REE Oxides Research Articles

Unusual mineralization in basaltic andesite of submarine volcano Esmeralda (Mariana Island Arc)

The results of studies of a basaltic andesite sample complicated by a mineralized crack and voids, with a crack and gas voids filled with secondary mineralization dredged on the Esmeralda underwater volcano, are presented. A detailed comparative study of the mineral composition of the substance lining the crack, the space around the crack, and the part of basaltic andesite unaffected by secondary changes made it possible for the first time for the underwater Esmeralda volcano to establish the presence of an association of minerals that is not characteristic of unaltered volcanic rocks. In the intracrack space and adjacent zones of basaltic andesite, wide ranges of plagioclase composition were determined, isomorphism in the Fe-Ca-pyroxene series was studied, REE oxides, hydroxides and fluorohydroxides were studied, and variability in the composition of minerals in the magnetite-hematite series was shown. It is assumed that tectonic movements led to the emergence of permeable zones in the previously formed basaltic andesites through which new portions of the melt leaked. In a limited space, high fluid gas saturation, temperature and pressure made it possible to extract metal compounds from the melt and host rocks.

Modeling from the first principles of the electronic properties of compositions of REE as precursors of high-temperature superconductors

Modeling of the first principles of the electronic properties of complex oxides of rare earth elements (BaY2O4, BaGd2O4, BaLu2O4) as precursors of high-temperature superconductors has been performed. The VASP software package was used as a modeling environment, in particular the method of coupled plane waves (PAW method), which allows us to obtain fairly accurate results for calculating the electron density and band structure. From the analysis of the obtained band energy structure, it follows that the studied REE oxides have a band gap width Eg = 3.29–3.84 eV, which is characteristic for dielectric materials. The studied compounds based on these rare earth elements selected from the yttrium (Y, La, Gd–Lu) and cerium (Ce–Eu) groups are characterized by an increase in Fermi energy and a decrease in the band gap as the atomic number (39, 64, 71) of the element in the periodic table increases. A method for modeling the quantum layers of the studied materials by simulating the restriction of the crystal structure along one of the coordinate axes is proposed. This representation approximates the model of the crystal lattice of REE oxides to the situation of analyzing a quantum layer whose thickness is equal to the size of the crystal cell along the specified axis. The rupture of atomic bonds in a crystal is simulated by increasing the distance between atomic layers along this axis to values at which the value of free energy is stabilized. In the quantum layer of rare earth element oxide (with its thickness close to 1 nm), a wider range of energy values is formed in which electrons are distributed than is observed in the continuous version, and the expansion of the electron distribution area extends to the energy levels of the band gap. This is explained by the fact that the geometric discretization of nanoscale structures determines the discreteness of the quantum-dimensional energy spectrum.

ПРЕКУРСОРЫ ОКСИДНЫХ СИСТЕМ AL2O3-ZRO2-DY2O3 И AL2O3-ZRO2-ND2O3, ПОЛУЧЕННЫЕ ЭЛЕКТРОХИМИЧЕСКИМ МЕТОДОМ

The study is devoted to the preparation of precursors of complex oxide systems by electrochemical method based on the processes of anodic dissolution of aluminium in the electrolyte containing Cl-, NO3-, Al3+, Zr4+, Y3+, Dy (III), Nd (III) ions. The synthesis of precursors of complex oxide systems was carried out in a coaxial diaphragmless electrochemical reactor with substantially different area electrodes. The process of precursor formation proceeds in the volume of the electrochemical reactor due to the interaction of electrogenerated Al3+, OH- ions and electrolyte components. It is caused by hydrolysis of anode dissolution products, formation of polyheteronuclear metal-hydroxo-aqua complexes, their polycondensation, formation of primary particles of solid phase and enlargement of the latter. A comparative analysis of the particle size distribution of samples differing in the content of Dy2O3 and Nd2O3 demonstrates the bimodal character of the distribution, expressed more clearly in the case of the system containing Nd. The average particle size of the synthesised precursors is approximately in the same range, except for the system containing Nd and obtained from an electrolyte with a higher content of this element. The results of particle size measurements are confirmed by electron microscopy data. These data correlate with the time dependence of ξ-potential of synthesised precursors of alumina-zirconium oxide systems containing REE. The proposed approach allows to obtain precursors of complex oxide systems based on aluminium, zirconium, REE oxides. Using X-ray fluorescence and particle size analysis methods, the particle size and chemical compositions of precursors of oxide systems were investigated.

Origin and mineralization processes of REE during magmatic-hydrothermal evolution: Insights from in-situ geochemistry of calcite from the Weishan REE deposit, eastern North China Craton

The Weishan REE deposit, hosting more than one million tons of light REE oxides (LREE2O3), is one of the largest LREE deposits in China. It has been considered to be a carbonatite-related REE deposit, but whether carbonatites occurred or not is still controversial, leading to the confusions of how the LREE originated and mineralized. Here, we conducted in-situ elemental and Sr-Nd isotopic analyses on different stages of calcite from the Weishan REE deposit, combined with petrographic and bulk C-O isotopic studies, with the aim to unravel the origin and mineralization processes of REE. Four stages of calcite (Cal-1, Cal-2, Cal-3 and Cal-4) were identified, of which the Cal-1 typically coexists with K-feldspar and quartz while the Cal-2 and Cal-3 coexist with sulfates and REE minerals (e.g., bastnäsite and parisite), respectively. The Cal-4 occurs in the post-ore veinlets and coexists with sulfides. The Cal-1 is characterized by exsolution of carbocernaite along its cleavage planes with highest Na, K, Sr, Ba and LREE contents. The other stages of calcite show continuous decrease of the above elements. Combined with petrographic features and elemental discrimination diagrams, it is concluded that the Cal-1 is magmatic while the others are hydrothermal. These calcites thus indicate a continuous magmatic-hydrothermal evolution. The four stages of calcite show similar isotopic compositions, which are consistent with those of the alkaline silicate rocks in the ore district, suggesting an uniform source or magma chamber for their derivation. Considering the magmatic features of Cal-1, it is inferred that carbonate melts coupled with abundant alkaline fluids were exsolved from the alkaline magmas. Alkalis (e. g., K and Na) were enriched in the magmatic-hydrothermal system with potassic metasomatism being more prevalent, which might play an important role in REE exsolution and transportation. Focused REE deposition occurred shortly after massive deposition of sulfates, indicating that REE-sulfate complexes might be the dominant transporting ligands of REE. The deposition of REE was mainly induced by fluid boiling, as indicated by the boiling/unmixing features of fluid inclusions. The Sr-Nd isotopic compositions of ores and associated alkaline rocks show affinities to the enriched lithospheric mantle (EM) beneath the study region, but are more depleted. Because subduction of the Paleo-Pacific oceanic plate beneath the eastern Asian occurred since the Jurassic, it is inferred that CO2- and REE-rich melts/fluids released from the subducted oceanic slab metasomatized the EM, leading to a REE-rich carbonated mantle. Rollback of the subducted slab occurred during the early Cretaceous, resulting in partial melting of the EM and thus generating the CO2- and REE-rich alkaline magmas. This deposit shows significant hydrothermal features with poorly-developed carbonatites, distinct from the typical carbonatite-related REE deposits in the other places. The REE mineralization is thus considered to be basically controlled by the alkaline magmas rather than the carbonatites.

Effect of rare-earths (La, Nd, Pr) on zirconate ceramics for thermal barrier coatings

Zirconium oxide-based powders with different concentrations of REE concentrate (La, Nd, Pr) in an amount from 25 to 35 mol.% were synthesized by the reverse chemical precipitation method. The formation of REE zirconates during consolidation has been studied by Raman spectroscopy, XRD and scanning electron microscopy. It has been established that the formation of REE zirconates with the pyrochlore structure occurs after annealing of synthesised powders at a temperature of 1000°C. It has been demonstrated that densifying processes during sintering at 1400 –1600°C occur most slowly in a ceramic material with 35 mol.% REE oxides, which has a stable phase composition at all sintering temperatures, consisting mainly of REE zirconates with the pyrochlore structure. The resulting ceramic material based on REE zirconates has phase stability at 1300°C.

Efficient Catalytic Conversion of Glucose into Lactic Acid over Y-β and Yb-β Zeolites.

In this work, a new type of modified β zeolites with rare earth elements (ree) was discovered for producing lactic acid from glucose and achieved a good catalytic effect. At first, the catalytic performances of ree-β zeolites, ree oxides, and single-transition-metal-β zeolites were compared, and the result showed that Y-β and Yb-β zeolites had the best catalytic activity under the same reaction conditions. Under the best reaction conditions, the maximum yields of lactic acid with Y-β and Yb-β catalysts were 45.3 and 43.6%, respectively. The acid characterization showed that Y/Yb-β zeolites had a similar number of Lewis acid sites as Sn-β zeolites, and they were also more than other transition-metal-β zeolites. Thus, Y-β and Yb-β zeolites had a higher lactic acid yield than those catalysts. It is interesting to note that Y-β and Yb-β zeolites owned more Brønsted acids but produced fewer byproducts. Combining the decomposition experiment of 5-hydroxymethyl furfural, fewer byproducts were produced with Y-β and Yb-β zeolites because the low amount of Brønsted acid contained could hinder the decomposition of 5-hydroxymethyl furfural, thereby slowing down the side reaction.

The Possibility of Separation of Heavy Minerals as Byproduct of the Danube River Gravel Sand Extraction

The history of exploitation of gold from the Danube River’s sandy gravels is centuries long. The extraction of valuable heavy minerals (VHM) concentrate was never intended. Our aim is to find out an effective separation process to produce monomineral concentrates of the following minerals: garnet, ilmenite, zircon, monazite, magnetite, rutile, gold. The essential condition is to use no chemistry (no flotation, leaching, activating). The experimental concentrates were prepared by sluicing on active river channel. Next, the separation results were achieved using gravity and electromagnetic methods with different magnetic intensities. The prepared rutile contained from 63.3% TiO2 to 87% TiO2. The ilmenite concentrate contained 20.5% TiO2 and 39.2% ilmenite. The garnet concentrate contained 94% garnet. The monazite concentrate contained 86.6% monazite, and the sum of REE oxides was 50.1%. The zircon concentrate containing 63.7% ZrO2 means that the prepared concentrate contained 96.1% zircon.

Zirconium dioxide. Review

A review of zirconium dioxide or zirconia ZrO2 is presented. The finding of zirconium compounds in nature, the physical and chemical properties of ZrO2 are given, the polymorphism of zirconium oxide, and the phase diagrams of systems with its participation are considered. The areas of application of zirconia compounds are highlighted: automotive industry, electronics industry, energy and industrial ecology, equipment manufacturing and mechanical engineering the production of zirconium-based refractories, ceramics, enamels, glass, superhard materials, applications in medicine, nuclear energetics, and many others areas of human activity. Cubic modification of zirconium dioxide, stabilized by oxides of rare earth elements,is a jewelry stone (fianite). Partially stabilized zirconium dioxide is a versatile structural material with very high resistance to crack propagation. Solid solutions of REE oxides, especially scandium, have a high oxygen conductivity, which is used in sensors for measuring the partial pressure of oxygen and in fuel cells. Attention is paid to heat-resistant oxide ceramic materials with low thermal conductivity used in the quality of heat-resistant coatings. Considerable attention was paid to the second most important mineral of zirconia - baddeleyite (ZrO2). Baddeleyite is widely used in the production of refractory materials. It is mined for the production of metallic zirconium. The achievements of Soviet and Russian scientists in thedevelopment of technologies for the production of fianite and artificial baddeleyite are presented.

Pyrochlore from the Bailundo Carbonatite Complex (Angola): Compositional variation and implications to mineral exploration

Pyrochlore is a common accessory in carbonatite rocks and its composition can provide useful insights on petrogenetic and post-magmatic metal-enrichment processes, especially those which favour its occurrence and concentration.Comprehensive compositional and textural characterization of a large set of pyrochlores from the Bailundo Carbonatite Complex (SW Angola) and associated surface rocks was the basis to (i) evaluate the main effects of metasomatism and weathering as causes of metal leaching or concentration; and (ii) assess pyrochlore compositions as potential petrogenetic or metallogenetic tools, with particular emphasis on pyrochlore enrichment in economic components, such as Ta, REE, U, Th and Pb, during weathering processes.Unweathered fluor- and hydroxyl-calciopyrochlores from deep-seated carbonatitic rocks (provided by a 600 m-deep drill-core) often present high Ta/Nb ratios, as well as high U and Th contents, and comparatively low overall REE concentrations. Metasomatic effects are not easy to assess, given the extreme compositional variability of these pyrochlores.On the other hand, some systematic trends can be established in pyrochlores from weathered surface rocks: these pyrochlores usually show strong depletion in most A-site cations (e.g., Na, Ca, U), and clear enrichment in Nb and in large-ion metals (e.g., Ba, Sr, Pb) usually absent in unweathered pyrochlores. REE seem to be relatively immobile and to become concentrated during weathering.Along with some REE phosphates and oxides, pyrochlore is often present in several domains of the weathering profile, occurring in the outcropping weathered carbonatite as well as in the regolith immediately overlying the intrusion. Thus, both the Bailundo carbonatite intrusion and its weathering products, concentrated inside the ridge formed by differential erosion of the fenitic aureole, constitute good exploration targets for Nb (±Ta ± REE). However, future exploration work should also include a 3-D understanding of the chemical and geological processes at work in both geological environments.

TiO2–Zr–Th–Y–rare‐earth elements ore deposit in unconsolidated fine‐grained sediments from Tongo Gandima in the Bétaré Oya Gold district, Eastern Cameroon

Tongo Gandima is an area located in the southeastern part of the Bétaré Oya Gold district (Eastern Cameroon). Geochemical investigations on rare metals (TiO2, Th, Y, and rare‐earth elements [REE]) were carried out on sample types (source rocks, unconsolidated fine‐grained sediments, and concentrated sediments) using X‐ray diffraction (XRD), X‐ray fluorescence (XRF), inductively coupled plasma‐mass spectrometry (ICP‐MS), and scanning electron microscope equipped with EDAX spectrometer (SEM‐EDS) methods. In this study, five layers of river terraces were selected (organic matter layer, clayey layer, fine sandy layer, coarse sandy layer, and gravel layer). One of them, the gravel layer, is mineralized. TiO2, Zr, and REE are more enriched in monzonites than in granites. Unconsolidated sediments derive mainly from the erosion of weathered materials developed on monzonites and granites. The mineral assemblage of fine‐grained sediments from the gravel layer is muscovite, kaolinite, quartz, rutile, smectite, and others, and the average concentrations in Th, Zr, and Y are high. Fifty concentrated fractions from the same samples were analysed separately and their mineralogy is smectite, kaolinite, gibbsite, muscovite, quartz, rutile, anatase, zircon, titanomagnetite, and ilmenite. The heavy mineral fractions are opaque minerals, biotite, zircon, rutile, tourmaline, garnet, diopside, zoisite, and kyanite. TiO2, Zr, Th, Y, and REE contents are high. The REE oxides (REO) total grade ranges from 0.0088 to 15.66 wt%, marked by LREO‐abundance, especially in La2O3, Ce2O3, Pr2O3, and Nd2O3. The Tongo Gandima REO deposit was classified as LREO‐dominated type. The chondrite‐normalized REE patterns exhibit strong negative Eu anomalies; their V‐shaped patterns are typical of ore varieties. The abundant TiO2, Zr, Y, Th, and REE might have been influenced by surface processes (peneplanation and chemical weathering) and variations in sediment grain size. SEM‐EDS data reveal that apatite with Ce‐ and La‐dominant, monazite‐(Ce), and Ce‐Mn‐bearing ilmenite are rare metal‐bearing minerals. This study demonstrates that the economic importance of the alluvial‐fluvial placers from Tongo Gandima results from their high Ti, Zr, Th, Y, and REE contents.

Multiphase carbonatite-related magmatic and metasomatic processes in the genesis of the ore-hosting dolomite in the giant Bayan Obo REE-Nb-Fe deposit

The origin of dolomite that hosts the Bayan Obo REE-Nb-Fe deposit (57.4 Mt.@6% REE2O3, 2.16 Mt.@0.13% Nb2O5, and >1500 Mt.@35% iron oxides) has been controversial for decades, but it is integral to understanding of the genesis of this giant deposit. In this study, based on the textures and in situ major and trace element composition of its carbonates, the dolomite was proved to be initially generated from magnesio-ferro‑carbonatite melts. It subsequently experienced magmatic-hydrothermal alteration and recrystallization in a low strain environment, caused by calcio‑carbonatitic fluids, with formation of finer-grained dolomite, interstitial calcite and increasing amounts of associated fluorocarbonates. Available stable isotope analyses indicate that the recrystallized ore-hosting dolomite has higher δ13C and δ18O ratios compared to its igneous coarse-grained precursor. Rayleigh fractionation during the recrystallization process, rather than crustal contamination, played a major role in the highly-variable stable isotope composition of carbonates in the dolomite. Low-T alteration increased variability with apparently random increases in δ18O within carbonates. The REE, Ba and Sr were added simultaneously with the elevated (La/Yb)cn from magnesio-ferro‑carbonatite melts to calcio‑carbonatitic fluids, and to carbonatite-derived aqueous fluids, through which extensive fluorine metasomatism and alkali alteration overlapped the recrystallization of the ore-hosting dolomite. Therefore, the multi-stage REE mineralization at Bayan Obo is closely related to metasomatism by calcio‑carbonatitic fluids of previously-emplaced intrusive magnesio-ferro‑carbonatite bodies during late evolution of the Bayan Obo carbonatite complex. Then, the ore-hosting dolomitic carbonatite was subjected to compressive tectonics during a Paleozoic subduction event, and suffered intense, largely brittle, deformation, which partially obscured the earlier recrystallization process. The complex, multi-stage evolution of the ore-hosting dolomite is responsible for the uniqueness, high grade and giant size of the Bayan Obo deposit, the world's largest single REE resource with million tonnes of REE oxides.

Distribution of TR2O3, P2O5 and Nb2O5 between two immiscible melts in the monazite–SiO2–NaF–Nb2O5–Fe2O3 system

Monacite-SiO2-NaF-Nb2O5-Fe2O3 system on 1200 C isotherm is characterized by a wide area of two immiscible melts: silicate and phosphate-fluoride, salt. The system is a mutual education in molten salt a new phase of rare earth double phosphates and fluoridahospital REE and Na in the composition of which is Fe and Nb. Iron has a great influence on the immiscibility of melts: in the absence of iron, the liquation area occupies 50% of the chart area, at 5% Fe2O3 - 57%, at 10% Fe2O3 - 70%. REE, P and Nb oxides are contrast distributed between the two immiscible melts. REE and P are 95% concentrated in phosphate-salt melt. Niobium is concentrated in an iron-silicate melt. In the absence of Fe2O3 in the silicate melt, the content of Nb2O5 = 4,91%, at 15,33% it = 6,89%, i.e. increased by 40%.

Intensification of Washing of Filter Materials Using Ultrasound

Experiments on washing of filter materials to remove uranium and REE (Ce) oxides using a Grad ultrasonic bath (model 180-35) with the generator power of 300 W and frequency of 35 kHz were performed. The following filter materials were tested: MTF metal fabric filter, high-performance fiberglass cellular folded filter (FYaS-E 13 N 0 05.1 P), two types of metal fabric filters with other gauze size, T-13 glass fabric [GOST (State Standard) 19170-2001 (19170-93)] and fine air cleaning filter (FTOV N13 270 × 640 × 500–11) made of glass paper based on microthin fiberglass. The influence exerted on the washing efficiency by the treatment time, ultrasonic generator power, working solution acidity, and process temperature was examined. Ultrasonic treatment intensifies washing of filter materials to remove surrogate powders based on UO2 and CeO2. More efficient washing of fiberglass filter materials requires increased power of the ultrasonic generator.

Mechanical and structural properties of radiation-damaged allanite-(Ce) and the effects of thermal annealing

The onset of thermally induced, heterogeneous structural reorganization of highly radiation-damaged allanite-(Ce) begins at temperatures below 700 K. Three strongly disordered allanite samples (S74 20414: ~ 0.55 wt% ThO2, 22.1 wt% REE oxides, and maximum radiation dose 3.5 × 1018 α-decay/g; LB-1: ~1.18 wt% ThO2, 19.4 wt% REE oxides, and maximum radiation dose 2.0 × 1019 α-decay/g; R1: ~ 1.6 wt% ThO2, 19.7 wt% REE oxides, and maximum radiation dose 2.6 × 1018 α-decay/g) were step-wise annealed to 1000 K in air. Using orientation-dependent nanoindentation, synchrotron single-crystal X-ray diffraction (synchrotron XRD), X-ray powder diffraction (powder XRD), differential scanning calorimetry and thermogravimetric analysis (DSC/TG), mass spectrometry (MS), 57Fe Mossbauer spectroscopy and high-resolution transmission electron microscopy (HRTEM), a comprehensive understanding of the structural processes involved in the annealing was obtained. As a result of the overall increasing structural order, a general increase of hardness (pristine samples: 8.2–9.3 GPa, after annealing at 1000 K: 10.2–12 GPa) and elastic modulus (pristine samples: 115–127 GPa, after annealing at 1000 K: 126–137 GPa) occurred. The initially heterogeneous recrystallization process is accompanied by oxidation of iron, the related loss of hydrogen and induced stress fields in the bulk material, which cause internal and surface cracking after step-wise annealing from 800 to 1000 K. HRTEM imaging of the pristine material shows preserved nanometer-sized crystalline domains embedded in the amorphous matrix, despite the high degree of structural damage. The results show that hardness and elastic modulus are sensitive indicators for the structural reorganization process.

Manganese Mineralization in the Mesozoic Siliceous Deposits of the Central Sikhote-Alin and Nadanhada-Alin

The stratiform ferromanganese bodies in the Mesozoic chert formations of central Sikhote-Alin (Katen R., J3) and Nadanhada-Alin (Khuntseling settlement, J2–3), and the vein manganese deposit (Ktab) at the Glubinny settlement area (central Sikhote-Alin) are characterized for the first time. Jurassic primary ores occur as interlayers in clayey–siliceous units. They consist of grains and globules of Mn and Fe oxides of the psilomelane–pyrolusite group and goethite. The interlayers also contain the allogenic products of eroded sialic rocks (quartz, potassium feldspar, albite, kaolinite, muscovite, paragonite, illite, and zircon) and accessory ore minerals (monazite, sphalerite, galena, apatite, cassiterite, barite, pyrite, titanite, rutile, native silver, auricupride, cerianite, tetrahedrite, and intermetallic Cu5Zn3 and Ni7Cu4). In the vein ores, spessartine and rhodonite fill veinlets and form a matrix of tectonic breccia. Manganese oxides form crusts (up to 4 cm) on the Triassic chert lumps and blocks. They likely represent the products of oxidation and breakdown of former hydrothermal–metasomatic manganese carbonates and silicates in a supergene environment. In contrast to the manganese minerals from the stratiform ores, those of the vein ores do not contain Co, Ni, Zn, and Pb, which are involved in the sulfides and sulfoarsenides (Co-gersdorffite and Ni-cobaltite, smaltite, pentlandite, and other minerals). Magnetite; titanomagnetite; barite; chalcopyrite; pyrrhotite; galena; argentite; zircon; titanite; wollastonite; anhydrite; REE phosphates, silicates, and oxides; bismuthine; native Ag, W, Cu, Zn, and Ni; and intermetallic compounds (Cu5Zn3, (Pd, Pt)5Cu and Pd4Cu) are also recognized in the vein manganese ores.

Separation of rare earths by solvent extraction using DEHPA

This paper presents results or the analysis of process variables for separating light REE and heavy REE, in chloride media, by solvent extraction. DEHPAIsoparaffin was used as the extraction system and the liquor was produced in the laboratory by dissolving REE oxides in HCl to simulate leaching liquor originating from monazitic ores after cerium removal. The following parameters were determined: pH of work, extractant concentration, reaction time, and number of extraction stages. A continuous extraction circuit was operated and its behavior was similar to that shown by batch extraction tests.

Geochemistry and nano-mineralogy of feed coals, mine overburden, and coal-derived fly ashes from Assam (North-east India): a multi-faceted analytical approach

In order to address the scarcity of information on the nature and mode of occurrence of minerals and elements in coal, coal mine overburden and coal ashes from North-east India, and also the relations between coal mineralogy and ash chemistry, the petrology, mineralogy and nano-mineralogy, and ash chemistry of some industrially important high-sulfur coals, mine overburden materials and fly ash samples from Assam (India) have been evaluated. A combined approach, using petrography, low-temperature ashing plus X-ray diffraction (LTA-XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscope (HR-TEM), Raman spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS), has provided new information on the mineralogy and nano-mineralogy of these sub bituminous coals and associated mine overburden. The presence of rare earth elements and yttrium (REY) in Northeast Indian coal, mine overburden and fly ash samples is also reported for the first time. The identification of these components may be significant from an economic point of view. Some Northeast Indian fly ashes, with REE oxides up to 1580ppm on an ash basis, might possibly represent sources for recovery of rare earth elements.

Fundamental kinetic aspects and the mechanism of oxidative dehydrogenation of 4-vinylcyclohexene into ethylbenzene and styrene on metal-containing zeolites of the pentasil family

In promotion of a Pt-Ga-containing pentasil with a binary mixture of REE oxides, a synergism of their effect on the catalyst activity in the reaction of oxidative dehydrogenation of 4-vinylcyclohexene is observed. A kinetic model of the process of oxidative dehydrogenation of 4-vinylcyclohexene is suggested. The model includes a stage-by-stage scheme and the corresponding reaction rate equations. It was found that the accumulation rate of 4-vinylcyclohexene dehydrogenation products is correlated with the isomerization capacity of the catalytic system.

Composites based on REE: The extraction-pyrolytic synthesis

The potential of the pyrolytic extraction method for the synthesis of composites based on REE oxides, including nanosized ones, is scrutinized. The experimental data are analyzed, and some criteria for choosing the extraction systems for the production of materials by pyrolysis are discussed.

Peculiarities of crystallization of alumina, yttria and rare-earth element oxides of yttria subgroup in an optical furnace

The peculiarities crystallization of alumina, yttria and the rare-earth element oxides of the yttria subgroup in an optical furnace have been studied. Direct evidence of oxygen dissolution during alumina melting in oxidizing atmosphere and its ejection during crystallization has been presented. The released oxygen was captured by the inside hollows of alumina ingots, and its quantity was controlled using gas chromatography. It was not less than 8 × 10 −6 g in 1 g of alumina. The quantity of the oxygen released is corresponding to that for REE oxides. The yttria specific volume increasing during crystallization was confirmed. The apparent ingot volume of Er, Ho, Tm, and Yb oxides does not change, while the specific volume of lutecia decreases.