, were used to analyze the influence law of magnesium sulfate solution on the pore structure of ionic rare earth ore. The result proves that pure H₂O leaching has little effect on the surface Zeta potential and the internal pore structure of the ore particles. In the leaching process of magnesium sulfate solutions with different concentrations, the absolute value of Zeta potential decreases, and the internal pore structure evolves from medium, large, and extra-large to small pores. In the leaching process of magnesium sulfate solutions with different pH, the absolute value of Zeta potential decreases and then increases slightly with the end of the ion exchange reaction. The internal pore structure generally shows a decrease in the number of small and extra-large pores and an increase in the number of medium and large pores. According to the analysis, the concentration and pH of the leaching agent cause the change of thickness of the electric double layer of the fine particles in the orebody, break the balance of interaction force between soil particles, and result in the evolution of a micropore structure of orebody during leaching.

During in-situ mining and leaching of ionic rare earth ore, a chemical replacement reaction occurs between the leaching agent and rare earth ore. The thickness of the shear layer on the surface of colloidal particles is an important physical parameter. Based on the Gouy–Chapman double-layer theory and Poisson–Boltzmann equation, the relational expression for the thickness of the shear layer in the electric double layer on the particle surface under the condition of 2:2 + 3:2 mixture electrolytes (MgSO₄ + RE₂(SO₄)₃) is derived. On this basis, an indoor column leaching experiment of MgSO₄ solution is conducted, and the surface Zeta potential of rare earth ore particles is measured using a Zetaprobe potential analyzer. The surface potential and the thickness of the shear layer in the leaching process with different concentrations solutions (2.5%, 3.0%, and 3.5%) are calculated. The effects of a MgSO₄ solution concentration and particle surface potential on the thickness of the shear layer in the electric double layer are analyzed. It provides a theoretical basis for the study of the internal seepage of the ore body under the condition of the coexistence of multiple ions in the leaching process.

In in situ leaching, fine particles can be stripped and transported with the leach solution, significantly altering the particle size distribution and pore structure of each layer of the rare earth ore body. In this study, water and magnesium sulfate were used as leaching agents. Based on indoor column leaching experiments, particle gradation experiments, and pore structure tests, this study investigates and analyzes the patterns of particle migration and changes in pore structure in rare earth ores with varying fine particle contents under leaching conditions. The results indicate that during the leaching process, the degree of change in particle gradation follows the order of upper layer > middle layer > lower layer. As the depth increases, the soil becomes denser, leading to reduced permeability, a slower seepage rate of the leaching solution, and a higher fine particle content, making the effect more pronounced. During magnesium sulfate leaching, the overall trend of porosity in the rare earth ore structure initially increases and then decreases. Additionally, a higher fine particle content corresponds to higher porosity. In the early and late stages of leaching, pore size changes involve the transformation of larger pores into smaller ones, followed by the conversion of smaller pores into larger ones. Moreover, the higher the fine particle content, the greater the degree of transformation between the pore sizes.

Due to the intersection of three mining rights in a mining area, the stability of the rock mass is mutually affected after mining operations. To study the optimal backfill ratio and the surface stability after backfilling in the adjacent goaf areas of the three mines in this mining area, a mineral deposit model is established using Rhino software. The model spans 2500 m in the east–west direction, 3000 m in the north–south direction, and ranges from an underground elevation of −610 m below. FLAC3D software was then used to analyze the surface stability under two different backfill ratios after the complete excavation of the ore body. Additionally, 52 monitoring points were set up at critical buildings and structures. The results revealed that after the complete excavation of the ore body, large-scale surface subsidence occurred in the mining area, with the main subsidence center located in the Yinzhushan mining area. Under backfill condition 1, six monitoring points experienced settlements exceeding 30.00 mm, with a maximum settlement of 53.98 mm. Under backfill condition 2, three monitoring points exceeded 30.00 mm, with a maximum settlement of 51.93 mm. The level displacement deformation at the monitoring points under both conditions met the stability requirements specified by national standards. By comparing the settlements at the monitoring points, it was determined that backfill condition 2 represents the optimal backfill ratio. This study provides a theoretical basis for practical backfilling operations in the mine.

The permeability of ionic rare is a crucial factor influencing the leaching rate of rare earth elements. In the Gannan region, many ionic rare earth ores exhibit poor permeability and high compressibility compared to sandy soils. The permeability coefficient is a key indicator of the hydraulic performance of these ores. Thus, this study investigates the permeability coefficients of ionic rare earth ores with varying fines contents during the leaching process, with a specific focus on analyzing the impact of fines on permeability performance. To provide a comprehensive assessment of the influence of fines, we prepared ionic rare earth ore samples with fines contents of 5%, 10%, 15%, 20%, 25%, and 30%, ensuring that the overall particle size distributions remained consistent with the original gradation. A constant head permeability test was employed to measure the permeability coefficients of these ore samples throughout the leaching process. We specifically examined how varying fines contents influenced permeability across the upper, middle, and lower layers of the ore body, as well as the overall permeability when subjected to both distilled water and magnesium sulfate solutions. To further elucidate the differences in permeability performance among the various rare earth ore samples, we performed a data fitting analysis of the initial permeability coefficients against fines content, uniformity coefficient, average particle diameter, and void ratio. This analysis aims to quantify the fines effect across different rare earth ores and establish correlations among state parameters, such as fines content, and the initial permeability coefficient.