High Rare Earth Research Articles

Rare earth elements in soil profiles of various ecosystems across Germany

Rare earth elements (REEs) are of emerging interest. In the environment, they occur in minerals, however, they are also used in many key technologies and in agriculture. In consequence, REEs are released into the environment and have thus an impact on it. However, our knowledge regarding REEs in soils is incomplete. We selected eight soil profiles across Germany aiming to determine REE contents (aqua regia) and potential mobilization (hydroxylammonium chloride and hot water extractable) and to explore relations between REEs and soil properties. The composition of the parent material strongly influenced by the ice ages during the Pleistocene (especially in northeastern Germany) is a crucial factor differentiating the content of REEs in our studied soils. The silty, clayey soils in the western part of Germany possessed higher REE contents than the sandy and peaty soils in the northeast (average REE content Cambisols: 825 μmol kg−1, Retisols: 407 μmol kg−1, Arenosol 180 μmol kg−1, Histosols 122 μmol kg−1) because REE can adsorb onto clay minerals. The characteristic soil genetic processes of each soil type were reflected by the vertical distribution of the REE content. The vertical distribution of REEs and the hydroxylammonium chloride-extractable REE contents were mainly controlled by Al, Fe, Mn and their oxides (additional to clay) which provide important sorption sites for REEs. High contents of clay, Al/Fe/and Mn oxides caused high REE contents. The hydroxylammonium chloride-extractable REE contents varied in average from 266 to 8 μmol kg−1 in the soils. The hot water extractable REE contents (in average 0.94 μmol kg−1) tended to be higher in horizons which were rich in organic matter. In future, mechanistic experiments concerning the dynamics of REE mobilization should be performed as well as monitoring in plants and wildlife to improve our knowledge about REEs in the environment.

Mineralogy of Cobalt-Rich Ferromanganese Crusts from the Perth Abyssal Plain (E Indian Ocean)

Mineralogy of phosphatized and zeolitized hydrogenous cobalt-rich ferromanganese crusts from Dirck Hartog Ridge (DHR), the Perth Abyssal Plain (PAP), formed on an altered basaltic substrate, is described. Detail studies of crusts were conducted using optical transmitted light microscopy, X-ray Powder Diffraction (XRD) and Energy Dispersive X-ray Fluorescence (EDXRF), Differential Thermal Analysis (DTA) and Electron Probe Microanalysis (EPMA). The major Fe-Mn mineral phases that form DHR crusts are low-crystalline vernadite, asbolane and a feroxyhyte-ferrihydrite mixture. Accessory minerals are Ca-hydroxyapatite, zeolites (Na-phillipsite, chabazite, heulandite-clinoptilolite), glauconite and several clay minerals (Fe-smectite, nontronite, celadonite) are identified in the basalt-crust border zone. The highest Ni, Cu and Co contents are observed in asbolane and Mn-(Fe) vernadite. There is significant enrichment of Ti in feroxyhyte−ferrihydrite and vernadite. The highest rare earth element (REE) content is measured in the phosphate minerals, less in phyllosilicates and Na-phillipsite. The geochemical composition of minerals in the DHR crusts supports the formation of crusts by initial alteration, phosphatization and zeolitization of the substrate basalts followed by oscillatory Fe-Mn oxyhydroxides precipitation of hydrogenous vernadite (oxic conditions) and diagenous asbolane (suboxic conditions).

Metallogenic Epoch and Tectonic Setting of Saima Niobium Deposit in Fengcheng, Liaoning Province, NE China

The Saima deposit is a newly discovered niobium deposit which is located in the eastern of Liaoning Province, NE China. Its mineralization age and geochemical characteristics are firstly reported in this study. The Nb orebodies are hosted by the grey–brown to grass-green aegirine nepheline syenite. Detailed petrographical studies show that the syenite consists of orthoclase (~50%), nepheline (~30%), biotite (~15%) and minor arfvedsonite (~3%) and aegirine (~2%), with weak hydrothermal alteration dominated by silicification. In situ LA-ICP-MS zircon U-Pb dating indicates that the aegirine nepheline syenite was emplaced in the Late Triassic (229.5 ± 2.2 Ma), which is spatially, temporally and genetically related to Nb mineralization. These aegirine nepheline syenites have SiO2 contents in the range of 55.86–63.80 wt. %, low TiO2 contents of 0.36–0.64 wt. %, P2O5 contents of 0.04–0.11 wt. % and Al2O3 contents of more than 15 wt. %. They are characterized by relatively high (K2O + Na2O) values of 9.72–15.51 wt. %, K2O/Na2O ratios of 2.42–3.64 wt. % and Rittmann indexes (σ = [ω(K2O + Na2O)]2/[ω(SiO2 − 43)]) of 6.84–17.10, belonging to the high-K peralkaline, metaluminous type. These syenites are enriched in large ion lithophile elements (LILEs, e.g., Cs, Rb and Ba) and light rare earth elements (LREEs) and relatively depleted in high field strength elements (HFSEs, e.g., Nb, Zr and Ti) and heavy rare earth elements (HREEs), with transitional elements showing an obvious W-shaped distribution pattern. Based on these geochronological and geochemical features, we propose that the ore-forming intrusion associated with the Nb mineralization was formed under post-collision continental-rift setting, which is consistent with the tectonic regime of post-collision between the North China Craton and Paleo-Asian oceanic plate during the age in Ma for Indosinian (257–205 Ma). Intensive magmatic and metallogenic events resulted from partial melting of lithospheric mantle occurred during the post-collisional rifting, resulting in the development of large-scale Cu–Mo mineralization and rare earth deposits in the eastern part of Liaoning Province.

Magmatism and metallogenic mechanism of the Ga’erqiong and Galale Cu-Au deposits in the west central Lhasa subterrane, Tibet: Constraints from geochronology, geochemistry, and Sr-Nd-Pb-Hf isotopes

The Ga’erqiong-Galale ore district in the Bangong-Nujiang metallogenic belt hosts two large skarn Cu-Au deposits, associated with voluminous Late Cretaceous volcanism and plutonism. In this study, we present new zircon U-Pb age and Hf isotopic data, whole-rock geochemical and Sr-Nd-Pb isotopic data to constrain the geodynamic mechanisms of Late Cretaceous magmatism and metallogenesis within the Ga’erqiong-Galale ore district. The intrusive rocks in the district include diorite, quartz diorite, granodiorite, granite, and dioritic porphyrite. Zircon U-Pb analyses suggest those rocks mainly emplaced at early Late Cretaceous (84–95 Ma), which coincide with the ore-forming age of Ga’erqiong and Galale deposits (87 and 88 Ma, respectively). Geochemically, the granodiorite and dioritic porphyrite are metaluminous with depletion of Nb, Ta, and Ti and characterized by high MgO (2.68–4.16 wt%), Mg# (55–87), Sr (414–616 ppm), Sr/Y (30–56), Cr (22.5–105.0 ppm), and Ni (26.6–59.7 ppm), low Y (10.6–14.0 ppm), and heavy rare earth elements (HREE), showing geochemical signatures of high Mg# adakitic rocks. Four dioritic porphyrite and three granodiorite samples exhibit homologous Sr-Nd-Pb isotope compositions and have positive whole rock εNd(t) values of +1.1 to +3.0, (87Sr/86Sr)i values of 0.7045–0.7048, (206Pb/204Pb)t ratios of 18.42–18.73, (207Pb/204Pb)t ratios of 15.58–15.63, and (208Pb/204Pb)t ratios of 38.54–38.88. Besides, 116 analyses from the Ga’erqiong-Galale adakitic rocks give positive zircon εHf(t) values (+4.3 to +12.1). The geochemical and isotopic data indicate that the early Late Cretaceous high Mg# adakitic rocks in the Ga’erqiong-Galale ore district originated from the delaminated juvenile lower mafic crust that has been modified by the previously subduction. Partial melting of previously subduction modified, delaminated juvenile lower crust not only formed the hydrous adakitic melts in highly oxidation state, but also provided the ore metals (e.g., Cu, Au, Mo) for the subsequent mineralization. Such melts reacted with surrounding mantle peridotite to elevate the contents of metallic elements again. Then the melts experienced varying degrees of fractional crystallization process in the shallow magma chamber to form the dioritic and granodioritic magmas. Those magmas emplaced into the limestone of Duo’ai and Jiega Formation to form the Ga’erqiong and Galale skarn Cu-Au deposits, respectively. Field observation, together with geochronological and geochemical data, indicate that the early Late Cretaceous mineralization events in the northern and central Lhasa subterranes took place in a transition tectonic setting from collisional orogeny to extension and the input of subduction modified juvenile crust play an important role in the Late Cretaceous ore-forming events.

Selective Extraction of Rare Earth Elements from Monazite Ores with High Iron Content

Rare earth elements are essential for modern life products and green technologies. Recent supply constraints have boosted the development of rare earth projects after the price peak of 2011. The feasibility of a project depends on the definition of a processing route, which in turn depends primarily on the rare earth mineral, with monazite and bastnaesite representing the two most relevant minerals. Monazite-type ores usually contain high acid consumption impurities, such as iron, aluminum, calcium, magnesium, and phosphates, and may also contain prohibitive levels of radioactive thorium in its composition. This work presents a thermodynamic analysis of a monazite system and discusses the fundamentals of a selective process route for rare earth extraction from monazite ores with high iron content. This process involves sulfation by means of concentrated sulfuric acid and roasting at a high temperature. The route yields high rare earth extraction with low iron and thorium extractions and low acid consumption. Rare earth extractions as high as 80% were achieved, while iron and thorium extractions were lower than 1%, and acid consumption was lower than 0.34 kg of sulfuric acid per kg of ore. The operational window was compared to the one predicted by thermodynamic modeling, with 700 °C representing the optimal roasting temperature.

Late-Variscan multistage hydrothermal processes unveiled by chemical ages coupled with compositiona.

The scheelite skarn from Los Santos and the W-Au veins from El Cabaco district, located in the Spanish Central System Batholith (SCSB), are some of the best-known tungsten ore deposits in Spain. Uraninite is an accessory mineral in both deposits, which underwent several hydrothermal flow events. Chemical and textural characteristics, as well as electron microprobe U-Th-Pb uraninite chemical data from the different stages of the skarn and the vein-type mineralizations, are presented here. Based on these data the uraninite was able to be classified into two groups. Group I uraninite has an octahedral habit and occurs as inclusions in K-feldspar relicts of the leucogranite related to Los Santos skarn formation. It shows high Th (6.95 to 8.51wt.% ThO 2 ) and high Rare Earth Elements (REEs) contents (0.55 to 1.38wt.% ∑REE 2 O 3 ). Group II uraninite occurs i) associated to El Cabaco granite, in a greenish selvage-style greisen and its reddish envelope and in the mineralized rimming quartz veins and ii) in Los Santos high-temperature endoskarn and anorthite skarn, where it is associated with U-rich mica. This uraninite type has lower Th and ∑REE 2 O 3 contents than Group-I uraninite. The mineral chemistry and the assemblage and textural relationships suggest that Group-I uraninite is magmatic and the attained U-Th-Pb chemical age of 300±4Ma is interpreted as the magmatic age of the skarn-forming aplite granites in the western part of the SCSB. Group-II uraninite includes two events: i) hydrothermal uraninite, which yields an age of 295±2Ma, dates a strong alkali mobilization and early tungsten deposition and ii) a later hydrothermal process, around 287±4Ma, that resulted in sulfides and late scheelite precipitation and widespread silicification. Finally, the gold deposition is younger than this silicification according to textural criteria. Therefore, W-Au deposits in the western part of the SCSB were formed by superposition of several processes that took place some 15Ma after the skarn-forming granite crystallized. Comparable W, W-Au and U deposits in the Variscan orogenic belt show a similar timing of hydrothermal events, suggesting that the hydrothermal history was controlled by large-scale Late-Variscan tectonic processes.

Appraisal of Crustal Contamination in Southern Bastar Mafic Dykes in Chattisgarh, India

The present work is an attempt to assess the effect of crustal contamination through the Granitoids host rock, within the southern Bastar mafic dykes of Chhattisgarh, India, in the light of geochemical characteristics. Petrographically, these dykes are classified as Amphibolite, Dolerite/Meta-Dolerite and Diorite. Geochemically, all dyke samples have been classified as “high iron sub-alkaline Tholeiites”. On account of overlapping magnesium and iron concentration in Amphibolite and Dolerite dykes, distinctly higher High-Field Strength Element (HFSE), higher Rare-Earth Element (REE) concentrations in the Dolerite dykes than in the Amphibolite dykes, it is inferred that both dyke swarms are fed from two different Tholeiitic magmas. Conclusively, these dykes are recognized as belonging to two different swarms, BD1 and BD2 respectively. This is also corroborated by differences in the LREE patterns i.e. BD2 dykes have relatively enriched LREE pattern than that of BD1 dykes. It is evident from higher LaN/LuN ratio in the BD2 swarm, than in BD1 dyke swarm. These dykes intrude in the coarse-grained leucocratic Bastar Granitoids/Granite Gneisses, which are the host for these dykes. The comparative study of the Primordial mantle-normalized multi-element spider grams, and Chondrite-normalized rare-earth element patterns for the average of BD1 and BD2 dykes and the average of Bastar Granitoids, clearly reflect that the great degree of variation in LIL elements, observed in the Bastar dykes, is either due to metamorphism or due to secondary alteration, and not due to crustal contamination. This is further supported by much higher average “Nb”/“La” ratios in Bastar Mafic Dykes, than in the Bastar Granitoids. Crustal assimilation plays almost no role in the petrogenesis of the Bastar mafic dykes. The Bastar mafic dykes owe their incompatible element characteristics, certainly mantle derived.

Electroluminescence from silicon-based light-emitting device with erbium-doped TiO<sub>2</sub> films: Enhancement effect of ytterbium codoping

In the past years, light-emitting devices (LEDs) based on erbium (Er)-doped insulators or wide-bandgap semiconductors have received intensive attention because the intra-4f transition (<sup>4</sup>I<sub>13/2</sub>→<sup>4</sup>I<sub>15/2</sub>) of Er<sup>3+</sup> ions at ～ 1540 nm has potential applications in the optical interconnection for silicon-based circuits. The LEDs with rare-earth (RE)-doped SiO<i><sub>x</sub></i> (<i>x</i> ≤ 2) or SiN<i><sub>x</sub></i> (<i>x</i> ≤ 4/3) films have been well investigated as the silicon-compatible emitters. However, they suffer difficulty in injecting current and easing fatigue. In this context, the LEDs with RE-doped oxide semiconductors have been extensively investigated out of research interest in recent years. Among the oxide semiconductors, TiO<sub>2</sub> is a desirable host for RE-doping because it is transparent for visible and infrared light, and cost-effective, and has considerably high RE solubility. In our previous work (Zhu C, Lü C Y, Gao Z F, Wang C X, Li D S, Ma X Y, Yang D R 2015 <i>Appl. Phys. Lett.</i> <b>107</b> 131103), we have realized erbium (Er)-related visible and near-infrared (～ 1540 nm) electroluminescence (EL) from the LED with a structure of ITO/TiO<sub>2</sub>:Er/SiO<sub>2</sub>/n<sup>+</sup>-Si, in which TiO<sub>2</sub>:Er refers to the Er-doped TiO<sub>2</sub> film as the light-emitting layer. In this work, we co-dope ytterbium (Yb) into the TiO<sub>2</sub>:Er film in the aforementioned LED to significantly enhance the Er-related visible and near-infrared EL. It is revealed that a certain amount of Yb co-doping enables the TiO<sub>2</sub>:Er film to transform its crystal phase from anatase to rutile. Such a phase transformation reduces the symmetry of crystal field surrounding the Er<sup>3+</sup> ions incorporated into the TiO<sub>2</sub> host. Moreover, the substitution of over-sized Yb<sup>3+</sup> ions for Ti<sup>4+</sup> ions in the TiO<sub>2</sub> host leads to the distortion of the crystal field around the Er<sup>3+</sup> ions. The aforementioned symmetry-reduction and distortion of the crystal field increase the probabilities of the intra-4f transitions of Er<sup>3+</sup> ions. Due to the aforementioned reason, the Yb co-doping into the TiO<sub>2</sub>:Er film remarkably enhances the EL from the corresponding LED. It is believed that the strategy of Yb-codoping can be adopted to enhance the EL from the LEDs with other RE-doped TiO<sub>2</sub> films.

Late Cretaceous volcanic rocks in the Sangri area, southern Lhasa Terrane, Tibet: Evidence for oceanic ridge subduction

Late Cretaceous magmatism in the southern Lhasa subterrane, Tibet, provides critical constraints on the subduction processes of the Neo-Tethyan oceanic plate. Here, we provide data on the whole-rock geochemistry, zircon UPb ages, trace element contents, and Hf isotopes of early Late Cretaceous volcanic rocks from Sangri County to Sangye Temple (SS) along the southern Lhasa subterrane. The SS volcanic rocks include basalts, andesites, and dacites. SIMS and LA–ICP–MS zircon UPb data indicate that the SS dacites were erupted at ca. 95 Ma, coeval with the early Late Cretaceous “flare-up” event in the southern Lhasa subterrane. The SS volcanic rocks belong to the calc-alkaline to high-K calc-alkaline series and have the geochemical features of subduction-related volcanic rocks with negative Nb, Ta, and Ti anomalies. The basalts have similar rare earth element (REE) patterns to E-MORB and are characterized by high Zr abundances (65–190 ppm) and Zr/Y ratios (3.3–6.5). They were possibly derived by high-degree partial melting of mantle peridotite that had been metasomatized by subduction-related fluids with an input of asthenospheric components. Positive whole-rock εNd(t) (+2.9 to +3.2) values for the andesites, and their variable Mg# values (35–61) and MgO (2.29–7.32 wt%), Cr (12–232 ppm), and Ni (10–127 ppm) contents can be attributed to medium-degree partial melting of mantle peridotite followed by fractional crystallization of clinopyroxene and olivine. The calc-alkaline SS dacites are similar to adakites with high Sr (663–1188 ppm) and low heavy rare earth element (HREE) and Y (10.7–11.5 ppm) contents. These adakitic dacites have positive whole-rock εNd(t) (+2.9 to +3.4) and zircon εHf(t) (+8.4 to +14.9) values with relatively high values of Mg# (36–57) and high contents of compatible elements, indicating that they were derived from the partial melting of subducted oceanic slab, and with the ascending magma interacting with mantle wedge peridotite. Our new data indicate a distinct rock association of coeval asthenosphere-component-involved basalts and slab-derived adakitic dacites. Such an association, together with the coeval high-temperature charnockites and high-temperature granulite-facies metamorphism of the charnockitic country rocks in the southern Lhasa subterrane, indicates an anomalous input of materials and heat during the early Late Cretaceous “flare-up” event. Such an event can probably be attributed to the northwards subduction of a Neo-Tethyan oceanic ridge that allowed for contributions from upwelling asthenosphere that differed from the typical results of normal-angle subduction or low-angle/flat subduction and subsequent slab rollback.

Magma origins and geodynamic implications for the Makran-Chagai arc from geochronology and geochemistry of Bazman volcano, southeastern Iran

Bazman is an isolated voluminous (3497 m elevation; >300 km2) composite volcano that is located within the western segment of the Makran-Chagai arc. This arc obliquely tracks the modern EW-trending trench offshore the Oman sea coast of Iran and Pakistan, with several Quaternary stratovolcanoes (Bazman and Taftan in SE Iran, and Kuh-i-Sultan in western Pakistan) superimposed on a preexisting Neogene arc. High spatial resolution and high sensitivity U-Pb geochronology using Secondary Ionization Mass Spectrometry (SIMS) yielded four clusters of zircon ages for Bazman volcanic rocks which range from ca. 8.6 Ma to 41 ka. Lava and pyroclastic materials erupted between 8.6 and 5.9 Ma forming a thick Neogene volcanic succession (Ngv). These deposits were intruded by hypabyssal andesite-dacite domes at ca. 4.1 Ma. The next younger group of the Quaternary Bazman center comprises several eruptive pulses at 1.37 Ma, 1.13 Ma, 0.943 Ma, 0.853 Ma and 0.635 Ma, which constructed the main edifice around a central vent through alternating eruptions of lava and pyroclastic rocks (Qtv and Qa2). Subsequently, ignimbrite flows also sourced from the main vent erupted at 0.59 and 0.47 Ma, and covered the earlier erupted deposits. The youngest dated eruptive phase (Qa3) comprises the emplacement of dacitic to andesitic lava around the top of volcano. Based on Uranium-series (238U-230Th) disequilibrium in Qa3 zircons, model ages of ca. 41 ka define a maximum eruption age of these lavas, which tapped a long-lived magma reservoir with zircon crystallization ages predating eruption by 10’s to 100’s of ka. Low- medium-K calc-alkaline basaltic-andesitic eruptions formed parasitic cones located on northeastern flanks of the edifice as the youngest unit (Qa4) of Bazman. Both Neogene and Quaternary rocks from Bazman volcano exhibit homogeneous trace element characteristics, including enrichments in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to the high field strength elements (HFSE) and heavy rare earth elements (HREE), respectively. High Th/Yb and negative anomalies of Ta, Nb and Ti are consistent with an enriched mantle source in a continental subduction zone. Trace element modeling for the most primitive basalts erupted at Bazman suggests an origin of parental magmas through ∼15% partial melting of an enriched spinell-lherzolite mantle, whereas the genesis of Bazman acidic volcanic rocks with SiO2 > 62% involves partial melting in the middle/lower continental crust which became subsequently overprinted through assimilation – fractional crystallization (AFC) processes. Compositional continuity of Quaternary Bazman volcanic rocks with their Neogene precursors implies a steady magma source above the subducted Oman slab. Consequently, subduction geometry in the Makran-Chagai arc has experienced little modification over the past few million years.

Mineralogy and geochemistry of sediments from Simbock Lake, Yaoundé area (southern Cameroon): provenance and environmental implications

Two cores of sediments, named NR and EB, were collected in the Simbock Lake (Mefou watershed, Yaounde) to assess their provenance and the degree of heavy metal pollution based on mineralogical and geochemical data. The sediments are sandy, sand-clayey to clayey, and yellowish brown to greenish brown, and with high amounts of organic matter (average value of TOC is 1.95%). The sediments are mainly composed of quartz, kaolinite, accessory goethite, smectite, rutile, feldspars, illite, gibbsite, and interstratified illite-vermiculite. Fourier transform infrared (FT-IR) spectroscopy shows that kaolinite is less crystallized in the NR core than in the EB core. The Index of Compositional Variability (ICV), Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA), and the Rb/Sr and K2O/Rb ratios indicate a high weathering intensity in the source area. These sediments have low contents in Al2O3, Fe2O3, Na2O, K2O, MgO, and CaO as well as high values in SiO2, P2O5, TiO2, and MnO relative to the upper continental crust. The concentrations of Cr, V, Ba, and Zr are higher in the NR core than those in EB. The total rare earth element (REE) content varies between 78 and 405 ppm. The light REE are abundant (LREE/HREE ~ 18–59; avg. = 25.61). The chondrite-normalized REE patterns exhibit (i) negative Eu anomaly (Eu/Eu* ~ 0.38–0.62; avg. = 0.5), (ii) slight positive Ce anomaly (Ce/Ce* ~ 1.11–1.34; avg. = 1.11), and (iii) high REE fractionation ((La/Yb)N ~ 12.3–51.75; avg. = 25.61). The enrichment factor (EF) shows that the Mefou watershed through the Simbock Lake sediments is slightly polluted by the agricultural and urban activities.

Bauxite formation on Tertiary sediments in the coastal plain of Suriname

Lateritic bauxites in the coastal lowlands of Suriname form part of a belt along the northern margin of the Guiana Shield that has long been one of the world's major bauxite producing regions. The Surinamese deposits, many of which with an extensive mining history, originated on Tertiary siliciclastic sediments and were mostly buried under a layer of young sediments. The bauxite-bearing sequences are generally topped with an iron-rich layer largely made up of hematite and goethite. It covers a gibbsite-rich bauxite horizon that passes downward into a kaolinitic bottom section containing anatase and zircon as main accessory minerals. Weathering profiles across formerly mined deposits were analyzed for geochemical and mineralogical properties aimed at exploring compositional diversity, underlying controls of bauxite-formation and the nature of precursor sediments.Studied profiles in different parts of the coastal plain reveal overall similarities between individual deposits in showing significant depletion of Si, K, Na, Mg and Ca and strong, primarily residual, relative enrichment of Al, Ti, Zr, Nb, Hf, Ta and Th. In detail, however, there are distinct differences in major and trace-element signatures, accessory mineral assemblages, facies distribution and provenance of the terrigenous precursor sediments. Enrichments in high field-strength elements and heavy rare earth elements are largely attributable to accumulation of heavy minerals like zircon in the precursor. Petrological and trace-element evidence does not support a direct genetic relationship between bauxite and the underlying saprolitic clays. The complex petrologic characteristics and compositional heterogeneity of the coastal-plain deposits can essentially be explained by element fractionation, primarily through selective leaching, in combination with relative and absolute enrichment processes, erosion and reworking during two-stage, polycyclic bauxitization of a heterogeneous precursor.

Rare earths separation from fluorescent lamp wastes using ionic liquids as extractant agents

Processing of end-of-life products has become essential in the rare earth elements (REEs) recovery field because the demand for these metals has increased over the last years due to their intensive use in advanced technologies. Fluorescent lamp wastes are considered one of the most interesting end-of-life products for investigation due to their high REEs content, mainly yttrium and europium. As a result, red phosphors (Y2O3:Eu3+ – YOX) have been chosen for evaluating their REEs’ recovery potential. The REEs from a YOX reach liquor, coming from a soft leaching process have been precipitated adding oxalic acid and calcined to get the REEs in oxide form. Cyanex 572, D2EHPA and the ionic liquids, Primene 81R·Cyanex 572 IL and Primene 81R·D2EHPA IL, have been chosen to investigate the efficiency of REEs separation in chloride media. Yttrium, europium and cerium have been individually recovered by a four stages cross-flow solvent extraction process using the Primene 81R·D2EHPA IL and the Primene 81R·Cyanex 572 IL as extractants. Ce(III), Eu(III) and Y(III) have been obtained at high purities ≥ 99.9%. 4 mol/L HCl has been used to recover the yttrium and the europium from the organic phases.

Effect of La-substitution on microstructure and magnetic property of melt-spun (Nd1−La )13Fe81B6 alloys

Abstract The expensive rare earth elements Nd, Pr, Dy and Tb have been extensively used for making NdFeB-based magnets, but the less expensive and high abundant rare earth (HARE) elements such as La and Ce have been over stocked. The marketing expansion of the HARE elements is of much interest in academia and industry to achieve effective and efficient utilization of HARE elements. In this paper, nanocrystalline (Nd1−xLax)13Fe81B6 (x = 0–0.5) alloys were fabricated by melt-spinning method. It is found out that the room temperature magnetic properties of the alloys decrease sharply when La is substituted for Nd up to 20 at.%. However, an anomalous increase in Jr value and improved thermal stability of the alloy ribbons are observed for 40 at.% La substituted alloy while the reduction in magnetic properties is only nominal up to 30 at.%. Furthermore, the Curie temperature decreases from 588 K to 561 K with 50 at.% La substitution, which is higher than the equal amount of Ce substitution in Nd-Fe-B. It is shown by the Henkel curves that the alloy with 40 at.% La has the biggest value of positive peak which demonstrates the strongest exchange coupling in the 40 at.% La substituted alloy. The TEM micrographs indicate that the alloy containing 40 at.% La has more uniform and refined microstructure resulted in the enhanced properties.

Microstructure, magnetic properties, thermal stabilities and coercivity mechanisms of Ta doped Nd-Fe-B ribbons

The purpose of this paper is to explore Dy-free Nd-Fe-B magnetic alloys which could be developed into Dy-free permanent magnets operating at high temperatures. Nd13.5Fe80.5-xB6Tax (x = 0.0–1.2) alloys have been fabricated by melt spinning technique. It is found out that the addition of Ta in Nd-Fe-B alloys improves the extrinsic and microstructural properties resulting in better magnetic properties and thermal stability. The thermal stability of the alloys measured in terms of temperature coefficient of coercivity (β) improved from −0.41%/K for Nd13.5Fe80.5B6 to −0.27%/K for Nd13.5Fe79.9B6Ta0.6 in the temperature range 300–400 K. It is demonstrated that Ta acts as refractory element, which refines grains and reduces the volume fraction of the undesirable non-magnetic phases. As a result the magnetic properties (Br, Hcj and (BH)max) of the alloys are enhanced, however the intrinsic properties (Tc, Tsr) remain unchanged. The domain wall pinning, determined to be the dominant coercivity mechanism in the investigated alloys, also strengthened by the addition of Ta. It is concluded that Ta alloying can improve the microstructures, magnetic properties and thermal stability of the designated alloys. This research may shed light on further research and development of Dy-free high temperature resistant rare earth magnets.

Baking process of mineral carrier of rare earth metals with sodium hydroxide using muffle furnace

Rare Earth Elements (REE) is one of the natural resources that are very strategic and high economic value. REE applications in industry are continues to grow such as LCD (liquid crystal display), LED (light emitting diode), magnet and hybrid batteries (NiMH batteries; Misch metal; Ce, La, Nd). This resulted in REE demand continues to increase up to 10%. Increased demand is not matched by the number of Rare Earth production in the world. This happens because the Chinese as the main actor in the producer REE world production (95%) restricting the export of Rare Earth up to 35% so that the world price of LTJ bounced up. Research & development processing, and purification REE continue to obtain high purity Rare Earth Metals. Baking process the mineral carrier of REE (raw material minerals) with solid NaOH using a muffle furnace has been carried out. The research aims to determine the effect of temperature and grain size of the monazite sand on the decomposition reaction monazite sand and reaction kinetics. The raw materials used are monazite sands containing rare earth oxides as much as 55.1% and 11.01% phosphate. At monazite sand baking using solid NaOH will occur monazite sand decomposition process and the release of the existing phosphate. The results showed that the optimal conditions baking process at a temperature of 400°C and 200 mesh particle size obtained 91.40% phosphate inseparable.

Cambrian magmatism in the Tethys Himalaya and implications for the evolution of the Proto‐Tethys along the northern Gondwana margin: A case study and overview

The Cuonadong Dome in southern Tibet is a newly discovered gneiss dome in the Tethys Himalaya. Here, we investigate the Late Cambrian augen gneiss (orthogneiss) within the core of this dome to address the controversy surrounding early Palaeozoic tectonic evolution of the northern margin of eastern Gondwana. We report new zircon laser ablation multicollector inductively coupled plasma mass spectrometry (LA‐(MC‐)ICP‐MS) U‐Pb ages, Lu‐Hf isotopes, whole‐rock major and trace element geochemistry, and Sr‐Nd‐Pb data on representative samples from the granitic gneiss. The weighted mean of 116 analyses of zircon grains yields an age of 498.2 ± 1.5 Ma (mean square weighted deviation [MSWD] = 1.2). Forty‐one spots analyses on these grains show consistent εHf (t) values of −2 to +4 (average = +1.1), corresponding to Hf crustal model age (TDM2) of 1.3 to 1.6 Ga (average = 1.39 Ga). The orthogneiss (metagranite) is characterized by high Si and K contents, with low Al, Mg, and Ti, and A/CNK values ranging from 0.87 to 0.98 with an average of 0.92, indicating a metaluminous composition and I‐type granitoid affinity. The granitoid displays significant enrichment in light rare earth elements (LREEs) and relatively flat high rare earth element (HREE) patterns, with strong negative Eu anomalies (Eu/Eu* = 0.26–0.31). The primitive mantle‐normalized trace elements show a relative enrichment in large‐ion lithophile elements, such as Rb, and high‐field strength elements, such as Th, U, Zr, and Hf, with depletion in Ba, Nb, Ta, Sr, P, and Ti. The rocks show high initial 87Sr/86Sr ratios (0.7221–0.7248) and low εNd (t) values (−8.9 to −7.3) with Nd model ages (TDM) of 1.79–1.91 Ga. Their radiogenic Pb isotopic compositions show (206Pb/204Pb)t = 18.804–19.110, (207Pb/204Pb)t = 15.730–15.768, and (208Pb/204Pb)t = 38.409–39.054, indicating an ancient upper middle continental crustal origin. Our study shows that the protolith of the metagranite was most likely derived from the partial melting of upper continental crust with a minor contribution of depleted mantle materials. Through integration of the regional information on early Palaeozoic magmatism and metamorphic events, we contend that the protolith of the Cuonadong granitic gneiss formed in an accretionary setting associated with the early Palaeozoic Proto‐Tethys Oceanic plate subduction beneath the Gondwana continent.

Pulling growth technique towards rare earth single crystals

Pulling growth technique serves as a popular method to grow congruent melting single crystals with multiscale sizes ranging from micrometers to centimeters. In order to obtain high quality single crystals, the crystal constituents would be arranged at the lattice sites by precisely controlling the crystal growth process. Growing interface is the position where the phase transition of crystal constituents occurs during pulling growth process. The precise control of energy at the growing interface becomes a key technique in pulling growth. In this work, we review some recent advances of pulling technique towards rare earth single crystal growth. In Czochralski pulling growth, the optimized growth parameters were designed for rare earth ions doped Y3Al5O12 and Ce:(Lu1− x Y x )2SiO5 on the basis of anisotropic chemical bonding and isotropic mass transfer calculations at the growing interface. The fast growth of high quality rare earth single crystals is realized by controlling crystallization thermodynamics and kinetics in different size zones. On the other hand, the micro pulling down technique can be used for high throughput screening novel rare earth optical crystals. The growth interface control is realized by improving the crucible bottom and temperature field, which favors the growth of rare earth crystal fibers. The rare earth laser crystal fiber can serve as another kind of laser gain medium between conventional bulk single crystal and glass fiber. The future work on pulling technique might focus on the mass production of rare earth single crystals with extreme size and with the size near that of devices.

The effect of diffusive re-equilibration time on trace element partitioning between alkali feldspar and trachytic melts

We present new experimental data on major and trace element partition coefficients between alkali feldspar and trachytic melt. Experiments were conducted at 500 MPa, 870–890 °C to investigate through short disequilibrium and long near-equilibrium experiments the influence of diffusive re-equilibration on trace element partitioning during crystallization. Our data show that Ba and Sr behave compatibly, and their partition coefficients are influenced by re-equilibration time, orthoclase (Or) content, growth rate and cation order-disorder. High field strength elements (HFSE) and rare earth elements (except Eu) are strongly incompatible, but alkali feldspar efficiently fractionates light (LREE) from heavy rare earth elements (HREE).Our crystallization experiments reveal a strong influence of disequilibrium crystal growth on the partitioning of Ba and Sr. In particular, short-duration experiments show that rapid alkali feldspar crystal growth after nucleation, promotes disordered growth and less selectivity in the partitioning of compatible trace elements that easily enter the crystal lattice (e.g., Ba and Sr). This produces partition coefficients of compatible elements higher than those obtained through long-duration experiments, in which growth is slower and more selective. On approach to equilibrium, decreasing growth rate and timescales of diffusive re-equilibration facilitates the incorporation of compatible elements within the crystal lattice (through ordered growth), on the basis of the charge and size of the octahedral site, resulting in lower partition coefficients of Ba and Sr. Therefore, our results indicate that besides crystal-chemical effects, i.e. lattice strain, the substitution mechanisms during growth (with different degrees of ordering) of Ba and Sr in alkali feldspar are strongly influenced by diffusive re-equilibration and crystal growth kinetics. This implies that partition coefficients of Ba and Sr can be used to establish timescales of crystallization processes under pre- and syn-eruptive conditions. The application of our results to alkali feldspar in rocks from Campi Flegrei, constrain the magma residence time at subliquidus conditions in a reservoir to a maximum of 6 days under disequilibrium conditions and to a minimum of 9 days upon approaching near-equilibrium conditions.

Compound Glass Microsphere Resonator Devices.

In recent years, compound glass microsphere resonator devices have attracted increasing interest and have been widely used in sensing, microsphere lasers, and nonlinear optics. Compared with traditional silica resonators, compound glass microsphere resonators have many significant and attractive properties, such as high-Q factor, an ability to achieve high rare earth ion, wide infrared transmittance, and low phonon energy. This review provides a summary and a critical assessment of the fabrication and the optical characterization of compound glasses and the related fabrication and applications of compound glass microsphere resonators.