Crust Elution-deposited Rare Earth Ore Research Articles

Role of Calcium Chloride on the Eluting Process of Residual Ammonium from Weathered Crust Elution-Deposited Rare Earth Ore Tailings

A large amount of ammonium salt leaching agent will remain in the leaching site of weathered crust elution-deposited rare earth ore (WREOs). The release of residual ammonium (RA) will seriously affect the water system ecology of the mining area, and it is urgent to control it. In this paper, column eluting was used to simulate the eluting process of RA in rare earth (RE) ore tailings, and the effects of calcium chloride concentration, eluting temperature, liquid-solid ratio, eluent pH and eluent flow rate on the eluting process of RA in rare earth ore tailings were discussed. It was found that calcium chloride could effectively elute the RA from ore tailings. Eluting agent pH almost had no effect on the eluting process of RA in the pH range of 4–6, and a greater impact on it at pH 8. The flow rate could effectively enhance the elution efficiency. The optimum conditions were calcium ion concentration of 0.1 mol/L, liquid-solid ratio of 2:1, pH 4–6, flow rate of 0.6 mL/min and elution at room temperature. At this time, the elution efficiency of RA was 91.85%. The eluting process of RA in ore tailings was controlled by the inner particle diffusing according to the kinetic analysis. The reaction order was 0.368, and the activation energy of the reaction is 12.450 kJ/mol. This will provide a theoretical basis and technical support for the efficient eluting process of residual ammonium in the leaching site of WREOs.

Insights into selective leaching of rare earths from weathered crust elution-deposited rare earth ore using magnesium sulfate

In this paper, a multi-stage leaching process for the weathered crust elution-deposited rare earth ore was proposed using MgSO4 as a leaching agent. The results indicate that with increasing the concentration of MgSO4 from 0.5 wt%–1.0 wt% to 2.0 wt%–4.0 wt%, the peak concentrations of rare earths increase from 1.87–3.59 to 5.49–10.21 g/L, and the collection periods of leach solution are shortened from 0.85–1.54 to 0.31–0.47 (liquid-to-ore ratio). When the rare earth ore is leached with leaching agent solution with high initial pH (3.0–5.0), the rare earths and aluminum are predominantly leached by Mg2+ instead of H+. However, H+ participate in the leaching process of rare earths and aluminum at lower initial pH (1.5–3.0) of the leaching agent solution. Especially, when the initial pH of leaching agent solution is 2.0, a large amount of aluminum is leached when the liquid-to-ore ratio is greater than 1.2. Based on the above insights, increasing the initial pH (3.0–5.0) of leaching agent solution in the injection stage using high-concentration MgSO4 (>1.0 wt%) can increase the peak concentration of rare earths in the leach solution and shorten the collection period. However, in the injection stage using low MgSO4 concentration (<1.0 wt%), an initial pH of leaching agent solution of 2.0 is selected to reduce the leaching amount of aluminum and the consumption of MgSO4. Comparing to the leaching process using constant MgSO4 concentration (2.0 wt%, initial pH of 5.0), the leaching efficiency of rare earths using a multi-stage leaching process is approximately equal (about 94.6%) under optimal conditions. The leaching amount of aluminum is reduced by 16.9%. The consumption of MgSO4 is reduced by 67.1%.

Optimization of a Rare Earth and Aluminum Leaching Process from Weathered Crust Elution-Deposited Rare Earth Ore with Surfactant CTAB

Ammonium sulfate is typically employed as a leaching agent in the in situ leaching of weathered crust elution-deposited rare earth ore. However, it is associated with challenges such as low efficiency in mass transfer for rare earth (RE) leaching, high usage of the leaching agent, and prolonged leaching duration. To address the issues mentioned above, the surfactant cetyltrimethyl ammonium bromide (CTAB) was compounded with 2% ammonium sulfate to form a leaching agent in this paper. The effects of CTAB concentration, temperature, pH, and leaching agent flow rate on the rare earth (RE) and aluminum (Al) leaching mass transfer process from RE ore were investigated using chromatographic plate theory. The results revealed that CTAB addition improved the RE mass transfer process while moderately inhibiting the Al mass transfer efficiency. Increasing the temperature and pH of the leaching solution led to higher theoretical plate numbers for RE and Al leaching, lowered theoretical plate height (HETP), and enhanced leaching mass transfer efficiency. However, under high temperature and alkaline conditions, the mass transfer efficiency begins to decrease, indicating that high temperature and alkaline conditions are not conducive to the synergistic enhancement of RE and Al leaching by CTAB. Considering that clay minerals have good pH buffering properties, adjusting the pH of the leaching solution during rare earth ore leaching operations was deemed unnecessary. The optimal mass transfer conditions for leaching RE and Al were identified as 2% ammonium sulfate concentration, 0.00103 mol/L CTAB concentration, pH range of 5.2–5.5 for the leaching solution, 0.6 mL/min leaching solution flow rate, and room temperature. The rare earth leaching mass transfer effect could be enhanced during summer operations.

Enhancement of weathered crust elution-deposited rare earth ores leaching process with the addition of PQ-10

To solve the problems of the long development period, low mass transfer efficiency and high impurity content in the in-situ leaching process of weathered crust elution-deposited rare earth ores (WCE-DREO), cationic hydroxyethyl cellulose (PQ-10) was composited with conventional leaching agent ammonium sulfate ((NH4)2SO4) to form a novel composite leaching agent. The effects of PQ-10 concentration, leaching temperature and leaching flow rate of the composite leaching agent on the leaching kinetics and mass transfer processes of rare earth (RE) and aluminum (Al) were investigated. Compared to the single leaching agent (NH4)2SO4, the composite leaching agent (2 wt% (NH4)2SO4+0.02 wt% PQ-10) can reduce the RE leaching equilibrium time from 465 to 130 min and increase the RE leaching efficiency and decrease the Al leaching efficiency. It also facilitates the leaching process of WCE-DREO by increasing the peak concentrations of RE and Al, reducing the theoretical tower plate height (HETP) and improving the leaching mass transfer efficiency. It is indicated that PQ-10 can promote the leaching of WCE-DREO. The leaching process of the composite leaching system conforms to the diffusion kinetic control model. When the PQ-10 concentration is in the range of 0.005 wt%–0.020 wt%, the reaction orders of RE and Al are 0.73 and 0.54, respectively, which shows a positive effect on the leaching velocity; when the PQ-10 concentration is in the range of 0.030 wt%–0.060 wt%, the reaction orders of RE and Al are –1.16 and –0.75, respectively, which show a negative effect on the leaching velocity. In the range of 10–50 °C, the apparent activation energies of RE and Al are 15.02 and 17.31 kJ/mol, respectively, and the higher the leaching temperature, the smaller the HETP and the higher the leaching velocity and mass transfer efficiency. The increase in leaching flow rate contributes to the increase in the longitudinal diffusion velocity of the leaching agent within WCE-DREO, causing a shorter time for RE and Al to reach leaching equilibrium. In addition, the flow rate and HETP are consistent with the Van Deemter equation. At a flow rate of 0.8 mL/min, HETP was minimized and the optimal mass transfer efficiencies is achieved for RE and Al.

Mass transfer in heap leaching of weathered crust elution deposited rare earth ore with Al2(SO4)3 solution

In order to increase efficiency and avoid NH4+–N pollution in the leaching process of weathered crust elution-deposited rare earth ores, the mass transfer in heap leaching with Al2(SO4)3 solution was simulated with column elution and experimentally optimized. The results indicate that the leaching yield is also up to 99 % for leaching with aluminum sulfate instead of ammonium sulfate. The optimal flow rate is 60 mL/h, the height equivalent to a theoretical plate (HETP) is 1.29 mm correspondingly. The peak value position of RE3+ is 60 mL/h, Fe3+ is 100 mL/h, however, Al3+ is 150 mL/h, and the heap leaching process has kinetic separation effect.

Leaching of rare earths and aluminum in weathered crust elution-deposited rare earth ore using magnesium sulfate: Effect of aluminum content in the leaching agent solution

Leaching of rare earths and aluminum in weathered crust elution-deposited rare earth ore using magnesium sulfate: Effect of aluminum content in the leaching agent solution

Effect of particle gradation on pore structure and seepage law of solution in weathered crust elution-deposited rare earth ores

Both CT and Avizo software were used to explore the effect of particle gradation on the evolution characteristics of pore structure and seepage paths in weathered crust elution-deposited rare earth ores during leaching. The results showed that the pore areas in four kinds of ore samples before leaching were mainly concentrated in 104–107 μm2, whose pore quantities accounted for 96.89%, 94.94%, 90.48%, and 89.45%, respectively, while the corresponding pore volume only accounted for 30.74%, 14.55%, 7.58%, and 2.84% of the total pore volume. With the decrease of fractal dimension, the average pore throat length increased, but pore throat quantities, the average pore throat radius and coordination number decreased. Compared with that before leaching, the change degree of pore structure during leaching increased with the fractal dimension decreasing. For example, the reduction rate of the average coordination number of ore samples was 14.36%, 21.30%, 28.00%, and 32.90%, respectively. Seepage simulation results indicated that seepage paths were uniformly distributed before leaching while the streamline density and seepage velocity increased with the fractal dimension decreasing. Besides, the phenomenon of the streamline interruption gradually reduced during leaching while preferential seepage got more obvious with the decrease of the fractal dimension.

Promotion Mechanism of Ammonium Formate in Ammonium Salt Leaching Process for Weathered Crust Elution-Deposited Rare Earth Ores

Weathered crust elution-deposited rare earth ores (WREOs) are significant strategic mineral resources. In industry, in situ leaching technology is usually applied with ammonium chloride and ammonium sulfate as the leaching solution. However, the slow seepage velocity of the leaching solution and low rare earth leaching efficiency still need to be improved. Ammonium formate can effectively improve the WREO leaching process. In order to further explore the effects of ammonium formate on the ammonium salt leaching process for WREOs, ammonium chloride and ammonium sulfate compounded with ammonium formate were used as leaching agents to determine their effects on leaching efficiency, seepage velocity and swelling. The results show that in the presence of ammonium formate, the rare earth leaching efficiencies with ammonium chloride and ammonium sulfate are both slightly increased, the seepage velocity of ammonium chloride and ammonium sulfate is increased by 1.67 × 10−4 cm·s−1 and 1.18 × 10−4 cm·s−1, and the swelling percentage falls by 0.14% and 0.37%, respectively. The thickness of the adsorbed water layer and thermogravimetric and XRD results confirm that ammonium formate can inhibit surface hydration and thus improve the WREO leaching process.

Leaching Behavior of Rare Earth Elements and Aluminum from Weathered Crust Elution-Deposited Rare Earth Ore with Ammonium Formate Inhibitor

In situ leaching of weathered crust elution-deposited rare earth ore usually uses ammonium sulfate as the leaching agent, which poses challenges such as low mass transfer efficiency, high consumption of the leaching agent and long leaching periods. In order to intensify the leaching process of rare earth elements and reduce the impurity of leaching accompanying rare earth, ammonium sulfate and ammonium formate were mixed as a novel compound leaching agent to treat weathered crust elution-deposited rare earth ore. The effects of ammonium formate concentration, liquid/solid ratio, leaching agent pH and leaching temperature on the leaching process of rare earth (RE) and aluminum (Al) were investigated and evaluated using the chromatographic plate theory. Results showed that ammonium formate could effectively enhance the mass transfer efficiency of rare earth and significantly inhibit the mass transfer efficiency of aluminum. Leaching agent pH has a greater impact on the mass transfer efficiency of aluminum. A higher leaching temperature could enhance the mass transfer efficiency of rare earth and aluminum by providing a driving force to overcome the resistance of diffusion. The optimum conditions for leaching rare earth and aluminum are 0.1 mol/L ammonium sulfate compounded with 0.032 mol/L ammonium formate, pH 4–8 of the leaching agent, 0.8:1 liquid:solid (mL/g) ratio and room temperature. Under this condition, the mass transfer efficiency of rare earth was improved, and the mass transfer efficiency of aluminum was significantly inhibited.

A reactive transport model for in-situ leaching of weathered crust elution-deposited rare earth ores using ammonium sulfate

This study presents a reactive transport model for the in-situ recovery of weathered crust elution-deposited rare earth ores and aims to provide predictive and optimization techniques for rare earth recovery. The model integrates Kerr's selection coefficient, dynamic reversible shrinking core model, and transport model to capture the dynamics of leaching fraction, rare earth elements (REEs), and exchangeable ions during in-situ leaching. The proposed model was validated through bench-scale equilibrium, kinetic, and column experiments, as well as numerical simulation. The results indicate that the deviation from using a single selection coefficient (referred to as 4.26 L2 mol−2 in this study) for modeling is acceptable. Both Darcy velocity and concentration of leaching solution mainly affect the peak value and bending degree of the post-peak leaching curve. Optimal cessation of leaching solution injection, such as substituting water after the peak of the leaching curve, enables effective conservation of leaching solution and reduction of environmental pollution. Differences of at least two orders of magnitude were observed between dynamic parameters derived from kinetic experiments (1.46 and 4.34 L mol−1 min−1) and those obtained from column experiments (2.60 × 10−3 and 1.71 × 10−2 L mol−1 min−1). This finding carries substantial implications for in-situ recovery and mineralization processes, highlighting the need for further investigation at the pore scale.

Influence of surfactant on clay swelling inhibition of weathered crust elution-deposited rare earth ores

Clay minerals are the main components of the weathered crust elution-deposited rare earth ores (WREOs), and their swelling properties have a significant effect on the safe and green in-situ leaching of WREOs. Few researches have been reported on the inhibition of clay swelling in WREOs and our teammates used combination of ammonium salts to suppress the clay swelling in previous work. Surfactants combined with (NH4)2SO4 were utilized as inhibitor in this study to reduce the amount of ammonium salts and thus decrease the ammonium pollution. Effects of different surfactants on inhibition of clay swelling were investigated, and the swelling inhibition mechanism was further discussed by DLVO theory. CTAB exhibited best performance among five surfactants. The swelling efficiency of kaolinite, halloysite and illite in DI water is 2.52%, 1.65% and 1.32% respectively, and these values can be reduced to 0.45%, 0.65% and 0.82% respectively in presence of single (NH4)2SO4. As (NH4)2SO4 was compounded with 0.04% CTAB, the swelling efficiency of kaolinite, halloysite and illite was further reduced to 0.25%, 0.45% and 0.31% respectively. The XRD and SEM analysis indicated that no change of the morphology and crystal structure of minerals after soaking with surfactants were presented. It was further clarified by DLVO theory that the London-van der Waals energy between clay particles increased, while both of the repulsion electrostatic energy and the total potential energy decreased in the presence of CTAB, and this was beneficial to the clay swelling inhibition.

Effect of particle size on the leaching of a weathered crust elution-deposited rare earth ore

Weathered crust elution-deposited rare earth ore is a typical porous medium, and the size of ore particles plays a crucial role in solution flow and rare earth ion transport. Ore particles with different sizes were obtained, and column leaching experiments were performed to study their seepage and leaching characteristics. Subsequently, the mechanisms underlying the effect of particle size on leaching were analysed. The results showed that the maximum concentration of the rare earth leachate and the penetration time of the samples decreased with the increase of the ore particle size, and the flow rate of the leachate exhibited an opposite trend. The breakthrough curves of the samples exhibited two forms: monotonically decreasing and parabolic. When the leaching solution was sufficient, the leaching efficiencies of the samples comprising ore particles larger than 5 mm and smaller than 0.075 mm were 75% and 95%, respectively, whereas the leaching efficiencies of the other samples reached 100%. The influencing mechanism showed that when ore particles are large, the pores among the particles lead to a low leaching efficiency. On the contrary, when the ore particles are small, the re-adsorption of rare earth ions to the surface of the ore particles can be easily promoted under the combined action of poor permeability, the high clay mineral content, the large specific surface area, the imbalance of the salt solution concentration between the ore and the solution and the weakly acidic leaching environment, resulting in a low leaching efficiency. Furthermore, the micromorphology of ore particles with a small size showed a rough surface, and the structure destroyed by leaching was unconducive to the flow rate of the solution in the orebody.

Development Review on Leaching Technology and Leaching Agents of Weathered Crust Elution-Deposited Rare Earth Ores

Weathered crust elution-deposited rare earth ores are key strategic resources and the main source of medium and heavy rare earths. This paper summarizes the development of leaching technology of rare earth ores, compares the advantages and disadvantages of the three generations of leaching technology, and introduces the improved heap leaching technology and the new technology of the leaching–extraction integration and enhanced leaching, focusing on the leaching of weathered crust elution-deposited rare earth ores. In this paper, the development of the leaching agents is expounded, and the research status and the development trend of the composite ammonium salt leaching agent, impurity inhibition leaching agent, swelling inhibition leaching agent, and seepage-promotion leaching agent are also introduced. And this paper summarizes the leaching mechanism and the development direction of leaching agents. Moreover, the future key research direction of weathered crust elution-deposited rare earth ores is proposed, which is green, efficient, safe development and utilization.

Leaching kinetics and permeability of polyethyleneimine added ammonium sulfate on weathered crust elution-deposited rare earth ores

At present, in-situ leaching of weathered crust elution-deposited rare earth ores (WCE-DREOs) encounter with problems such as long leaching cycles, slow infiltration rate and low product purity. In order to solve the above problems, the conventional leaching agent ammonium sulfate ((NH4)2SO4) was compounded with polymeric surfactant polyethyleneimine (PEI) to form a composite leaching agent. The effects of leaching temperature, PEI concentration, flow rate and pH on leaching kinetics and permeability of rare earths (RE) and aluminum (Al) in orebody were studied. It is found that with temperature increasing, the time required to reach leaching equilibrium for both RE and Al is shortened, the apparent activation energies of RE and Al are 14.79 and 13.45 kJ/mol, respectively, and the leaching processes are in accordance with the outer diffusion control. When the concentrations of (NH4)2SO4 and PEI in the composite leaching agent are 2.0 wt% and 0.4 wt%, the time required to reach leaching equilibrium for RE and Al is about 50% shorter than that using (NH4)2SO4 alone, and the leaching efficiencies of RE are slightly higher than that of Al. Properly increasing the temperature and flow rate of the composite leaching agent can improve the leaching efficiencies of RE and Al, but pH has neglected effects on the leaching efficiencies of RE. At PEI concentrations below 0.4 wt%, the addition of PEI promotes the leaching of RE and Al. In column leaching studies of the WCE-DREO, the addition of 0.4 wt% PEI to the traditional leaching agent (NH4)2SO4 has no impact on the leaching efficiencies of RE. However, it can significantly increase the infiltration rate of WCE-DREO, shortening the leaching time per 10 mL effluent from about 30 min for (NH4)2SO4 leaching system to 20 min for the composite leaching system. The leaching time is shortened by one-third, and the leaching cost is reduced, which can provide theoretical guidance for the development and commercial implementation of novel composite leaching agent for WCE-DREO.

Study on the Leaching Kinetics of Weathered Crust Elution-Deposited Rare Earth Ores by Hydroxypropyl Methyl Cellulose

In the process of the in situ leaching of weathered crust elution-deposited rare earth ores (WCE-DREOs), there are many problems in the conventional leaching agent, such as a slow leaching rate, low leaching yield and long leaching period. In order to solve the above problems, 2.0 wt% ammonium sulfate was mixed with hydroxypropyl methyl cellulose (HPMC). The effects of the HPMC concentration, temperature, pH and flow rate on the leaching kinetics of rare earth (RE) and aluminum (Al) were investigated. The results showed that when the concentration of HPMC was 0.05 wt%, the leaching equilibrium time of RE and Al was about 60% shorter than that of single ammonium sulfate. With an increase in the leaching temperature, the leaching equilibrium time of RE and Al decreased, and the apparent activation energy of RE and Al was 23.13 kJ/mol and 17.31 kJ/mol, respectively. The leaching process was in line with the internal diffusion kinetic control model. When the pH of the leaching agent was 4.02~8.01, the leaching yield of RE and Al was basically the same, but the leaching yield of Al was greatly increased at pH 2.0 due to a large amount of adsorbed hydroxy-Al in the RE ore eluded. The leaching yield reached the maximum when the flow rate was 0.7 mL/min. The leaching time and the leaching cost of RE can be saved by the composite leaching agent. The results provide theoretical guidance for the development and industrial application of the new composite leaching agent.

Effect of surfactant addition on leaching process of weathered crust elution-deposited rare earth ores with magnesium sulfate

Surfactants were proposed to be added into magnesium sulfate solution to improve the leaching process of weathered crust elution-deposited rare earth ores (WREOs). Effects of surfactants and their concentration on the seepage of leaching solutions and the leaching efficiency of rare earth (RE) and aluminum (Al) were investigated, and the leaching kinetics, the mass transfer process, the adhesion work and the adhesion work reduction factor were analyzed to reveal its strengthening leaching mechanism. The results show that cetyltrimethylammonium bromide (CTAB) has a better strengthening effect on the leaching process than dodecyl trimethyl ammonium bromide (DTAB), sodium dodecyl sulfate (SDS), sodium oleate and oleic acid. In the presence of 0.04% CTAB in 0.2 mol/L solution, the permeability coefficient of WREOs increases from 0.945×10−5 to 1.640×10−5 cm·s−1, and the leaching efficiency of RE increases from 80% to 90%, confirming the promotion of surfactants on the leaching process of WREOs. Kinetic analysis shows that the leaching process conforms to the inner diffusion control model, and the leaching kinetics equations of RE and Al related to CTAB content are obtained. Mass transfer discussion shows a smaller height equivalent to theoretical plate (HETP) of RE and Al at CTAB content of 0.04%, suggesting the higher mass transfer efficiency here. According to the interfacial properties of leaching solutions, the calculated adhesion work and the adhesion work reduction factor further demonstrate the strengthening leaching effect of CTAB on the leaching process of WREOs.

Influence of ammonium sulfate leaching agent on engineering properties of weathered crust elution-deposited rare earth ore

Influence of ammonium sulfate leaching agent on engineering properties of weathered crust elution-deposited rare earth ore

Mechanisms of swelling inhibition and seepage promotion of weathered crust elution-deposited rare earth ore by hydroxypropyl methyl cellulose

In-situ leaching process of weathered crust elution-deposited rare earth ore (WCE-DREO) often faces problems such as poor permeability and occurrence of landslides. The main reasons are the swelling of clay minerals by water absorption and blockage of seepage channels by fine particles. This study proposed using hydroxypropyl methyl cellulose (HPMC) as a novel green swelling inhibitor with the combination of ammonium sulfate ((NH4)2SO4) as an efficient composite leaching agent. The swelling inhibition performance of HPMC on swelling inhibition was evaluated through linear swelling tests and mud ball immersion tests. The mechanisms of HPMC on swelling inhibition and seepage promotion were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Scanning electron microscopy (SEM), Surface area analysis (BET), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), and the contact angle, zeta potential and particle size distribution were characterized. The results indicated that HPMC showed a good performance on swelling inhibition, which improved with the increase of HPMC concentration. HPMC expels the water from the interlayer. Moreover, HPMC adsorbs onto the surface of clay minerals by hydrogen bonding to form a hydrophobic film, which can prevent the clay minerals from hydration swelling. Due to the electric neutrality property of HPMC, the electrostatic repulsion of clay minerals can be reduced. Therefore, the fine particles of the clay minerals can be bridged to form larger particles by the long carbon chain of HPMC which leads to expansion of the seepage channels as well as the improvement of the permeability of the ores. According to the column leaching tests, the novel leaching agent composed of 0.05 wt% HPMC and 2 wt% (NH4)2SO4 not only showed a good leaching capacity of rare earth, but also inhibited the swelling of clay and enhanced the seepage when comparing with traditional leaching agent ((NH4)2SO4). Developing a novel leaching agent benefits the green, safe and high-efficiency exploitation of WCE-DREO.

Occurrence and vertical distribution of aluminum and rare earths in weathered crust elution-deposited rare earth ore: Effect of soil solution pH and clay minerals

Weathered crust elution-deposited rare earth ore is crucial source of medium and heavy rare earths, with in-situ leaching being the most common mining method. The high contents of impurity of aluminum in the leach solution are a significant challenge for the subsequent enrichment process of rare earths. A comprehensive understanding of the occurrences and vertical distribution of aluminum and rare earths within typical vertical profiles can provide valuable insights into entire design of the in-situ leaching. This paper improves a five-step sequential extraction method to analyze the occurrence and vertical distribution of rare earths and aluminum in vertical profiles from Chongzuo and Longyan. Experimental results demonstrate that soil solution pH is the main factor affecting the vertical distribution of ion-exchangeable rare earths. Both samples have distinct areas of enrichment for ion-exchangeable rare earths or aluminum. Ion-exchangeable rare earths are primary concentrated in the middle and lower parts of the ore layer (4–13 m in Chongzuo, 14–22 m in Longyan), while the ion-exchangeable aluminum is mainly enriched in the upper part of the ore layer (1–5 m in Chongzuo, and 2–14 m in Longyan). The vertical distribution of inorganic hydroxy aluminum is likely influenced by the micromorphology and particle size of the clay minerals. The inorganic hydroxy aluminum concentration in Chongzuo samples decreases continuously from 415.65 to 120.95 mg/kg with increasing sampling depth, whereas the concentration in Longyan samples (110.55–171.27 mg/kg) is almost independence with sampling depth. These results provide direct guidance for the entire design of the injection well depth and the leaching parameters, thereby inhibiting the leaching of impurity of aluminum and lower the consumption of leaching agent.

Effects of cations on rare earth adsorption and desorption in binding sites of montmorillonite

The exchangeability of rare earth (RE) in weathered crust elution-deposited rare earth ores largely depends on its interaction with clay minerals, which may be significantly influenced by various cations. Therefore, the effects of K&lt;sup&gt;+&lt;/sup&gt;, Ca&lt;sup&gt;2+&lt;/sup&gt; and Al&lt;sup&gt;3+&lt;/sup&gt; on RE&lt;sup&gt;3+&lt;/sup&gt; adsorption and desorption in binding sites of montmorillonite (MMT) were investigated. Through the pre-saturation, the interlayer ions of MMT had been replaced by K&lt;sup&gt;+&lt;/sup&gt;, Ca&lt;sup&gt;2+&lt;/sup&gt; or Al&lt;sup&gt;3+&lt;/sup&gt;. RE&lt;sup&gt;3+&lt;/sup&gt; can adsorb on the interlayer sites of Ca-MMT and K-MMT, but nearly not Al-MMT. The basal spacing of Ca-MMT is larger than K-MMT, which provides a smaller hinder effect of interlayer collapse for the interlayer diffusion of RE&lt;sup&gt;3+&lt;/sup&gt;. The adsorption capacity followed the order: Ca-MMT＞K-MMT＞Al-MMT and La&lt;sup&gt;3+&lt;/sup&gt;＞Y&lt;sup&gt;3+&lt;/sup&gt;＞Eu&lt;sup&gt;3+&lt;/sup&gt;. It can predict that the grade of the exchangeable RE in ores abundant in Ca&lt;sup&gt;2+&lt;/sup&gt; is the most, followed by the ore rich in K&lt;sup&gt;+&lt;/sup&gt; and Al&lt;sup&gt;3+&lt;/sup&gt; the least. Clay minerals tend to adsorb light RE and hard to adsorb middle and heavy RE. The reversibility of RE adsorbed in interlayers, especially in collapsed interlayers, is far worse than that on externals. The desorption rates of RE were in the order of RE-Al-MMT＞RE-K-MMT＞RE-Ca-MMT and Eu&lt;sup&gt;3+&lt;/sup&gt;＞Y&lt;sup&gt;3+&lt;/sup&gt;＞La&lt;sup&gt;3+&lt;/sup&gt;. For the desorption of interlayer RE&lt;sup&gt;3+&lt;/sup&gt;, NH&lt;sup&gt;4+&lt;/sup&gt; is better than Mg&lt;sup&gt;2+&lt;/sup&gt; because the larger change of the basal spacings (Δd) provides more minor activation energy barriers (ΔE) for NH&lt;sup&gt;4+&lt;/sup&gt; diffusion within interlayers. It can enrich the metallogeny theory of weathered crust elution-deposited rare earth ores and provide a certain theoretical basis for its efficient exploitation.