Ion-adsorption Rare Earth Ores Research Articles

Untargeted metabolomics reveals the mechanism for leaching rare earth elements from ion-adsorption rare earth ores using a composite lixiviant

Rare earth elements (REEs) are an important strategic scarce resource, and how to mine and utilise them efficiently and greenly is a difficult problem. In this study, to reduce the use of chemical reagents in the leaching process, Bacillus thuringiensis fermentation broth and magnesium acetate were used as composite lixiviants to leach REEs from ionic rare earth ores via biochemical synergy. The effectiveness of composite lixiviant for leaching REEs was studied, and the optimum leaching conditions were determined. In addition, untargeted metabolomics was used to explore metabolite differences and metabolic pathway profiles before and after leaching with the composite lixiviant. The interaction between the composite lixiviant and the rare earth minerals was also investigated by combining various characterisation tools. The results showed that the leaching rate was 96.3 % when the concentration of magnesium acetate in the composite lixiviant was 0.3 mol/L, the pH was 4, and the liquid–solid ratio was 2:1. Metabolomics analysis showed that lipids and lipid-like molecules, benzenoids, and organic acids, and derivatives contained in the fermentation broth of the complex leach play an important role in the leaching process. This study provides a new composite lixiviant for leaching ionic REEs, which can reduce the dosage of chemical reagents, provide a reference for the biochemical synergistic leaching of ionic rare earth ores, and help guide environmentally friendly and efficient leaching of ionic rare earth ores in the future.

Interactive effects of ammonium sulfate and lead on alfalfa in rare earth tailings: Physiological responses and toxicity thresholds

Ion-adsorption rare earth ore contains significant levels of leaching agents and heavy metals, leading to substantial co-contamination. This presents significant challenges for ecological rehabilitation, yet there is limited understanding of the toxicity thresholds associated with the co-contamination of ammonium sulfate (AS) and lead (Pb) on pioneer plants. Here, we investigated the toxicity thresholds of various aspects of alfalfa, including growth, ultrastructural changes, metabolism, antioxidant system response, and Pb accumulation. The results indicated that the co-contamination of AS-Pb decreased the dry weight of shoot and root by 26 %–77 % and 18 %–92 %, respectively, leading to irregular root cell morphology and nucleus disintegration. The high concentration and combined exposures to AS and Pb induced oxidative stress on alfalfa, which stimulated the defense of the antioxidative system and resulted in an increase in proline levels and a decrease in soluble sugars. Structural equation modeling analysis and integrated biomarker response elucidated that the soluble sugars, proline, and POD were the key physiological indicators of alfalfa under stresses and indicated that co-exposure induced more severe oxidative stress in alfalfa. The toxicity thresholds under single exposure were 496 (EC5), 566 (EC10), 719 (EC25), 940 (EC50) mg kg−1 for AS and 505 (EC5), 539 (EC10), 605 (EC25), 678 (EC50) mg kg−1 for Pb. This study showed that AS-Pb pollution notably influenced plant growth performance and had negative impacts on the growth processes, metabolite levels, and the antioxidant system in plants. Our findings contribute to a theoretical foundation and research necessity for evaluating ecological risks in mining areas and assessing the suitability of ecological restoration strategies.

Variations in pore structures and permeabilities of ion adsorption rare earth ores during simulated in-situ leaching: Effect of newly formed clay particles and their swelling

In-situ leaching is essential for mining rare earth elements (REEs) from ion-adsorption rare earth (RE) ores. The efficiency of RE mining is dependent on the permeabilities of ion-adsorption RE ores, and the permeabilities are controlled by their pore structures. However, the current understanding of the pore structures and permeabilities of the RE ores during leaching is limited, particularly their dynamic variations, the controlling roles of different pore structure parameters on the permeability, the roles of the influencing factors and the mechanisms causing the variations. To investigate the above-mentioned issues, we conducted an experimental study of simulated in-situ leaching on undisturbed ion-adsorption RE ore samples under different conditions via constant waterhead permeability tests. The leaching conditions included leaching time, concentration and waterhead of the (NH4)2SO4 solution. Three-dimensional (3-D) pore structures of the RE ores before, during, and after leaching were constructed via X-ray computed tomography, and their pore structure parameters were measured using 3-D image computation. It was observed that the dynamic variations in both the pore structure parameters and permeability coefficients of the RE ores occurred in three distinct stages: rapid reduction, less rapid reduction, and little reduction. The experimental results also revealed that the permeability coefficients of the RE ores were primarily dependent on the average coordination number among the seven pore structure parameters examined, and that the pore throats larger than 30 μm in diameter served as the most effective seepage channels within the RE ores. The waterhead of the leaching solution had a stronger influence on the variations in pore structures and permeabilities compared to that of the concentration. Analysis of the particle/aggregate size distribution and mineralogical compositions of the RE ores before and after leaching indicated that the decreases in the pore structure parameters and permeabilities were largely attributed to clogging of the pore throats and pores by migrated and newly formed clays, as well as swelling of the latter. The newly formed clays were the products of the decomposition of K-feldspar and mica resulting from chemical reactions with the leaching solution. The clays from the two sources occurred in disaggregated and aggregated forms. The results of this study provide an important reference for the mining of RE ores via leaching.

Precipitation behavior of calcium sulfate in leach solution of ion-adsorption rare earth ore after reverse osmosis

Ion-adsorption rare earth ore (IAREO) is a crucial source of mid-heavy rare earths elements (M-HRE). Reverse osmosis technology is a promising technique for the pre-concentration of the leach solution from in-situ leaching of IAREO. However, calcium sulfate scaling is inevitably formed in sulfate system, causing decreases in the flux and life time of membrane. Herein, to simulate the precipitation behavior of calcium sulfate in the leach solution of IAREO during reverse osmosis, a series of experiments was conducted in binary and quaternary supersaturated calcium sulfate solution systems. Experimental data show that the concentration of Ca2+ decreases with the increase of the concentration of Mg2+, and increases with the increase of the concentration of RE3+ in both binary and quaternary systems. Whereas, the influence of Al3+ on the concentration of Ca2+ is different. This variation of the Ca2+ concentration is explained by thermodynamic analysis. The difference of association concentration for Mg2+, Al3+ and RE3+ with SO42− in binary or quaternary system is the main reason. Finally, the influence and mechanisms of antiscalant on the precipitation behavior of calcium sulfate are discussed. X-ray diffraction (XRD), Zeta potential and scanning electron microscopy (SEM) analyses reveal that polyacrylic acid (PAA) effectively inhibits the crystal growth of calcium sulfate, and the precipitation time of calcium sulfate is prolonged, indicating that PPA is a potential inhibitor for calcium sulfate scaling during the process of reverse osmosis.

Sedimentary characteristics of ion-adsorption rare earth elements and assessment of their resource reuse potential due to soil and water erosion in western Fujian.

With severe soil and water erosion, the crucial ion-adsorption rare earth elements (REEs) have attracted much global attention. REEs play a vital role in tracing material sources and exploring sedimentary characteristics due to their unique and stable geochemistry properties. In the present work, three representational possible redeposition areas in western Fujian were selected as the study areas. The geochemical characteristics of REEs in the sediments of the study areas were evaluated to elucidate that REEs are the products of soil and water erosion and to assess their redeposition characteristics. In the research results, the properties of the parent rocks shown in the samples, together with the negative correlation between the content of REEs in the samples and altitude as well as the relief degree on the land surface (RDLS), fully indicate that the sediments in the study areas are the products of migration caused by soil erosion and redeposition in the downstream areas. At the same time, according to the widely applicable standard of rare earth resources exploitation, that is the boundary grade of ion-adsorption rare earth ore in southern China (∑REE = 500mg·kg-1), we found that the content of REEs in the study areas was close to or exceeded this standard, and the maximum ∑REE of Guozhai Reservoir (869.11mg·kg-1) was much larger than this standard. Therefore, the redeposited rare earth in Changting Country has high reuse potential under the current scarce resources.

The effect of a new process on the environment of soil in ion adsorption rare earth ores

Rare earths are a kind of mineral resource with important strategic value, playing an irreplaceable key role in modern high-tech development and other fields. However, how to realize the efficient and green mining of rare earth resources has been a key issue that the rare earth industry has been trying to break through, because the rare earth mining process is prone to pollute ecological environments such as soil and water. Ion adsorption rare earth ore, mainly distributed in the south of China, is one of the rare earths, for which rare earth researchers have developed a new process leaching system with magnesium salt. In this study, the soil environmental problems as well as the microbial community structure underneath this new process heap-leaching demonstration site are evaluated. The results of the study showed that under the new process, there was a significant accumulation of sulfate content in the soil of the heap-leaching site and an imbalance in the soil calcium-magnesium ratio, which may disrupt the soil structure and reduce soil fertility. Meanwhile, the microbial community structure before and after the leaching site showed large differences at different points and depths, but didn't cause ecological risks. This study helps us to understand the environmental problems and impacts that may be caused by the new process of magnesium salt, and also helps to promote the application of the new process of magnesium salt leaching of ion adsorption rare earth ore, which lays the foundation for the exploitation of rare earth resources.

Environmental risk of ion-absorbed rare earth ores: concentration of leaching agent and fractionation of Pb.

Rare earth (RE) is an important strategic resource; however, there has been a growing concern about the environmental problems caused by RE mining, such as ammonia nitrogen pollution and heavy metal pollution. There is a limited research about the behavior of leaching agents and the fractionation of RE and heavy metal during the mining process for ion adsorption of rare earth ore (IRE-ore) in the previously available papers. In this study, (NH4)2SO4 solution, which commonly used in the production of mining IRE-ore, was used as a leaching agent. The adsorption behavior of ore soils on ammonium ions was explored by batch experiments. The adsorption process of IRE-ore on ammonium ions followed a pseudo-second-order equation and was controlled by the kinetics of surface adsorption and intra-particle diffusion; the ammonium ion adsorption isotherm conformed to the Freundlich isotherm equilibrium equation, and the higher concentration advantage made the ore soils possess a higher adsorption capacity of ammonium ion. In addition, the fractionation characteristics of lanthanum (La), cerium (Ce), and lead (Pb) in the ore soil during the leaching process were simulated based on the batch and column leaching experiments. The results demonstrated that the exchangeable states of La and Ce in IRE-ore were high, and the exchangeable, carbonate-bound La and Ce were almost all leached out by (NH4)2SO4 leaching agent, while the most of exchangeable Pb flowed out along with leaching agent, and a small amount of leached Pb in the ore soil was converted to iron and manganese oxide-bound Pb and enriched in the direction of migration of the leaching solution, and when the environment (e.g., pH and Eh) changed, this part of Pb may be re-activated. Our research might serve as crucial baseline knowledge for the adsorption of ammonium ions by ore soils, and provide a data reference for reducing the use of leaching agents and developing sustainable technologies for green mining of ion-adsorption RE ores.

Wetting front migration model of ion-adsorption rare earth during the multi-hole unsaturated liquid injection

In the process of ion-adsorption rare earth ore leaching, the migration characteristics of the wetting front in multi-hole injection holes and the influence of wetting front intersection effect on the migration distance of wetting fronts are still unclear. Besides, wetting front migration distance and leaching time are usually required to optimize the leaching process. In this study, wetting front migration tests of ion-adsorption rare earth ores during the multi-hole fluid injection (the spacing between injection holes was 10 cm, 12 cm and 14 cm) and single-hole fluid injection were completed under the constant water head height. At the pre-intersection stage, the wetting front migration laws of ion-adsorption rare earth ores during the multi-hole fluid injection and single-hole fluid injection were identical. At the post-intersection stage, the intersection accelerated the wetting front migration. By using the Darcy's law, the intersection effect of wetting fronts during the multi-hole liquid injection was transformed into the water head height directly above the intersection. Finally, based on the Green-Ampt model, a wetting front migration model of ion-adsorption rare earth ores during the multi-hole unsaturated liquid injection was established. Error analysis results showed that the proposed model can accurately simulate the infiltration process under experimental conditions. The research results enrich the infiltration law and theory of ion-adsorption rare earth ores during the multi-hole liquid injection, and this study provides a scientific basis for optimizing the liquid injection well pattern parameters of ion-adsorption rare earth in situ leaching in the future.

Bioleaching of ion-adsorption rare earth ores by biogenic lixiviants derived from agriculture waste via a cell-free cascade enzymatic process

Biogenic organic acids are considered environmentally friendly alternatives to ammonium sulfate for leaching ion-adsorption rare earth ores. Fermentation is popular for their production, but undesired cell metabolites and residual medium components could dampen the leaching performance. High feedstock cost is another major barrier for their applications. To tackle these challenges, a cell-free cascade enzymatic process was developed to produce gluconate from low-cost rice straw. Gluconate production by fermentation and enzymatic catalysis was first compared, and it was found that the enzymatic process gave a 99% yield within 24 h, while it was only 60% for fermentation after 48 h. The gluconate from enzymatic process was superior to that from fermentation in terms of leaching efficiency (100% vs. 18.1%). The precipitation of rare earth elements (REEs) by residual phosphate was identified as the major contributor to the low leaching performance by gluconate produced via fermentation. The gluconate derived from rice straw via the cascade enzymatic process did not show a compromised leaching efficiency, reaching 100% as well. This study sheds lights on how enzymatic process could be adopted to circumvent interferences for REEs recovery by fermentative impurities, and opens a new avenue for potentially economical production of biogenic lixiviants from renewable and cheap feedstocks.

Heap leaching of ion adsorption rare earth ores and REEs recovery from leachate with lixiviant regeneration

In this work, semi-industrial scale heap leaching of 200 t ion adsorption rare earth ores (IRE-ore) and rare earth elements (REEs) recovery from lixivium was first conducted. Biosynthetic citrate/(Na)3Cit, a typical microbial metabolite, was chosen as the lixiviant to conduct heap leaching. Subsequently, an organic precipitation method was proposed, which used oxalic acid to effectively recover REEs and reduce the production cost by lixiviant regeneration. The results showed that the heap leaching efficiency of REEs reached 98 % with a lixiviant concentration of 50 mmol/L and a solid-liquid ratio of 1:2. The lixiviant can be regenerated during the precipitation process, with REE yields and impurity aluminum yields of 94.5 % and 7.4 %, respectively. The residual solution can then be cyclically used as a new lixiviant after simple adjustment. High-quality rare earth concentrates with a rare earth oxide (REO) content of 96 % can be finally obtained after roasting. This work provides an eco-friendly alternative for IRE-ore extraction to solve the environmental issues caused by traditional technology. The results proved feasibility and provided a foundation for in situ (bio)leaching processes in further industrial tests and production.

Leaching Mechanism of Aluminum during Column Leaching of Ion-Adsorption Rare Earth Ore Using Magnesium Sulfate

Aluminum is a significant impurity in the ion-adsorption rare earth ore. The changes in the occurrences of aluminum have a great influence on the leaching of the rare earth ore. In this paper, the column leaching method was employed using magnesium sulfate as a leaching agent to investigate the effects of pH and magnesium sulfate concentration in the leaching agent on the leaching of aluminum and rare earths. The results show that at low magnesium sulfate concentrations, the leaching of rare earths is greatly enhanced, while the leaching of aluminum is not significantly affected by a decrease in the pH of leaching agent. At high magnesium sulfate concentrations, a slight increase in the leaching of rare earths is observed, accompanied by a significant increase in the leaching of aluminum upon decreasing the pH of the leaching agent. The leaching behavior of aluminum is related to the changes in the occurrences of aluminum during the leaching process. At low magnesium sulfate concentrations, low pH promotes the transition of Hy-Al to Sol-Al, but due to the low Mg2+ concentration in the leaching agent, Sol-Al is back-adsorbed onto the clays and transformed into Ex-Al, resulting in no significant increase in the aluminum content in the leach solution. However, at higher magnesium sulfate concentrations, aluminum in the leach solution comes mainly from the transformation of Ex-Al. Lowering the pH of the leaching agent can significantly promote the transition of Hy-Al to Sol-Al, thereby greatly increasing the aluminum content in the leach solution. The above results provide theoretical support for the optimization of the in situ leaching of ion-adsorption rare earth ore using magnesium sulfate.

Research on quantitative inversion of ion adsorption type rare earth ore based on convolutional neural network

Rare earth resource is a national strategic resource, which plays an essential role in the field of high technology research and development. In this paper, we aim to use remote sensing quantitative inversion prospecting technology, use surface-to-surface mode, and model inversion and evaluation through convolutional neural network model to achieve a new research method for large-scale, low-cost, rapid and efficient exploration of ion-adsorbed rare earth ore. The results show that the RE2O3 content of samples has significant negative correlation with the second, third and fourth band of GF-2 image, but has no significant correlation with the first band of GF-2 image; the convolution neural network model can be used to reconstruct the RE2O3 content. The content distribution map of RE2O3 obtained by inversion is similar to that of geochemical map, which indicates that the convolution neural network model can be used to invert the RE2O3 content in the sampling area. The quantitative inversion results show that the content distribution characteristics of ion adsorption rare earth ore in the study area are basically consistent with the actual situation; there are two main high anomaly areas in the study area. The high anomaly area I is a known mining area, and the high anomaly area II can be a prospective area of ion adsorption type rare earth deposit. It shows that the remote sensing quantitative inversion prospecting method of ion adsorption type rare earth deposit based on Convolutional Neural Networks (CNN) model is feasible.

Adsorption of Hydrated Pr3+ and NH4+/Mg2+ Ions onto the (001) Surface of Montmorillonite: A DFT Analysis with Experimental Verification

Montmorillonite is a major mineral present in ion-adsorption rare earth ores, and the microscopic adsorption states of rare earth ions on its surface are of a great significance for the efficient exploitation of ion-adsorption rare earth ores. In this article, density functional theory calculations were used to investigate the adsorption mechanisms and bonding characteristics of hydrated Pr, Mg and NH4 ions on the (001) surface of montmorillonite. Pr3+ exhibited a directed tendency geometry with Pr(H2O)103+, which was adsorbed onto montmorillonite by hydrogen bonding with an adsorption energy of −1182 kJ/mol, and one coordinated H2O ligand was separated from the first hydration layer of Pr. Both hydrated Mg and NH4 ions were adsorbed onto the montmorillonite surface through hydrogen bonds, and the adsorption energies were −206 and −188 kJ/mol, respectively, indicating that the adsorption stability of the hydrated Mg ion was slightly higher than that of the hydrated NH4 ion, but both were lower than that of hydrated Pr (−1182 kJ/mol). Hence, higher concentrations of Mg and NH4 ions than rare earth ions would be necessary in the leaching process of ion-adsorption rare earth ores. Additionally, desorption experiments revealed that the recovery of Pr3+ by Mg2+ with a concentration of 38 mmol/L is 80%, while it is only 65% with the same concentration of NH4+, and the concentrations of Mg2+ and NH4+ were much higher than that of Pr3+ in lixivium, which is consistent with the DFT calculations.

Simulated bioleaching of ion-adsorption rare earth ore using metabolites of biosynthetic citrate: An alternative to cation exchange leaching

Ion-adsorption rare earth ore (IRE-ore) is a strategic resource that provides almost all the market demand for heavy rare earth elements (HREEs). The commonly used ammonium sulfate technology in industrial production is gradually being restricted for use due to environmental damage, thus resulting in the huge challenge of the IRE-ore industry. Bioleaching has potential prospects in the clean and efficient utilization of IRE-ore, mainly due to its advantages of low-cost and eco-friendliness. Since IRE-ore is mainly extracted by in-situ leaching in industrial production, contact/direct bioleaching seems infeasible. Hence, noncontact/indirect bioleaching of IRE-ore by microbial metabolites would be the best choice. In this work, Aspergillus niger and Yarrowia lipolytica were found to be effective in IRE-ore bioleaching, and citrate was reported to be the main microbial metabolite. To further investigate the bioleaching mechanism and process intensification, simulated bioleaching of IRE-ore by biosynthetic citrate/((NH4)3Cit) was conducted. Erlenmeyer flask leaching results showed that more than 90% of the total REE leaching yield can be obtained at extremely low citrate concentrations (approximately 3.3 mmol/L), which was only 10% of the commonly used ammonium sulfate concentration. Analytical results showed that Cit species directly transferred REEs from the IRE-ore surface to solution via a complexation reaction, which was synchronized and synergistic with the ion-exchange reaction of NH4+. This work provides a new idea for the clean and efficient utilization of IRE-ore and is expected to overcome the common disadvantages and bottlenecks of traditional technology of inorganic salt leaching and the principle of cation exchange.

Step-Leaching and Pre-Enrichment of Light and Heavy REEs from Kaolinite and Montmorillonite

Kaolinite (Kao) and montmorillonite (Mt) are the primary minerals present in ion-adsorption rare earth ores. Better understanding the adsorption/desorption characteristic for light and heavy rare earth elements (REEs) of Kao and Mt will be beneficial for the step-leaching and pre-enrichment of light and heavy REEs from ion-adsorption REE ores. The experiments show that the more negative ζ potential and the larger specific surface area of Mt contribute to the higher adsorption capacity of REEs. The stability of REEs onto Kao and Mt increases with the increase in adsorption pH. There are obvious differences in the desorption characteristic among Nd3+, Eu3+, and Lu3+ due to the different adsorption mechanisms. Lu3+ almost adsorbed on Kao through electrostatic force, and its recovery is 88% when the desorption pH was higher than 4; however, the recoveries were only 50% for Nd3+ and 56% for Eu3+, which interact with the Kao surface dominated by coordination bonds. However, the opposite desorption characteristic occurred on Mt. Based on these different desorption characteristics of light and heavy REEs, step-desorption and pre-enrichment for Nd3+ and Lu3+ from Kao and Mt were feasible. In the first lixivium of Kao, the percentage of Lu3+ is high, up to 68.4%, and Nd3+ is enriched in the second lixivium, with a percentage of 73.9%. As for Mt, Lu3+ is difficult to be desorbed and enriched in the second lixivium with a percentage of 87.7%.

Column leaching of ion adsorption rare earth ore at low ammonium concentration

Ammonium sulfate ((NH4)2SO4) is currently the most commonly used leaching agent for the extraction of ion adsorption rare earth ore (IARE-ore) in industrial production. However, ammonium sulfate technology has been gradually restricted to use mainly due to its environmental damage, thus resulting in serious challenges in the IARE-ore industry. Based on the leaching mechanism of cation exchange, a high ammonium concentration is required in ammonium sulfate leaching. In addition, the anion of sulfate radicals has almost no ability to leach rare earth elements (REEs), which are also a component of environmental pollution. Therefore, it is important to reduce the concentration of the leaching agent, especially the ammonium concentration in the IARE-ore leaching process. In this work, ammonium citrate was used as a new leaching agent in IARE-ore leaching. The column leaching results showed that high REEs recovery can be obtained at relatively low ammonium concentration. Both of the cation and anion components of ammonium citrate were effective in the REEs leaching process, thus resulting in cooperative effects. A liquid/solid ratio of 4:1 and a pH of 6 were the appropriate conditions for the extraction of rare earth with ammonium citrate, while the appropriate pH for ammonium sulfate was 2. This work provides a new approach to solving the challenge of traditional ammonium technology by designing and changing the molecular structure of ammonium leaching agents.

A Capillary Model for Predicting Saturated Hydraulic Conductivity of Ion-Adsorption Rare Earth Ore Based on Improved Kozeny–Carman Equation

During the in-situ leaching process of ion-adsorption rare earth ore, the seepage velocity of the leaching solution is one of the core problems in studying the leaching efficiency. The determination of the saturated hydraulic conductivity is of great significance to reveal the leaching process. The classical Kozeny–Carman (KC) equation is widely employed to predict the hydraulic conductivity of sandy soils. However, in the equation, the effect of tortuosity on the hydraulic conductivity is not considered, and the specific surface area is difficult to determine in practice. In this study, the capillary model for predicting the saturated hydraulic conductivity of ion-adsorption rare earth ore was established. First, we assumed that all the pores in the ore body are a series of parallel and tortuous capillaries with equal diameters. Based on the assumption and Hagen–Poiseuille’s law, the KC equation was improved by introducing the tortuosity. Second, the constant head permeability tests were carried out to derive the seepage velocity and hydraulic head loss under the steady seepage state. According to the experimental results, the diameter of the capillary was calculated with Darcy's formula. Then we obtained a linear-fit relationship between capillary diameter and porosity to express the specific surface area variation with porosity. Third, by validating with experimental data, when the pore shape coefficient is 0.4, the saturated hydraulic conductivity calculated by the capillary model is in good agreement with the tested value. The proposed model can be considered to have a satisfactory capability to predict the saturated hydraulic conductivity of ion-adsorption rare earth ore.

Characterisation of rare earth elements from Malaysian ion-adsorption clay

This article aims to characterise Malaysian ion-adsorption clay rare earth element (IAC REE) ore in Malaysia. The study's goal was to determine the physical and chemical properties of ion-adsorption rare earth ore to provide direction to the industry for future research on rare earth element (REE) extractions. The mineral composition and mineral phase of the sample were analysed using X-ray diffraction (XRD) and X-ray fluorescence (XRF), respectively. The ore samples were mostly made up of SiO2 (60.09%) and Al2O3 (24.63%), and were mainly hosted in quartz, feldspar, kaolinite, halloysite, and coesite. The sample's elements were identified using inductively coupled plasma mass spectrometry (ICP-MS) and the result shows that the ore contained 62.21% of light rare earths (LREEs) and 37.79% of heavy rare earth (HREEs). The concentration of yttrium, lanthanum, cerium and neodymium was significant among other REEs. This finding is crucial for future reference on rare earth element’s extraction.

Theoretical investigation of hydrated [Lu(OH)2]+ adsorption on kaolinite(0 0 1) surface with DFT calculations

Kaolinite is a major mineral present in ion-adsorption rare earth ores, which are the primary source of lutetium (Lu). In those ores, Lu is mainly found to be adsorbed on the kaolinite surface in the form of hydrated or hydroxyl-hydrated ions, and can therefore be desorbed by ion-exchange leaching. This study used density functional theory calculations to investigate the adsorption mechanisms and bonding nature of hydrated [Lu(OH)2]+ ions on the kaolinite (0 0 1) surface. Lu3+ exhibited directed tendency geometry with high coordination number of nine. [Lu(OH)2(H2O)6]+, the most stable ion in aqueous system, was considered as the initial structure for the adsorption models. To investigate bonding between hydrated [Lu(OH)2]+ and the kaolinite surface, outer-layer (related to hydrogen bonding) and inner-layer (related to coordination bonding) adsorption models were applied. The surface charge and HOMO distribution of the deprotonated Al-OH surface were also investigated. Owing to the high reactivity of the deprotonated hydroxyls, inner-layer adsorption was dominated by coordination bonds between Lu and surface oxygen, with bidentate complexation at Ol site giving the largest adsorption energy (-663.86 kJ/mol). Moreover, partial density of state projections and Mulliken bond populations showed that the antibonding combination of Lu 5d and Os 2p is the dominant orbital contribution of Lu and surface oxygen. These insights into the Lu adsorption mechanism can aid in developing improved ion-exchange leaching techniques.

Extraction mechanism and separation behaviors of low-concentration Nd3+ and Al3+ in P507–H2SO4 system

In order to clarify the solvent extraction and separation behaviors of rare earths and impurity of Al during the extraction and enrichment of low-concentration leach solution of ion-adsorption rare earth ore, the extraction mechanism and separation behaviors of Nd3+ and Al3+ in the Nd2(SO4)3–Al2(SO4)3 mixed solution using P507 were studied in this work. The extraction of Nd3+ and Al3+ follows the cation exchange mechanism. With the increase of the equilibrium pH, βNd/Al in the extraction of the Nd2(SO4)3–Al2(SO4)3 mixed solution using P507 is always higher than that in the extraction of single Nd2(SO4)3 and Al2(SO4)3 solutions. It can be attributed to the fact that the extraction of Nd3+ using P507 is much faster than that of Al3+, and Al3+ is more prone to be hydrolyzed at lower pH. βNd/Al in the extraction of the Nd2(SO4)3–Al2(SO4)3 mixed solution decreases gradually with the increase of mixing time within the equilibrium pH range of 1.5–1.9. The extraction of Nd3+ using P507 is much faster than that of Al3+, but the stability of Al3+-loaded organic phase is better than that of Nd3+-loaded organic phase, thus Nd3+ in the Nd3+-loaded organic phase is gradually replaced by Al3+ in the aqueous phase with the increase of mixing time.