Rare Earth Mixtures Research Articles

Separation of rare earths by split-anion extraction

Split-anion extraction is a new approach to the separation of mixtures of rare earths by solvent extraction. The rare-earth ions are extracted from a concentrated chloride aqueous phase to an organic phase, consisting of a water-immiscible thiocyanate or nitrate ionic liquid. This allows for efficient extraction of trivalent rare-earth ions from a chloride aqueous phase, without the need of using acidic extractants. The process is called split-anion extraction because the aqueous and organic phases contain different anions. Thiocyanate and nitrate anions have a strong affinity for the organic phase, while chloride anions have a strong affinity for the aqueous phase. In split-anion extraction, the source of complexing anions is the organic phase which allows for the use of chloride aqueous feed solutions and easy stripping of the rare-earth ions from the loaded ionic liquid phase by water (instead of strong inorganic acids). The principle of the new extraction approach is described in detail for the extraction of rare earths from aqueous chloride solutions by the ionic liquids tricaprylmethylammonium thiocyanate and trihexyl(tetradecyl)phosphonium thiocyanate. Rare-earth and chloride concentrations can be varied to optimize the separation process. Separation factors between the end members of the lanthanide series (La–Lu) exceed the value of 200,000.

Fluoride Technology of Processing Oxides of Rare Earth Elements

The paper describes the advantages and characteristics of the fluoride technology applicable for the recovery of oxides of rare earth elements with the help of a fluorinating agent of elemental fluorine. A metallurgical mixture (2.5 m2/g) of rare earth elements oxides of the cerium subgroup, containing % wt.: CeO2 - 50-55; La2 O3 - 23-25; Pr6O11 - 6-9, and Nd2O3 - 13-16 were studied. It has been shown, that using fluoride technology allows recovering mixture of rare earth elements with outlet no less than 98.9 %.

Fluorination of Rare Earth, Thorium and Uranium Oxides and Phosphates from Monazite: A Theoretical Approach

Monazite is a light rare earth phosphate which is difficult to process when using conventional chemical processes. It is considered to be one of the most important commercial sources of thorium and lanthanides. Using conventional chemicals to process monazite have caused severe environmental damage as has been demonstrated in the Baotou region, China. Monazite is found in combination with other minerals in nature such as bastnaesite and xenotime. The conventional techniques and chemicals used for the processing of monazite are expensive. In order to address this issue, South Africa would like to beneficiate monazite as part of its mineral beneficiation strategy. Doing so competitively would require a new cheaper and more environmentally friendlier process. A new method for the processing of monazite is currently being investigated. It is proposed to feed the monazite is fed into a plasma reactor to crack it. Potentially the cracking will allow the monazite to be more reactive and susceptible to react with less harsh chemicals. The plasma treated monazite is reacted with a fluorinating compound such as ammonium bifluoride. Ammonium bifluoride is used rather than fluorine or hydrogen fluoride as it is less dangerous to handle. The fluorinated rare earth mixture can now be separated using various methods.

Liquid-liquid solvent extraction of rare earths: a crystallographic analysis.

Liquid-liquid solvent extraction has become the primary research topic for separating mixtures of rare-earths. [1] Current research on this topic focuses on extraction processes involving ionic liquids as basic extracting agents. In the aqueous phase, the rare-earth is coordinated by the anionic entities of the ionic liquid, forming an anionic complex. The large organic cation of the ionic liquid neutralizes the complex (ion-pair complex) and migrates the entity to an organic phase. The choice of these agents is solely based on the calculation of thermodynamical extraction parameters, whilst structural information about these compounds is rare or even non-existent. Our research focuses on obtaining structural information via crystallography on the above-mentioned molecules and relating the interactions between anion and cation to the stability of the complexes. A difference in stability between the anionic complex and cation can give a different extractability. Different rare-earth chloride salts were dissolved in an aqueous phase, containing ionic liquids with β-diketonate anions and 1-alkyl-3-methylimidazolium cations. After the extraction, crystals of the formed compounds are grown from the organic phase and measured. Current results show us that an intermolecular non-classical C-H ... O hydrogen bond is persistent across the different molecules, whilst small interactions between the cation side chain and halogens on the β-diketonate add extra stability to the crystal structure. Structures formed with 2-thenolytrifluoroactylacetonate anions have no intention to form side chain interactions, leaving the alkyl chain of the 1-alkyl-3-methylimidazolium in a void, whilst structures formed with hexafluoroacetylactonate have strong side chain interactions, which leads to a better packing. The different solubility of both compounds can be related to the different interactions and stability in the crystal structure.

Experimental Study on Catalytic Reduction of SO<sub>2</sub> by Rare Earth Compound

Compared with a great deal of traditional desulphurization crafts, the catalytic reduction of SO2 with CO to elemental sulfur is considered to be the best technology for the removal of SO2 from flue gas. Adding rare earth oxide CeO2 with variable valences to La2O3 formed a mixture of rare earth oxides. By means of dipping CeO2, La2O3 and their mixture, whose carriers are allγ-Al2O3, are used as the catalyst for the reduction of SO2 by CO. The activation process of this catalyst without O2 was investigated. The result shows that the rare earth oxide mixture composing of CeO2 and La2O3, as the catalyst for the reduction of SO2 by CO, can remove SO2 mostly without O2.

Cellular response to rare earth mixtures (La and Gd) as components of degradable Mg alloys for medical applications

Rare earth (RE) elements have been proposed to improve the corrosion resistance of degradable Mg alloys for medical applications. However, good biocompatibility of the elements released by Mg alloys during degradation is essential for their use in implants. Most studies are focused on material science and engineering aspects, but the effects of ions released at the biological interface are not frequently addressed. The aim of this study was to contribute to the knowledge of in vitro toxicological effects of two RE Mg-alloying elements, La and Gd, as individual ions and in mixtures with and without Mg ions. Different combinations (Mg+Gd, Mg+La, and Mg+Gd+La) were used to evaluate their possible synergistic effects on CHO-K1 cells. Two sets of experiments were designed to assess (1) the cyto-genotoxic effect of La and Gd ions by neutral red (NR) technique, Reduction of tetrazolium salt (MTT), Viability with Acridine Orange staining, Clonogenic test, and Comet assay; and, (2) the possible synergistic toxicological effect of La and Gd ions in mixtures, and the influence of osmolarity increase on cellular response. Cytotoxic effects of RE were found at concentrations ≥200μM RE while DNA damage was detected for doses ≥1500μM and ≥1600μM for La and Gd, respectively. When mixtures of ions were evaluated, neither synergistic cytotoxic effects nor biological damage related to osmolarity increase were detected.

Effect of Rare Earth Elements on Feed Digestibility, Rumen Fermentation, and Purine Derivatives in Sheep

The experiment was conducted to evaluate the effect of rare earth elements (REE) on feed digestibility, rumen fermentation, and urinary purine derivatives (PDs) in sheep. Eight sheep (44.58±2.9 kg of body weight) fitted with ruminal cannulas were used in a replicated 4×4 Latin square design 20-day experiment. Sheep were fed a basal diet containing 100, 200 and 300 mg REE-citrate per kg dry matter (DM). Mixture of REE mainly consisted of cerium (56.8%), lanthanum (35.0%) and praseodymium (6.5%). Ruminal pH value was linearly (P<0.01) and quadratically (P<0.01) decreased, and ammonia N concentration (9.73 to 11.83 mg/100 mL) was quadratically (P<0.05) decreased, whereas total volatile fatty acids concentration was linearly increased with increasing REE supplementation (P<0.05). The ratio of acetate to propionate was linearly (P<0.01) and quadratically (P<0.01) decreased due to increase of propionate concentration (P<0.05). In situ ruminal neutral detergent fibre (aNDF) degradation of Leymus chinensis was improved (P<0.01), but the in situ ruminal crude protein (CP) degradation of soybean meal was decreased by feeding REE (P<0.01). Moreover, digestibility of DM, organic matter, aNDF, acid detergent fibre and CP in the total tract and urinary excretion of PD were also linearly (P<0.01) and quadratically (P<0.01) increased with increasing REE addition. In conclusion, supplementation of the basal diet with REE improved rumen fermentation and feed digestion in sheep. It was suggested that REE stimulated rumen microbial activity, digestive microorganisms or enzyme activity in a dose-dependent manner. The optimum supplemental dose of REE was about 200 mg/kg dietary DM in sheep.

Adsorption and chromatographic separation of rare earths with EDTA- and DTPA-functionalized chitosan biopolymers

Dysprosium is enriched in comparison with neodymium at low pH values on EDTA- and DTPA-functionalized chitosan. The observed differences in selectivity are used to separate mixtures of rare earths by column chromatography.

Adsorption performance of functionalized chitosan–silica hybrid materials toward rare earths

Functionalized chitosan–silica hybrid materials were synthesized, characterized and used for adsorption of rare-earth ions. These adsorbents can be used for the separation of mixtures of rare-earths.

Stability of Thermally Processed LaNi&lt;sub&gt;5&lt;/sub&gt;-Based Alloys for Hydrogen Storage

Hydrogen-absorbing compounds of AB5-type are widely studied in view of their application not only as anode material in fuel cells but also in high-energy Ni-MH cells. Within this work nanocrystalline MmNi3.55Al0.3Mn0.4Co0.75 compounds, where Mm is La–rich mixture of rare earth elements, synthesized by High-Energy Ball Milling (HEBM) of arc-melted alloy and AB5-type alloy/carbon composites prepared by CVD method were studied. As the compounds subjected to high temperature during preparation their thermal stability has been established after annealing at various temperatures. X-ray phase analysis has unambiguously proven that over 400°C single-phase MmNi3.55Al0.3Mn0.4Co0.75 starts to decompose into a multi-phase mixture with Ni-based solid solution as a main phase. Similar behaviour has been observed for composite material. Moreover, carbon distribution on surface of alloy particles is inhomogeneous as seen in microanalysis. Nevertheless, a substantial increase of hydrogen capacity has been observed for composite material in comparison with pure intermetallic compound, when used as anode material in direct borohydride fuel cell (DBFC).

Studies on selection of solvent extractant system for the separation of trivalent Sm, Gd, Dy and Y from chloride solutions

In this paper, solvent extraction of mixture of rare-earths (Sm(III), Gd(III), Dy(III) and Y(III)) from chloride solutions using acidic, neutral and basic type extractants and their mixtures has been investigated. The main objective of the work was to select a suitable solvent extractant system for the separation of mixture of rare-earths using organophosphoric acid (TOPS 99), phosphonic acid (PC 88A), phosphinic acid (CYANEX® 272), monothiophosphinic acid (CYANEX® 302), phosphine oxide (CYANEX® 923, CYANEX® 921) and amine based (ALAMINE® 336, ALIQUAT™ 336) extractants. The composition of the synthetic mixture of rare-earths was Sm — 1.835g/L, Gd — 0.862g/L, Dy — 0.303g/L, Y — 0.589g/L which was prepared according to the leach liquor of the Korean domestic ore. From the effect of aqueous phase acidity and extractant concentration on the extraction efficiency of rare-earths, PC 88A (0.1mol/L) considered as better extractant with high separation factor for Dy–Y pair with Sm–Gd pair. Mixture of extractants has shown no significant effect on the separation factors of rare-earths than individual extractants.

Depth-Sensing Indentation on REBa2Cu3O7−δ Single Crystals Obtained from Xenotime Mineral

A natural mixture of heavy rare earths oxides extracted from xenotime mineral have been used to prepare large single crystals of high-temperature REBa2Cu3O(7-\delta) superconductor grown using the CuO-BaO self-flux method. Its mechanical properties along the ab-plane were characterized using instrumented indentation. Hardness and elastic modulus were obtained by the Oliver and Pharr method and corresponds to 7.4 \pm 0.2 GPa and in range 135-175 GPa at small depths, respectively. Increasing the load promotes the nucleation of lateral cracks that causes a decrease in hardness and the measured elastic modulus by instrumented indentation at higher loads. The indentation fracture toughness was estimated by measuring the radial crack length from cube-corner indentations at various loads and was 0.8 \pm 0.2 MPa.m1/2. The observed slip systems of REBa2Cu3O(7-\delta) single crystals were [100](001) and [010](001), the same as for YBa2Cu3O(7-\delta) single crystals. The initial stages of deformation and fracture in the indentation process were investigated. The hardness and elastic modulus were not strongly modified by the crystallographic orientation in the ab-plane. This was interpreted in terms of the resolved shear stresses in the active slip systems. Evidence of cracking along the {100} and {110} planes on the ab-plane was observed. As a conclusion, the mechanical properties of REBa2Cu3O(7-\delta) single crystals prepared from xenotime are equivalent to those of YBa2Cu3O(7-\delta) single crystals produced by conventional rare earths oxides.

Effect of Ca and Rare Earths on Compressive Creep Behavior of Mg-4Al Alloy

The effect of Ca and rare earths on compressive creep behavior of Mg-4Al alloy was investigated with a special apparatus. The microstructures were analyzed by OM, XRD, SEM and EDS before and after compressive creep test. The results reveal that a small amount of Ca was added into AE41 alloy in order to refine the crystalline structure and improve the creep resistance. Comparing with NdPr rare earths alloy, the creep resistance of LPC rare earths alloy decreases, but is still better than AE41 alloy. The as-cast microstructure of AE41 alloy is mainly composed of α-Mg matrix and Al11Nd3 phase. The acicular Al11Nd3 phase is prone to decompose at high temperature, which leads to the poor creep resistance of AE41 alloy. The acicular Al11RE3 phase is gradually replaced by Al2Ca and Al2RE with Ca addition into AE41. LPC rare-earth mixture is in cluster at grain boundaries so that the creep resistance is worse than that of alloy containing NdPr rare-earth mixture.

Electrochemical effect of carbon nanospheres on an AB5 alloy

In this paper, the effect of the addition of carbon nanospheres (CNE) by high energy mechanical milling to the active material of the negative electrode of a Nickel–Metal Hydride (Ni–MH) battery is studied. The hydrogen storage alloy (MH) is an AB5-type (Lm0.95Ni3.8Co0.3Mn0.3Al0.4), where Lm is a mixture of rare earths, and it was prepared by melting the constituent elements in an electric induction furnace. The CNE were synthesized by two-stage polymerization of furfuryl alcohol, drying and carbonization, and were subsequently doped with different proportions of Ni (0–20%) by the method of wet impregnation with Nickel nitrate hexahydrate. The behavior of electrochemical cells consisting of a working electrode with 45% of MH, 5% of CNE pure and doped with different proportions of Ni and 50% carbon Teflon acting as electrical and mechanical support, a counter electrode of Ni mesh, and a reference electrode Hg/HgO was studied. The experiments covered electrochemical activation and cycle stability, rate capability and electrochemical impedance spectroscopy. The results show that the addition of CNE improves the electrochemical performance, and particularly the CNEs pure and doped with 20% of Ni present the best electrochemical performance in discharge capacity, rate capability and impedance spectroscopy.

Solvent extraction and separation of rare-earths from phosphoric acid solutions with TOPS 99

TOPS 99, an equivalent to di-2-ethylhexyl phosphoric acid has been employed for the solvent extraction and separation of a mixture of rare-earths (four light rare-earths (LREs) La, Ce, Pr, Nd, and seven heavy rare-earths (HREs) like Tb, Dy, Y, Ho, Er, Yb and Lu) into some fractions from phosphoric acid solutions. From the acid and extractant effects, 0.1 and 1M TOPS 99 were suitable for the separation of a mixture of REs into three concentrates at 3M acid, which is similar to wet phosphoric acid solutions (WPA). McCabe–Thiele extraction isotherm predicts the separation of Yb+Lu at an aqueous-to-organic (A/O) phase ratio of 2 in three stages using 0.1M TOPS 99. Counter-current batch extraction simulation (CCES) of Yb and Lu at an A/O of 2 resulted in a raffinate containing 3.6mg/L of Yb+Lu, corresponding to an extraction efficiency of 91.9%, whereas other five HREs loss was about 6.7%. Stripping of Yb and Lu as per the predictions of McCabe–Thiele plot from loaded organic (LO) was selected at O/A phase ratio of 3 with 4M HCl and counter-current stripping simulation studies resulted 100% stripping efficiency. From the Yb+Lu raffinate, remaining five HREs were extracted about 94.4% with 1M TOPS 99 at an A/O ratio of 3 in three stages. The LRE (Pr and Nd) co extraction is 9.8%. Quantitative stripping of HREs from LO is achieved with 7M HCl at an O/A ratio of 3 in two stages. Finally, a process flowsheet was presented for the separation of rare-earths into three groups, two HRE fractions (Yb+Lu and Tb, Dy, Ho, Y, Er) and one LRE fraction from 3M phosphoric acid.

Complexation and Spectrophotometric Study of Samarium(III) Using Pyrimidine Azo Derivatives in the Presence of Cetyltrimethyl Ammonium Bromide

The complexation of samarium(III) using 5-(2′-bromophenylazo)-6-hydroxy pyrimidine-2,4-dione (Ra), 5-(4′-chlorophenylazo)-6-hydroxypyrimidine-2,4-dione (Rb), and 5-(2′,4′-dimethylphenylazo)-6-hydroxypyrimidine-2,4-dione (Rc) was studied in the presence and absence of cetyltrimethyl ammonium bromide (CTMAB). Binary Sm-R2 and ion associate (Sm-R2)–(CTMAB) complexes were formed at pH 7.2, 7.7, and 8.2 and showed an absorption maxima at 577, 610, and 597 nm in the absence and 595, 625, and 613 nm in the presence of CTMAB, respectively. The stability constant and the stoichiometric ratio of the formed complexes were also calculated. The ion associate complex formation was completed spontaneously and the resulting complexes were stable for at least 12 h. Under the optimum experimental conditions employed, the molar absorptivity, Sandell sensitivity, optimum concentration ranges, detection, and quantitation limits were calculated. Interfering species of different anions and cations have been studied. The precision and recovery for the developed procedures are both satisfactory. The proposed procedure is successfully applied to determine samarium in standard samples of rare earth mixture, synthetic, and monazite samples.

The persistence of the magnetocaloric effect in (La1−xAx)0.67Ba0.33Mn1.05O3−δ

Polycrystalline samples of (La1−xAx)0.67Ba0.33Mn1.05O3−δ, with A being a mixture of lanthanides containing 66% La, 22% Nd, 8% Pr, and 4% Ce, were prepared by the glycine-nitrate method, with target compositions of x=0, 0.33, 0.67, and 1. The effect of the mixture of lanthanides on the Curie temperature, TC, and the magnetocaloric properties was investigated. The prepared samples are single phase, with space group R3¯c. The lattice parameters and average A-site ionic radius, rA decrease linearly with x while the size disorder, as characterized by the variance, σ2, increases from 0.014 to 0.017 with x. As x is increased, the increase in σ2 drives a linear decrease in TC. The magnetic entropy change, ΔSM, for a field change of 1 T is obtained by magnetization measurements, giving a maximum value of 1.7 J/kg K, and a relative cooling power of 43 J/kg, independent of x. These results suggest that replacing lanthanum with a mixture of lanthanides is a realistic way to tune the working temperature of magnetocaloric manganites while maintaining a constant magnetocaloric effect.

Effect of Rare Earth La&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; on Digestive System of the Red-Eared Slider

Numerous studies reported that mixtures of Rare Earth Elements (REEs) could produce quite sensational growth-promoting effects in all categories of farm animals; but many people thought that REEs could affect human healthy. Therefore, experiments were done to understand the effects of La2O3 on red-eared sliders. The results showed that lower dose of La2O3 could probably improve the metabolism of Red-eared Slide turtle, and the higher dose of La2O3 could probably cause pathologic reaction. Lanthanum trichloride (La) could cause the Histological changes in tortoise livers. A very lower dosage of La2O3 could damage the livers of red-eared slides obviously though diversity pathway. The wild animal should be protected from harm in the RE diggings. If the RE is used or must be used as an additives in animal foods, an appropriate dose of RE was necessary, and the safety evaluation should be done.

An investigation of rare earth chloride mixtures: combinatorial optimisation for AA2024‐t3 corrosion inhibition

AbstractRare earth (lanthanides) cations have demonstrated exceptional activity as cathodic corrosion inhibitors for aluminium alloys (AAs). While Ce is generally regarded as the most active, there have been reports of synergistic interactions between mixtures of rare earths, which show increased inhibitive activity. In this study a combinatorial experimental approach was used to evaluate the corrosion inhibition of four rare earth chlorides (Ce, La, Pr, Nd) singly and as mixtures. The estimation of corrosion currents using both potentiodynamic scans and electrochemical impedance spectroscopy (EIS) provided the quantification of corrosion inhibition. The results were then modelled to determine the best predicted inhibition activity. A partial least squares (PLS) regression indicated that the optimal response directly correlated with the amount of Ce present. From the regression analysis, Ce alone demonstrated the best inhibition activity, with the optimum mixture predicted to contain 100% Ce. The addition of La, Pr or Nd, was not observed to improve the inhibition activity. This study represents one of the first applications of combinatorial design to a fundamental question of corrosion inhibition. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Hydrometallurgical separation of rare earth elements, cobalt and nickel from spent nickel–metal–hydride batteries

The separation of rare earth elements, cobalt and nickel from NiMH battery residues is evaluated in this paper. Analysis of the internal content of the NiMH batteries shows that nickel is the main metal present in the residue (around 50% in weight), as well as potassium (2.2–10.9%), cobalt (5.1–5.5%), rare earth elements (15.3–29.0%) and cadmium (2.8%). The presence of cadmium reveals that some Ni–Cd batteries are possibly labeled as NiMH ones. The leaching of nickel and cobalt from the NiMH battery powder with sulfuric acid is efficient; operating variables temperature and concentration of H 2O 2 has no significant effect for the conditions studied. A mixture of rare earth elements is separated by precipitation with NaOH. Finally, solvent extraction with D2EHPA (di-2-ethylhexyl phosphoric acid) followed by Cyanex 272 (bis-2,4,4-trimethylpentyl phosphinic acid) can separate cadmium, cobalt and nickel from the leach liquor. The effect of the main operating variables of both leaching and solvent extraction steps are discussed aiming to maximize metal separation for recycling purposes.