Mixed Rare Earth Research Articles

Preparation of crystalline mixed rare earth carbonates by Mg(HCO3)2 precipitation method

In acid treatment technology of Baotou mixed rare earth ore, large quantities of ammonia-nitrogen wastewater are produced in the step of ammonium bicarbonate precipitation to transform rare earth sulfate. In this paper, we adopted a green precipitant magnesium bicarbonate (Mg(HCO3)2) to substitute ammonium bicarbonate to eliminate ammonia-nitrogen pollution. The effects of n(HCO3−):n(RE3+), aging temperature and aging time on the crystallization using Mg(HCO3)2 precipitation method were investigated. The results indicate that the rare earths could be completely recovered when n(HCO3−):n(RE3+) is higher than 3.15:1. The crystal water content of rare earth carbonates is affected by the aging temperature. The precipitate has a bad filterability when the aging temperature is over 40 °C. This can be attributed to the less crystallized water molecules of the hydrated rare earth carbonate precipitation. The mixed rare earth carbonates are prone to be crystalline, and have a good filterability at aging temperatures below 40 °C. Meanwhile, the evolution mechanism of crystalline mixed rare earth carbonates is reasonably deduced, the amorphous rare earth carbonates are first dissolute and then recrystallized. Under the optimized aging conditions, the purity of the crystalline precipitate meets the requirements of the fine product standard (GB/T 16479-2008). The filtrated could be used to produce Mg(HCO3)2, thus to realize the recycling of magnesium sulfate.

Mechanochemical decomposition of mixed rare earth concentrate in the NaOH-CaO-H2O system

This paper describes mechanochemical decomposition of the mixed rare earth concentrate (mixed concentrate) in the NaOH-CaO-H2O system. Phase transformation and effects of NaOH, CaO and time on mechanochemical decomposition of mixed concentrate were investigated. We also studied strengthening mechanism of mechanochemical decomposition by comparing its results with the results obtained by pressurized decomposition. Mixed concentrate first decomposed into RE(OH)3, CaF2 and Ca2P2O7. Then, Rare Earth Elements (REEs) and phosphorus were extracted by HCl, while CaF2 remained in the leach residue. After mechanochemical decomposition, leaching efficiency of REEs, which represented decomposition efficiency of the mixed concentrate, reached 91.8%. At the same time, 93.8% of fluoride and over 99% of phosphorus remained in the decomposition residue when 35% of NaOH and 20% of CaO (relative to mixed concentrate weight) were added and decomposition time was 4 h. Mechanochemical treatment improved concentrate decomposition efficiency from 58.9% of the pressurized decomposition to 91.8%. Such an improvement was attributed to the beneficial effect of the mechanical force, which loosened the surface structure as well as decreased particle size in the decomposition residue.

Simple Preparation of LaPO4:Ce, Tb Phosphors by an Ionic-Liquid-Driven Supported Liquid Membrane System.

In this work, LaPO4:Ce, Tb phosphors were prepared by firing a LaPO4:Ce, Tb precipitate using an ionic-liquid-driven supported liquid membrane system. The entire system consisted of three parts: a mixed rare earth ion supply phase, a phosphate supply phase, and an ionic-liquid-driven supporting liquid membrane phase. This method showed the advantages of a high flux, high efficiency, and more controllable reaction process. The release rate of PO43− from the liquid film under different types of ionic liquid, the ratio of the rare earth ions in the precursor mixture, and the structure, morphology, and photoluminescence properties of LaPO4:Ce, Tb were investigated by inductively coupled plasma-atomic emission spectroscopy, X-ray diffraction, Raman spectra, scanning electron microscopy, and photoluminescence emission spectra methods. The results showed that a pure phase of lanthanum orthophosphate with a monoclinic structure can be formed. Due to differences in the anions in the rare earth supply phase, the prepared phosphors showed micro-spherical (when using rare earth sulfate as the raw material) and nanoscale stone-shape (when using rare earth nitrate as the raw material) morphologies. Moreover, the phosphors prepared by this method had good luminescent properties, reaching a maximum emission intensity under 277 nm excitation with a predominant green emission at 543 nm which corresponded to the 5D4-7F5 transition of Tb3+.

Selective cerium removal by thermal treatment of mixed rare earth oxalates or carbonates obtained from non-purified rare earth sulphate liquor

One of the world́s most abundant of all the rare earth elements (REE) is cerium. It represents about 50 wt% of total REE content in the main rare earth minerals used industrially (monazite and bastnaesite). However, cerium is not a valuable product if compared with the other REE. In the most current pyro-hydrometallurgical processes routes, a high amount of cerium goes to the rare earth liquor, incurring in high operational and capital costs in the solvent extraction step used in the separation of each individual rare earth element. In this context, this study evaluates the use of thermal treatment for rare earth oxalates and carbonates and also hydrochloric acid leaching of calcination products for selective separation of cerium from other REE. This investigation also sheds light on the mechanisms involved in the processes proposed. For this purpose, mixed rare earth and cerium oxalates, also mixed rare earth and cerium carbonates were used as precursors. The mixed rare earth salts used in the experiments were generated from a non-purified rare earth sulphate liquor. The results indicated that the minimum required temperature to fully decompose the mixed rare earth oxalates, cerium oxalate, mixed rare earth carbonates and cerium carbonate to their respective rare earth oxides (REE2O3) or CeO2, was 1100 °C, with 1 h of residence time. In the experiments carried out with mixed rare earth oxalates, Ce3+ was not fully oxidized to Ce4+, it formed a mixture of Ce2O3 and CeO2 represented by Ce4O7, which was completely dissolved in the hydrochloric acid solution (37 wt%). Therefore, in such case, cerium was not selectively removed from the mixed rare earth oxalates by thermal treatment and hydrochloric acid leaching. On the other hand, the Ce3+ presented in the composition of the pure cerium oxalate or carbonate was fully oxidized to Ce4+ (CeO2) under the same condition of calcination. As expected, CeO2 was not dissolved by the hydrochloric acid solution (37 wt%). It was concluded that mixed rare earth carbonates generated Ce0.60Nd0.40O1.80 (Ce1-xNdxO2-x/2, x = 0.40) when calcined under the same condition. This crystalline structure was not also dissolved by hydrochloric acid solution (37 wt%). As a result, a process flowsheet was proposed to remove cerium selectively from a rare earth ore.

Effect of neodymium and lanthanum oxides on alumino phosphate vitreous and devitrified states

Alumino phosphate glasses containing up to 25 mole % of oxides of neodymium and lanthanum have been prepared using the melt quenching method and their devitrified states were obtained using heat treatment. X-ray diffraction, FTIR, Raman and EXAFS were employed to examine the materials both in the vitreous and devitrified states. The density of the glasses is found to be lower by 5% to 10% than that for the corresponding devitrified states depending on the rare-earth inclusion. The network connectivity was found to decrease in the mixed rare earth glass as compared to the glass containing either oxide of Nd or La. Deconvolution of Raman peaks was used to quantify the presence of the Q0, Q1, Q2 and Q3 structural units in the glass samples. The main structural units in both the glasses and devitrified states were found to be the Q1 and Q2 tetrahedral units. For the mixed Nd-La, these units appear as an average of the numbers appearing in the single rare-earth included materials. The main structural vibrations present in the devitrified state are found to have survived in the glassy state. The EXAFS study indicates that the coordination number of oxygen around the rare earth ion increases by about 5% in going from the vitreous to the devitrified state.

Lanthanide substitution effects in iron containing garnets

The main aim of the present work was to fabricate for the first time the mixed rare earth iron garnets by an aqueous sol-gel method and investigate the lanthanide-substitution effect on the crystal structure of garnets. In this study, the mixed-metal iron garnet Sm3−xYbxFe5O12 (x = 0.75, 1.5, 2.25), Dy1.5R1.5Fe5O12 (R = Ho, Er, Tm) and Lu3−xEuxFe5O12 (x = 0.75, 1.5, 2.25) samples were prepared by an aqueous sol-gel method. X-ray diffraction analysis revealed the formation of the single phase mixed rare earth iron garnets. It was demonstrated, that contraction of the crystal lattice appears with the substitution of the bigger rare earth ion with the smaller one on dodecahedral site of mixed rare earth iron garnets.

Grouping separation of mixed rare earths from their coexisting aqueous solutions by liquid-column elution

Abstract A new approach was proposed for grouping separation of 14 lanthanide rare-earth ions from their co-existing mixed aqueous solutions, by performing liquid-column elution using the aqueous solution containing 14 lanthanide rare-earth ions as the stationary phase and the dispersed organic oil droplets containing P507 extractant as the mobile phase. It was revealed that 14 lanthanide rare-earth ions could be separated into four groups, according to the lanthanide tetrad effect, respectively eluting out from the liquid column at different time in a certain order. Various effects including the saponification degree of P507, the concentration of P507 in organic phase, the length and inner diameter of the extraction column on the performance of grouping separation of rare-earth ions were discussed. The changes of the mass transfer coefficients were also investigated. The separation efficiency of the four groups of rare-earth elements (REEs) was evaluated based on the elution resolution, Rs, of the elution peaks of La(III), Gd(III), Ho(III) and Lu(III), the four representative elements respectively from each of the four groups of REEs. Experimental results demonstrated that the separation of REEs by liquid-column elution mainly depended on the competitive adsorption of different rare-earth groups onto the surface of ascending P507 oil droplets. The affinity of different rare-earth groups with P507 extractant and a limited adsorption capacity of P507 molecules at the surface of the oil droplets ascending in liquid column play the important role. The present work highlights a promising technique for grouping separation of multiple lanthanide elements co-existing complex systems.

Effect of Rare Earth Metals on the Properties of Zn-20Sn High-Temperature Lead-Free Solder

Cerium–lanthanum mixed rare earth (RE) (0.5 wt.%) was added to Zn-20Sn high-temperature lead-free solder to study the effect of RE on the solder properties. The Zn-20Sn-0.5RE solder has a better corrosion resistance than that of Zn-20Sn alloy. RE addition increases the γ-Cu5Zn8 layer thickness, promotes growth of a e-CuZn5 layer shaped like bamboo shoots, and increases the roughness of the e-CuZn5 layer, which increases the shear strength of the solder joints. Compared with the Zn-20Sn alloy, the creep resistance of the Zn-20Sn-0.5RE solder was improved after soldering. The indentation hardness increases in an order of Zn-20Sn-0.5RE solder, Zn-20Sn solder, e-CuZn5 layer, and γ-Cu5Zn8 layer.

Decomposition mechanism of a mixed rare earth concentrate with sodium hydroxide in the microwave heating process

In this paper, a novel process is proposed for extracting rare earth elements through intensifying the decomposition of mixed rare earth concentrates by microwave heating. The objective of the present study was to investigate the phase transition mechanism of a mixed rare earth concentrate with sodium hydroxide in a microwave field. To this end, the decomposition and separation efficiencies of the rare earth elements and fluorine were analyzed. The results showed that the decomposition reaction of the tested mixed rare earth concentrate in the microwave irradiation field occurred in three stages. The rare earth elements initially presented in bastnaesite and monazite were gradually converted to rare earth hydroxides (RE(OH)3), rare earth oxides (RE2O3), and composite oxides (Ce0.5Nd0.5O1.75), with fluorine eventually forming sodium fluoride. The decomposition ratio of the mixed concentrate and conversion ratio of the fluoride reached 88.73% and 89.32%, respectively. Furthermore, the decomposition temperature of the mixed concentrate with microwave heating was lower than that required with conventional heating, which indicated that microwave heating could decrease the thermodynamic reaction temperature. The results of the microscopic morphology analysis showed that after microwave heating, the samples exhibited two distinct particle morphologies, which was different from that of a mixed concentrate in any case. The decompositions of bastnaesite, monazite, and fluorite were somewhat non-interfering in nature, and sodium fluoride and calcium phosphate were separated from the rare earth oxides in the decomposition products. These results indicated that the proposed process was conducive to the separation of rare earth elements and fluoride and helpful for improving the efficiency of rare earth leaching.

Microwave strengthens decomposition of mixed rare earth concentrate: Microwave absorption characteristics

The potential application of microwave heating technology for processing the mixed rare earth concentrate was systematically investigated by analyzing the microwave absorption characteristics in this study. The complex permittivity was measured through resonant cavity perturbation method. The variations of permittivity, the loss factor, loss tangent and the penetration depth with the increasing temperature were investigated numerically. The results indicate that the permittivity increases as the temperature increases, and temperature has a pivotal effect on it. The mixed concentrate is high loss material at the temperature range from 600 to 800 °C according to theoretical analyses of loss tangent and penetration depth. The results of phase transition analysis prove that the variation of microwave absorption characteristics of mixed concentrate is caused by the changes of crystal and lattice structures. The reflectivity, loss factor and penetration depth of the mixed concentrate were also calculated, and the results indicate that processing the mixed concentrate by microwave heating is of high feasibility and industrial potential.

Studies on the possibility of determination of uranium and thorium concentration in the Thai monazite ore processing samples using gamma-ray spectrometry technique

The possibility of the determination of U and Th concentration in the Thai monazite ore processing samples using gamma-ray spectrometry technique was investigated. The studied samples were monazite ore, tri-sodium phosphate, mixed rare earth hydroxide, enriched cerium, uranium cake, thorium cake, La2O3 and CeO2. The measured activity concentrations of 238U and 232Th were converted into the concentrations of U and Th under the assumption of secular equilibrium. The results showed that the major daughter nuclides found in the studied samples, were 214Pb 214Bi and 226Ra for 238U series with additional radionuclides of 228Ac, 212Pb, 208Tl and 212Bi for 232Th series. The concentrations of U and Th estimated via each daughter products of their series were not significantly different for all samples. Wavelength Dispersive X-ray Fluorescence (WDXRF) with different sample preparations (loose powder, pressed pellet and fused bead methods) was also used to determine the concentrations of both U and Th in these samples. A good agreement between the concentration of U and Th measured by gamma-ray spectrometry (U = 0.42 wt%, Th = 6.54) and WDXRF prepared by fused bead method (U = 0.41 wt%, Th = 7.37) was observed for monazite ore sample.

Mixed transition and rare earth ion doped borate glass: structural, optical and thermoluminescence study

The present work report on physical, structural, optical and thermoluminescence properties of Dy3+ doped manganese potassium borate glasses. The conventional melt quenching technique is used to prepare the glass samples. The amorphous nature of the prepared glass sample is confirmed by X-ray diffraction study. The different B–O vibrational bands and change in the coordination number of boron (BO3 → BO4) with the inclusion of Dy3+ ions in the prepared glasses were analyzed through FTIR. The physical parameters such as density, molar volume, average molecular weight, ion concentration, polaron radius, internuclear distance and optical parameters have been determined. The optical analysis reveals that the optical band gap energy decreases with the increase of dysprosium oxide concentration. The TL glow curve of gamma irradiated samples showed single prominent peak in the temperature range 425–460 K with varying concentration of Dy2O3. Analysis of kinetic parameters reveals that the glasses demonstrate second order kinetics.

Influence of mixed rare earth elements(Y and Ce) on the microstructure and corrosion behaviour of Mg-4Al-3Ca alloy

Microstructure of Mg-Al-Ca based alloys was studied by using x-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalyzer (EPMA). Corrosion morphologies and corrosion behaviour of the alloys were analysed using static weight loss test, electrochemical characterization and SEM imaging. The results reveal that when adding mixed rare earth (RE) elements (Y and Ce) to Mg-4Al-3Ca alloy, the thick strip shaped (Mg,Al)2Ca phase was refined and the continuity was changed. Granular Al-RE phase was distributed in the matrix. The Mg-4Al-3Ca-0.5RE alloy has the best corrosion resistance, which is attributed to the combination of a good corrosion barrier, a suitable amount of precipitate phases and a small amount of RE elements addition on the purification of the alloy.

Synthesis and Characterization of Mixed Rare Earths Hydroxide Catalyst

This work presents the synthesis and characterization of mixed rare earths hydroxide heterogeneous catalyst. The catalysts were prepared by co-precipitation of mixed rare earths with NaOH at different pH (6, 7 and 12). The prepared catalysts were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDS). The XRF results showed that the catalyst composed of cerium (Ce), neodymium (Nd), lanthanum (La), praseodymium (Pr) and samarium (Sm) being predominant at pH up to 7. Particularly, cerium (Ce) was favorable precipitation at pH 7. This results were confirm by SEM-EDS. The Ce (OH)3 phase was clearly observed for the mixed rare earth catalyst precipitated at pH 7. The XRF, SEM-EDS and XRD results were consistency.

Effect of (La+Yb) addition on the fluidity of an A356.2 aluminum alloy

ABSTRACTThe effect of mixed rare earth (La+ Yb) addition on the fluidity of A356.2 was investigated by fluidity tests, optical microscope (OM), environmental scanning electron microscope (ESEM) with energy diffraction spectrum (EDS) and X-ray diffraction (XRD). Varying amounts of (La+ Yb) addition were tested, 0%，0.3%，0.6%, and 0.9% (wt.%). The fluidity of A356.2 was improved with the addition of mixed rare earth (La+ Yb). The fluidity length of the A356.2 + 0.6% (La+ Yb) alloy (670mm) was increased by 19% compared to that of A356.2 (565mm). The fluidity of the alloy was related to the morphology of α-Al and Al8Si6Mg3Fe（Fe phase）in the alloy. A refined microstructure of the alloy corresponded with better fluidity. A higher pouring temperature also improved fluidity. However, this trend declined when the pouring temperature increased above 730°C.

Application of a functionalized ionic liquid extractant tributylmethylammonium dibutyldiglycolamate ([A336][BDGA]) in light rare earth extraction and separation.

A type of functionalized ionic liquid extractant, tributylmethylammonium dibutyldiglycolamate ([A336][BDGA]), was synthesized, and its extraction ability of light rare earth elements, namely, La(III), Ce(III), Pr(III) and Nd(III), wascompared with that of other functionalized ionic liquid extractants, including tributylmethylammonium dioctyldiglycolamate and diglycolic amide extractants N,N,N,N-tetrabutyl-3-oxapentane-diamide (TBDGA) and N,N,N,N-tetraoctyl-3-oxapentane-diamide (TODGA). The study of extraction behavior indicated that the ionic liquids exhibited better extraction properties than the amides under lower acidity conditions. The effects of the pH and concentration of the extractant on the extraction behavior of [A336][BDGA] on light rare earths were determined. A separation strategy of mixed light rare earths was investigated by means of extraction chromatography using [A336][BDGA] as the stationary phase. As a result, nearly pure La(III), Ce(III), Pr(III) and Nd(III) were obtained, respectively. A new strategy of separating mixed light rare earths was established by means of extraction chromatography. The stationary phase of [A336][BDGA] was used in this strategy. The four rare earths elements, La(III), Ce(III), Pr(III) and Nd(III), achieved baseline separation.

Kinetics of nitric acid leaching of cerium from oxidation roasted Baotou mixed rare earth concentrate

The kinetics of nitric acid leaching of cerium was investigated for the oxidation roasted Baotou mixed rare earth concentrate. The effects of leaching temperature, HNO3 concentration, liquid–solid ratio (L/S) and stirring rate on rare earth extraction were studied. The XRD and SEM mapping analysis of the samples before and after acid leaching shows that the roasted bastnaesite is completely leached. Besides, the decomposition process of oxidizing roasting was also obtained by TG–MS and XRD. Different kinetics models were applied in this leaching process. The results of dynamic fitting show that the leaching process can be described by a new variant of the shrinking-core model. And the leaching rate is controlled by both the interfacial transfer and diffusion through the product layer. The apparent activation energy is calculated as 76.78 kJ/mol and the reaction orders with respect to HNO3 concentrations and liquid–solid ratio are determined to be 7.609 and 2.516, respectively. Besides, an empirical rate equation is obtained to describe the process.

Recovery of rare earths from nitric acid leach solutions of phosphate ores using solvent extraction with a new amide extractant (TODGA)

The rare earths in phosphate ores are not effectively utilized and they cannot be directly extracted from leach liquor with the traditional extractants, such as organic phosphoric acid. This paper presents a new solvent extraction method for rare earths from nitric acid leaching of phosphate rock using N,N,N′,N′-tetraoctyl diglycol amide (TODGA) without interfering with the normal route for fertilizer production. When the concentration of extractant increased to 0.1 mol/L, the extraction rate of lanthanum, cerium, praseodymium, and neodymium have been found to be 98.1%, 99.1%, 98.8% and 98.6%, respectively. The recovery rate reached to 99.9% when a three-stage countercurrent extraction was carried out on the simulated leach solution. There was almost no extraction of other impurity ions and the rare earths could be separated with TODGA from Ca2+, PO43−, Fe3+, and Mg2+. The presence of phosphoric acid in solution enhanced the extraction of rare earth ions. The stripping of the loaded rare earth in the organic phase was readily carried out with water under room temperature with high efficiency. The mixed rare earth oxides (REO) with an assay of >95% could be recovered as a final product.

Luminescence and low temperature trap centers in mixed rare earth borate crystal

The single crystal of this compound has been grown from melt by using a conventional Czochralski technique. The temperature dependent luminescence spectra were measured using a 265 nm laser as an exciting source in the range of 10–300 K. The scintillation decay time profile was measured and found to have three components. The influence of the trap centers on the luminescence properties was studied by means of thermoluminescence (TL) glow peak analysis. Low temperature TL glow peaks were measured in the temperature range of 10–300 K at the heating rate of 0.1 K/s for X-ray irradiated sample. The TL glow peak consists of two dominant peaks at 88 and 109 K. Several glow peaks with a complex nature causes the decrease in the light yield at temperatures below 250 K, and along with long scintillation decay components were observed. The trap parameters such as activation energy (E), frequency factor (s) and order of kinetics (b) were calculated using various standard methods such as peak shape (PS), variable heating rate (VHR), initial rise (IR) and computerized glow curve deconvolution (CGCD).

‘Trade-Off’ Photoluminescent Behavior of Eu3+ Ions in (EuxGd1−x)2(C2O4)3(H2O)6 Molecular Alloys

A series of molecular alloy based on rare earth (RE) oxalate (EuxGd1−x)2(C2O4)3(H2O)6 (abbr. as EuxGd1−x-OX, x = 0.1–0.9) were synthesized using hydrothermal reaction. The PXRD profiles of EuxGd1−x-OX (x = 0.1–0.9) match well with the simulated pattern calculated from the single crystal data of Nd2(C2O4)3(H2O)6 reported previously, indicating that the as-prepared molecular alloys are isomorphic to Nd2(C2O4)3(H2O)6. EDS and ICP measurements proved the coexistence of Eu and Gd elements in this series of alloys. The photoluminescent (PL) behaviors of EuxGd1−x-OX (x = 0.1–0.9) as well as the physical mixed RE oxalates solids were carefully studied. It is found that the PL intensity of EuxGd1−x-OX with small amount of Gd3+ ion is obviously enhanced due to reducing dipole–dipole, dipole–quadrupole or quadrupole–quadrupole interaction between emitters of Eu3+ ions as well as energy transfer from Gd3+ ion to Eu3+ ion. This study demonstrates that forming molecular alloy by introducing proper ion is an efficient strategy to get improved PL materials.