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In order to understand the crystal chemical properties of hydrous rare-earth (RE) phosphates, REPO4,hyd, that form at ambient temperature, we have synthesized REPO4,hyd through the interaction of aqueous RE elements (REEs) with aqueous P at room temperature at pH < 6, where the precipitation of RE hydroxides does not occur, and performed rigorous solid characterization. The second experiment was designed identically except for using hydroxyapatite (HAP) crystals as the P source at pH constrained by the dissolved P. Hydrated RE phosphate that precipitated at pH 3 after 3 days was classified into three groups: LREPO4,hyd (La → Gd) containing each REE from La-Gd, MREPO4,hyd (Tb → Ho), and HREPO4,hyd (Er → Lu). The latter two groups included increasing fractions of an amorphous component with increasing ionic radius, which was associated with non-coordinated water. REallPO4,hyd that contains all lanthanides except Pm transformed to rhabdophane structure over 30 days of aging. In the experiments using HAP, light REEs were preferentially distributed into nano-crystals, which can potentially constrain initial RE distributions in aqueous phase. Consequently, the mineralogical properties of hydrous RE phosphates forming at ambient temperature depend on the aging, the pH of the solution, and the average ionic radii of REE, similarly to the well-crystalline RE phosphates.

In this study, the core/shell/shell-structured SiO2/YPO4:Nd/SiO2 composite microspheres with near-infrared luminescence property were prepared by sol-gel method. The morphology and structure of the as-prepared microspheres were observed by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and infrared spectroscopy (IR). These tests show that the composite microspheres have a sandwich structure. The diameter of the core SiO2 microspheres is ~ 220 nm, the intermediate layer thickness of rare-earth phosphate is ~ 5 nm, and the outer SiO2 layer is ~ 20 nm thick. The core/shell/shell microspheres are emitted at 1063 nm in the near-infrared region, which attributes to optical transparent windows of biological tissues. Meanwhile, the interaction between the composite microspheres and bovine serum albumin (BSA) was investigated. The results showed that the composite microspheres could quench the emission intensity of BSA by binding the tryptophan residues in BSA. The synthesized core/shell/shell composite microspheres may be used as near-infrared luminescence probes in the field of biological tissue imaging.

Environmental particulate deposits are the most severe factor causing high-temperature corrosion failure in advanced structural materials. Yet, the primary mechanisms of molten material corrosion under extreme conditions remain unclear, hindering the development and improvement of new crucial corrosion-resistant materials. “Ultra-high entropy” rare earth orthophosphates (REPOs) are one such promising class of materials. Here, we investigate the high-temperature structural state and properties of a wide range of substitutions involving 15 (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) rare earth elements in phosphates. Using stepwise stoichiometric compositional design, we aim to systematize our understanding of the corrosion resistance behavior of these complexes RE phosphates. We observe that high compositional complexity slows the reaction kinetics. Increasing rare-earth ionic radius, correlates positively with the chemical inertness of the synthesized material. This is overlain by phase state considerations whereby single-phase compositions exhibit the highest corrosion resistance. In summary, we infer that 1) the grade of complexity of rare earth mixtures; 2) the proportions of the individual rare earths and 3) the phase state of solid solution stoichiometries are the key factors in determining the corrosion resistance of these complex phosphate materials. Using ultra-high-entropy rare-earth phosphates, the authors show that single-phase solids with high compositional complexity and larger rare-earth ionic radii slow reaction kinetics and increase chemical inertness, leading to improved high-temperature corrosion resistance.

Many microbial species are capable of solubilising insoluble forms of phosphate and are used in agriculture to improve plant growth. In this study, we apply the use of known phosphate solubilising microbes (PSM) to the release of rare-earth elements (REE) from the rare-earth phosphate mineral, monazite. Two sources of monazite were used, a weathered monazite and mineral sand monazite, both from Western Australia. When incubated with PSM, the REE were preferentially released into the leachate. Penicillum sp. released a total concentration of 12.32 mg L −1 rare-earth elements (Ce, La, Nd, and Pr) from the weathered monazite after 192 h with little release of thorium and iron into solution. However, cultivation on the mineral sands monazite resulted in the preferential release of Fe and Th. Analysis of the leachate detected the production of numerous low-molecular weight organic acids. Gluconic acid was produced by all microorganisms; however, other organic acids produced differed between microbes and the monazite source provided. Abiotic leaching with equivalent combinations of organic acids resulted in the lower release of REE implying that other microbial processes are playing a role in solubilisation of the monazite ore. This study demonstrates that microbial solubilisation of monazite is promising; however, the extent of the reaction is highly dependent on the monazite matrix structure and elemental composition.

Based on the physicochemical properties of waste phosphate-based rare earth phosphors containing glass, this paper proposes a novel recovery method for rare earth elements (REEs) that integrates pre-enrichment, alkali roasting, and enhanced leaching. Initially, preliminary enrichment of REEs was achieved through sieving to remove silicon (from glass components) and pickling to reduce calcium content (originating from calcium phosphate compounds). The enriched material was then subjected to alkaline roasting, followed by washing for impurity removal, hydrochloric acid leaching, and finally oxalic acid precipitation to extract the rare earth elements. Experimental results demonstrate that the overall recovery rate of rare earth oxides (REO) reached 96.6%, indicating highly efficient extraction and separation of REEs from the waste phosphors. Furthermore, the mechanism of the alkali roasting process was investigated via differential thermal analysis (TG-DSC). Microstructural and phase changes in the waste phosphors before and after roasting were systematically characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that green phosphor (REPO4) was converted into rare earth oxides and water-soluble sodium phosphate under alkaline roasting conditions. The Na3PO4 could be effectively removed through washing, while the rare earth elements were retained in the form of oxides within the washed residue. This study provides an important theoretical foundation and technical approach for the efficient recovery of rare earth resources from waste phosphate-based phosphors.

Karst bauxite is a major source of aluminum and contains high concentrations of trace elements such as Li, Ga, Sc, and rare earth elements (REEs). It is regarded as a potential non-conventional REE source due to the increasing demand for REEs. This study provides new mineralogical and geochemical evidence of a Lindai bauxite deposit in central Guizhou Province, aiming to analyze the genesis of REE minerals and reveal the forms of REEs occurring in these deposits. The results indicate that a large number of detrital and authigenic rare-earth phosphate minerals, including monazite and xenotime, were identified. In terms of their genesis, the authigenic monazite was mainly precipitated under alkaline and reducing conditions, whereas the authigenic xenotime was formed in acidic and reducing conditions. The mineralogical evidence detected by scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) and a TESCAN Integrated Mineral Analyzer (TIMA) suggests that the REEs in the Lindai bauxite exhibit multiple forms, including rare-earth phosphate minerals (monazite and xenotime) and REE scavenging by hematite and anatase phases. Among them, the anatase controls some LREE (such as La, Ce, and Pr) distributions in addition to monazite, whereas the hematite also controls relatively large amounts of Sm, Eu, and HREE (such as Gd, Tb, Dy, Ho, Er, Tm, and Lu) distributions. According to the calculation of the percentage of REE-bearing mineral phases obtained by a TIMA analysis, REE scavenging by hematite accounted for 93.28% of all forms of REEs, REE scavenging by anatase accounted for 5.88%, monazite accounted for 0.67%, and xenotime accounted for 0.17%. This study provides new evidence of the forms of REEs occurring in Carboniferous karst bauxite in central Guizhou Province.

Lanthanum phosphate (LaPO4) belongs to the family of rare earth phosphates characterized as a fluorescence material. Europium ion is known for its orange –red fluorescence. In order to include orange –red fluorescence for pure white light generation we are doping LaPO4 with Eu3+. The crystalline planes are identified from the XRD pattern show that the particles have monoclinic structure with pure LaPO4. The addition of sodium ions to the LaPO4: Eu3+ sample it is found that the luminescence property gets increased. It is also found that reversal of the emission spectrum intensity takes place for the sodium doped sample which indicates that Eu3+ ions are located in a highly symmetric environment.

To explore the occurrence phases and enrichment mechanism of rare earth elements (REEs) in cobalt-rich crusts, this study analyzes the mineral composition and REE contents of the samples from Marcus-Wake Seamounts by XRD, ICP-OES and ICP-MS. The results show that, (1) the cobalt-rich crusts contain the major crystalline mineral (vernadite), the secondary minerals (quartz, plagioclase and carbonate fluorapatite), and a large amount of amorphous ferric oxyhydroxides (FeOOH). (2) The cobalt-rich crusts contains higher Mn (10.83% to 28.76%) and Fe (6.14% to 18.86%) relative to other elements, and are enriched in REEs, with total REE contents of 1 563–3 238 µg/g and Ce contents of 790–1 722 µg/g. Rare earth element contents of the old crusts are higher than those of the new crusts. Moreover, the non-phosphatized crusts have positive Ce and negative Y anomalies, and yet the phosphatized crusts have positive Ce and positive Y anomalies, indicating that cobalt-rich crusts is hydrogenetic and REEs mainly come from seawater. (3) Analytical data also show that the occurrence phases of elements in cobalt-rich crusts are closely related to their mineral phases. In the non-phosphatized crusts, REEs are adsorbed by colloidal particles into the crusts (about 67% of REEs in the Fe oxide phase, and about 17% of REEs in the Mn oxide phase). In contrast, in the phosphatized crusts (affected by the phosphatization), REEs may combine with phosphate to form rare earth phosphate minerals, and about 64% of REEs are enriched in the residual phase containing carbonate fluorapatite, but correspondingly the influence of Fe and Mn oxide phases on REEs enrichment is greatly reduced. In addition, the oxidizing environment of seawater, high marine productivity, phosphatization, and slow growth rate can promote the REE enrichment. This study provides a reference for the metallogenesis of cobalt-rich crusts in the Pacific.

The fracture characteristics of rare-earth phosphate (LuPO 4 ) and silicate (Lu 2 SiO 5 ) environmental barrier coating (EBC) materials under molten calcium–magnesium aluminosilicate (CMAS) corrosion are analyzed. EBCs are crucial for protecting SiC-based ceramic matrix composite components in the hot section of gas turbine engines. Recently the rare-earth phosphates as EBC materials have shown better performance than third-generation rare-earth silicates under CMAS corrosion. However, the fracture of EBCs under CMAS corrosion during service remains a significant concern. This work investigates the fracture characteristics of LuPO 4 and Lu 2 SiO 5 using a combined experimental and computational approach. The computational model uses experimental micrographs and material properties obtained from fabricated EBC samples for fracture simulations. The simulation results are compared with experimental fracture toughness data and validated using statistical tests ( p  < 0.01). The results show significant degradation in fracture strength of EBC materials caused by CMAS penetration. EBC materials lost more than 40% of their initial fracture strength even at low penetration levels of 3% by volume. Simulation results show that LuPO 4 degraded more than Lu 2 SiO 5 . However, experimental observations from CMAS reaction tests demonstrate that LuPO 4 may exhibit higher fracture resistance than Lu 2 SiO 5 under similar CMAS corrosion conditions due to the formation of dense and thick passivation reaction layer. The insights gained from this study could be used to design EBCs with improved fracture resistance under CMAS corrosion.

Thermal insulation materials play an increasingly important role in protecting mechanical parts functioning at high temperatures. In this study, a new porous high-entropy (La 1/6 Ce 1/6 Pr 1/6 Sm 1/6 Eu 1/6 Gd 1/6 )PO 4 (HE (6RE 1/6 )PO 4 ) ceramics was prepared by combining the high-entropy method with the pore-forming agent method and the effect of different starch contents (0–60vol%) on this ceramic properties was systematically investigated. The results show that the porous HE (6RE 1/6 )PO 4 ceramics with 60vol% starch exhibit the lowest thermal conductivity of 0.061 W·m −1 ·K −1 at room temperature and good pore structure stability with a linear shrinkage of approximately 1.67%. Moreover, the effect of large regular spherical pores (>10 µm) on its thermal insulation performance was discussed, and an optimal thermal conductivity prediction model was screened. The superior properties of the prepared porous HE (6RE 1/6 )PO 4 ceramics allow them to be promising insulation materials in the future.