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.

The ionic rare earth (RE) ore body undergoes particle transport and pore structure change during the leaching process, resulting in "uneven percolation, preferential channel, leaching blind area," and other problems, leading to structural changes in the ore body, low leaching efficiency, and waste of resources. The unsaturated infiltration process is also the key stage that causes these problems. The initial pore structure evolution of the ore body plays a decisive role in the permeability coefficient of the ore body, and the direct influencing factor of the permeability coefficient is the distribution of the pore radius. We carried out research through indoor simulated leaching, the filter paper method for determining matrix suction, and nuclear magnetic resonance (NMR) testing. An ionic rare earth ore soil-water characteristic curve within a large matrix suction range was obtained by the filter paper method. With the increase in volumetric water content, the matrix suction presents a sharp downward trend. When the volumetric water content is less than 20%, this rule is particularly obvious. With the increase in matrix suction, the thickness of the adsorbed water film on the particle surface and pore radius show a decreasing power function trend. Under percolation, the porosity of an ionic rare earth ore sample tends to increase linearly with the increase in volumetric water content during the process from non-saturation to saturation; the porosity of a saturated ore sample after seepage expanded by 17.5 times compared to that of an unsaturated ore sample before seepage. The change rule of the internal microstructure of the ore sample is reflected in the gradual disappearance of micro pores and the gradual formation of small, medium, large, and mega pores, which shows a gradual increase trend. In the pore radius distribution, the more large and medium pores, the larger the permeability coefficient; the more micro and small pores, the smaller the permeability coefficient. For some ore bodies with poor permeability, the ore body is infiltrated with clear water under small water pressure before leaching with a leaching solution, which can improve the permeability of the ore body, effectively improve the efficiency of rare earth leaching, and increase the economic benefits.

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.

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.