Rare Earth Resources Research Articles

Recovery of rare earths from rare earth molten salt electrolytic slag using alkali phase reconstruction method with the aid of external electric field

Rare earth molten salt electrolytic slag (RMES) has emerged as a promising secondary resource for rare earth elements (REEs). This study introduces an innovative leaching technique for extracting REEs from RMES under atmospheric conditions, employing an alkali phase reconstruction method followed by an acid leaching process. Additionally, the external electric field was employed to enhance the reaction. Under the optimal reaction conditions: NaOH initial concentration of 70 wt%, NaOH-slag mass ratio of 4:1, temperature of 160 °C, current density of 1000 A/m2, reaction time of 90 min, stirring speed of 300 r/min, HCl concentration of 4 mol/L, liquid-solid ratio of 15:1, and leaching time of 20 min, the leaching efficiencies of Nd and Pr reach up to 99.21% and 99.14%, respectively. Phase analysis indicates that the rare earth fluorides transform into rare earth hydroxides, significantly enhancing their solubility in acid solution. The imposition of an external electric field leads to pronounced disruption of the RMES surface, thereby promoting the formation of stable reactive oxygen species in the alkaline medium. This facilitates the decomposition of fluorinated rare earths and hastens the phase reconstruction, resulting in an enhanced leaching process. The achieved leaching efficiency with an external electric field is 37% higher than that without an electric field.

Establishing carbon dots assisted high speed countercurrent chromatography and its application for efficient separation of rare earth element ions

Rare earth elements with unique magnetic properties and optical properties, known as the ‘industrial vitamin’, has a very high commercial value. As a secondary resource of rare earth elements, low-concentration solution includes mixed rare earth ions, which need to realize efficient separation and recovery urgently. High speed countercurrent chromatography is suitable for the separation and purification of rare earth element ions due to its advantages of large loading, good tolerance to samples, and simple pretreatment. In this study, a carbon dots assisted high speed countercurrent chromatography method was designed and established, the carbon dots were applied to the mobile phase of high speed countercurrent chromatography for the first time. The low concentration of REEs solution was enriched, and the effective separation of La (III), Ce (III), Gd (III) and Er (III) was successfully achieved. The complete separation of La (III), Ce (III), Gd (III) and Er (III) was achieved with a solvent system of 0.05 mol L−1 P507 (PE), 0.05 mol L−1 HNO3, and 0.1 mol L−1 CDs2 carbon dots (1:1:0.01, v/v/v), the upper phase as stationary phase, the lower phase as mobile phase. Density functional theory result showed that the binding energy of REEs (III)-CDs2 was larger than that of REEs (III)-P507, so the affinity of CDs2 to REEs (III) was stronger than that of P507. Therefore, with the addition of CDs2, the ability of mobile phase to elute REEs from the stationary phase was enhanced, and the separation effect was improved.

Efficient Self-cleaning and antibacterial ceramics with active sites fully exposed obtained from rare earth waste

The utilization of rare earth polishing powder waste (RPW) to prepare antibacterial ceramics can effectively avoid problems of pollution in the recycling process and waste of rare earth resources. Herein, a novel RPW-based antibacterial ceramics was developed, which possesses the core-shell structure with ceramics as the cores and the CeO2/BiOCl as the superficial coating. The antibacterial ceramics display notable antibacterial activity, and the inactivation rates of 3.3 log under visible light irradiation in 30 min and 2.4 log under darkness in 1 h were achieved, and the zone of inhibition values was found to be 16.6 mm for E.coil. The hardness of antibacterial ceramics was measured to be 897 (±38) HV, higher than commercial porcelain's hardness (600 HV). The antibacterial mechanism was verified by the Ce ion release, reactive species, and fluorescence-based live/dead cells. This study presents a novel antibacterial ceramic structure and green economic reuse method of rare earth waste.

High-efficiency dysprosium-ion extraction enabled by a biomimetic nanofluidic channel

Biological ion channels exhibit high selectivity and permeability of ions because of their asymmetrical pore structures and surface chemistries. Here, we demonstrate a biomimetic nanofluidic channel (BNC) with an asymmetrical structure and glycyl-L-proline (GLP) -functionalization for ultrafast, selective, and unidirectional Dy3+ extraction over other lanthanide (Ln3+) ions with very similar electronic configurations. The selective extraction mainly depends on the amplified chemical affinity differences between the Ln3+ ions and GLPs in nanoconfinement. In particular, the conductivities of Ln3+ ions across the BNC even reach up to two orders of magnitude higher than in a bulk solution, and a high Dy3+/Nd3+ selectivity of approximately 60 could be achieved. The designed BNC can effectively extract Dy3+ ions with ultralow concentrations and thereby purify Nd3+ ions to an ultimate content of 99.8 wt.%, which contribute to the recycling of rare earth resources and environmental protection. Theoretical simulations reveal that the BNC preferentially binds to Dy3+ ion due to its highest affinity among Ln3+ ions in nanoconfinement, which attributes to the coupling of ion radius and coordination matching. These findings suggest that BNC-based ion selectivity system provides alternative routes to achieving highly efficient lanthanide separation.

Preparation of (Nd, Ce)-Fe-B Regenerated Magnets by In-Situ Restoration of Grain Boundary Structure Using Nascent Nd-Fe-B Powder.

Rare earth resource recycling is an important endeavor for environmental protection and resource utilization. This study explores the method of preparing regenerated magnets using waste magnets as raw materials based on existing processes. By utilizing existing Nd-Fe-B production equipment, various waste magnets are transformed into recycled powder. Next, nascent Nd-Fe-B powders with slightly higher rare earth content are selected as the repairing agent. The regenerated magnets are prepared by incorporating the nascent powder into the recycled powder. The focus lies in investigating the repairing effect of the nascent powder repairing agent on the microstructure of regenerated magnets and exploring the influence of sintering temperature and powder addition on the magnetic properties and microstructure of the regenerated magnets. The results showed that the nascent powder increased the proportion of grain boundary phases and effectively repaired the grain boundary structure of the regenerated magnets. In addition, the Pr element in the nascent powder replaces the Ce element in the recycled powder, which ultimately improves the magnetic properties of the regenerated magnet in a comprehensive manner. This study provides valuable insights and guidance for rare earth resource recycling and the preparation of regenerated magnets.

Characterization of Rare Earth Elements in Cassiterite-Associated Minerals in Bangka-Belitung Islands, Indonesia

Rare earth elements (REEs) are crucial to numerous industries of high-technology as raw materials. The growth of a long-term relationship between REE supply and demand to develop hi-tech industries is becoming tight in the world market, while the mineral supply chain is being distorted by COVID-19. The availability of information and data regarding the REE resource potential and characteristics are interesting research subjects to examine its economic value as alternative sources. This research aims to provide basic information about the existence and characteristics of REEs in cassiterite-associated minerals located in Bangka and Belitung Islands. Fifty-one samples consisting of primary deposits, placer deposits, concentrates, and tailings were collected from the southern Bangka and Belitung region. The samples were analyzed using microscope, x-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), and inductively coupled plasma mass spectrometry (ICP-MS). The results show that the REE-bearing minerals comprised monazite and xenotime. Monazite, the most dominant REE-bearing mineral, contains light REEs (Ce-dominant), while xenotime contains heavy REE (Y-dominant). The results of SEM with energy-dispersive spectroscopy show that monazite contains other LREE (La and Nd), and xenotime also contains other HREE (Dy and Yb). Moreover, zircon and ilmenite can be considered as economical cassiterite-associated minerals that have other mineral inclusion, but have no REE contain.

On the pre-treatment for recycling spent NdFeB permanent magnets: from disassembling, characterisation to de-coating

An evaluation of neodymium‑iron‑boron permanent magnets (NdFeB PMs) from different end-of-life products, as a secondary resource of rare-earth elements (REEs), is presented. De-coating of PM was investigate as pre-treatment to facilitate efficient direct magnet recycling. Thus, critical aspects from disassembling to the de-coating of the magnets were addressed. A challenge for the de-coating process is that the magnets have different sizes, weights, and their coating compositions are not known beforehand. It was shown that ammonia-based solutions was thermodynamically suitable to dissolve nickel and zinc coatings selectively, while keeping the bulk magnet stable. Nevertheless, the dissolution of Zn was much faster than the Ni one, and more efficient.

Microstructural Investigation of Discarded NdFeB Magnets After Low-Temperature Hydrogenation

Due to continuously increasing demand and limited resources of rare-earth elements (REEs), new solutions are being sought to overcome the supply risk of REEs. To mitigate the supply risk of REEs, much attention has recently been paid to recycling. Despite the more common recycling methods, including hydrometallurgical and pyrometallurgical processes, hydrogen processing of magnetic scrap (HPMS) is still in the development stage. Magnet-to-magnet recycling via hydrogenation of discarded NdFeB magnets provides a fine powder suitable for the production of new magnets from secondary sources. One of the crucial aspects of HPMS is the degree of recovery of the magnetic properties, as the yield efficiency can easily reach over 95%. The amount, morphology, and distribution of the Nd-rich phase are the key parameters to achieve the excellent performance of the magnet by isolating the matrix grain. Therefore, a better insight into the microstructure of the matrix grains and the Nd-rich phase before and after hydrogenation is essential. In this study, a low-temperature hydrogenation process in the range of room temperature to 400 °C was conducted as the first step to recycle NdFeB magnets from discarded hard disk drives (HDDs), and the hydrogenated powder was characterized by electron microscopy and X-ray diffraction. The results show that there are three different morphologies of the Nd-rich phase, which undergo two different transformations through oxidation and hydride formation. While at lower temperatures (below 250 °C) the degree of pulverization is higher and the experimental evidence of hydride formation is less clear, at higher temperatures the degree of pulverization decreases. The formation of neodymium hydride at higher temperatures prevents further oxidation of the Nd-rich phase due to its high stability.Graphical

Potential and characteristics of rare-earth metals acid bioleaching from the rare-earth-rich tailings with the enriched functional bacterial consortium: Comparison between one-step and two-step processes

The irreplaceable roles of rare-earth metals (REMs) in modern technologies have renewed interest in the grand challenges of mineral processing and metallurgical engineering—the efficient extraction of REMs. However, traditional methods for extracting REMs are inefficient, costly and harmful to health and the environment. In this study, a method of biological extraction (bioleaching), which has been proved to be effective in the field of mineral processing for extraction of the metals, was employed for REMs bioleaching from Bayan Obo rare-earth-rich tailings (RERT) using the acid functional bacterial consortium, and the optimal culture and leaching conditions were optimized. Under the optimal conditions for 18 days, the total bioleaching rate of the five main REMs of La, Ce, Pr, Nd and Sm was obtained at 82.78 % for one-step process and 83.51 % for two-step process, which has a significant improvement comparing to previous studies. The results demonstrated that REMs could be efficiently bioleached by acid bioleaching functional bacterial consortium, and the difference in leaching efficiency between the one-step and two-step bioleaching process was not significant. In addition, by analyzing the mineral composition of the RERT and leaching residue, the extensively bioleach of REMs in bastnaesite are observed. To sum up, the rare-earth resources of Bayan Obo RERT could be effectively leached by acid bioleaching method.

Synchronously enhancing the creep performance along two different loading directions in hot-rolled Mg-2wt%Sn alloy plate

To save rare-earth (RE) resource and develop creep-resistant Mg alloys in a low-cost way, RE-free Mg alloys are strongly recommended recently. However, serious creep anisotropy and poor creep resistance are still the main problems of safely using RE-free Mg alloys. In the present research, one binary Mg-2wt%Sn hot-rolled plate was employed for studying the compressive creep performance at 393 K. It was found that different activities of basal slip, twinning and pyramidal slip weakened the creep performance along the rolling direction and caused the inevitable creep anisotropy. To weaken the creep anisotropy between the rolling direction and normal direction, multi-directional forging (MDF) with three passes was performed at 393 K. Through inducing high-density twins before creep loading, detwinning was frequently activated during creep loading instead of inducing new twins. As a result, the creep anisotropy was successfully weakened in the MDF processed alloy. Moreover, the creep performance was synchronously enhanced along both loading directions rather than deteriorating the creep performance along the normal direction. It is thus expected that this RE-free way of preparing creep-resistant Mg alloys can be widely accepted in the relative application fields.

Unleashing the Power of Closed-Loop Supply Chains: A Stackelberg Game Analysis of Rare Earth Resources Recycling

Unleashing the Power of Closed-Loop Supply Chains: A Stackelberg Game Analysis of Rare Earth Resources Recycling

Exploring Ho substituted Y-Fe-B nanocrystalline alloys and hot worked magnets

Aiming to balance the utilization of rare earth (RE) resources and develop Y-Fe-B based permanent magnets, Ho is employed as strategic substitution for enhancing the magnetic properties and thermal stability of nanocrystalline Y-Fe-B alloys. Ho substituting Y can enhance the coercivity of Y-Fe-B alloys while maintaining their excellent thermal stability. 30 at.% Ho substitution leads to an abnormal increase of remanence J r and (Y0.7Ho0.3)2Fe14B alloy exhibits good magnetic properties with remanence J r = 0.73 T, intrinsic coercivity H cj = 303 kA m−1, and maximum energy product (BH)max = 66 kJ m−3. High thermal stability with temperature coefficient of remanence α = −0.124%/K and temperature coefficient of coercivity β = −0.245%/K were obtained between 300–400 K. The results for RE-rich (Y1−xHox)2.5Fe14B alloys also show that the magnetic properties change with Ho content are similar to those of (Y1−xHox)2Fe14B alloys, but the coercivity is higher. In addition, nanocrystalline (Y0.5Ho0.5)2.5Fe14B magnets were prepared by hot-pressing and hot deformation process. Due to the lack of low melting point RE-rich phase, this alloy is difficult to be densified and deformed. The formation of high temperature RE2O3 and RE6Fe23 phases and the lack of continuously distributed RE-rich grain boundary phase are responsible for the poor texture of hot deformed magnet. The hot deformed magnet has the magnetic properties of J r = 0.50 T, H cj = 739 kA m−1, and (BH)max = 40 kJ m−3 together with high thermal stability. The micro-analysis demonstrated the chemical segregation of Y and Ho elements. Higher proportion of Ho than Y existed in main phase and grain boundary phase indicate excess Y were precipitated as Y-rich oxides.

Rapid and efficient synthesis of energy-saving cool pigments and environmental restoration materials using rare earth secondary resources

This paper proposes a method for the short-process recovery and reuse of rare earth secondary resources. Low-value rare earth polishing powder waste (WP), trichromatic phosphor waste (WT), NdFeB permanent magnetic waste (WN), and SmCo permanent magnetic waste (WS) were used as the raw materials. Based on the concept of combinatorial chemistry, energy-efficient cool pigments and environmental remediation materials were synthesized by a solid-phase method. The results showed that the synthesized materials had fluorite-type and garnet-type structures. In terms of cool pigments, doping with different rare earth permanent magnets can enrich the color (including yellow, green, brown, gray, and blue) and cause fluctuations in the near-infrared (NIR) reflectance (59.05–99.54 %) and NIR solar reflectance (55.32–95.64 %). Yellow fluorite-type pigments (WP: WT = 1:1) have the highest NIR reflectance (R = 99.54 %), while brown fluorite-type pigments (WP: WN = 1:0.1) and blue garnet-type pigments (WP:WS = 1:0.1) have relatively high NIR reflectance, 88.18 % and 59.30 %, respectively. The synthesized pigments possessed better chemical stabilities and thermal insulation performance. In terms of environmental remediation materials, the adsorption capacities of fluorite-type materials for F− and PO43− can reach 84.03 mg/g and 85.3 mg/g, respectively. In summary, materials synthesized from rare earth waste exhibit excellent potential for use in energy-efficient wastewater treatment and promote the sustainable utilization of secondary rare earth resources.

Afghanistan’s raw materials policy regarding rare earth elements after the Taliban victory [Polityka surowcowa Afganistanu dotycząca metali ziem rzadkich po zwycięstwie Talibów

The Taliban victory in Afghanistan in 2021 has not only raised geopolitical concerns but has also sparked questions about the state’s policies and strategies concerning its rare earth elements reserves. The main objective of the presented article is to indicate how the current political change in Afghanistan may affect the raw material policy regarding the extraction of rare earth elements, taking into account geopolitical factors. Rare earth elements are a group of critical minerals that are of great importance to modern technologies, ranging from electronics and renewable energy to defence systems. Afghanistan is known to possess significant deposits of these valuable resources, which have the potential to play a crucial role in global supply chains, especially in the face of ongoing rivalry between the People’s Republic of China and the United States of America. The research problem of the considerations undertaken in this article is to assess the key challenges and opportunities in harnessing Afghanistan’s rare earth element resources after the Taliban’s return to power. The research conducted shows that despite having a significant amount of rare earth elements, Afghanistan lacks the infrastructure necessary to extract and process these valuable minerals. After the Taliban victory, the newly established government sees the potential benefit in extracting rare earth elements and is willing to align itself with China to exploit them.

Study on the adsorption/desorption characteristics and dynamic diffusion mechanism of rare earth hydrated ions on the kaolinite (001) surface

Coal gangue (CG) contains abundant rare earth elements (REEs), which is a potential REE resource. REEs are mainly present in clay minerals as hydrates. The adsorption, desorption, and diffusion of REEs-hydrates on the surface of clay minerals are the key to regulating the leaching effect of REEs. The paper focuses on the typical clay minerals kaolinite and REEs-hydrates and combines quantum mechanics and molecular dynamics methods to systematically study the adsorption, desorption, and dynamic diffusion behavior of REEs-hydrates in acid solution. The research results indicate that stable REEs-hydrates La(H2O)9 and Y(H2O)7 are formed, with ion bonds between REEs and water molecules. La(H2O)9 and Y(H2O)7 mainly interact with the kaolinite (001) surface through hydrogen bonding. Competitive adsorption is formed between water molecules, hydrated hydrogen ions, and REEs-hydrates. Water molecules and hydrated hydrogen ions occupy the adsorption active sites of REEs-hydrates and form a dense water molecular layer on the surface. The distance between H3O+ and REEs-hydrates and the number of H3O+ in the solvent layer affect the desorption and diffusion behavior of hydrates. The bonding law, dynamic desorption, and diffusion mechanism of REEs-hydrates can provide meaningful references for selective leaching of REEs from CG.

Mineralization of Zr-REE-Y in the Ngaoumbol iron formations, central Cameroon: Insights from petrography, mineral chemistry and whole rock geochemistry

The increasing importance of rare earth elements (REE) and critical metals in contemporary society has led us to investigate the mineral potential of the Ngaoumbol area, located within Cameroon's Central African Fold Belt (CAFB). In this study, we have conducted a comprehensive analysis that includes petrography, whole rock geochemistry, and mineral chemistry, along with the application of an outlook coefficient known as Koult, with the aim to evaluate the prospectivity of the Ngaoumbol iron formations as a potential source of REE-Y resources. This coefficient is defined as the ratio of the relative abundance of critical Rare Earth Elements to the relative abundance of excess REE. The iron formations in the Ngaoumbol area are fine-to medium-grained foliated rocks with alternating magnetite and actinolite bands and quartz bands, suggesting a sedimentary parentage. These rocks have an average REE-Y content of 1438.43 ppm and a Koult of 0.77, indicating their potential as raw sources for REE. Furthermore, the investigated samples exhibit high average Zr content (7748 ppm), suggesting that the rocks may host potentially economic Zr ore. The Zr-REE-Y mineralization in the Ngaoumbol area is hosted in detrital zircon, monazite and xenotime, probably deriving from the weathering of alkaline/subalkaline rocks surrounding the deposits. Our findings suggest that the Ngaoumbol area has promising REE and Zr resources. However, further exploration and evaluation are necessary to determine the extent and economic viability of these resources.

Synergistic enhancement of coercivity and thermal stability of nanocrystalline multi-main-phase Nd-Ce-Fe-B magnet via Gd60Y10Cu15Al15 addition

Nanocrystalline multi-main-phase (MMP) Nd-Ce-Fe-B magnet can effectively suppress the magnetic dilution effect of Ce. However, its low coercivity and poor thermal stability have not been adequately overcome. In this work, a novel low-melting-point Gd60Y10Cu15Al15 alloy was introduced into MMP Nd-Ce-Fe-B magnet through intergranular addition for simultaneously enhancing its coercivity and thermal stability. The results show that the intrinsic coercivity Hcj is obviously improved, and its maximum increment is ∼12.3 % at 4 wt% Gd60Y10Cu15Al15 alloy. Especially, the increase in Hcj is more significant, and an abnormally increase in the maximum energy product (BH)max occurs at high temperature of 150 °C. Meanwhile, the reversible temperature coefficients of Hcj (β) and Br (α) are improved simultaneously. These findings imply the enhanced thermal stability for the MMP magnet with Gd60Y10Cu15Al15 addition. The microstructural characterizations, compositional analyses and micromagnetic simulations reveal that the competitive effects of the formed non-ferromagnetic grain boundary (GB) phase and Y or Gd diffusion into the main phase lead mainly to a synergistic improvement in the coercivity and thermal stability of the magnet. This work is expected to provide a promising cost-effective approach for developing the high-performance thermally-stable Nd-Ce-Fe-B magnet and explore more possibilities for effective utilization of Y or Gd rare-earth resources.

Efficient rare earth enrichment through highly reversible physisorption on a negatively charged few-layer nanobelt platform

Effective extraction of rare earth elements (REE) from the surrounding aqueous environment would relieve the thirsty demand of mining as well as the environmental pollution, thus advancing sustainability progress. Nevertheless, limited extraction capability and harsh enrichment conditions are still the notorious critical problems hindering this environmentally favorable path. Herein, we showcase a physisorption driving platform (InVO4) for effective REE enrichment. This delicately designed platform exhibits a unique few-layer structure and thus robust negatively charged surface in the aqueous environment, which implies its powerful attraction towards positively charged species. The adsorption trials towards REE ions have proved this anticipation with a superior adsorption capability of 317.3 mg/g towards Yb3+ and the adsorption reached quasi-equilibrium in only about 10 min. Moreover, this platform could be regenerated quickly and completely in a mild NaCl environment based on the quasi-cationic exchange strategy benefiting from the physisorption nature. Impressively, a ppb-level enrichment of REE ions from the aqueous was realized 78-fold increase from an initial concentration of 100 ppb. This environmentally benign and highly efficient adsorbent will be inspiring for a more sustainable utilization route for the recovery of REE resources.

Selective recovery of Sm from Sm-Co magnet scrap by vacuum distillation

Sm-Co rare earth permanent magnet materials are widely used in special fields such as new energy and electronic information. Sm-Co permanent magnet scraps are generated during the preparation and the use of end-of-life permanent magnets, which need to be recycled for the sustainable development. It is proposed to selectively recover Sm from the Sm-Co permanent magnet scraps by vacuum distillation. The experimental investigations were carried out in a vacuum furnace with double temperature zones for the efficient condensation of Sm vapor based on the thermodynamic and kinetic calculations. The recycling feasibility of the recovery of rare earth and the evaporation mechanism of Sm were also demonstrated in this work. The results show that Sm with the purity over 99% was obtained by the molybdenum condenser used as a condensing collectors at given conditions, providing a reference for the pyrometallurgical recovery of rare earth secondary resources.

Rare Earth and Resource Nationalism: What Happened Before and After China’s Embargo on Japan?

ABSTRACT The ban on the export of rare earth elements (REE) to Japan following the 2010 Senkaku boat collision is a salient case of economic sanctions. Chinese state media’s recent consideration of REE as a weapon in the trade war with the United States has brought China’s rare earth policy back into the limelight. This article discusses China’s REE policy from a theoretical perspective of resource nationalism. After examining how China adopted resource nationalism on REE before 2010, it continued to examine how Japan’s response to the ban on REE exports had an impact on China’s rare earth policy and thus, China’s rare earth resource nationalism has grown more thorough since 2010. On the one hand, Beijing has taken countermeasures against Tokyo’s bid to decrease its dependency on China’s REE supply and deter Beijing from placing export restrictions. On the other hand, lessons from its failure to control REE prices have led to the continuation and acceleration of China’s resource nationalism concerning its REEs.