Presence Of Rare Earth Elements Research Articles

Sample Preparation for Determination of Rare Earth Elements in Geological Samples by ICP-MS: A Critical Review

The presence of rare earth elements (REE) in geological materials provides important information about the formation and the geochemical processes that rocks undergo. Therefore, there is a constant necessity for accurate data and reliable and fast analytical methods. However, the low concentrations of these elements typically found in rocks require quantification by sufficiently sensitive techniques, such as Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The preparation of these samples to the introduction in ICP-MS is a critical part of the process. Traditional wet dissolution methods, such as acid digestion or alkaline fusion followed by dissolution are mostly employed. The acid digestion requires a mixture of strong acids due to the presence of low soluble constituents common in rock samples, such as silicates or clays. The alkaline fusion is fast and efficient, but the dissolution of the melted material results in solutions with a high amount of total dissolved solids (TDS), which can be a problem due to the possibility of deposition in parts of the ICP-MS. Other instrumental approaches have been spread rapidly, as the coupling of a laser ablation accessory or an electrothermal vaporizer to the ICP-MS, as they can allow the direct sample introduction, or at least with minimum preparation. This paper presents a review of sample preparation methods, aimed at the quantification of rare earth elements by ICP-MS and focusing on works published in the last decade.

Effect of rare earth elements on the thermal cracking resistance of high speed steel rolls

The effect of rare earth elements on the thermal cracking resistance of high speed steel (HSS) rolls was investigated. Laser rapid heating was used for thermal fatigue experiments. Thermal cracks and microstructure were observed using metalloscopy and scanning electron microscopy. The results showed that thermal cracks initiated from the interface between the matrix and eutectic carbides (including M 6C and M 7C 3 type carbides), and propagated along the interface between the two phases. MC type carbides enriched with vanadium could prevent the propagation of thermal cracks. The presence of rare earth elements decreased the quantity of big eutectic carbides, and proportionally increased spherical and rod-shaped MC type carbide content. HSS0 (0.00% RE) had approximately three times the thermal cracking density of HSS3 (0.12 wt.% RE). Rare earth elements were shown to significantly improve the microstructure and thermal cracking resistance of HSS rolls.

Crystallization properties of RE-doped (RE = Eu, Er, Tm) Zn2TiO4 prepared by the sol–gel method

Samples of pure and rare earth (RE)-doped nanocrystalline Zn2TiO4 (RE=Eu, Er, Tm) have successfully been prepared by the single batch sol–gel method in a form of powders. The powders were annealed up to 1200°C and analyzed by DTA and XRD methods. Sizes of formed nanocrystals were calculated from the Scherer equation and verified by the SEM analysis. Activation energies of crystallization were calculated using the Kissinger, Ozawa and Augis–Bennett approximations and reaction mechanisms were proposed evaluating the Avrami exponents from the Johnson–Mehl–Avrami equation. It has been found that RE elements particularly substitute zinc ions in the crystal lattice and are fully soluble up to 0.5at.% related to the some of cations. Furthermore, the results have shown that the presence of RE elements blocks the crystallite growth and supports the nucleation process leading to the formation of smaller and more uniform nanocrystals compared to the undoped Zn2TiO4.

Microwave Dielectric Ceramics with Rare-Earth (II)

Nearly half of the microwave dielectric materials includes rare-earth elements based on a database presented by Sebastian MT. The presence of rare-earth elements helps to improve the microwave dielectric properties which come from the crystal structure adjusted by the ionic radius of rare-earth. The microwave dielectrics are grouped by the crystal structure: (1) pseudo-tungstenbronze type solid solutions Ba6–3x R 8+2x Ti18O54, (2) homologous compounds Ba n La4Ti3+n O12+3n , (3) green phases Y2BaCu2O5, (4) aeschynite LaYTiO6 and scheelite BaWO4, (5) perovskite-type compounds ABO3, (6) garnet compounds A 3 B′2 B″3O12. The materials group (1)-(2) are presented in “Microwave Dielectric Ceramics with Rare-earth (I)”. In this paper we discuss the groups (3)-(6).

The corrosion behaviour of rare-earth containing magnesium alloys in borate buffer solution

In this work, the corrosion behaviour of magnesium alloys ZK31, EZ33 and WE54 was studied in sodium borate buffer solution at pH 9.2. The electrochemical processes were studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The composition and morphology of the alloys and corrosion products formed were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The experimental findings highlighted the differences in the corrosion mechanisms of the different alloys tested. The results showed that the presence of rare-earth elements (RE) only increases the corrosion resistance when present in solid solution, as is the case of the WE54 alloy. At pH 9.2, an amorphous yttrium oxide/hydroxide thick film was formed, which possesses greater stability when compared to magnesium oxide/hydroxide. The role of RE in the corrosion mechanism was discussed.

Development of the Microstructure and Texture of RE Containing Magnesium Alloys during Hot Rolling

Commercial magnesium alloys such as AZ31 exhibit strong crystallographic textures during massive deformation such as rolling. A randomisation of the texture, however, was found in alloys with rare earth (RE) elements in solid solution. This paper describes the development of microstructure and texture during rolling of the Al-free RE-containing wrought magnesium alloy ZEK100 during hot rolling. This alloy develops a strong texture with a pronounced component towards the transverse direction (TD) of the sheets. This TD component forms already after the first rolling pass, persists through all following passes and is further enhanced by subsequent heat treatment. These results are contrasted with results from a study on texture development of binary RE containing Mg-alloys, which show that the presence of RE elements alone is not responsible for the tilt of basal planes towards the TD. There is, however, a threshold concentration at which the texture begins to weaken.

Effects of La3+, Ce3+ on nitrogen removal in sequencing batch reactor

Batch experiments were conducted to study the short-term biological effects of rare earth ions (La3+, Ce3+) and their mixture on the nitrogen removal in a sequencing batch reactor (SBR). The data showed that higher NH4+-N removal rate, total inorganic nitrogen removal efficiency, and denitrification efficiency were achieved at lower concentrations of rare earth elements (REEs) (<1 mg/L). In the first hour of the aeration stage of SBR, the presence of REEs increased the total inorganic nitrogen removal efficiency and NH4+-N removal efficiency by 15.7% and 10%–15%, respectively. When the concentrations of REEs were higher than 1 mg/L, the total inorganic nitrogen removal efficiency decreased, and nitrate was found to accumulate in the effluent. When the concentrations of REEs was up to 50.0 mg/L, the total inorganic nitrogen removal efficiency was less than 30% of the control efficiency with a high level of nitrate. Lower concentrations of REEs were found to accelerate the nitrogen conversion and removal in SBR.

Determination of RE 2Ce 2O 7 pyrochlore phases from monazite–allanite ores

By using a specific chemical process, it was possible to extract a pyrochlore RE 2Ce 2O 7 phase directly from waste materials composed of allanite–monazite minerals mixed with aluminosilicate and other phosphate phases. The pyrochlore phase is well known for its interesting thermal properties. Monazite (Ce, La, Nd, Pr, Th) PO 4 is a mineral rich in rare earth elements (cerium, lanthanum). Polycrystalline waste samples were submitted to a series of chemical treatments followed by alkaline fusion. After reaction with nitric acid and addition of oxalic acid, soluble ions were separated from insoluble ones, resulting in rare earth oxalate intermediate phases. After filtration, these oxalate phases were dried and heated at 900 °C. The resulting solid was analyzed by transmission electron microscopy and X-ray diffraction. These analyses showed that the as-extracted phase was composed of a complex RE 2 3+Ce 2 4+O 7 2− system, rich in cerium and lanthanum along with other rare earth elements (RE). The mean crystal structure of these complex phases was determined from Rietveld diffraction profile refinement; it was close to pyrochlore structure La 2Ce 2O 7 with space group Fd3m. The refined cell parameter a, and the lattice distortion ɛ, calculated from profile broadening analyses, were related to the presence of RE 3+ ions occupying the La site.

Influence of Rare Earth Elements on Microstructure and Mechanical Properties of Cast High-Speed Steel Rolls

Abstract The influence of rare earth (RE) elements on the solidification process and eutectic transformation and mechanical properties of the high-V type cast, high-speed steel roll was studied. Test materials with different RE additions were prepared on a horizontal centrifugal casting machine. The solidification process, eutectic structure transformation, carbide morphology, and the elements present, were all investigated by means of differential scanning calorimetry (DSC) and scanning electron microscopy energy dispersive spectrometry (SEM-EDS). The energy produced by crack initiation and crack extension was analyzed using a digital impact test machine. It was found that rare earth elements increased the tensile strength of the steel by inducing crystallization of earlier eutectic γ-Fe during the solidification process, which in turn increased the solidification temperature and thinned the dendritic grains. Rare earth elements with large atomic radius changed the lattice parameters of the MC carbide by forming rare earth carbides. This had the effect of dispersing long-pole MC carbides to provide carbide grains, thereby, reducing the formation of the gross carbide and making more V available, to increase the secondary hardening process and improve the hardness level. The presence of rare earth elements in the steel raised the impact toughness by changing the mechanism of MC carbide formation, thereby increasing the crack initiation energy.

Electrochemical behaviour of a magnesium alloy containing rare earth elements

The corrosion of a magnesium alloy containing rare earth elements (WE43 type alloy) was studied in 0.05 and 0.5 M Na2SO4 or 0.1 and 1 M NaCl solutions using electrochemical techniques: linear polarization resistance, potentiodynamic polarization, impedance measurements. The electrolytes favoured anodic magnesium oxidation but the presence of rare earth elements improved the tendency of magnesium to passivation. The dissolution rates in chlorides were higher than in sulphates because chlorides, in contrast to sulphates, interfered with the formation and maintenance of a protective layer of corrosion products which decreased the severity of the attack. The effects of galvanic corrosion due to cathodic intermetallic precipitates at grain boundaries were particularly evident in chloride media at long testing times.

Influence of rare earth elements La, Nd and Yb on the acidity of H-MCM-22 and H-Beta zeolites

The influence of rare earth (RE) elements on the acidic properties of H-MCM-22 and H-Beta was studied by pyridine adsorption followed by infrared spectroscopy (FTIR) and n-heptane cracking, as a model reaction. The zeolites were submitted to ion exchange with rare earth nitrate solutions of La, Nd and Yb. The FTIR spectra of REH-MCM-22 indicate the presence of RE elements inside supercages and in the sinusoidal channels of the zeolite. After pyridine adsorption two additional bands are detected in REH-MCM-22 and REH-Beta, related to pyridine bonded to RE 3+ cations. The n-heptane cracking reaction shows that the effect of rare earth elements is related not only to the acidity but also with the porous structure of both zeolites. In H-Beta zeolite, the presence of RE elements enhances the acidity of the catalysts. In H-MCM-22 zeolite, the most relevant effect of rare earth elements is on the shape selectivity that becomes more pronounced with the ionic radius of the RE elements. The nature of the coke deposited on the two materials shows distinct profiles that are also related to its porous structure.

Defining the mechanisms that disturb the Sm-Nd isotopic systematics of the Martian meteorites: Examples from Dar al Gani 476 and Allan Hills 77005

Microbeam studies of Martian meteorites Dar al Gani (DaG) 476 and Allan Hills (ALH) 77005 have been conducted to identify potential causes of disequilibrium exhibited in their Sm-Nd isotopic systematics. Olivine and maskelynite mineral fractions on the DaG 476 isochron are displaced relative to their positions as dictated by measured mineral compositions. The olivine mineral fractions from ALH 77005 not only have a relatively low Sm/Nd ratio, but appear to contain an unradiogenic component that shifts the olivine mineral fraction off the isochron defined by the pyroxene and maskelynite mineral fractions. Trace components such as melt inclusions, impact melt, high-Si mesostasis, and altered olivine were analyzed using scanning electron microscopy, quantitative electron microscopy, and secondary ion mass spectrometry to determine their potential for disturbing the isotopic systematics of the mineral fractions, assuming that the mineral fractions were not completely pure. Mixing models indicate that the presence of melt inclusions in the DaG 476 olivine mineral fraction lowered its Sm/Nd ratio. The maskelynite mineral fraction contains a related but more evolved mesostasis component that raised the Sm/Nd ratio of the fraction. The position of two olivine mineral fractions below the ALH 77005 isochron is interpreted to reflect small additions of impact melt with a light rare earth element enriched pattern and a non-indigenous, unradiogenic Nd component. Furthermore, the presence of rare earth elements in olivine and maskelynite from both igneous and non-igneous components such as melt inclusions, mesostasis, and impact melt is observed on a fine (<30 μm) scale. Despite the addition of this material, the Sm-Nd ages are not affected. This study demonstrates that detailed mineral separation procedures as employed by modern geochronology laboratories permit reliable ages to be derived from shocked and altered samples.

Rare earth element geochemistry of groundwater in the Palouse Basin, northern Idaho–eastern Washington

Concentrations of rare earth elements (REE) were determined in groundwaters from the Palouse Basin, located in northern Idaho and eastern Washington. Samples were taken from wells and springs tapping waters in four different rock units: loess, Wanapum Basalt, Grande Ronde Basalt, and Moscow Mountain Granite. In general, unfiltered aliquots of the waters had higher concentrations of REE than those filtered through a 0.45 μm filter, sometimes by several orders of magnitude, indicating the presence of REE as suspended particles or large colloids. Overall REE concentrations in the waters decrease, and the unfiltered and filtered aliquots become more similar in concentration, with increasing depth within the stratigraphic section (i.e. loess → Wanapum → Grande Ronde). There are some distinctions in NASC (North American Shale Composite)-normalized REE patterns among the four groups of waters, but there is considerable variation among the waters within each group. When normalized to their host rocks, most filtered and many unfiltered aliquots of groundwaters from all four units show depletion of the LREE relative to the HREE. The results are consistent with a model in which meteoric water enters the basalt aquifers via the loess, picking up a heavy particulate and some dissolved REE load, followed by infiltration downward through the units. While moving downwards, the waters are subjected to natural filtration processes in which the particulate REE are largely removed.

LPE InP layers grown in the presence of rare-earth elements

Preparation and characterisation of InP layers grown by Liquid Phase Epitaxy with the addition of several rare-earth (RE) elements into the growth melt is reported and the influence of Ho, Er, Nd Pr, and Yb is compared. Low-temperature photoluminescence (PL) spectra have been measured for various levels of excitation power and temperature. The major manifestation of the RE admixture is the pronounced narrowing of PL curves and the corresponding appearence of fine spectral features. Particularly in the case of Nd and Pr admixtures the acceptor related PL band exhibits a structure that permits an individual determination of acceptor and donor binding energies. Temperature dependent Hall effect and capacitance–voltage curves also show quite dramatic impact of Pr and Nd on shallow impurity and free-carrier concentrations: they were reduced by as much as three orders of magnitude.

Ytterbium-decreasing Streptomyces sp. and its naphthoquinone-pigment production in the presence of rare-earth elements

We screened for oligotrophic microorganisms capable of decreasing the concentration of ytterbium (Yb), a representative of the heavy rare-earth elements, in a culture medium. From 476 strains of oligotrophic microorganisms (grown on 1 100 diluted nutrient agar) isolated from soil and river water samples, 5 strains capable of reducing the concentration of Yb in diluted nutrient broth containing 5 ppm Yb were selected. Among them, a strain capable of reducing the concentration of all rare-earth elements to a great extent was identified as Streptomyces sp. (strain YB-1). This strain produced redish-purple pigment(s) only in the presence of rare earths, but not in that of other metals. The pigment was extracted with ethyl acetate and purified by a series of column chromatography steps. From the results of structural analysis using ultraviolet or infrared absorption spectrometry and 13C-NMR, the pigment was determined to be a kind of naphthoquinone similar to nanaomycin produced by a Streptomyces sp. These results suggested that rare earths might affect the physiological activity of this strain.

A study on the Deactivation of Usy Zeolites with Different Rare Earth Contents

The deactivation of USY zeolites with different rare earth contents due to the coke formed from n-heptane at 450oC was studied. The results show that the presence of rare earth elements decreases the cracking and coking activities, increasing catalytic stability. However, reaction selectivity was not significantly influenced. The greater the rare earth content, the lower the coking rates and the coke contents. The TPO/DSC profiles suggested that the catalytic effect of the rare earth elements promoted coke oxidation.

AMMONO method of BN, AlN and GaN synthesis and crystal growth.

Microcrystals of BN, AlN and GaN were obtained by the AMMONO method, in which nitridization of metal occurs in supercritical ammonia, at relatively low temperature and pressure conditions (below 550°C and 5 kbar). The reaction rate was regulated by the amount of mineralizers, i.e. alkali metal amides.All crystals obtained by AMMONO method revealed intense and homogenous luminescence. Significant improvement of the optical properties was observed for crystals grown in the presence of Rare Earth elements. For such GaN crystals, helium temperature photoluminescence spectra were dominated by near-band-gap recombination. Exciton lines were extremely narrow, with full-width half-maximum (FWHM) as low as 1 meV. The concentration of uncompensated shallow donors in AMMONO GaN determined by electron paramagnetic resonance measurements was below 5×1015 cm−3.

Some structural aspects of neodymium praseodymium oxalate single crystals grown in hydro silica gels

The mixed crystals of neodymium praseodymium oxalate are grown by the diffusion of a mixture of aqueous solutions of neodymium nitrate and praseodymium nitrate (as an upper reactant) into the set gel embedded with oxalic acid. By varying the concentration (by volume) of rare earth nitrates in the upper reactant, the incorporation of Nd and Pr in the mixed crystals has been studied. Tabular crystals with the well defined hexagonal basal planes are observed in the mixed crystals of varying concentrations. X-ray diffraction patterns of these powdered samples reveal that these mixed crystals are ‘isostructural’, while IR and FTIR spectra establish the presence of oxalate groups. TGA and DSC analyses show the correctness of the chemical formula for the mixed crystals, by the release of water molecules (endothermic) and of CO and CO2 (exothermic), with the rare earth oxides as the stable residue. X-ray fluorescence (XRF) and energy dispersive X-ray analyses (EDAX) establish the presence of heavy rare earth elements qualitatively and to a good extent quantitatively. X-ray photoelectron spectroscopic (XPS) studies confirm the presence of rare earth elements (Nd and Pr) as their respective oxides. The findings of these techniques of characterization are in excellent agreement with the proposed empirical structure for the mixed rare earth oxalates. The implications are discussed.

Role of rare-earth elements on high temperature oxidation behavior of FeCr, NiCr and NiCrAl alloys

The influence of rare-earth elements (REEs) on oxidation behavior of FeCrNi, FeCr and NiCr alloys has been studied and the role of REEs on oxidation behavior of chromia forming alloys discussed. The REEs were (a) applied superficially to Fe-18Cr-8Ni (AISI 304) and Fe-25Cr-20Ni (AISI 310) alloys, and (b) added as alloying additions or as oxide dispersions to Fe-20Cr and Ni-20Cr alloys. Superficial application of rare-earth oxides (REOs) and concentrates of Y and Ce improved the isothermal and cyclic oxidation resistance of the low Cr alloys, but not that of the high Cr alloy. The oxides of Y, Cc, Nd, La, Sm and Gd influenced oxidation resistance in decreasing order. The addition of 0.1 % Ce and Y as well as 1% CeO 2 or Y 2O 3 as dispersoids to FeCr and NiCr alloys improved their oxidation resistance and the alloy with Al and Y was found to be the most resistant. In the presence of Y or Cc (as alloying addition or as oxide on the surface) the oxide formed on the surface was convoluted and fine grained chromia. The increase in oxidation resistance of chromia forming alloys in the presence of REEs is due to changes in the cation diffusion process. This is brought about by segregation of REEs to the grain boundaries of the scale, and consequent variations in ionic defect concentrations.

Determination of trace amounts of gold in the presence of rare earth elements in rock samples from Makhtesh Ramon (Southern Israel), by instrumental epithermal neutron activation analysis

Epithermal neutron activation analysis (ENAA), followed by high resolution gamma-ray spectrometry, was applied to determine trace amounts of Au in the presence of rare earth elements (REE) from vein samples in the basaltic rocks of Makhtesh Ramon, located in southern Israel. The contribution of152Eu (411.1 KeV) to the 411.8 keV peak of198Au was determined using multiple gamma-peak, ratios derived from Eu standards and mixtures of Au and Eu. The concentration of Au was found to be in the range of 10–80 ppb. A group of rare earth elements: La, Eu, Ce, Tb, Sm, Lu, Yb was identified; the concentration of Eu was found to be 0.5 ppm.