Heavy Rare Earth Research Articles

Liquid-liquid extraction and separation of light and heavy rare earth elements from chloride solution using a mixture of tertiary amine and phosphinic acid: recycling strategies for NdFeB magnet

ABSTRACT This piece of work aims to study the extraction behavior of light and heavy rare earth elements, which are often found in permanent magnets, using a mixture of tri-octyl amine and bis-(2,4,4-trimethylpentyl) phosphinic acid from a chloride medium. The study showed that the extraction efficiency of Dy(III) is more than that of Nd(III) and Pr(III). Benzene proved to be an effective diluent. Increasing the pH of the aqueous phase improved the extraction percentages, with maximum extractions of 98.4% for Dy(III), 61.2% for Nd(III), and 58.3% for Pr(III) at pH 5.04 using 0.1 mol/L of each extractant. Adding sodium chloride enhanced the extraction efficiency due to the salting-out effect. The extraction mechanism has been proposed based on the slope analysis and FTIR data. From thermodynamic variables, the process was found to be exothermic. The simulated leach liquor of NdFeB magnets showed the highest separation factors of 67.7 (Dy/Pr) and 56.9 (Dy/Nd) at pH 2.05 with 0.25 mol/L extractants. The counter-current study showed that 4.15 mg/L Dy(III) was left behind in the raffinate indicating 97.4% removal of Dy(III) in two stages at unity phase ratio. Testing with actual leach liquor from hard disk magnets revealed a preference for iron extraction, which impeded REE extraction.

A Review on Uranium Mineralization Related to Na-Metasomatism: Indian and International Examples

Uranium mineralization related to Na-metasomatism is known as Na-metasomatite or albitite-type. They represent the fourth-largest uranium resource globally and constitute fifty thousand tons of U resources. The present work gives details about well-known Na-metasomatic uranium occurrences worldwide in terms of structures, metasomatic stages, geochemical characteristics, fluid inclusions, and compositions of stable isotopes. The host rocks are granite, granitoid, and metamorphosed volcano-sedimentary rocks, and these rocks experienced two/three deformational stages. U mineralization is mainly confined to faults and characterized by granitic intrusive, cataclasis, mylonitization, and albitization. The albitized rocks exhibit two to three metasomatic and late hydrothermal stages. The first stage is marked by the replacement of pre-existing host minerals during a ductile shear regime. The second stage is related to U mineralization contemporaneous with the brittle deformation. The albitized rocks exhibit depletion in Si, K, Ba, and heavy rare-earth elements relative to the host rocks and enrichments in Na, Ca, U, Zr, P, V, Sr, and light rare-earth elements. U-enrichment is positively correlated with Na, Mo, Cu, and high-field strength elements. The pressure–temperature (P-T) conditions of U mineralization are considered to be epithermal and mesothermal. Fluid inclusion studies indicate that the mineralizing fluids were rich in Na+, Mg2+, Cl−, CO2, H2O, F−, and PO43− and meteoric–magmatic derived. The geological processes responsible for the genesis of Na-metasomatic U deposits of the North Delhi Fold Belt (India) are comparable with some international examples, i.e., Australia, Ukraine, Cameroon, Brazil, Guyana, China, and the USA.

Molybdenum isotopes demonstrate that multistage upgrading is required to generate heavy rare earth element–enriched carbonatites

Carbonatites with heavy rare earth element (HREE) enrichment are a rare and intriguing prospect for economic geology research, due to the growing global demand for HREEs in various industries. However, debate persists over the mechanism responsible for HREE enrichment in carbonatites, with the mantle source, magmatic-hydrothermal evolution, or a combination of these factors proposed to be responsible. This study examines three adjacent Late Triassic carbonatites (from the Huanglongpu, Huayangchuan, and Jialu carbonatite dike systems) in the Lesser Qinling of Central China and uses Mo isotope systematics to provide unique insights into the HREE enrichment process of these magmas. All three carbonatites exhibit elevated total REE (ΣREE) concentrations (up to 4600 ppm), along with significant HREE enrichment (ΣHREE/ΣREE = 0.1−0.4). Notably, Jialu carbonatite stands out for having the highest total HREE concentrations (≥360 ppm) and ΣHREE/ΣREE ratios (0.2−0.4). Regardless of their variable degrees of HREE enrichment, the three carbonatites display similar Sr-Nd-Pb isotope signatures, which indicates a shared enriched mantle source. The Huanglongpu and Huayangchuan carbonatites mostly display significantly lighter δ98/95Mo (−1.71‰ to −0.15‰) values than the depleted mantle, which indicates an origin from an enriched mantle influenced by recycled pelagic clays and Fe-Mn nodules. Both types of marine sediments are enriched in REEs and would have undergone initial HREE enrichment during slab dehydration and metamorphism, resulting in an HREE-enriched mantle source region. In contrast, Jialu carbonatite possesses significantly heavier δ98/95Mo (0.13‰−1.89‰), which is indicative of the subsequent influence of hydrothermal processes. Additional evidence of this hydrothermal influence at Jialu is preserved in calcite crystal fluid inclusions, elevated δ18O (8.71‰−10.72‰), non-charge-and-radius−controlled (CHARAC) Y/Ho ratios (36−41), and low Sr concentrations (<4800 ppm). Secondary upgrading of HREEs at Jialu occurred due to preferential complexation and transportation during hydrothermal exsolution. This study demonstrates that maximum HREE enrichment in carbonatites is achieved through a two-stage process that involves both a refertilized mantle source and late-stage hydrothermal exsolution.

Chemical and Thermal Changes in Mg3Si2O5 (OH)4 Polymorph Minerals and Importance as an Industrial Material

Serpentine (Mg3Si2O5(OH)4), like quartz, dolomite and magnesite minerals, is a versatile mineral group characterized by silica and magnesium silicate contents with multiple polymorphic phases. Among the phases composed of antigorite, lizardite, and chrysotile, lizardite and chrysotile are the most prevalent phases in the serpentinites studied here. The formation process of serpentinites, which arise from the hydrothermal alteration of peridotites, influences the ratio of light rare earth elements (LREE) to heavy rare earth elements (HREE). In serpentinites, the ratio of light rare earth elements (LREE)/heavy rare earth elements (HREE) provides insights into formation conditions, geochemical evolution, and magmatic processes. The depletion of REE compositions in serpentinites indicates high melting extraction for fore-arc/mantle wedge serpentinites. The studied serpentinites show a depletion in REE concentrations compared to chondrite values, with HREE exhibiting a lesser degree of depletion compared to LREE. The high ΣLREE/ΣHREE ratios of the samples are between 0.16 and 4 ppm. While Ce shows a strong negative anomaly (0.1–12), Eu shows a weak positive anomaly (0.1–0.3). This indicates that fluid interacts significantly with rock during serpentinization, and highly incompatible elements (HIEs) gradually become involved in the serpentinization process. While high REE concentrations indicate mantle wedge serpentinites, REE levels are lower in mid-ocean ridge serpentinites. The enrichment of LREE in the analyzed samples reflects melt/rock interaction with depleted mantle and is consistent with rock–water interaction during serpentinization. The gradual increase in highly incompatible elements (HIEs) suggests that they result from fluid integration into the system and a subduction process. The large differential thermal analysis (DTA) peak at 810–830 °C is an important sign of dehydration, transformation reactions and thermal decomposition, and is compatible with H2O phyllosilicates in the mineral structure losing water at this temperature. In SEM images, chrysotile, which has a fibrous structure, and lizardite, which has a flat appearance, transform into talc as a result of dehydration with increasing temperature. Therefore, the sudden temperature drop observed in DTA graphs is an indicator of crystal form transformation and CO2 loss. In this study, the mineralogical and structural properties and the formation of serpentinites were examined for the first time using thermo-gravimetric analysis methods. In addition, the mineralogical and physical properties of serpentinites can be recommended for industrial use as additives in polymers or in the adsorption of organic pollutants. As a result, the high refractory nature of examined serpentine suggests that it is well-suited for applications involving high temperatures. This includes industries such as metallurgy and steel production, glass manufacturing, ceramic production, and the chemical industry.

Petrography and geochemistry of volcanic rocks of the Kulf-Amba area, in the Northwestern Ethiopian plateau: Implication for petrogenesis of felsic volcanic suites

The Kulf-Amba area, located on the Northwestern Ethiopian plateau, is primarily composed of Cenozoic volcanic rocks with minor intertrappean sediments. To understand the petrogenesis of these rocks, we conducted field investigations, petrographic studies, and geochemical analyses. The main volcanic products include basalt (upper and lower), rhyolite lava flows, rhyolitic ignimbrite, volcanic glass, and agglomeratic tuff. Basalts exhibit aphanitic, porphyritic, and glomerophyric textures, with phenocryst of olivine, Ca-rich plagioclase, clinopyroxene, and Fe-Ti oxides. Felsic rocks display porphyritic, aphyric, and glassy textures, with phenocryst of quartz, alkali feldspar, and Fe-Ti oxides. Geochemical data reveal a bimodal composition. The mafic rocks resemble high titaniferous (HT2) basalts of Northwestern Ethiopia and are classified as transitional to tholeiitic. Felsic rocks are primarily peralkaline comendites. The mafic rocks exhibit a depleted heavy rare earth element (HREE) pattern with (Dy/Yb)N = 1.75–2.02 and enriched light rare earth element (LREE) values with (Ce/Yb)N = 7.16–9.26, without a significant negative Eu anomaly. Enrichment in LREE with (Ce/Yb)N = 6.27–15.03 and flat HREE with (Dy/Yb)N = 1.23–1.79, with varying Eu negative anomaly are characteristics of the felsic volcanic rocks, indicating removal of plagioclase throughout their evolutionary process. The consistent Nb/Ta (17.29–23.67 ppm) and Zr/Hf (37.53–45.08 ppm) ratios in both mafic and felsic rocks suggest that fractional crystallization was the dominant process in their formation, with small crystal contamination. The primitive mantle-normalized variation diagram for the mafic rocks reveals LREE enrichment and HREE depletion, indicating garnet in the source. Melting models using primitive mantle normalized values of Sm/Yb vs. La/Sm ratios further confirm garnet's presence and suggest a low degree (2%) of partial melting a source with less than 2% of garnet. The trace element signatures and geochemical modelling of the mafic lavas indicate a plume-related origin, potentially related to the Afar mantle plume.

The Subduction-Related Metavolcanic Rocks of Maroua, Northern Cameroon: New Insights into a Neoproterozoic Continental Arc Along the Northern Margin of the Central African Fold Belt

The metavolcanic rocks around Maroua in the Far North Region of Cameroon are located at the northern margin of the Central African Fold Belt (CAFB) and have not been studied to date. The petrographic and whole-rock geochemical data presented in this paper highlight their magma genesis and geodynamic evolution. The lavas are characterized by basaltic, andesitic, and dacitic compositions and belong to the calc-alkaline medium-K and low-K tholeiite series. The mafic samples are essentially magnesian, while the felsic samples are ferroan. On a chondrite-normalized REE diagram, mafic and felsic rocks display fractionated patterns, with light REE enrichment and heavy REE depletion (LaN/YbN = 1.41–5.38). The felsic samples display a negative Eu anomaly (Eu/Eu* = 0.59–0.87), while the mafic lavas are characterized by a positive Eu anomaly (Eu/Eu* = 1.03–1.35) or an absence thereof. On a primitive mantle-normalized trace element diagram, the majority of the samples exhibit negative Ti and Nb–Ta anomalies (0.08–0.9 and 0.54–0.74, respectively). These characteristic features exhibited by the metavolcanic rocks of Maroua are similar to those of subduction-zone melts. This subduction would have taken place after the convergence between the Congo craton (Adamawa-Yadé domain) and the Saharan craton (Western Cameroonian domain). Petrological modelling using major and trace elements suggests a derivation of the Maroua volcanics from primitive parental melts generated by the 5–10% partial melting of a source containing garnet peridotite, probably generated during the interaction between the subducted continental crust and the lithospheric mantle and evolved chemically through fractional crystallization and assimilation.

Functional recycling of grain boundary diffusion processed Nd-Fe-B sintered magnets

Sintered Nd-Fe-B magnets industrially produced employing the grain boundary diffusion process (GBD) were recycled by the so-called functional or short-loop recycling approach, based on hydrogen decrepitation (HD). Microstructural and magnetic differences between the original and the recycled materials were analyzed. The functional recycling of GBD magnets leads to the dissolution of the core (heavy rare earth lean) - shell (heavy rare earth rich) structure through the different heat treatment steps which include hydrogen decrepitation, sintering, and annealing. The recycled magnets show similar rectangular demagnetization curves with squareness of 96 %, and only a slightly decreased remanence of 5 % to 1.31 T, but a larger decrease in coercivity of 21 % to 1703 kA/m. A new GBD step using 1.5 wt.% Tb with a pure Tb-foil as diffusion source leads again to the formation of a core-shell structure with 0.5 µm thick Tb-shells which is similar to the microstructure of the original magnets prior to recycling. The coercivity of the recycled magnets is increased by 35 % from 1315 kA/m to 1780 kA/m at 50°C and shows similar magnetic values as the original industrial magnets at 150°C and 200°C, respectively. The temperature coefficients for the remanence, α, and for the coercivity, β, can also be fully restored and even exceed the original values which leads to an improved temperature stability of the recycled magnets compared to the original magnets.

Hydrothermal mineral replacement of bastnäsite by rhabdophane and monazite: effects of temperature on mineralogy, REE immobilisation, and fractionation

The rare-earth elements (REEs, La–Lu, Y) are essential for the development of renewable technologies. Bastnäsite (REECO3F) is a common REE ore mineral that is often subject to hydrothermal alteration at all crustal levels. Mechanisms of hydrothermal bastnäsite alteration therefore govern the evolution of REE deposits, though these mechanisms remain poorly understood. This experimental work investigates the hydrothermal replacement of bastnäsite by rhabdophane (REEPO4∙xH2O, x = 0–1) and monazite (REEPO4) in phosphatic fluids. Two temperature-dependent alteration pathways were identified; both follow the coupled dissolution-reprecipitation (CDR) mechanism. At 90 °C, bastnäsite was replaced by highly-porous metastable rhabdophane which was then replaced by monazite, forming an inner layer of rhabdophane and an outer layer of monazite. At 220 °C, bastnäsite was replaced directly by monazite. Although replacement initiated more quickly at 220 °C, greater overall replacement occurred at 90 °C (~ 61 wt.% after 500 h, compared to ~ 13 wt.% at 220 °C) due to surface passivation by monazite at 220 °C. Geochemical analyses showed REE fractionation during bastnäsite alteration. At 90 °C, rhabdophane was enriched in heavy REEs (Eu–Lu, Y), likely due to the evolving fluid chemistry, while at 220 °C secondary monazite was enriched in Sm and Ho compared to bastnäsite. These results indicate that: 1) the hydrothermal alteration of bastnäsite by rhabdophane and monazite in ore deposits leads to REE immobilisation, with little net loss of REEs to solution; 2) rhabdophane is metastable relative to monazite at 90 °C, and; 3) variable temperatures can cause different mineral textures and REE fractionation trends during hydrothermal alteration and mineral replacement.

Rare earth element patterns in sediments from the Great Lakes basin

This study presents a comprehensive analysis of rare earth element (REE) concentrations in >100 sediment samples from Lakes Erie and Huron, two of the North American Great Lakes. Significant intra- and inter-lake variability in REE concentrations is observed for both lakes Erie and Huron (<10 μg/g < versus <6 mg/g ƩREE, respectively). Light (L) REE were enriched over heavy (H) REE in surface sediment samples across both lakes, particularly in the North Channel of Lake Huron. Sediment cores from both lakes contained REE concentrations that are equally variable over time and correlated with major elements and other trace metals, reflective of the strong control of sediment accumulation rates on REE concentrations. Sequential extractions show that REE are predominantly associated with the residual (silicate) fraction (>50%) and likely originated from geogenic sources (basin weathering). However, considerable REE fractions (up to 16%) were also associated with oxide, phosphate minerals and organic/reducible material, particularly for the LREE. We attribute this apportionment and LREE enrichment to aqueous complexation and export from the water column. Finally, REE normalization and pattern-fitting reveal positive Ce anomalies (up to 16.2) in specific locations that could be indicative of hypolimnic redox gradients, whereas minor Gd and Eu anomalies (0.9 for Eu, and 1.02 for Gd, on average) likely relate to the parent rock signature. Our findings contribute valuable baseline data and insights into the complex interplay of geological, hydrodynamic, and environmental factors influencing REE distribution patterns in these lake sediments.

Hyper-enrichment of heavy rare earth elements in highly evolved granites through multiple hydrothermal mobilizations

Abstract Highly evolved granites can be important hosts of rare earth element (REE) resources, and more importantly, they commonly serve as the protolith for regolith-hosted REE deposits to form during weathering. Highly evolved granites in the Zudong pluton, South China, are extremely rich in the heavy (H)REE (up to 8000 ppm total HREE), and display significant REE fractionation. Moreover, the HREE enrichment is positively correlated with the degree of REE fractionation, indicating a unique process in preferentially enriching the HREE during the evolution of the granites. Multiple stages of hydrothermal re-mobilization of the REE can account for the HREE mineralization, and these are recorded in the texture and composition of the zircon. In these processes, fluctuations in the F activity of the fluid caused alternating dissolution-reprecipitation and continuous growth of the zircon. REE were repeatedly mobilized and enriched in the fluid to precipitate the major HREE mineral synchysite-(Y), and partially incorporated into the growth zone of zircon, while other elements were largely lost to the fluid during the extensive dissolution of the rock-forming minerals. LREE were also likely substantially mobilized in the late hydrothermal stage and lost through complexation with Cl, causing the significant LREE depletion and, thus REE fractionation. This process continuously enriched host granites in the HREE to a potentially economic grade, making them favorable protoliths for subsequent supergene regolith-hosted HREE deposits.

Tracking HFSE associated with high salinity fluid during HP metamorphism in the Zavkhan Terrane, Western Mongolia

Garnets often exhibit high concentrations of heavy rare-earth elements, which provide crucial insights into element mobility and fluid dynamics during metamorphism. This research reports on the distributions of trace and major elements in garnets from the Khungui eclogite of the Zavkhan Terrane in Western Mongolia. Within the eclogite sample, two types of garnets were identified, featuring dissimilar microstructures and compositional zoning: aggregate-type garnet with asymmetric zoning (Grt1) and euhedral garnet with concentric zoning (Grt2). Previous studies determined that Grt2 formation occurred in the pre-eclogite stage to eclogite facies (2.1–2.2 GPa and 580–610 °C), associated with the infiltration of high-saline fluids. The hexagonal-shaped pseudomorphs of Ti-bearing minerals associated with Grt1 suggest that the nucleation of titanite and garnet was simultaneously accelerated by the destabilization of Ti-augite during pre-eclogite metamorphism. This process could have contributed to the formation of aggregation textures, where Ti-bearing minerals are closely associated with Grt1 in the Khungui eclogite. Based on major divalent elemental composition zoning and trace element characteristics, both Grt1 and Grt2 in the Khungui eclogite are formed simultaneously from the pre-eclogite to eclogite stages. The cores (high Fe + Mg + Mn; Y + REE) of Grt1 and Grt2 are attributed to Rayleigh fractionation or a diffusion-limited uptake process. In contrast, the growth mechanisms of the Grt1 rim and Grt2 rim are distinct during the eclogite stage. The Grt1 rim is explained by a dissolution–reprecipitation, which resulted in the atoll texture observed in Grt1. The Grt2 rim (high Ca; low Y + REE) grew through a mechanism consistent with that of the Grt2 core. The major and trace element zonings of these garnets provide insights into element mobility related to Ti-bearing minerals and infiltration of high salinity fluids at different stages: (1) the mobilization of Ti and V increased under eclogite facies conditions (growth stage of garnet) compared to the pre-eclogite stage, with the mobility of Ti, Nb, Ta elements being pronounced under the exhumation stage (Rt–Ilm–Ttn2), possibly because of the infiltration of high-saline fluids and an increase in temperature, and (2) post-growth compositional modification of Grt1 was induced by a localized transport of Fe, Mg, Mn, and Ca elements in response to the replacement of ilmenite by titanite during decompression (0.1–0.5 GPa and 421–534 °C). The contrasting zoning of garnet in Khungui eclogite indicates dissimilar scales of element mobility under eclogite facies conditions (over a thin-section scale) and during decompression (up to several centimeters or beyond).

Investigating Physicochemical Methods to Recover Rare-Earth Elements from Appalachian Coals

The demand for rare-earth elements is expected to grow due to their use in critical technologies, including those used for clean energy generation. There is growing interest in developing unconventional rare-earth element resources, such as coal and coal byproducts, to help secure domestic supplies of these elements. Within the U.S., Appalachian Basin coals are particularly enriched in rare-earth elements, but recovery of the elements is often impeded by a resistant aluminosilicate matrix. This study explores the use of calcination and sodium carbonate roasting pre-treatments combined with dilute acid leaching to recover rare-earth elements from Appalachian Basin coals and underclay. The results suggest that rare-earth element recovery after calcination is dependent on the original mineralogy of samples and that light rare-earth minerals may be more easily decomposed than heavy rare-earth minerals. Sodium carbonate roasting can enhance the recovery of both light and heavy rare-earth elements. Maximum recovery in this study, ranging from 70% to 84% of total rare-earth elements, was achieved using a combination of calcination and sodium carbonate roasting, followed by 0.25 M citric acid leaching.

Recovery of Xenotime and Florencite from Silicate Minerals Using a Combined Technique of Magnetic Separation and Flotation

Xenotime (YPO4), a significant phosphatic minerl rich in heavy rare earth elements (HREEs), typically associates with granitic rocks, exemplified in the Wolverine rare earth deposit in Australia. A mineral composition analysis indicates that the primary valuable minerals in the deposit are principally xenotime and minor florencite, with quartz and illite as the main gangue minerals, showing a relatively simple mineral composition. The grade of rare earth concentrate was increased to 14.29% and the recovery reached 94.48% through the magnetic separation pre-enrichment test. However, a high-grade rare earth concentrate could not be achieved using magnetic separation alone. Further purification of the magnetic concentrate is conducted through flotation. The grade of rare earth concentrate reached 51.26%, and the recovery rate reached 90.47%. In summary, this process achieves the efficient recovery of xenotime and florencite, having substantial industrial potential.

Rare-earth elements in dictyonema shales of the Baltic sedimentary paleobasin

The results of a study of rare-earth metals in dictyonema shales of the Paleozoic Baltic sedimentary basin, have been given. On the territory of the studied Kaibolovo-Gostilitsy prospecting area, high up to potentially industrial contents of rare-earth elements were confirmed on a large factual and analytical material. The average REE concentration is 289 g/t with maximum up to 724 g/t. REE are found in dictyonema shales in various forms (mineral, organic, ionic, molecular, colloidal). Apparently, the occurrence of REE in the mineral part of dictyonema shales prevails. The proportion of heavy (and most valuable) lanthanides (15.6% in the relative total amount) in the studied dictyonema shales is twice the ore deposits range. This, and the presence of large geological resources of the REE in the dictyonema shales of the Baltic region of Russia, determine the need for their integrated development with other associated components.

Dopaminergic- and Serotonergic-Dependent Behaviors Are Altered by Lanthanide Series Metals in Caenorhabditis elegans.

The lanthanide series elements are transition metals used as critical components of electronics, as well as rechargeable batteries, fertilizers, antimicrobials, contrast agents for medical imaging, and diesel fuel additives. With the surge in their utilization, lanthanide metals are being found more in our environment. However, little is known about the health effects associated with lanthanide exposure. Epidemiological studies as well as studies performed in rodents exposed to lanthanum (La) suggest neurological damage, learning and memory impairment, and disruption of neurotransmitter signaling, particularly in serotonin and dopamine pathways. Unfortunately, little is known about the neurological effects of heavier lanthanides. As dysfunctions of serotonergic and dopaminergic signaling are implicated in multiple neurological conditions, including Parkinson's disease, depression, generalized anxiety disorder, and post-traumatic stress disorder, it is of utmost importance to determine the effects of La and other lanthanides on these neurotransmitter systems. We therefore hypothesized that early-life exposure of light [La (III) or cerium (Ce (III))] or heavy [erbium (Er (III)) or ytterbium (Yb (III))] lanthanides in Caenorhabditis elegans could cause dysregulation of serotonergic and dopaminergic signaling upon adulthood. Serotonergic signaling was assessed by measuring pharyngeal pump rate, crawl-to-swim transition, as well as egg-laying behaviors. Dopaminergic signaling was assessed by measuring locomotor rate and egg-laying and swim-to-crawl transition behaviors. Treatment with La (III), Ce (III), Er (III), or Yb (III) caused deficits in serotonergic or dopaminergic signaling in all assays, suggesting both the heavy and light lanthanides disrupt these neurotransmitter systems. Concomitant with dysregulation of neurotransmission, all four lanthanides increased reactive oxygen species (ROS) generation and decreased glutathione and ATP levels. This suggests increased oxidative stress, which is a known modifier of neurotransmission. Altogether, our data suggest that both heavy and light lanthanide series elements disrupt serotonergic and dopaminergic signaling and may affect the development or pharmacological management of related neurological conditions.

Bipyridyldicarboxamides and f-metals: the influence of electron effects on the structure, stability, separation, and photophysical properties of their complexes.

In this work, three isomeric fluorinated bipyridyldicarboxamides were studied to evaluate the impact of the fluorine atom position on the structure, stability, Am(III)/Ln(III) separation, and photophysical properties of their complexes. The complexes of the fluorinated amides have a metal-to-ligand composition of 1 : 1, which is independent of the fluorine atom position or lanthanide metal. The bipyridyl fragments in the fluorinated complexes are flattened compared with those in unsubstituted ones. Ln-to-heteroatom distances are more affected by steric hindrance in the ligand and further by lanthanide ion radius contraction. This leads to significant effectivity of heavy lanthanide extraction compared with the light ones, particularly for 4F diamide. Fluorination leads to a slight variation in the excited triplet state of the complexes, and hence, the effectiveness of luminescence increases for Eu, Sm, and Tb complexes. Moreover, fluorination significantly affects the CIE chromaticity coordinates for the complexes.

Aeschynite Group Minerals Are a Potential Recovery Target for Niobium Resources at the Giant Bayan Obo Nb–REE–Fe Deposit in China

With the development of the steel industry, China’s demand for niobium is increasing. However, domestic niobium resources are not yet stably supplied and are heavily dependent on imports from abroad (nearly 100%). It is urgent to develop domestic niobium resources. The Bayan Obo deposit is the largest rare earth element deposit in the world and contains a huge amount of niobium resources. However, the niobium resource has not been exploited due to the fine-grained size and heterogeneous and scattered occurrences of Nb minerals. To promote the utilization of niobium resources in the Bayan Obo deposit, we focused on the mineralogical and geochemical characterization of six types of ores and mineral processing samples from the Bayan Obo deposit, using optical microscopes, EPMA, TIMA, and LA–ICP–MS. Our results show that: (1) the niobium mineral compositions are complex, with the main Nb minerals including aeschynite group minerals, columbite–(Fe), fluorcalciopyrochlore, Nb–bearing rutile, baotite, fergusonite–(Y), fersmite, and a small amount of samarskite–(Y). Aeschynite group minerals, columbite–(Fe), and fluorcalciopyrochlore are the main niobium-carrying minerals and should be the primary focus of industrial recycling and utilization. Based on mineralogical and geochemical investigation, the size of the aeschynite group minerals is large enough for mineral processing. Aeschynite group minerals are thus a significant potential recovery target for niobium, as well as for medium–heavy REE resources. The Nb–rich aegirine-type ores with aeschynite group mineral megacrysts are suggested to be the most significant niobium resource for mineral processing and prospecting. Combined with geological features, mining, and mineral processing, niobium beneficiation efforts of aeschynite group minerals are crucial for making breakthroughs in the utilization of niobium resources at the Bayan Obo.

Selective separation of light and heavy rare earth elements from acidic mine waters by integration of chelating ion exchange and ligand impregnated resin

This study addresses the potential of sourcing Critical Raw Materials (CRMs) using Acidic Mine Waters (AMWs) as a secondary resource. AMWs, often viewed as waste, contain valuable metals like zinc and copper, as well as critical metals like magnesium and cobalt. Moreover, recent studies also reported the presence of Rare Earth Elements (REEs) at concentrations (mg/L) that make their extraction both technically and economically viable. The research focuses on a circular process to recover these metals from AMWs, specifically from the Aznalcóllar open-pit mine, which contains 216 mg/L of Al, 47 mg/L of Fe, 547 mg/L of Zn, and 18.56 mg/L of REEs. The proposed method involves pre-treating the AMW to remove Fe and Al, achieving removals of over 99.9 % and 90 %, respectively, at pH 4.5. Following this, transition metals like Zn, Cd, and Cu were removed as sulphides with a removal efficiency exceeding 99 %. This pre-treatment step reduced the concentration of competing metals in the ion-exchange process, thereby enhancing the recovery and purity of REEs. To separate heavy and light REEs, two types of resins in series were used: an impregnated resin (TP272) and a chelating resin (S930), which can be regenerated using sulphuric acid (H2SO4). The final recovery of REEs as oxalates was achieved using oxalic acid and ammonia at pH 1, with further optimization of the elution process to minimize ammonia consumption and undesired precipitation of other oxalates. Finally, REE oxalates with purities exceeding 90 % were obtained. This research demonstrates a sustainable method for efficiently recovering valuable REEs from AMWs, while also addressing environmental concerns related to hazardous sludge generation.

Selective separation and recovery of rare-earth elements (REEs) from acidic solutions and coal fly ash leachate by novel TODGA-Impregnated organosilica media

Rare-earth elements (REEs) are essential in a wide range of applications including magnets and satellite technology, with demand driven by geopolitical factors. While multiple techniques exist for REE recovery including solvent extraction and selective precipitation, solid–liquid extraction offers key advantages in selectivity, scalability, and recyclability. N, N, N′, N′-tetraoctyl diglycolamide (TODGA) is a tridentate ligand widely used in solvent extraction, but the incorporation in a solid support to separate individual lanthanides from acid solutions remains largely unexplored. A novel TODGA-organosilica sorbent material was developed and tested to evaluate recovery of 17 elements (REEs and thorium) in terms of selectivity, kinetics, and equilibrium isotherms in 0.01 to 15.9 M nitric acid. Characterization of the new sorbent was performed before and after sorption using FTIR, XPS, and SSA techniques to help elucidate sorption mechanisms and limiting variables. REE adsorption increased from 1.26 mg g−1 to 10 mg g−1 with nitric acid concentrations of 0.01 M and 15.9 M, respectively. TODGA-organosilica exhibits high selectivity towards heavy REEs (Dy to Lu), with minimal sorption of lighter REEs (Ce to Gd). Batch adsorption experiments confirm pseudo-second-order kinetics and a Langmuir adsorption isotherm with TODGA binding to REEs in a 3:1 complex. A packed bed column study confirmed the high selectivity of TODGA-impregnated organosilica towards heavy REEs and a proof-of concept experiment with coal fly ash leachate shows high selectivity for REEs over Al, Fe, and Ca present in several orders of magnitude higher concentrations. Fractionation was observed where loading cycle effluent contained 84 % light REEs while strip cycle effluent contained 80 % heavy REEs. More than 90 % of loaded REEs were successfully stripped with water as the stripping agent.

U-Pb Ages of Zircon Grains in the Playa Azul Beach Sediments, Guerrero State, Mexican Pacific

ABSTRACT The mineralogy of bulk sediments, U-Pb ages and chemistry of 195 detrital zircon grains recovered in the Playa Azul beach, Mexican Pacific coast were performed to infer their provenance. The bulk sediments were composed of minerals like quartz, feldspar, titanite, plagioclase, zircon, and magnetite. The average Th/U ratio in zircon grains was ~ &amp;gt; 0.2, indicated an igneous origin. The chondrite normalized rare earth element (REE) patterns of zircons were depleted in low REE (LREE) and enriched in heavy REE (HREE), with positive cerium and negative europium anomalies, indicating a granitoid source. U-Pb ages of zircon grains revealed the predominance of Cenozoic and Mesozoic ages in samples PAC2 (~ 33.8 - 61.8 Ma, n = 90 and ~ 67 - 132 Ma, n = 10, respectively) and PAC19 (~ 0.1 -39.6 Ma, n = 55 and ~ 67 - 251 Ma, n = 20, respectively). Minor peaks were represented by Palaeozoic (n = 9) and Precambrian (n = 11) ages in PAC19. Zircon ages and their morphology indicated that they were mostly derived from the nearby terranes. The source terranes, which supplied Cenozoic zircons to the beach area were the coastal Cenozoic plutons and Cuicateco terrane. The Mesozoic zircons in the Playa Azul coastal sediments were derived from the Mixteca (Acatlan Complex), Guerrero, and Xolapa terranes, located along the Mexican Pacific coastal zone. The Proterozoic zircons were represented by the coastal Oaxacan Complex. In addition, the Arteaga Complex in the Guerrero State, adjacent to the playa Azul beach was the potential source for the Eocene zircons.