Light Rare Earth Ions Research Articles

Elucidating the selective adsorption of heavy rare earth by phosphate modified silica: The cooperation of pore confinement and surface structure regulating

Rare earths are considered strategic metals, with heavy rare earth elements of greater importance due to their supply and utilization field. However, efficient separation of heavy rare earth elements is a great challenge as the similar physicochemical properties between light and heavy rare earths. In this study, the highly efficient adsorbents with confinement effect are synthesized by the modification of MCM-41 materials with dimethyl clodronate (NP2) and methylene dichlorophosphate (NDP2). The adsorbents were characterized by XRD, TEM, SEM-EDS, N2 adsorption–desorption, FTIR, TG, 13C NMR, and XPS. It was discovered that the pore size of MCM-41 affected markedly the adsorption selectivity, and the cooperation of the organic adsorption center and pore confinement of MCM-41 support enabled the selective adsorption of heavy rare earth ion. The adsorbent modified by NP2 exhibited high adsorption selectivity toward heavy rare earth ions (Lu3+) with the increase in pore size of MCM-41. In contrast, the expanded pore of MCM-41 enhanced the selectivity of light rare earth ions for the NDP2 modified adsorbents. The distribution coefficient of Lu3+ adsorption over NP2-MCM-41(III) adsorbent reached 20,132 mL g−1 and the separation factor of Lu to La reached 82.17. DFT calculations revealed that a vital driving force for the selective adsorption of Lu was the gap of binding energy between Lu and La complexes with the surface NP2/NDP2 groups. The synergy of pore confinement and organic functional groups in adsorbents in this paper offers a valuable strategy for designing efficient materials in the separation of rare earth elements.

Synthesis, spectroscopic characterization and biological activities of complexes of light lanthanide ions with 3-hydroxyflavone

New solid compounds of light lanthanide ions with 3-hydroxyflavone were synthesized in good yields (up to 85 %). The resulting complexes have been thoroughly characterized using various analytical and spectral techniques, including elemental analysis, complexometry, thermogravimetry, UV–VIS, FT-IR, 1H NMR, 109AgNPET LDI MS and fluorescence spectroscopy. The molecular formulas of the complexes were determined as follows: Ln(3HF)3, where 3HF-3-hydroxyflavone, Ln = La(III), Pr(III), Nd(III) and Ln(3HF)3·nH2O, where n = 1 for Ln = Ce(III), Sm(III), Eu(III), and n = 2 for Gd(III). Thermogravimetric studies revealed that the water molecules in the hydrated compounds are located in the outer coordination sphere. Based on the spectral data, it was noted that lanthanide ions interacted with the 3OH and 4CO groups of 3-hydroxyflavone. The effect of lanthanide ion chelation on the excited-state intramolecular proton transfer (ESIPT) process and fluorescence emission of 3HF was investigated. It was found that coordination with metal ions can suppress the ESIPT process and enhance the fluorescence emission of 3HF. The synthesized compounds were also screened for their antibacterial activity, free radical scavenging capacity, and interaction with BSA. The results showed that the complexes exhibit higher biological activity compared to the ligand.

Preparation of a class of cucurbit[6]uril-light rare-earth-based supramolecular assemblies and its efficient detection of chloramphenicol

By introducing 4,4′-naphthalenedisulfonic acid (4,4′-H2BPs) as a structure-induced agent, four novel cucurbit[6]uril-based supramolecular assemblies have been successfully prepared in the cucurbit[6]uril (Q[6]) system with light rare-earth elements (La3+, Ce3+, Pr3+, Nd3+) under hydrothermal conditions. Crystal structure analysis shows that the assemblies 1 (La3+), 2 (Ce3+), 3 (Pr3+) are isomorphism 3D frameworks, where Q[6] can directly coordinate with light rare-earth metal ions to form 1D −Ln(III)- Q[6]-Ln(III)- chains, while the 4 (Nd3+) presents 3D structures stacking by the unit of Q[6]@Nd3+@Q[6]@Nd3+@Q[6], respectively. In these structures, 4,4′-H2BPs ligands all can act as an organic counter anion and bridging via the outer-surface interaction of cucurbit[n]uril (OSIQ) in the system, which is the main driving force from low-dimensional to high-dimensional. Meanwhile, the fluorescence sensing performance of the two assemblies for antibiotics was investigated, and the results showed that assembly 1 could be used as a promising fluorescent sensor material to detect chloramphenicol (CAP).

Geochronology and Geochemistry of Ore‐related Granitoids in the Giant Gariatong Rb Deposit, Tibet and Implications for Rb Metallogeny in China

AbstractRubidium (Rb) deposits mostly occur in the South China and Central Asia orogenic belts and are often closely associated with highly differentiated granites. This study investigates a newly‐discovered giant Rb deposit at Gariatong in the Central Lhasa terrane in Tibet. Detailed field studies and logging data revealed that the Rb mineralization mainly occurs in monzogranite and is related to greisenization. LA‐ICP‐MS U‐Pb dating of zircon yielded ages of 19.1 ± 0.2 Ma and 19.0 ± 0.2 Ma for greisenized monzogranite and fresh monzogranite, respectively. The monzogranites are characterized as strongly peraluminous, with high contents of SiO2, Al2O3, K2O and Na2O as well as a high differentiation index. They are enriched in light rare earth and large ion lithophile elements with significant negative Eu anomalies and depleted high field‐strength elements. Petrological and geochemical features of these ore‐related monzogranites suggest that they are highly fractionated S‐type granites, derived from remelting of crustal materials in a post‐collisional setting. The geochemistry of zircon and apatite points to a low oxygen fugacity of the ore‐related monzogranite during the magma's evolution. The discovery of the Gariatong Rb deposit suggests that the Central Lhasa terrane may be an important region for rare metal mineralization.

Selective Recovery of Low-Concentration Light Rare Earth Ions from High-Concentration Ammonium Sulfate System by Coordination Ability

Selective Recovery of Low-Concentration Light Rare Earth Ions from High-Concentration Ammonium Sulfate System by Coordination Ability

Tailoring abundant active-oxygen sites of Prussian blue analogues-derived adsorbents for highly efficient Yb(III) capture.

The removal of rare earth elements in mineral processing wastewater is highly desirable but still challenging. In this study, three bimetallic Prussian blue analogues (PBA) and six corresponding oxides are prepared by co-precipitation and calcination methods, and then utilized to adsorb aqueous Yb(III) solution. The results of XRD, SEM, BET, and XPS indicate the successful synthesis of all the adsorbents. Among them, three PBA-oxide samples (PBO-800) exhibit the superior adsorption capacities (˃250mg/g). The adsorption processes of Yb(III) are in accordance with the pseudo-second-order kinetic model and Langmuir model, simultaneously showing the spontaneous and endothermic thermodynamics. Moreover, PBO-800 can be reused after alkaline solution regeneration with less than 10% degradation after five consecutive adsorption-desorption cycles. More importantly, PBO-800 exhibits the impressive separation selectivity of Yb(III) and most light rare earth ions (e.g., 5.51 of Yb/La, 4.03 of Yb/Pr), as well as the selectivity of Yb(III) and alkali metal ions (e.g., 300.5 of Yb/Na, 256.2 of Yb/Ca). According to the characterization analysis and DFT calculation, the adsorption mechanism of Yb(III) by PBO-800 is mainly attributed to the strong interaction between the abundant active-oxygen sites and Yb(III), and the significant electrostatic attraction.

Less-precious nitrogen-rich covalent organic frameworks capable of effective rare earth recovery from water

The development of stable and inexpensive adsorbents for La(III) recovery from wastewater is of great importance for rare earth industries. In this work, two novel N-rich covalent organic frameworks (COFs) synthesized via a one-step solvothermal method were termed as COF-PA-CC and COF-ML-CC, and employed as the adsorbents for removal of rare earth (RE) ions from aqueous solution. The structures and properties of COFs were characterized with X-ray diffractometer, total reflection infrared spectrometer, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption–desorption instrument and thermogravimetric analyzer. The results revealed that COF-PA-CC composed of nanowires with the average length of 500 nm, whereas COF-ML-CC displayed the spherical morphology with the diameter of 100 ∼ 300 nm. Specific surface areas of COF-PA-CC and COF-ML-CC were calculated to be 82.13 and 191.08 m2/g, respectively. The adsorption process of La(III) was well-fitted with pseudo-second-order kinetic model and Langmuir isotherm model, exhibiting the high adsorption capacities of 150.88 and 168.19 mg/g for COF-PA-CC and COF-ML-CC after 120 min. Moreover, the influences of pH, temperature, different RE ions on adsorption performances were comprehensively tested, yielding an optimal adsorption condition (pH = 5.5, 65 °C and 120 min) and a better affinity for some light RE ions. Importantly, the fabricated COFs possess the excellent reusability after five adsorption-regeneration cycles, remaining 97.84 % and 95.51 % of initial capacities for COF-PA-CC and COF-ML-CC, respectively. The adsorption mechanism revealed that the complexation interaction between La(III) and the unoccupied N sites of N-rich COFs was recommended to interpret the remarkable adsorption performance of La(III) on the basis of the characterization analysis after the adsorption with elemental mapping, EDS and XPS. Consequently, these low-cost and robust COFs with abundant active N sites supplied a promising strategy for the recovery of RE ions from wastewater.

Study of the thermal behavior, evolved gas analysis and temperature diffraction patterns of new light lanthanide complexes with niflumic acid

Seven new complexes of niflumic acid with light lanthanide ions (La-Gd except Pm) were obtained in solid state. With the application of chemical, elemental and thermal analysis, the minimal formulas of the complexes were established, which were different despite the fact that the syntheses of the complexes were carried out under the same conditions. The complex with La(III) ions is mononuclear and its stoichiometry is represented by the formula La(nif)3∙2.5 H2O. The remaining complexes are binuclear and their stoichiometry is expressed by the formula Ln2(nif)4(OH)2∙nH2O (where: Ln is Ce or Pr, n is equal to 4 or 5, respectively) or Ln2(nif)3(OH)3∙4 H2O (where: Ln = Nd, Sm, Eu or Gd). On the basis of the FTIR spectra, it was stated that the carboxylate groups of the ligand can coordinate metal ions in a bidentate chelating or tridentate chelating-bridging mode. XRPD analysis of the obtained compounds showed that they are amorphous. Based on the TG/DTG–DSC analysis, it was shown that the thermal decomposition of the complexes is a multistage process, depending on the metal ion and the used atmosphere. It was found that the stability of the dehydrated compounds in air atmosphere increases in the order: La < Pr < Nd < Sm < Gd = Eu < Ce, while in nitrogen atmosphere, the stability of these complexes is as follows: La < Nd < Ce = Pr < Eu < Sm < Gd. Using coupled TG-FTIR-MS techniques, the decomposition pathways of the synthesized compounds were examined and the gaseous products released during thermal oxidation and pyrolysis of the complexes were identified. The EGA analysis showed that the gaseous products contained mainly H2O, CO2, COF2, fragments from the partial decomposition of the organic ligands (both in air and nitrogen atmosphere), NO (in air) and CO (in N2). Moreover, based on the temperature diffraction patterns, it was found that the thermal degradation of most of the studied complexes, both in air and nitrogen atmosphere, did not end at 1000 °C. It has been experimentally proven that during thermal decomposition of niflumic acid complex with Nd(III) ions in an oxidizing atmosphere at approximately 440 °C NdF3 is formed as one of a solid intermediate product. At the temperature of 570 °C, the tetragonal form of this compound appears additionally in the solid residue. At 800 °C, the solid residue is a mixture of Nd2O3 and NdOF, while the final product obtained at 1000 °C is Nd2O3 and NdOF. Under pyrolysis conditions, only at a temperature of 800 °C it was possible to identify solid intermediate products and in the case of the niflumic acid complex with Nd(III) ions complex it was a mixture of NdOF and NdF3. NOF has been identified as one of the solid products of thermal degradation.

Permian arc magmatism in southern Tibet: Implications for the subduction and accretion of the Zhikong–Sumdo Paleo-Tethys Ocean

The tectonic evolution of the Zhikong–Sumdo Paleo-Tethys Ocean (Hereafter referred to as Zhikong–Sumdo Ocean) in southern Tibet is controversial due to the limited records of arc magmas. Here, the newly discovered Zhangda complex in the Zhikong area of Tibet is selected as the research object. Zircon U–Pb geochronology, zircon Hf isotopes, whole-rock geochemistry and Sr-Nd isotope analyses performed based on field geological surveys show that the Zhangda complex is composed of Early Permian hornblende gabbro (278.3 ± 1.1 Ma), cumulate gabbro (277.4 ± 1.7 Ma), tonalite dike (281.1 ± 1.9 Ma), Middle–Late Permian gabbro diorite (267.8 ± 2.9 Ma, 269.0 ± 3.1 Ma), and tonalite (258.0 ± 2.7 Ma). The Zhangda mafic rocks show weak fractionation of light and heavy rare earth elements, and they are enriched in large ion lithophile elements and depleted in high field strength elements. Meanwhile, the Zhangda tonalites show the characteristics of metaluminous calc-alkaline I-type granite. They are enriched in light rare earth and large ion lithophile elements and are depleted in heavy rare earth and high field strength elements. The ɛHf(t), ɛNd(t) and the initial 87Sr/86Sr values of the mafic rocks are + 9.3–+14.4, +4.2–+5.9 and 0.702803–0.704264, respectively, while the ɛHf(t), ɛNd(t) and initial 87Sr/86Sr values of the tonalites are + 9.8–+16.3, +5.5–+6.1 and 0.703105–0.704071, respectively. Combined with the regional geological survey results, the Permian Zhangda complex was found to be formed in a tectonic setting of subduction north of the Zhikong–Sumdo Ocean. The Zhangda mafic rocks were formed by partial melting of the depleted mantle modified by subducted metasomatic fluids, while the Zhangda tonalites were the products of partial melting of the juvenile crust. During the Zhikong–Sumdo Ocean subduction, mantle-derived magma underplating led to the growth of juvenile crust in southern Tibet.

Coordination Chemistry-Driven Approaches to Rare Earth Element Separations.

Current projections for global mining indicate that unsustainable practices will cause supply problems for many elements, called critical raw materials, in the next 20 years. These include elements necessary for renewable technologies as well as artisanal sources. Energy critical elements (ECEs) comprise a group used for clean, renewable energy applications that are in low abundance in the Earth's crust or require an economic premium to extract from ores. Sustainable practices of acquiring ECEs is an important problem to address through fundamental research to provide alternative energy technologies such as wind turbines and electric vehicles at cheaper costs for our global energy generation and usage. Some of these green technologies incorporate rare-earth (RE) metals (Sc, Y and the lanthanides), which are challenging to separate from mineral sources because of their similar sizes (i.e., ionic radii) and chemical properties. The current process used to provide REs at requisite purities for these applications is counter-current solvent-solvent extraction, which is scalable and works efficiently for any ore composition. However, this method produces large amounts of caustic waste that is environmentally damaging, especially to areas in China that house major separation facilities. Advancement of the selectivity of this process is challenging since exact molecular speciation that affords separations is still relatively unknown. In this context, we developed a program to investigate new RE separations systems that were aimed at minimizing solvent use, controlled by molecular speciation, and could be targeted at problems in recycling these critical metals.The first ligand system that was developed to impart solubility differences between light and heavy rare-earth ions was [{(2-tBuNO)C6H4CH2}3N]3- (TriNOx3-) (graphic below). A differential solubility allowed for a separation of Nd and Dy of SFNd:Dy = ∼300 in a single step. In other words, a 50:50 Nd/Dy sample was enriched to give 95% pure Nd and Dy through a simple filtration, which is potentially impactful to recycling magnetic materials found in wind turbines. This separations system compares favorably to other state-of-the-art molecular extractants that are based on energetic differences of the thermodynamic parameter to affect separations for neighboring elements. This straightforward, thermodynamically driven method to separate REs primed our future research for new coordination chemistry approaches to separations.Another separations system was accomplished through the variable rate of a redox event from one arm of the TriNOx3- ligand. It was determined that the rate of this one electron oxidation, which operated through an electrochemical-chemical-electrochemical mechanism, was dependent on the identity of the RE ion. This kinetically driven separation afforded a separation factor (SF) of SFEu:Y = 75. We have also described other transformations such as ligand exchange, substituent dependent, and redox-driven chelation processes with well-defined speciation to afford purified RE materials. Recently, we determined that magnetic properties can be used to enhance both thermodynamic and kinetic RE separations processes to give an approximately 100% boost for pairs of paramagnetic/diamagnetic REs. These results have shown that both thermodynamic and kinetic RE separations were efficient for different selected RE binary pairs through coordination chemistry. The focus of this Account will detail the differences that are observed for RE separations when promoted by thermodynamic or kinetic factors. Overall, the development of rationally adjusted speciation of REs provides a basis for future industrial separations processes for technologies applied to ECEs derived from wind turbines, batteries for electric vehicles, and LEDs.

Mixed-lanthanide clusters: A bridging approach that permits the design of molecular magnetic materials by introducing heavy lanthanides into the 3d-light lanthanide clusters without breaking structural integrity

Theoretical studies suggest that the ring 3d-4f clusters {MnIII4Ln4} may be a good material for magnetic refrigeration. However, only {MnIII4Ln4} constructed from light lanthanide ions have been obtained, while the attempt for their analogue containing the magnetically isotropic Gd(III) ions has failed. By applying the strategy of synthesizing mixed-lanthanide clusters, mixed-lanthanide clusters {MnIII4LaxGd4-x} and {MnIII4NdxGd4-x} without breaking structural integrity of {MnIII4Ln4} have been successfully made. It is found that smaller ionic radius difference between the lanthanides tends to increase the introduction of Gd(III) when applying the strategy. Moreover, the magnetic property measurements show that the obtained mixed-lanthanide clusters exhibit magnetothermal effect as predicted.

Geochronology, geochemistry, and petrogenesis of Early Cretaceous highly differentiated I-type granites in the central Great Xing’an Range, northeastern China

In this study, we undertook zircon U–Pb dating and Hf isotopic and whole-rock geochemical analysis of Mesozoic granites from the Zhalantun and Arxan areas of the Great Xing’an Range, northeastern China. Zircon U–Pb dating of four samples indicates they formed in the Early Cretaceous (ca. 140.7–130.0 Ma). Geochemically, the samples have high silica (74.00–77.29 wt.%) and total alkali (8.52–8.90 wt.%) and low CaO (0.21–0.71 wt.%), MgO (0.06–0.48 wt.%), and P2O5 (0.01–0.06 wt.%) contents and exhibit the weakly peraluminous (A/CNK = 0.98–1.06) and high-K calc-alkaline characteristics, with highly differentiated I-type granite affinities (differentiation index = 93.19–96.93). The studied granites are enriched in light rare earth and large ion lithophile elements and depleted in heavy rare earth and high field strength elements. Their zircon εHf(t) values are mainly positive (+2.49 to +11.64) and yield two-stage Hf model ages of 1023–445 Ma. The geochemical and isotopic data indicate they might have been derived from the partial melting of medium- to high-K basaltic crust material during the Mesoproterozoic to Phanerozoic. They underwent fractional crystallization in the magma evolution process, and K-feldspar and plagioclase were the major crystallization phases. Combined with the temporal–spatial migration of the Mesozoic magmatic events in the whole northeastern China, we propose that the generation of Early Cretaceous highly differentiated I-type granites in the central Great Xing’an Range was associated with the delamination effect caused by the roll-back of the Paleo-Pacific plate.

Mixed valence effects in Pr:YbF3 nanocrystals and influence to EPR, magnetic and Faraday rotation properties of diamagnetic glasses

The co-existence of light and heavy rare earth ions will arouse interesting optical, magnetic and magneto optical properties to matrix due to energy transfer between various rare earth ions and spin-orbit interactions of electric dipoles and magnetic dipoles. Pr and Yb co-doped orthorhombic Pr:YbF3 nano-crystals have been prepared by hydrothermal method, the structure and properties of Pr:YbF3 were characterized using X-ray diffraction, scanning electron microscopy, electron paramagnetic resonance, Raman & Infrared spectra and superconducting quantum interference device. The introduction of Pr into YbF3 induced changes on morphology, structure and properties due to different ionic radius, electronegativity and bond strength.The fabricated Pr:YbF3 nanocrystal doped glasses show good transparency and morphology. Pr:YbF3 nanocrystals were well dispersed in glass with slightly increased size (25 nm). X-ray photoelectron spectra confirmed the co-existence of Yb2+, Yb3+ and Pr3+ in 1% and 2% doped glasses, and additional Pr4+ in 4% doped one. Optical absorption edge red-shifted and emission intensity increased with the doping amount. Energy transfer between Pr3+ and Yb3+ ions was observed around 1000 nm. Due to the electron transition and energy transfer, the magnetization changed from diamagnetic to ferromagnetic and showed temperature-dependent behaviors. The Faraday rotation was significantly reinforced by Pr:YbF3 and a giant Verdet constant of -0.32 min/G.cm was obtained at 533 nm wavelength for 4% Pr:YbF3 doped glass which is promising for magneto optical devices.

Solvent extraction and separation of light rare earths from chloride media using HDEHP-P350 system

Solvent extraction is the most important method for rare earth extraction and separation. Currently, di(2-ethylhexyl) phosphoric acid (HDEHP) and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH/EHP) are widely used in industrial production, but there are still obvious deficiencies that require further research to resolve. In this paper, the unsaponification extraction of light rare earth ions in a hydrochloric acid medium by di(2-ethylhexyl) phosphoric acid-di(1-methyl-heptyl) methyl phosphonate (HDEHP-P350) system was studied. The results show that the addition of P350 reduces the extraction capacity of HDEHP, and also greatly reduces the concentration of acidity required for the back-extraction. It still has a good separation factor for light rare earths without saponification, and the extractant is not easy to emulsify. With an aqueous phase of pH = 2.85, and HDEHP mole fraction XHDEHP = 0.9 (compared with O/A = 2), the separation effect of light rare earth is the best, resulting in the separation coefficient βCe/La = 3.39, βPr/Ce = 1.67 and βNd/Pr = 1.45, respectively. The loaded light rare earth ions extracted by HDEHP-P350 can be easily stripped when 2 mol/L HCl is used as the stripping agent. Finally, the extraction mechanism is discussed using a slope method, and the final structure of the extracted complex is determined to be RECl[(DEHP)2]2P350(o), based on a combination of infrared spectra and 1H NMR and 31P NMR analyses.

The Devonian accretionary orogen of the North Patagonian cordillera

The Andean basement of NW Patagonia contains remnants of a Devonian accretionary orogen that lasted for about 50 Ma. We present and review U-Pb geochronology, major and trace element geochemistry and O- and Hf-isotope analyses of zircon for Devonian igneous and metasedimentary rocks from the western edge of the North Patagonian Massif to the Pacific coast. Two contrasting magmatic domains are characterised. The Foreland Devonian Domain (FDD) of the North Patagonian Massif is dominated by subduction-related calcalkaline granite, granodiorite and tonalite emplaced in the interval c. 405–395 Ma and here named the San Martín arc. They are generally enriched in alkalis, light rare earth and Large Ion Lithophile elements, and have igneous zircon with δ18O mostly in the range +6 to +9‰ and ƐHft typically +3 to −5, indicating magmas that incorporated continental crustal material, possibly Mesoproterozoic. A younger (374 ± 3 Ma) body in this group has lower δ18O (down to +5‰) and Hf-isotope characteristics at the primitive end of this range. The Pacific Devonian Domain (PDD) lies on the western flank of the Andes and has uniformly primitive character. Granitic rocks here represent a more extended magmatic history (c. 395–355 Ma) and are mostly subalkaline tonalites with δ18O (<+6‰) that fall within or below the normal mantle field: with one exception their ɛHft values are > +4 and closer to Devonian depleted mantle composition. The PDD also has metabasalts of both N-MORB and E-MORB affinities, interbedded with Devonian turbidite metasandstones in which detrital zircon O- and Hf-isotope compositions and morphology indicate coetaneous derivation from the FDD arc. The results lead to a tectonic model involving continental arc, forearc rifting, Chaitenia oceanic arc and marginal basin formation, double arc subduction, and marginal basin closure in Mississippian times. This is recognisable as part of a more extensive Devonian accretion scenario along the SW Gondwana margin.

Extraction and complexation of trivalent rare earth elements with tetraalkyl diglycolamides

The extraction and complexation behaviors of four tetraalkyl diglycolamide (TRDGA, where R represents n-butyl, n-hexyl, n-octyl and 2-ethylhexyl) ligands with linear chain or branched chain structure were described with respect to La3+, Pr3+, Nd3+; Eu3+, Gd3+; Y3+, Er3+ and Yb3+ as the representatives of light, middle and heavy rare-earth group ions in HNO3 solution. Effects of acidity, ligand concentration and temperature on the distribution ratio of these ions were examined. High acidity was good for the extraction. For same metal ion, the extractability of DGA ligands followed the order of T2EHDGA < THDGA < TODGA < TBDGA at the same acidity, which was also supported by nuclear magnetic resonance (NMR) analyses. Meanwhile, for different metal ions, their extracted efficiencies by the same DGA ligand increased in the sequence of lanthanide contraction. The average separation factors of adjacent lanthanides within light, middle and heavy rare-earth groups could attain about 2.4, 1.7 and 2.1, respectively. Slope analysis indicated that the formation of predominant 1:3 and 1:2 metal/ligand extracted species for linear chain and branched DGA, respectively. In methanol solution, 1:1, 1:2 and 1:3 Eu3+/DGA species were also observed using fluorescence spectroscopy titration. Fourier transform infrared spectroscopy (FT-IR) analyses suggested that the carbonyl oxygens compared with ether oxygen play a dominant role in coordination. Moreover, the stability constants (log β) and the thermodynamic parameters (ΔH, ΔS and ΔG) for the complexation of Eu3+ with DGAs were also presented.

Synthesis of DCAP and its effects on extraction separation of light rare earth ions

ABSTRACT A de-tert-butyl calix arene phosphate (DCAP) with a complete elimination of the upper edge and a complete substitution of the lower edge was synthesized by dealkylation and substitution reactions. The chemical structure of DCAP was further characterized by FTIR, mass MS and 1 H NMR. The ability of DCAP to extract light rare earth ions was studied as a function of concentration, aqueous phase pH, phase ratio, and extraction time. The results showed that DCAP had a 4% higher extraction rate of Pr3+ compared to Nd3+ under the same conditions. Preliminary extraction mechanism was also investigated.

On the Hydration of the Rare Earth Ions in Aqueous Solution

The totally symmetric stretching mode nu_{1} Ln–(OH2) of the first hydration shells of all the rare earth (RE) ions across the series from lanthanum to lutetium has been measured on dilute aqueous perchlorate solutions at room temperature. An S-shaped relationship has been found between the nu_{1} Ln–(OH2) peak positions and the Ln–(OH2) bond distances of the lanthanide(III) aqua ions. While the light rare earth ions form nona-hydrates, the heavy ones form octa-hydrates and the rare earth ions in the middle of the series show non integer hydration numbers between 9 and 8. A relationship between wavenumber positions nu_{1} Ln–(OH2) and the Ln–(OH2) bond distances of the RE hydrates has been given. Recent quantum mechanical calculations support the given interpretation.

Uranyl oxide hydrate frameworks with lanthanide ions.

Two uranyl oxide hydrate frameworks (UOFs) incorporating either Eu(iii) or Gd(iii) ions were synthesized hydrothermally and structurally studied. The uranyl oxide hydroxide layers similar to those in β-U3O8 with both tetragonal and pentagonal bipyramidal uranium polyhedra are connected with pairs of pentagonal bipyramidal uranium polyhedra through uranyl cation-cation interactions to form three-dimensional frameworks with Eu(iii) or Gd(iii) ions inside the channels. Both SEM and TEM examinations revealed needle crystal morphologies and a U:Eu/Gd ratio of 5.5, with the TEM-SAED pattern indexed to the orthorhombic crystal structure C2221, as also determined using synchrotron single-crystal X-ray diffraction. Raman spectroscopy revealed the band splitting of uranyl symmetric stretching vibrations, reflecting the presence of a unique pentavalent uranium centre in octahedral coordination geometry. The presence of pentavalent uranium in both UOFs was confirmed with diffuse reflectance spectroscopy. Given that layer-structured uranyl oxide hydroxy hydrate phases are dominant for both light and heavy lanthanide ions under similar reaction conditions, the ionic radius plays an important role in controlling the structure types, with UOFs formed only for Eu(iii) and Gd(iii) ions in the lanthanide series. These new UOFs with lanthanide ions may have various implications especially in nuclear materials.

Permo-Triassic arc-like granitoids along the northern Lancangjiang zone, eastern Tibet: Age, geochemistry, Sr–Nd–Hf isotopes, and tectonic implications

Large volumes of Permo-Triassic granitoids are exposed along the Northern Lancangjiang zone, eastern Tibet, and these rocks provide insights into the tectonic evolution of the Paleo-Tethys Ocean. We conducted detailed geological fieldwork and geochemical analysis of the Xiaochangdu and Kagong plutons that crop out along the Northern Lancangjiang magmatic belt. Zircon U–Pb data constrain the emplacement of the Xiaochangdu quartz diotites to between ~263 and ~257 Ma, and the Kagong granites and diorites to between ~234 and ~232 Ma. The Xiaochangdu quartz diorites are enriched in light rare earth (LREE) and large ion lithophile elements (LILE), depleted in high field strength elements (HFSE), have low (87Sr/86Sr)i ratios, and near-positive εNd(t) (−0.26 to 1.58) and εHf(t) (0.68–8.83) values, similar to typical subduction- related mantle-derived arc magmas. They are also characterized by high Al2O3 concentrations and low Nb/U (3.48–7.59) and Ce/Pb (3.22–4.86) ratios, indicating that their mantle source was modified by subducted pelagic sediments; Coeval granites and diorites from the Kagong pluton exhibit low A/CNK values, high LREE/HREE (heavy rare earth element) ratios, enrichment in LILE, and depletion in HFSE, also characteristic of typical arc magmas. Their variable SiO2 contents (57%– 75%), (87Sr/86Sr)i ratios, and εNd(t) (1.02–4.49) and εHf(t) (2.52–6.93) values, and relatively high zircon saturation temperatures (721–827 °C), suggest underplating of mantle-derived mafic melts beneath the lower crust. Their magmatic evolution can be explained using a MASH model.In combination with regional geological studies, our geochemical and geochronological results suggest that the late Permian Xiaochangdu and Late Triassic Kagong arc-like granitoids represent a section of a Permo-Triassic magmatic arc that was associated with the eastward subduction of the Paleo-Tethys oceanic slab beneath the Northern Qiangtang–Changdu terrane. Combined with other geological evidence, the ~263–232 Ma arc-like granitoids clearly indicate that final closure of the Paleo-Tethys ocean have not occurred until the end of the Triassic.