Rare Earth Phosphates Research Articles

Study on selective green leaching of rare earth elements from coal gangue using mechanochemical activation

This study proposes a sustainable method for the selective leaching of rare earth elements (REEs) from coal gangue. By combining 600 °C calcination, the addition of 5 % Fe2(SO4)3, and one hour of mechanical-chemical activation, we achieved a leaching efficiency of 65 % for REEs. This method alters the surface and crystalline structure of coal gangue, facilitating the release of rare earth phosphate minerals and the formation of water-soluble compounds (rare earth sulfates). Fe2(SO4)3 transforms into insoluble iron oxide, which immobilizes impurities and promotes the selective leaching of rare earth elements. Notably, during the leaching process, the leaching rates of aluminum (Al) and iron (Fe) were only 0.37 % and 1.27 %, respectively. Kinetic analysis indicates that this process follows a mixed reaction-controlled shrinking core model. This method effectively reduces the environmental risks associated with traditional acidic reagents, providing a sustainable pathway for the recovery of rare earth elements.

Structure and optical properties of alkali rare-earth double phosphates of M3RE(PO4)2 (M = K, Rb; RE = Y, La, and Lu)

Designing and synthesizing phosphate nonlinear optical materials with novel structures and excellent properties remains challenging. In this work, the electronic structure and optical properties (second harmonic generation (SHG) response or birefringence) of alkali rare-earth double phosphates M3RE(PO4)2 (M = K, Rb; RE = Y, La, and Lu) are systematically investigated. It is worth mentioning that P31m-Rb3Lu(PO4)2 was successfully synthesized by a flux-method, and the UV–vis–NIR diffuse reflectance spectroscopy showed that Rb3Lu(PO4)2 exhibits a short absorption edge at 207 nm and a high transmittance of 77.9 %. Based on first-principles calculations, the results show that the birefringence of the M3RE(PO4)2 series of crystals exhibits significant differences (0.009-0.028@1064 nm). Subsequently, analysis of the electronic structure and the real-space atom cutting method reveals that rare-earth polyhedra play a major role in enhanced birefringence. Overall, this work enriches the study of nonlinear optical crystals of rare earth phosphates and provides a case for further exploration.

Anti-thermal quenching and temperature sensing properties of Er3+/Yb3+ co-doped Sc2O3 phosphors

Up-conversion luminescence from rare earth doped phosphor is a potential candidate as non-contact temperature sensor. In this work, different Er3+ concentration doped Sc2O3: Er3+/Yb3+ phosphors were prepared through typical sol–gel method. The emission intensity reached the maximum as the doping concentration of Er3+ was 1.0 mol%. While, different from high concentration (0.5, 1.0 and 2.0) of Er3+ doped samples, an abnormal enhancement in the two green emissions and red emission in Sc2O3: 0.3 mol% Er3+/ 2 mol% Yb3+ phosphors was observed through elevate temperature and the enhancement factor reaches 1.3 as the temperature changed from 303 to 513 K. The reason for this concentration dependent thermal enhancement could be interpreted by the competition between increased energy transfer and non-radiative transition. The temperature sensing properties of samples, including relatively sensitivity, temperature resolution and repeatability were investigated and the maximum values reached 1.03 × 10−2 K−1 (303 K), 0.524 K (303 K) and 99.65 % (303––513 K), respectively, in Sc2O3: 1 mol% Er3+/2 mol% Yb3+ phosphors. The results imply that they have good temperature sensing ability and can be used as an optical temperature probe in research and production.

Synthesis and luminescent properties of multi-mode core-shell-shell LaPO4:RE (RE³⁺ = Er³⁺, Eu³⁺) microspheres for anti-counterfeiting ink applications

To meet the demands for product and consumer protection, we developed biocompatible multi-mode emitting core-shell-shell rare earth phosphates for anti-counterfeiting inks. These core-shell-shell structures feature SiO2 microspheres as the core, with LaPO4 nanocrystals doped with erbium (Er) and europium (Eu) as the interlayer, and an outer SiO2 shell. The SiO2@LaPO4:Er0.1,Eux@SiO2 (x = 0.01, 0.02, 0.03, 0.04, 0.05) microspheres display dual emissions when excited by 254 nm and 365 nm UV light, offering a novel anti-counterfeiting approach. Another core-shell-shell structure was created with LaPO4:Er3+ and LaPO4:Eu3+ separately coated on SiO2 cores, mixed, and then covered with a SiO2 shell. Under 980 nm near-infrared laser excitation, these structures emit bright upconverted green light, while 254/365 nm UV light induces red/yellow down-conversion luminescence. This design minimizes up-conversion luminescence quenching of Er3+ ions from cross-relaxation with Eu3+ ions. The SiO2 core minimizes energy loss, regulates particle size, and enhances luminescence. A certain thickness of the silicon shell layer also protects against luminescence quenching. The inks exhibit high dispersibility, non-reproducibility, and excellent luminescence, making them effective for anti-counterfeiting.

Synthesis of YPO4:Tb3+ core-shell nanophosphors and their application in fingerprint detection

In order to enhance the fluorescent performance of rare-earth phosphates, YPO4:Tb3+ nanophosphors were synthesized using a one-step hydrothermal method, employing both homogeneous and heterogeneous coatings devoid of organic compounds. By adjusting the molar ratio of core to coating material, a series of core-shell structured luminescent nanomaterials YPO4:Tb3+@Y(Gd,La) LnPO4 (LnY, Gd and La) were prepared, and the optimal molar ratio to enhance the fluorescent performance of the YPO4:Tb3+ core was determined. Comprehensive analyses, employing techniques such as X-ray diffraction, scanning and transmission electron microscopy, fluorescence spectrophotometry, and ultraviolet spectrophotometry, characterized the composition, structure, morphology, and optical properties of the synthesized materials. Additionally, the energy bands and density of states of YPO4 were theoretically analyzed using first-principles calculations. These results indicate that the structure and morphology of the products was preserved post-coating, but the fluorescence intensity was significantly enhanced. Among them, the homogeneously coated YPO4:Tb3+@YPO4 nanophosphors exhibited the strongest fluorescence intensity, more than threefold that of the uncoated sample. Theoretical calculations confirmed that YPO4 is a direct bandgap phosphate with a calculated bandgap value of 5.88 eV, which is consistent with the experimental value. The prepared YPO4:Tb3+@YPO4 nanophosphors demonstrated clear potential in visualizing fingerprints on various materials; even fingerprints aged for 30 days were successfully visualized. Therefore, the coated nanophosphors not only enhance fluorescent performance but also broaden their applicability in latent fingerprint recognition.

Recovering rare earth elements from svanbergite ores by roasting and phosphoric acid leaching

Rare earth elements (REEs) are regarded as key global strategic metals, and recovering REEs from phosphate ores might constitute an alternative method of acquiring rare earth resources. Svanbergite ores in Sichuan are particular phosphates rocks that contain abundant REEs, which are valuable resources that have not been fully developed and utilized. Consequently, the development of crucial technologies for extracting REEs from svanbergite ores hold strategic and scientific significance. This study employed roasting and phosphoric acid leaching processes to recover REEs from svanbergite ores. Response surface methodology (RSM) was applied to optimize the hydrometallurgical process parameters. This study found that the optimal conditions for REEs recovery were: a roasting temperature 600℃, a roasting time of 38.72 min, a phosphoric acid concentration of 40%, a leaching liquid/solid mass ratio of 10, a leaching temperature of 75℃ and a leaching time of 70 min, resulting in a maximum predicted REE recovery rate of 83.57%. The experimental values exhibited a high degree of proximity to the predicted values, thereby substantiating the accuracy of the model and validating the plausibility of the optimized solution. Mechanistic analysis revealed that after the roasting process, the crandallite formed new acid-soluble new phases. Following the phosphoric acid leaching process, REEs were present predominantly in the form of REE3+ in the leaching solution, consequently separating the REEs from the svanbergite ores. This study provides a valuable reference for the recovery of REEs from associated rare earth phosphate ores.

A systematic study of thermomechanical properties and calcium-magnesium-aluminosilicate (CMAS) corrosion of multicomponent rare-earth phosphates

A systematic study of thermomechanical properties and calcium-magnesium-aluminosilicate (CMAS) corrosion of multicomponent rare-earth phosphates

Ca9-yMgyNaGd0.667(PO4)7:Eu2+: A Single Eu2+-Doped Full-Spectrum White Light Emission Phosphor with High Color Rendering Index.

The multi-cationic site occupation control of rare earth doped phosphor materials is one of the key factors in achieving single-phase full-spectrum emission. In this work, the site distribution of Eu2+ in Ca9NaGd0.667(PO4)7 (CNGP):x%Eu2+ phosphors with multi-cationic sites was determined. Under 385 nm excitation, CNGP:x%Eu2+ samples exhibited a cyan emission composed of three sub-Gaussian components. The CNGP:1.5%Eu2+ phosphor was structurally modified through the partial substitution of Mg2+ for Ca2+ according to the crystallographic site engineering theory, and corresponding luminescent properties had been adjusted. When the concentration of Mg2+ changed, the Ca9-yMgyNaGd0.667(PO4)7:1.5%Eu2+ (CNGPE:yMg2+) phosphors exhibited a tunable emission from cyan to orange and achieved white light emission at y = 0.6. Based on the change of the crystal field environment, the mechanism of Mg2+ substitution affecting the luminescence characteristics of CNGP:x%Eu2+ phosphors was researched in detail. The light-emitting diode device consisted of a CNGPE:0.6Mg2+ phosphor and a 385 nm chip and had a high color rendering index (CRI = 91.9), low correlated color temperature (CCT = 4852 K), and excellent color stability. The optical performance of this device makes it promising to be used in full spectrum lighting.

Thermal evolution of mercury from waste rare earth phosphor: Effect of thermal treatment conditions and kinetic analysis

Waste phosphor (WP) from fluorescent lamp is a hazardous waste and an important secondary resource for recycling mercury and rare earths. To avoid mercury pollution during rare earth recovery, it is necessary to conduct deep mercury removal before rare earth recovery. However, the mechanism of mercury removal in WP is not clear, which restricts the progress of efficient mercury removal methods. Effects of treatment temperature and time on thermal evolution of WP were analyzed by different characterization methods. Model-free, model-fitting and z(α) master plots method are used in combination to explain the complex mechanism of mercury removal in WP. The mechanism of mercury removal will change gradually with the process of mercury removal. The average Eα for mercury removal is 100.76 kJ/mol and 190.36 kJ/mol at conversion α (i.e. mercury removal efficiency) of 0.1–0.3 and 0.3–0.9, respectively. Simple mercury compounds are decomposed at α less than 0.3 (∼600 °C), according with the model of random nucleation and subsequent growth. A large amount of tightly combined mercury is released rapidly at α of 0.3–0.75 (600–700 °C), ascribing to the decomposition of carbonate and the structure transformation of silicon oxide. The process mechanism gradually change from 1D/2D diffusion to 3D diffusion, increasing the mass transfer resistance of mercury diffusion. Thermal desorption of residual bound mercury at α larger than 0.75 (∼700 °C) is controlled by phase boundary reaction. More efficient mercury removal effects can be obtained by adding additives to roasting. The results are beneficial to the research of deep mercury removal methods of WP.

Tuning β-Si3Al3O3N5 phosphors by Eu or Ce doping for white light-emitting diodes (wLEDs)

SiAlON-based phosphors have garnered considerable attention in the field of white lighting owing to their excellent thermal stability, and rare earth doped SiAlON-based phosphors are expected to be used in a new generation of lighting sources. In this work, Eu2+ or Ce3+ doped Si3Al3O3N5 phosphors were synthesized by high temperature solid phase method. The microstructure of the phosphors exhibited irregular grain. The two phosphors exhibit green and cyan luminescence under 365 nm excitation, which are derived from the 5d-4f transitions of Eu2+ and Ce3+, respectively. The quenching concentrations are 3 % and 4 % for Eu2+ and Ce3+doped phosphors, respectively. The fluorescence intensity of Eu2+ and Ce3+ activated SiAlON powders decreased to 50 % of the room temperature intensity at 179 °C and 170 °C, respectively. The thermal activation energy values of the two phosphors were 0.35 eV, and the coordinate configuration diagram was constructed to comprehensively analyze the thermal quenching behavior of phosphors. Finally, the two phosphors powders were mixed with red and blue fluorophore to obtain white LEDs, showing low color temperature, high color rendering, high power unsaturation and long half-life. The SiAlON-based phosphors with excellent thermal stability obtained in this work achieve different wavelengths of luminescence in the green region. The results show that the β-Si3Al3O3N5 phosphor can be used as a candidate material for high-quality green light supplement for wLEDs.

Towards Improved Measurement of Chemical Composition and Isotope Ratios of Rare-earth Phosphates in Atom Probe Tomography

Towards Improved Measurement of Chemical Composition and Isotope Ratios of Rare-earth Phosphates in Atom Probe Tomography

Comprehensive impact assessment on resource and environment of emerging recycling technologies for waste materials: Evidence from waste rare earth phosphors recycling

The recycling of waste materials has dual attributes of resource and environment, and current technical evaluation methods are difficult to balance the comprehensive impact of resource and environment, failing to meet the selection requirements of emerging recycling technologies. Focusing on the emerging recycling technology for rare earth phosphors, we developed a resource and environment composite assessment model, employing emergy accounting principles to uniformly quantify resource inputs and environmental impacts. The results indicated that the composite emergy of resource and environment of the recycling technologies is reduced by over 89.05 % compared to that of natural ores development technology. Moreover, the synergistic recycling of zinc (Zn) along with yttrium oxide (Y2O3) achieves an additional emergy reduction by 88.37 %. The resource emergy of natural ores development technology accounts for 95.15 %, indicating its heavy reliance on resource depletion. Due to the utilization of various chemicals, the recycling technologies exhibit stronger environment attribute.

Prediction of optical properties of rare-earth doped phosphate glasses using gene expression programming

The progression of optical materials and their associated applications necessitates a profound comprehension of their optical characteristics, with the Judd–Ofelt (JO) theory commonly employed for this purpose. However, the computation of JO parameters (Ω2, Ω4, Ω6) entails wide experimental and theoretical endeavors, rendering traditional calculations often impractical. To address these challenges, the correlations between JO parameters and the bulk matrix composition within a series of Rare-Earth ions doped sulfophosphate glass systems were explored in this research. In this regard, a novel soft computing technique named genetic expression programming (GEP) was employed to derive formulations for JO parameters and bulk matrix composition. The predictor variables integrated into the formulations consist of JO parameters. This investigation demonstrates the potential of GEP as a practical tool for defining functions and classifying important factors to predict JO parameters. Thus, precise characterization of such materials becomes crucial with minimal or no reliance on experimental work.

Bio-inspired super-wetting coatings constructed from interfacial mineralization of rare earth phosphate for oil/water separation applications

The oil fouling problem of lipophilic polymer matrix causes severe decline of separation performance, becoming one of the most serious challenges for oil/water separation. A chemical-stable and mechanical-strong anti-fouling coating is highly emerged. Herein, to achieve anti-fouling performance on diverse polymer substrates, a biomimic super-wetting coating is fabricated by interfacial mineralization of lanthanum phosphate (LaPO4). The strong interaction between ions makes LaPO4 very stable against acid, base, oil and mechanical impact, while the dense charges on the surface of LaPO4 attract water molecules and create a hydration layer to repulse oil under water. The membranes and meshes modified by such mineralized coating exhibit good separation efficiency (>99 %) and high permeation flux for oil-in-water emulsions and oil/water mixtures, respectively. In addition, notable cyclic flux recovery ability was fulfilled by water rinsing. The fabrication of such mineralized coating is easily operated through solution process and no harmful byproducts will be generated. Basically, the low-cost and eco-friendly mineralized coating is promising for oily water treatment in the practical complicated environment.

Alkali rare earth double phosphates: Promising new high temperature scintillators

Alkali rare earth double phosphates were investigated for their X-ray induced scintillation. Double phosphates with stoichiometry A3Ln(PO4)2 (A = K or Rb, Ln = Eu or Tb) were synthesized via a eutectic molten salt flux yielding high quality single crystals. The systematic variation of the alkali and rare earth elements in the structure allowed for insights into the effects of the chemical composition on the scintillation output. The radioluminescence of these compositions under X-ray excitation is reported with a discussion of the variance of their luminosity as a function of both the constituent alkali and lanthanide elements. The relative luminosity of Rb3Tb(PO4)2 surpasses BGO by 30 %. The dependance of the scintillation on temperature is also investigated, including an unusual peak intensity increase for higher temperatures that can reach 1.4x of its value at room temperature for Rb3Tb(PO4)2 at 255 °C, and 2.1x for K3Tb(PO4)2 at 495 °C.

Porous high-entropy rare-earth phosphate (REPO4, RE = La, Sm, Eu, Ce, Pr and Gd) ceramics with excellent thermal insulation performance via pore structure tailoring

Porous high-entropy rare-earth phosphate (REPO4, RE = La, Sm, Eu, Ce, Pr and Gd) ceramics with excellent thermal insulation performance via pore structure tailoring

Beneficiation of rare earth elements contained in phosphogypsum using sequenced treatment process

Concerns regarding the availability of rare earth elements (REEs) and the depletion of natural resource reserves have made it necessary to look for a significant breakthrough that may pave the way for the mining of several low-grade deposits and secondary resources. Phosphogypsum (PG) is one of the promising alternatives to preserve a steady flow of REEs and mitigate the loss of natural reserves. Nonetheless, the low concentration of REEs in PG implies the necessity of an enrichment step prior to any extraction attempt. To tackle the difficult challenges of REEs concentration from diluted phosphate-derived by-products, this study concentrated on determining the likely speciation of REEs and their beneficiation, as well as conducting an economic assessment of the potential industrial value of REEs present in PG. It was found that the alkaline solubilization of the gypsum phase of PG using Na4EDTA favored the beneficiation of different qualities of PG. Moreover, it was found that the abatement of residual undesirable phases by mineral acid (HF) for quartz (SiO2) elimination, or pyrometallurgical process, improved the enrichment of REEs in the residual concentrate. A REEs concentration of 4390.23 ppm and 4317.55 ppm were achieved after sequenced alkaline, neutral, and acidic treatment of low-grade PG (238.22 ppm); and sequenced alkaline, neutral, and pyrometallurgical treatment of high-grade PG (389.75 ppm), respectively. Furthermore, an elementary assessment of REEs speciation revealed that REEs could potentially be present as insoluble rare earth fluorides (REF3) and/or rare earth phosphates (REPO4).

Direct and efficient catalytic conversion of biomass-derived 2-methyltetrahydrofuran to 1,3-pentadiene via acid-base coupling of lanthanum phosphate

It is critical to increase the reaction selectivity and atom economy, avoid side reactions during the catalytic process, and achieve the desired single-target product. Here, an efficient and novel method of producing 1,3-pentadiene via the acid-base coupling of rare-earth phosphate-catalyzed dehydra-decyclization of 2-methyltetrahydrofuran (2-MTHF) is reported, resulting in a previously unreported 1,3-pentadiene yield of 97.2% at 350 ℃. This method efficiently addresses two significant problems encountered in the dehydra-decyclization of 2-MTHF to generate 1,3-pentadiene research: the occurrence of retro-Prins condensation and the competitive reaction of 1,4-pentadiene. Density-Functional-Theory calculations demonstrated that 2-MTHF was adsorbed on the surface of rare-earth phosphate catalysts in a multi-site parallel mode, resulting in a lower apparent activation energy and ring-opening energy barrier. Space-time investigations and in situ diffuse reflectance infrared Fourier transform spectroscopy provided evidence for direct synthesis of pentadiene on rare-earth phosphate catalysts with Lewis acid-base sites. The acid-base coupling catalysis was demonstrated by poisoning experiments. In-situ self-regeneration of Brønsted acid sites was confirmed by infrared spectroscopy of adsorbed pyridine, facilitating the isomerization of 1,4-pentadiene to 1,3-pentadiene. Therefore, a unique reaction pathway for the dehydra-decyclization of 2-MTHF on the surface of rare-earth phosphates was proposed, and a new rotational isomer was discovered.

Secondary Enrichment of REE in Weathered Granite, South Bangka, Indonesia

Rare earth elements (REEs) are essential materials for the manufacture of advanced technology. Secondary REE indications were found in alluvial and lateritic tin deposits within Southeast Asia Tin Belt. This study aims at the REE enrichment of weathering profiles underlain by Toboali Pluton of the main range S-type granite of this belt. Granite and weathering samples were collected and analyzed using XRF, ICP-MS/OES, XRD, SEM-EDX, and EPMA. The Chondrite-normalized REE patterns of granite in Toboali showed enrichment in REE with the highest value of 1,126 ppm. The Toboali Pluton is enriched in LREE and depleted in HREE. The enrichment of REE from the upper to lower horizon of weathering profiles was pointed out by the increase in REE values from a range of 156-188 ppm (horizon B) to 196-268 ppm (horizon C) in Toboali, and from a range of 230-330 ppm (horizon B) to 342-450 ppm (horizon C) in Air Gegas. These coincided with the presence of kaolinite with elevated REE and CeO2 in horizon C of weathering profile. Leaching test result proved that kaolinite plays a role in REE enrichment in the weathering profile through ion adsorption mechanisms in the Air Gegas. The weathering process of REE fluoro-carbonate (bastnäsite-(Ce)) and parisite-(Ce) in granite is believed to contribute in enrichment due to its high dissolution rate, which enhances kaolinite adsorption. In contrast, REE phosphates such as monazite-(Ce) and xenotime-(Y), because of their strong resistance and low solubility, are thought to be only slightly soluble, and most of these minerals remain in Toboali weathering products.

Nature of ree accumulation in clayey interlayers and coals in Karaganda coal basin

It is the first completed complex mineralogical and geological research of REE (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in the coals of Karaganda coal basin in Central Kazakhstan. This paper presents the results of the research of REE (from lanthanum to lutetium and Y) distribution in 85 samples of coal and clayey interlayers of stratum k7 of Karaganda coal basin in the faces of Saranskaya, T.Kuzembayev, Aktasskaya mines. The ultimate composition of clayey interlayer and coal samples was analyzed by the methods of inductively coupled plasma optical emission spectroscopy and inductively coupled plasma mass spectrometry (ICP-OES and ICP-MS). Research of the lateral and vertical discontinuity of the total REE concentration has indicated the presence of mixed types of REE distribution in coals, which supposes various forms of REE migration and different mobility of heavy and light lanthanides within the hypergenesis zone. The established lanthanum-ytterbium (La/Yb) ratio in the coal, which is normalized to UCC and equals La/Yb<1, relates to the coals with Н type of REE distribution, and the one that equals La/Yb>1 and normalized to chondrite belongs to the coals with L type of REE distribution, which allows making conclusions on the presence of independent sources and different mechanisms of REE accumulation in the sediments of Karaganda coal basin. It is also established that the La/Yb ratio grows from coals to clayey interlayers, which indicates a predominantly clastogenic mechanism of REE input to the coals. The prevailing mineral form of the REE in the coal and clayey interlayer samples from the Karaganda coal basin is light lanthanide phosphates. Sparry crystals with CeLaNdPO composition were found in the coal and clayey interlayer samples. It was established that xenotime is the main deportment for Y in many coals.