Due to the special properties of the ammonium salts, ammonium acetate and ammonium citrate were used to explore the best leaching conditions of rare earth with compound ammonium carboxylate. This paper explored the influence of the molar ratio, ammonium concentration, experimental temperature, and pH of the compound leaching agents on the leaching efficiency of rare earth and aluminum, and it analyzed the leaching process based on the leaching kinetics, which provides a new method for leaching rare earth from the weathered crust elution-deposited rare earth ore. The results showed that under the conditions where the molar ratio of ammonium acetate and ammonium citrate was 7:3 and the ammonium concentration was 0.15 mol/L, the leaching efficiency of rare earth was the highest when the pH of leaching agent was 4.0 and the experimental temperature was 313 K. Meanwhile, when CH₃COONH₄ and (NH₄)₃Cit were used to leach rare earth ore, the leaching reaction kinetics equation of rare earth and aluminum were obtained. In the temperature range of 283–323 K, the apparent activation energy of rare earth was 14.89 kJ/mol and that of aluminum was 19.17 kJ/mol. The reaction order of rare earth was 0.98 and that of aluminum was 0.79. The results were in accordance with the shrinking core model and indicate that the concentration of the leaching agent had a greater influence on rare earth than aluminum. This process can reduce the use of ammonium salt, and it is of great significance to extract rare earth elements from weathered crust elution-deposited rare earth ore and improve the utilization rate of resources.

To reveal the regularity of variation in the rare earth occurrence states of weathered crust elution-deposited rare earth ores, ore samples from different weathering crust layers were obtained by performing the sequential extraction procedure. The order of rare earth contents firmly obeyed the following sequence: the weathered layer > humic layer > partly weathered layer. The occurrence states of rare earth elements were mainly the ion exchange state, carbonate bound state, iron–manganese oxide state, organic binding state and residual state. The proportions of rare earth elements found in the rare earth ion exchange state of the weathered layer, humic layer and partly weathered layer were 78.55%, 73.53% and 53.88%, respectively. The light rare earth elements (LREEs) found in the rare earth ion exchange state were enriched in the upper part of the weathering crust, while the heavy rare earth elements (HREEs) were enriched in the lower part. There were also obvious negative anomalies in the content of cerium in the ion exchange state. The content of rare earth elements found in the carbonate bound state was small, and the rare earth partition pattern was basically consistent with that of the ion exchange state, which had little effect on the differentiation of the rare earth elements. The iron–manganese oxide state was mainly enriched with cerium, and the content of cerium increased with the depth of the weathering crust. The iron–manganese oxide state was the main factor causing the phenomenon of the anomaly in the cerium content. Meanwhile, the iron oxides in the iron–manganese oxide state were mainly hematite and goethite. The organic binding state mainly beneficiated yttrium and cerium by complexation and certain adsorption. The content of elements found in the rare earth residual state was related to the degree of weathering and reflected the release sequence of rare earth elements in the mineralization process. Clarifying the rare earth occurrence states is conducive to better revealing the metallogenic regularity of weathered crust elution-deposited rare earth ores. In addition, the results can provide a valuable reference for expanding the available rare earth resources and the efficient comprehensive utilization of rare earth ore.

With the production of electric vehicles grows, the rare earth elements Pr and Nd, become increasingly significant, which are key to apply in the magnetic materials production. In order to achieve the green and efficient recovery of rare earth elements Pr and Nd from the rare earth leachate, this paper selected kaolinite and halloysite as adsorbents to conduct rare earth solution adsorption experiments for exploring the effects of the initial leachate concentration, the solution pH and the adsorption temperature on the adsorption process. The adsorption characteristics of Pr and Nd by typical clay minerals were analyzed by quantum chemical calculation. The results showed that the adsorption effects of clay minerals on Pr and Nd decreased with the rise of leachate concentration. When leachate pH increased, the adsorption efficiency of kaolinite and halloysite for Pr firstly increased and then decreased, and the optimal adsorption efficiency was 13.33% and 24.778% at pH 6, respectively. The adsorption effects of kaolinite and halloysite on Nd enhanced gradually with the increase of pH, which increased to 15.925% and 30.482% at pH 7, respectively. With temperature increased, the adsorption of Pr and Nd by kaolinite and halloysite was positively correlated. The isothermal adsorption model was fitted to the experimental data, and it was found that the adsorption of Pr and Nd by kaolinite and halloysite was consistent with the Langmuir model, with R2 above 0.96, indicating that the adsorption process was a single molecular layer adsorption. The results provide theoretical support for the effective recycling of Pr and Nd, which is of great significance for the utilization of rare earth permanent magnets.

Weathered crust elution-deposited rare earth ores represent a significant source of medium and heavy rare earth elements. Their mineralization mechanism fundamentally involves the adsorption and enrichment of rare earth ions on the surfaces of secondary minerals within the weathering crust. To elucidate the role of nano-sized iron oxide–clay mineral composites in the migration and enrichment of rare earth elements (REEs) in weathered crusts, α-Fe₂O₃, oolitic hematite, Fe₂O₃-kaolinite, and FeOOH-kaolinite composites were selected as adsorbents. Using La³⁺, Ce³⁺, and Y³⁺ as target ions, their adsorption performance and fractionation mechanisms were systematically investigated through batch adsorption experiments combined with characterization techniques including Langmuir/Freundlich model fitting, Zeta potential, XPS, and FT-IR. The results demonstrate that the adsorption of REEs on iron oxides and their composites follows the Langmuir model (R² > 0.96), indicating monolayer homogeneous adsorption. The FeOOH-kaolinite composite exhibited the highest adsorption capacity (0.6531 mmol/g for Ce). Amorphous iron oxide–clay mineral composites showed superior complexation adsorption and enrichment capabilities due to their higher oxygen vacancy concentration (Oβ/Oα = 3.86 for FeOOH-kaolinite), whereas crystalline iron oxide–clay mineral composites contributed significantly to REE fractionation and enrichment. Among the influencing factors, elevated temperature (20–60 °C) favored the adsorption process, with an activation energy > 4.2 kJ/mol indicating chemical adsorption dominance. Within the pH range of 3.0–7.0, adsorption capacity increased with rising pH, with Ce being more sensitive to ionic strength and pH variations. The adsorption mechanism was further elucidated through post-adsorption XPS, FT-IR in the low-wavenumber region, and desorption studies. This study confirms that iron oxide–clay mineral composites regulate the enrichment and fractionation of REEs in weathered crusts through the interplay of their surface properties and environmental factors, providing a scientific basis for refining the metallogenic theory and guiding the exploration and development of weathered crust elution-deposited rare earth ore resources.

Particle migration can affect the ore bodies stability of weathering crust elution-deposited rare earth ores during leaching. It may trigger geological disasters such as landslides. Therefore, direct shear tests, microstructure characterization tests, and numerical simulation tests were adopted. The mechanical behavior characteristics of ore samples with different burial depths were explored. Simultaneously, the evolution characteristics of their microstructure, mineral composition, and failure modes were also studied. The results showed that after leaching, the cohesion (c) initially rose and then dropped as the proportion of −0.075 mm particles increased. The internal friction angle (φ) initially dropped, then increased, and finally stabilized. When its proportion was greater than 20%, the c of the middle-upper part of the ore sample was greater than that of the upper part. Meanwhile, the φ was smaller than that of the upper part. Especially when its proportion was greater than 30%, the c increased gradually with depth. XRD analysis revealed that illite and kaolinite were the main mineral components for the fine particle migration. Simulation experiment results revealed that in ore samples with 10% fine particles, there was noticeable migration and deposition in the upper part. However, it was the least in the upper middle and lower parts. Contact number and coordination number sharply decreased with depth, then increased, and finally gradually reduced. As deposition increased, the shear zone tilt angle grew larger. More secondary shear zones formed. The cracks became more evenly distributed.