REE Recovery Research Articles

A Method of Producing Al–REE Master Alloys Using Exchange Reduction Reaction

Modern aerospace engineering relies on Al-based alloys with enhanced high-temperature strength properties and oxidation resistance. These requirements can be fulfilled by modifying alloys’ structure employing rare earths metal doping. Direct addition of metallic rare earths to aluminium is complicated due to high chemical activity of molten rare-earth metals and significant vapor pressure of aluminium at elevated temperatures. To overcome these drawbacks, lanthanide-containing master alloys with relatively low REE content can be employed instead of pure scandium.Currently there are three methods for preparing aluminium-based alloys containing rare earths, i.e. direct fusing, molten salt electrolysis and exchange or metallothermic reduction reactions. In the last case, Al–Gd and Al–Sc master alloy can be prepared by aluminothermic reduction of GdF3 or ScF3 in a molten binary NaF–KCl salt mixture at 800–1050 °С.In the present work we suggest the modification of the above mentioned method for aluminium–cerium and aluminium–neodymium master alloy production with a lanthanide concentration of 1 to 7 wt. %. Based on thermodynamic calculations we proposed that the high-temperature exchange reaction between metallic aluminum and corresponding fluoride containing salt electrolyte should be carried out at temperatures from 740 to 780 ° C to provide the higher recovery of REE. The influence of the time of the exchange reaction and «aluminium–salt» ratio on the process to obtain ligatures of various compositions is analyzed. The yield higher than 85 % is achieved.The microstructure of the alloys represents a metal matrix of aluminum in which intermetallic compounds of Ln3Al11 compositions are distributed In the case of an exchange reaction between aluminum and cerium fluoride, the formation of a new phase, presumably related to the Al4Ce intermetallic compound, is found.

Effects of contaminant metal ions on precipitation recovery of rare earth elements using oxalic acid

Solution equilibrium calculations were performed in this study to understand the impact of contaminant metal ions on the precipitation efficiency of selected rare earth elements (Ce3+, Nd3+, and Y3+) using oxalic acid as a precipitant. Trivalent metal ions, Al3+ and Fe3+, are found to considerably affect the precipitation efficiency of REEs. When Al3+ and Fe3+ concentrations are increased by 1 × 10−4 mol/L, in order to achieve an acceptable cerium recovery of 93% from solutions containing 1 × 10−4 mol/L Ce3+, oxalate dosage needs to increase by 1.2 × 10−4 and 1.68 × 10−4 mol/L, respectively. Such great impacts on the required oxalate dosage are also observed for Nd3+ and Y3+, which indicates that oxalic acid consumption and cost will be largely increased when the trivalent metal ions exist in REE-concentrated solutions. Effects of the divalent metal ions on the oxalate dosage are minimal. Furthermore, solution equilibrium calculation results show that the precipitation of Fe3+ and Ca2+ (e.g., hematite and Ca(C2O4)∙H2O(s)) likely occurs during the oxalate precipitation of REEs at relatively high pH (e.g., pH 2.5), which will reduce rare earth oxalate product purity. In addition to the metal ions, anionic species, especially SO42−, are also found to negatively affect the precipitation recovery of REEs. For example, when 0.1 mol/L SO42− occurs in a solution containing 1 × 10−4 mol/L Ce3+ and 4 × 10−4 mol/L oxalate, the pH needs to be elevated from 2.0 to 3.3 to achieve the acceptable recovery. Overall, findings from this study provide guidance for the obtainment of high-purity rare earth products from solutions containing a considerable amount of contaminant metal ions by means of oxalic acid precipitation.

Thermodynamic and application study of complicated extraction system Ce(IV)–HF–H3BO3–H2SO4 using Cyanex 923

This article aims to reduce the environmental pollution while maximizing the recovery of REEs as well as associate resource-fluorine (F) from bastnaesite. This paper investigates the extraction equilibrium process and mechanism of Ce(IV)–HF–H3BO3–H2SO4 system using Cyanex 923. Extraction equilibrium process of different systems, including HF–H2SO4, H3BO3–HF–H2SO4, and Ce(IV)–HF–H2SO4, were studied in detail and the corresponding extraction mechanisms were also determined. It is noteworthy that a synergistic effect between B–F and an antagonistic effect between Ce(IV)–F were discovered first in the extraction process by Cyanex 923. Besides, H3BO3 is found to be able to promote the extraction of F in quantitation by Cyanex 923. FTIR and 11B and 19F NMR were adopted to characterize the different loaded organic phase. Based on these results, the extraction mechanism of complicated system Ce(IV)-HF-H3BO3–H2SO4 was further determined. Besides, the effect of H3BO3 on the extraction and stripping of Ce(IV) in complicated system was studied. Moreover, it shows that the addition of H3BO3 has nothing to do with the purity of obtained CeF3 particle from bastneasite liquor in the practical system. Adding H3BO3 into bastnaesite leach liquor, on the one hand, will be beneficial for the recovery yield of Ce and F. On the other hand, it can avoid from environmental pollution caused by emission of F-containing waste water as well as reducing the waste residue.

Accumulation of dysprosium, samarium, terbium, lanthanum, neodymium and ytterbium by Arthrospira platensis and their effects on biomass biochemical composition

The growth of Arthrospira platensis and physiological changes in biomass under the effects of six rare earth elements Dy, Sm, Tb, La, Nd and Yb were evaluated. Elements were tested by three concentrations of 10, 20 and 30 mg/L. According to neutron activation analysis data A. platensis's accumulation capacity toward studied elements changes in the following order of La > Dy > Nd > Sm > Yb > Tb. The results show that Dy and La ions stimulate biomass growth and Yb ions inhibit it, while Sm, Tb and Nd ions do not affect biomass accumulation. The contents of proteins and chlorophyll a are not affected by the presence of rare earth elements in the cultivation medium. Studied elements affect to different extents carbohydrates, phycobilins, β-carotene, lipids and MDA contents in spirulina biomass. Changes in the antioxidant activity under applied metal loads reveal a moderate stress in exposed A. platensis. Cyanobacterium A. platensis can be successfully used for bioremediation of natural water contaminated with REEs as well as REEs recovery from low polluted industrial effluents.

The Effect of Energy Impacts on the Acid Leaching of Eudialyte Concentrate

ABSTRACT Using a combination of energy – dispersive X-ray spectroscopy, X-ray diffraction, X-ray fluorescence, Infrared and X-ray photoelectron spectroscopies, the effect of acids (sulfuric, hydrochloric, and nitric) and energy impacts (electrochemical, mechanochemical, high power electromagnetic pulses, ultrasound) on the leaching parameters of eudialyte concentrate was studied. Zr and Σ REE recovery after a single stage when using sulfuric acid was 91.5% and 82.4%, when using hydrochloric acid – 83.9% and 83.6%, when using nitric acid – 76.9% and 79.6%, respectively. Using sulfuric acid leads to the formation of the maximum amount of silicate gel and high loss of valuable components, while hydrochloric acid is highly aggressive to the process equipment. The possibility of nitric acid leaching intensifying by applying ultrasonic impacts was determined which disperse colloidal silicate gel, prevents the formation and precipitation of the gel on the mineral surface, provides the formation of numerous defects and microcracks on the eudialyte grains surface, including breakage thereof. Three stages of nitric acid leaching of eudialyte concentrate with an ultrasonic treatment in the first stage provide the highest recovery of zirconium (97.1%) and rare earth elements (94.5%) at a minimal loss of valuable components with silica gel. The process is recommended for commercialization.

Major element composition controls rare earth element solubility during leaching of coal fly ash and coal by-products

Coal combustion ash and pre-combustion coal refuse are currently under consideration as potential sources of rare earth elements. One of the early steps in recovering REEs from coal by-products is often acid leaching, which can result in low pH leachates with complex aqueous chemistry. The aim of this work was to understand the connection between REE solubility, pH, and major elemental components of leachates for coal by-products. To accomplish this, we investigated the effects of solids concentration (i.e., pulp density) and pH adjustment on REE solubility in acid leachates of coal fly ashes from the Powder River Basin (PRB) and Appalachian Basin in the United States, and a coal processing refuse from the Southwestern U.S. For PRB ashes, the concentrations of soluble REEs generally increased with increasing pulp density; however, at pulp density values above 80–100 g/L, the soluble REE concentrations in the leachates were markedly lower. Similarly, the soluble concentrations of other major solutes (Fe, Al, Si) that leached from PRB fly ashes were also non-linear with pulp density. These major elements tended to reach maximum concentration values at 60–70 g/L pulp density. In contrast, for the Appalachian fly ashes and the coal by-product, soluble concentrations of REE and major elements in leachates increased linearly with pulp density. Chemical equilibria calculations of mineral saturation indices indicated that trends in soluble REE concentrations could be explained by saturation conditions for Fe and Al-(hydr)oxides and possibly sulfate minerals, but not lanthanide hydroxides. Furthermore, pH adjustment of the acid leachates showed that REEs and many major solutes were removed from solution at pH values above 4.5, also consistent with Fe- and Al-(hydr)oxide precipitation. These results highlight the importance of understanding the chemical composition of leachates when designing REE recovery processes for low-grade geologic feedstocks and that precipitation of hydr(oxide) or sulfate minerals of major elements rather than discreet formation of REE mineral phases could be used for process optimization.

Extraction Properties of Diphenyl{[N-(2-diphenylphosphinylethyl)-N-alkyl]carbamoylmethyl}phosphine Oxides in Nitric Acid Solutions

Extraction of micro amounts of U(VI), Th(IV), and REE(III) from HNO3 solutions with solutions of diphenyl{[N-(2-diphenylphosphinylethyl)-N-alkyl]carbamoylmethyl}phosphine oxides in organic solvents has been studied. Extracted complexes stoichiometry has been determined, effect of extractant structure, organic solvent nature, and aqueous phase composition on the efficiency of U(VI), Th(IV), and REE(III) recovery into organic phase have been considered. It has been shown that the modification of diphenyl(dialkylcarbamoylmethyl)phosphine oxide by the introduction of additional phosphoryl group into the amide moiety leads to increase in extraction ability toward Th(IV) and slight change in the recovery degree of U(VI) from nitric acid solutions. The efficiency of U(VI), Th(IV), and REE(III) recovery into organic phase increases considerably in the presence of ionic liquid: 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide.

Thermodynamics and crystallization kinetics of REEs in CaO–SiO2–Ce2O3 system

AbstractRare earth elements (REEs) have become increasingly important as ceramic materials. The RE‐bearing slags contain massive REEs resources, whereas the lack of thermodynamic and kinetic data of REEs has brought great difficulties to efficient recovery of REEs from RE‐bearing slags and the application in ceramics. According to the compositions of the RE‐bearing slags in industrial production, the isothermal phase equilibria of CaO–SiO2–Ce2O3 system at 1500°C and 1300°C were constructed by means of liquid‐quenching method combined with a series of analyses, which provides the thermodynamic data for the equilibria of REEs. On this basis, the crystallization behaviors of the RE phase (Ce9.33−xCax(SiO4)6O2−0.5x) was investigated, and the temperature range in which the RE phase crystallized singly in RE‐bearing slags with a selected compositions was acquired. CCT and TTT diagrams for CaO–SiO2–Ce2O3 system were established to characterize the crystallization kinetics of the RE phase, and the favorable conditions for its crystallization and growth in RE‐bearing slags were determined. In this study, the complete thermodynamic and kinetic basic data of REEs in CaO–SiO2–Ce2O3 system are provided for RE‐bearing slags.

Recovery of rare earth elements from spent fluid catalytic cracking catalyst using hydrogen peroxide as a reductant

A hydrochloric leaching process was applied to recover rare earth elements (REEs, mainly La and Ce) from spent fluid catalytic cracking (FCC) catalysts using H2O2. The Ce of CeO2 in FCC catalyst is firstly reduced to Ce3+ ions with H2O2, and then it is easily leached out by HCl acid. Followed by ion exchange extraction with octyl phosphate, precipitation with ethanedioic acid and calcination at high temperature, high recovery of REEs (93.0%) is achieved. The leached REEs were extracted with P507 in kerosene diluent extracting 94.5% of the REEs at 40 °C for 30 min at 1:1 distribution. Then, 98.1% of the loaded REEs was stripped under the conditions of 1.8 mol/L HCl at the temperature of 30 °C for 20 min. This reduction and leaching process provides a high efficiency method for valuable metal elements from spent catalyst.

Effect of super gravity on successive precipitation and separation behaviors of rare earths in multi-components rare-earth system

Re-concentrate is a complex multi-components Re-system consisting of Ce, La, Pr and Nd, which brings great difficulties for investigating the transformation and separation behaviors of REEs. The effect of super-gravity field on the mass transfer and phase separation behaviors of REEs was investigated in this paper, and the phenomenon of successive precipitation and separation of REEs was discovered. The Re3+ was firstly precipitated into Re-oxyfluoride phase with OF3-, which overcame the interface tension to be evidently separated into the bottom layer under the action of super gravity. Subsequently, the Re3+ were successively precipitated with FeO33-, SiO44- and PO43- into Re-ferrate phase and britholite phase, which were separated further into the middle and top layers along the super gravity direction. Moreover, various REEs were efficiently recovered into the different Re-phases, respectively. The theoretical and experimental results verified the significant enhancement of super gravity on the mass transfer and phase separation of REEs, and its efficient application in REEs recovery from multi-component Re-system.

Recovery of REE from red mud by reduction smelting

Recovery of REE from red mud by reduction smelting

Conversion of lanthanum and cerium recovered from hazardous waste polishing powders to hazardous ammonia decomposition catalysts.

The polishing process in high-tech industries produces a large amount of waste polishing slurry, which is harmful to the environment, and the solid powders in the slurry contain a lot of La and Ce, which have been widely used as catalyst materials. The aim of this study was to convert this hazardous material into hazardous material decomposition catalyst. A novel and simple approach was successfully developed for the recovery of La and Ce from hazardous waste polishing powders to synthesize a composite metal oxide catalyst for decomposition of harmful ammonia. Here, La and Ce were leached from waste polishing powder by using nitric acid, and the Ce, La, and total REE recovery rates were approximately 100%, 83.3%, and 96.4%, respectively. The elemental concentrations of leached acidic solution was analyzed, after which stoichiometry was performed to replenish elements with insufficient mole numbers. Finally, the catalyst material was prepared using the glycine-nitrate combustion process. The catalyst prepared from the recovered polishing powders achieved a 100% ammonia conversion rate at the relatively low temperature of 250 °C. The proposed environmentally friendly method does not require complex purification and separation procedures and can be used for the synthesis of catalysts for decomposing other harmful pollutants.

Extraction of Rare Earth Elements from Hydrochloric Acid Solutions with Carbamoylmethylphosphine Oxides in the Presence of Quaternary Ammonium Dinonylnaphthalenesulfonates

Interphase distribution of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y between aqueous HCl solutions and solutions of carbamoylmethylphosphine oxides in the presence of binary extractants, quaternary ammonium dinonylnaphthalenesulfonates, has been studied. It has been shown that the efficiency of extraction of rare earth elements(III) (REE) with carbamoylmethylphosphine oxides increases considerably in the presence of binary extractant in organic phase. The stoichiometry of extracted complexes has been determined, effect of cation nature of the binary extractant, organic solvent, structure of carbamoylmethylphosphine oxides, and HCl concentration in aqueous phase on efficiency of REE(III) recovery into organic phase has been considered.

A Short Review on REE Recovery from Ion-Adsorption Clays

A Short Review on REE Recovery from Ion-Adsorption Clays

Recovery of REEs, Zr(+Hf), Mn and Nb by H2SO4 leaching of eudialyte concentrate

In this study three hydrometallurgical methods are described for leaching of a eudialyte concentrate with H2SO4: (i) direct leaching, (ii) fast leaching and (iii) water leaching of dehydrated acid/concentrate mixture. It is demonstrated how to obtain a silica free solution, how parameter variations impact the properties of precipitated silica and which processes lead to losses of valuable components during leaching. Furthermore, the acid solubility of gangue minerals in the concentrate is analyzed and the resulting consequences in terms of leach solution contamination and acid consumption are discussed. The best result in terms of the average yield of value components (REEs, Zr(+Hf), Mn and Nb) of 86% is obtained by direct leaching under mild conditions (cH2SO4 = 1 mol/L; TL = 60 °C). However, released silicic acid does not precipitate and aggregates at pulp density ρPD,L = 100 kg/m3 by gelling. Fast leaching allows the efficient removal of silica at high solid-liquid ratios in the pre-treatment stage. Due to mass transfer limitations, high efficiency stirrers are crucial for achieving high yields in short reaction times. Dehydration of the acid/concentrate mixture before water leaching can be a good alternative if well-defined amount of acid is used; however, high energy input is needed.

Selective Recovery of Rare Earth Elements from Coal Fly Ash Leachates Using Liquid Membrane Processes.

Coal combustion residues and other geological waste materials have been proposed as a resource for rare earth elements (REEs, herein defined as the 14 stable lanthanides, yttrium, and scandium). The extraction of REEs from residues often generate acidified leachates that require highly selective separation methods to recover the REEs from other major soluble ions in the leachates. Here, we studied two liquid membrane processes (liquid emulsion membranes, LEM, and supported liquid membranes, SLM) and compared them to standard solvent extraction techniques for selective recovery and concentration of REEs from a leachate of coal fly ash. All separation methods involved an organic solution of di(2-ethylhexyl)phosphoric acid dissolved in kerosene or mineral oil and an acid strippant solution of 5 M nitric acid for the liquid-based separations. The LEM configuration, which separated REEs by immersing an acid-in-oil emulsion in the ash leachate, resulted in similar recovery percentages of individual REEs as the conventional solvent extraction approach. The recovery of REEs in the SLM configuration, which involved the impregnation of the solvent in a hydrophobic membrane, was slower than the LEM process. However, the SLM process was notably more selective for the heavy (and higher value) REEs, while the conventional extraction and LEM processes were more selective for the light REEs. A flux-based model of the extraction processes suggested that recovery rates were limited by REE affinity for the solvent chelator in the SLM, while the rates of REEs separation via LEM were limited by diffusive mass transfer across the liquid membrane. Altogether, these results help to identify specific steps in the recovery process that future work should target in the development of scalable liquid membrane separations for REE recovery.

Calcination pretreatment effects on acid leaching characteristics of rare earth elements from middlings and coarse refuse material associated with a bituminous coal source

The pretreatment of middlings and coarse refuse material collected from a Pocahontas No.3 coal source using calcination was investigated for the potential of improving the leaching recovery of rare earth elements. Calcination at 600 °C significantly and preferentially improved light REE (LREE) recovery to values in the range of 80–90% using 1.2 M HCl. The positive effect was due to the increased pore diameter and volume as well as thermal decomposition of the minerals associated with the LREEs. Heavy REE recovery was not increased after calcination at 600 °C due to the need for higher temperatures to achieve thermal decomposition of HREE minerals. Furthermore, some HREEs were also associated with sulfide minerals (e.g., pyrite) which were transformed into low-solubility oxides (e.g., hematite) after roasting at 600 °C. Based on the leaching characteristics of the major elements (Fe, Al, Ca and Mg) and REEs along with SEM-EDX data, it was concluded that REEs in the two samples mainly occurred as phosphate minerals. In the middlings, some of the minerals were completely encapsulated by kaolinite, which was less apparent in the coarse refuse. In addition, it was found that a portion of the REEs (10–25%) in the samples were associated with the organic matter and micro-dispersed minerals in the organic matrix, was released after calcination and easily recovered using 0.1 M (NH4)2SO4 solution at pH 5. Scandium primarily occurred in mineral forms with minimum amounts associated with ion-adsorbed clays and organic association.

Extraction of rare earth oxides from discarded compact fluorescent lamps

Discarded CFL samples are evaluated as a potential source of REEs (Y, Eu, Ce, Tb). The phosphors powder obtained from mechanical separation contains 31% rare earth values. The quantitative XRD analysis of phosphor sample yielded 39.9% red (YOX: Y1.90Eu0.10O3), 14.6% green (CAT: Al11Ce0.67MgO19Tb0.33), and 21.4% blue (BAM: Al10.09Ba0.96Mg0.91O17: Eu2+) phosphor along with 14.1% silica. Planetary ball milling was found promising in the liberation of REEs from given phosphor sample. A short milling of 20–30 min and 3–4 M acid concentration was found adequate for optimal recovery (>90%) of REEs. Calcination of the precipitates resulted in the formation of REO with Y-Eu purity of >98% and >90% recovery rate. Eu, Y phase dissolution behavior was found completely different than Ce, Tb phase due to inert nature of Al11Ce0.67MgO19Tb0.33 till 120 min milling and 6 M acid concentration in leaching. Excessive milling promotes overall dissolution along with impurities dissolution and which further restrict the precipitation process. Based on the complete material balance 13 g of a mixed oxide of Y and Eu can be obtained from 100 units of CFLs.

Extraction of Rare Earth Elements(III) with Picrolonic Acid Mixtures with Phosphoryl-Substituted Aza Podands

Extraction of rare earth element(III) (REE) ions from chloride solutions with picrolonic acid mixtures with phosphoryl-substituted aza podands in chloroform has been studied. A considerable synergetic effect observed has been caused by the formation of hydrophobic mixed-ligand complexes of REE. The stoichiometry of extracted complexes has been determined and extraction constants have been calculated. The effect of aqueous phase composition, organic solvent nature, and the structure of phosphoryl-substituted aza podands on the efficiency of REE(III) recovery into organic phase have been considered.

A novel approach for synthesis of exfoliated biopolymeric-LDH hybrid nanocomposites via in-stiu coprecipitation with gum Arabic: Application towards REEs recovery

Delamination and exfoliation of layered double hydroxides (LDH) is an interesting way for the synthesis of novel nanocomposites. Herein, we report the synthesis of various exfoliated biopolymeric-LDH nanocomposites via in-situ coprecipitation method with gum Arabic (GA). The influence of various divalent ions on the morphological characteristics of GAnXA (n = wt% of GA and X = Mg, Ca, Ba, Sr) was explored Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), and Scanning Electron Microscopy (SEM). X-ray diffraction pattern was used for the determination of phase composition of synthesized nanocomposites. The surface functional groups of GAnXA were investigated by Fourier Transform Spectroscopy (FTIR). Furthermore, the surface charge characteristics was explored by zeta potential analysis. Specific surface area of GAnXA was determined by BET analysis. The overall adsorption of REEs decreased with an increase in ionic size of divalent ions and the noticeable difference in the morphologies of exfoliated GAnXA was observed. In a single component system, the REEs adsorption capacities followed the order: Sc > Y > Nd > Ce > Eu > La, whereas, in multicomponent system, adsorption seems to be competitive and presence of competing ions affect the overall REEs removal. Moreover, HREEs removal superseded over LREEs and the nanocomposites (GA5CA, GA5SA, GA5BA) were highly selective for Sc recovery. The post-adsorption FTIR and SEM results revealed the importance of surface hydroxyl and carboxyl functional groups enacting as the principal REE binding sites. Overall, ability to extract REEs at pH 4 (slightly acidic) presented a facile route for the recovery and separation of REEs from aqueous medium and enhances the possibility of its use in many industrial applications.