Separation Of Lanthanides Research Articles

Uptake and separation of rare earth elements and late transition metal cations by nanoadsorbent grafted with diamino ligands

Recycling of magnetic materials based on Rare Earth Elements (REE) is of major interest in the view of growing clean energy production and transportation. One of the major challenges in its realization is the need to separate smaller amounts of Late Transition Metals (LTM) from REE. Hybrid adsorbents are very attractive in finding such a solution. Here, novel silica-based nanoadsorbents were synthesized by grafting the surface of dense silica nanoparticles with a diamino functional ligand grafted via an arene linker to improve selectivity towards LTM. The produced adsorbent materials were characterized using SEM, TEM, AFM, XPS, FTIR, and TGA in its pure form and by DLS in suspension, and tested for the adsorption and separation of LTM (Co2+ and Ni2+) and REE (Sm3+ and Nd3+) in single and mixed solutions. Prepared organo-silica material showed rapid uptake of all tested cations with higher affinity towards LTM. Adsorption capacities reached values of 1.18–1.45 mmol/g for Co2+ and Ni2+, respectively, with a 1:1 metal-to-ligand stoichiometry for Ni cations. Investigation of reusability demonstrated the potential of the prepared materials as an environmentally friendly alternative in specific separation of LTM to conventional separation techniques. Investigations of the molecular structures of the Ni2+ complex with the selected molecular function and of Co3+ with a closely related tris-aminoethyl amine ligand in combination with XPS data for corresponding surface complexes helped explaining the molecular mechanisms for adsorption and desorption of the LTM cations.

Recovery of Rare Earth Elements from the Leaching Solutions of Spent NdFeB Permanent Magnets by Selective Precipitation of Rare Earth Oxalates

After mechanical pre-treatment, the typical hydrometallurgical route of NdFeB magnet recycling starts with leaching in acidic solutions. However, due to the high concentration of iron ions in the leaching solution, the selective recovery of rare earths from the solution is challenging. In our work, the selective precipitation of rare earth oxalates as a potential separation method was proposed. The precipitation of neodymium oxalate was first tested on model solutions, which was then followed by experimental tests carried out on real solutions after the leaching of NdFeB magnets. The recovery of rare earths in the form of oxalates was investigated with the use of different amounts of oxalic acid in relation to its stoichiometric amount. The most efficient separation of rare earths was observed in the case where sulfuric acid was used for leaching. The use of oxalic acid in stoichiometric amounts resulted in the precipitation of about 93% of all rare earths present in the solution, whereas the concentration of Fe and other elements (Ni, Co, and B) practically did not change. An increase in oxalic acid of 20% and 40% more than the stoichiometric amount (100%) led to the increase in the precipitation efficiency of rare earths to 96.7% and 98.1%, respectively. However, the use of oxalic acid in a 1.4 ratio caused a 7% decrease in Fe concentration, which suggests Fe co-precipitation. In order to investigate a possibility of further increasing the separation of rare earths from iron, an additional method was tested, in which iron was first oxidized from Fe2+ to Fe3+ before the precipitation of rare earth oxalates.

Developing N,N,N’,N’-tetra (2-ethylhexyl) diglycolamide encapsulated polymeric beads as promising rare earth extracting agents

ABSTRACT The multi-faceted applications of rare earth elements (REE) in science and technology are not unknown. Scarcity in the primary sources of RE makes it necessary to explore different secondary sources available. Availability of REE in significant amount in spent NdFeB magnetic scrap makes the recycling of REE from this scrap, a lucrative option. In this work, synthetic solutions of 10 g/L (containing the rare earths Nd, Pr and Dy along with Fe) were equilibrated with the organic extractant N,N,N,’N’-tetra (2-ethylhexyl) diglycolamide (TEHDGA) encapsulated in polyethersulfone beads to study the extraction behavior of the REEs from nitric acid medium. Iron (Fe), the major component present in NdFeB scrap, poses the biggest challenge for rare earth extraction from the scraps. The TEHDGA impregnated polymeric beads were found to selectively extract the REEs, leaving Fe(III) in the feed solution. TEHDGA displayed higher selectivity towards the heavier rare earth Dy followed by Nd and Pr. The loading capacity of the beads was measured to be > 1700 ppm. The effect of different experimental parameters, such as contact time, solid-liquid ratio, TEHDGA concentration, feed acidity, were investigated. Contact time of 24 h, TEHDGA concentration of 0.75 M, solid-liquid ratio either 1:5 or 1:10 and feed acidity between 2 and 5 M have been found to suitable for quantitative extraction of REE particularly Dy(III). The recovery of the REEs from the loaded TEHDGA beads was > 90%. Furthermore, the experiment was carried out with higher quantity of beads and feed solution to study applicability of the same in bulk scale. A novel, easy and single-step separation of REE from Fe has been presented in this work.

Free Energy Calculations and Conformational Analysis of Dibenzo-30-crown-10 with Sm2+, Eu2+, and Three Halide Salts in THF Using the AMOEBA Force Field.

Crown ether complexes have been tailored for use in industrial separations of lanthanides (Ln) as a part of rare earth mining and refining. Dibenzo-30-crown-10 (DB30C10) is one of the most efficient complexants for the separation of rare earth mixtures based on the cation size. To understand the origin of this complexation, molecular dynamics (MD) simulations of DB30C10 have been performed using different combinations of divalent Sm and Eu and three halide salts Cl-, Br-, and I- in tetrahydrofuran (THF) solvent. DB30C10 was parameterized here for the polarizable atomic multipole optimized energetics for biomolecular simulation (AMOEBA) force field, and the existing parameters of THF, Sm2+, and Eu2+ were employed from our previous efforts. The large conformational fluctuations present in the DB30C10 systems were found to be dependent both on the identity of the lanthanide and halide complexes. For Cl- and Br- systems, there were no observed conformational changes at 200 ns, while in I- systems, there were two conformational changes with Sm2+ and one with Eu2+ within that same timeframe. In SmI2-DB30C10, there were three stages of conformational changes. In the first stage, the molecule is unfolded, in the second stage, the molecule is partly folded, and finally, in the third stage, the molecule is completely folded. Lastly, the Gibbs binding free energies of DB30C10 with SmBr2 and EuBr2 have been computed, which resulted in nearly identical ΔGcomp values for each lanthanide with Sm2+ being slightly more favorable. Considering the folding mechanism of the SmI2 system with DB30C10, the Gibbs binding free energies of DB30C10 and dicyclohexano-18-crown-6 (DCH18C6) with SmI2 were calculated separately and compared to probe their complexation affinities, in which the former was found to be more favorable.

Separation of Rare Earth Elements in Multistage Extraction Columns in Chromatography Mode: Experimental Study and Mathematical Simulation

The application of liquid–liquid chromatography principles to solvent extraction processes in hydrometallurgy can greatly simplify rare earth metal separation technologies by separating multicomponent mixtures in one technological operation. In this study, the chromatographic separation of rare earth elements (REEs) in multistage extraction columns was experimentally studied under conditions of impulse sample injection—single and multiple loading of large volumes of metal salt solution into the installation. The results obtained showed the feasibility of operating sieve plate extraction columns in the liquid–liquid chromatography mode. A closed-loop recycling technology is proposed for the separation of rare earth elements in multistage extraction columns operating in the liquid–liquid chromatography mode. For further development and industrial implementation of this technology, experimental studies should be conducted on intensified multistage extraction columns, such as sectioned columns with agitators and vibrating plate columns. Computer simulation of the chromatographic separation of rare earth elements by closed-loop recycling liquid–liquid chromatography was carried out.

Adsorption of rare earth elements onto diatomite M45: Experimental investigations and modeling with statistical physics theory

The separation of rare earth elements using diatomite M45 from aqueous solutions was studied. The experimental isotherms for the adsorption of trivalent lanthanum, cerium, and neodymium cations on this adsorbent were quantified under strongly acidic conditions (pH 2) at 298–328 K. The adsorption equilibria of these earth elements were analyzed using two statistical physics models (homogeneous and heterogeneous monolayer models). The results show that the adsorption of these ions implies a multi-ionic mechanism, which is exothermic. Si-containing functional groups are responsible for the adsorption of these rare-earth elements on the diatomite surface. A heterogeneous statistical physics model confirms that two Si-based functional groups participate in the separation of these cations. The calculated adsorption capacities at saturation follow the order: neodymium > cerium > lanthanum. Calculated interaction energies range from 28600 to 40100 J/mol, indicating physical adsorption on diatomite M45. This study demonstrates that diatomite M45 is a promising separation medium that can be used for the recovery of REEs dissolved in aqueous solutions via adsorption.

Simulation of Solvent Extraction Circuits for the Separation of Rare Earth Elements

The separation of Rare Earth Elements (REEs) is an important step in the valorization of REE ore and aims at producing individual rare earth compounds for the market. The separation is carried out industrially by solvent extraction (SX) using interconnected circuits consisting of cascades of mixer-settlers. The design of a REE separation circuit implies the selection of the operating conditions and of the number of mixer-settlers required to achieve a target degree of purity for the separated elements. This design work is either carried out by piloting a circuit or using a mathematical simulation. Independent of the method, the world expertise in this area is limited. This paper describes a simulation method requiring a minimum of calibration effort, which can be used to design a complete REE separation plant. The simulation enables assessment of the effect of the number of mixer-settlers per extraction, the scrubbing and stripping stage, as well as the pH of the aqueous solution and organic-phase contents of free and loaded extractant on the purity of the separated REEs. The simulation tool presented here has been developed from a fundamental analysis of the chemical reactions involved in the solvent extraction process. Unlike most of the simulation methods documented in the literature, the method requires no empirical calibration. The proposed method is validated using data from laboratory batch tests and with published data from continuous pilot and industrial REE separation circuits. The application of the simulation tool is illustrated with the planning of the test conditions for a forthcoming pilot test work and with the simulation of a 9-REE product SX separation plant.

P350-N235 synergistic extraction system used for the recovery of Nd(III) from waste NdFeB magnets

The recovery of Nd(III) from NdFeB permanent magnets is gaining increasing attention. In the rare earth elements separation industry, wastewater produced through saponification has become a serious environmental problem. In this work, a novel non-saponification P350-N235 synergistic extraction system was established for the extraction of Nd(III) from nitric acid medium. Almost 100% of Nd(III) was extracted by using a P350-N235 system when the molar fraction (X) of P350 was 0.3. And the synergistic enhancement factor Rmax reached 60.03. Firstly, the effects of time, pH, volume ratio and other variables were investigated to determine the extraction behaviors. Response surface methodology (RSM) was used to optimize the extraction conditions. The mechanism of synergistic extraction was investigated by FT-IR, UV–vis, NMR methods and ESP maps, indicating that the composition of the extracted complex was Nd(NO3)3·(P350)2.5(N235)2.5. Then, the extraction thermodynamics and kinetics were also thoroughly investigated, the extraction process is demonstrated to be a spontaneously exothermic reaction. In the NdFeB leaching solution, the synergistic system showed excellent separation factor (β) for Nd/Sm (1.43), Nd/Gd (7.33), and Nd/Dy (9.81). Finally, after 5 cycles, the P350-N235 synergistic system maintained high extraction efficiency. In conclusion, this study overcame the saponification problem in traditional extraction techniques and proposed an environmentally friendly green extraction system.

Separation of La(III), Ce(IV) and Ca(II) from bastnaesite using acidic phosphonic chitosan and rotating disk membrane

The separation of rare earths is difficult due to their similar properties and the complex characteristics of associated vein ores. Complexation-ultrafiltration (CUF) and shear induced orderly dissociation coupling with ultrafiltration (SIODUF) were used to separate metal ions (M, M = La(III), Ce(IV) and Ca(II)) from simulated bastnaesite leaching solution using acidic phosphonic chitosan (aPCS) and rotating disk membrane. Effect of simultaneous removal of metallic ions was investigated by CUF, and suitable conditions were obtained for C/M 10.0 (mass ratio of complexant to metal ions) and pH 5.0. The shear stabilities of aPCS-M complexes were explored at different pH values and the results show that the complexes can dissociate at a certain rotational speed, the critical one. The critical shear rates of aPCS-La, aPCS-Ce and aPCS-Ca complexes at pH 5.0 were calculated as 1.42 × 105, 1.69 × 105 and 9.75 × 104 s−1, respectively. The order of complexes shear stability is aPCS-Ca < aPCS-La < aPCS-Ce. The high selective separation of M and regeneration of aPCS were achieved by SIODUF in the light of the difference of aPCS-M complexes shear stabilities. The separation coefficients βLa/Ce and βCa/La reach 31.2 and 53.9, respectively.

Enhanced Selective Adsorption of Lanthanum(III) by Dual-Site Polymeric Ion-Imprinted Nanoparticles from Aqueous Media

Selective recognition and separation of rare-earth elements (REEs) is considered a real challenge for the RE industry. In this work, two dual-site ion-imprinted polymers (IIP-AM and IIP-MAA) were synthesized via a radical copolymerization method for the removal of La(III) from aqueous solutions. The structures of samples were characterized and confirmed with various kinds of techniques, including IR, X-ray diffraction, field emission scanning electron microscopy, Brunauer–Emmett–Teller, thermogravimetry analysis, and X-ray photoelectron spectroscopy (XPS). Adsorption studies reveal that the pseudo-second-order kinetic model and the Langmuir isotherm model were well-fitted with the adsorption of La(III), showing high adsorption capacities of 45.65 and 50.05 mg/g for IIP-AM and IIP-MAA, respectively, after 120 min at pH = 5.5 and 25 °C. Impressively, the fabricated IIPs possess remarkable selectivity between La(III) and other REEs, as well as excellent reusability after five successive adsorption–regeneration cycles with less than 9% reduction of capacities. The adsorption mechanism indicates that the surface complexation and electrostatic attraction contribute to the adsorption of La(III) based on the characterization analysis of XPS, elemental mapping, and energy-dispersive spectrometry, as well as density functional theory calculations. Accordingly, these samples with tailored ion-imprinted cavities and abundant active O sites entirely exhibit the potentials for the selective recovery of REEs from aqueous solutions.

Organophosphorus Extractants: A Critical Choice for Actinides/Lanthanides Separation in Nuclear Fuel Cycle.

The separation of actinides from lanthanides in spent nuclear fuel reprocessing is a vital step of nuclear fuel cycle process. As one class of mature industrial extractants, the organophosphorus extractants have been widely used for the extraction and separation of actinides and lanthanides in spent fuel reprocessing due to their strong extraction ability and low-cost acquisition. In this concept, the application scope of tributyl phosphate (TBP), bis(2-ethylhexyl) phosphate (HDEHP), octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO), trialkyl phosphine oxide (TRPO), and purified Cyanex 301 (bis(2,4,4-trimethylpentyl) dithiophosphinic acid, HA301) are introduced, and their extraction mechanism, as well as structure-function relationships for separation of actinides over lanthanides are also discussed. Furthermore, the design criteria, extraction properties and mechanism of several typical newly developed organophosphorus extractants (CMPO-modified calixarene/pillarene, phenanthroline-derived organophosphorus extractants, and phosphate-modified carborane) based on pre-organized skeletons are briefly reviewed. Finally, the important role played by those organophosphorus extractants is emphasized and potential applications in separation of actinides over lanthanides in future advanced nuclear fuel cycle are identified.

Low and High LET Degradation Studies of Metal-Loaded Organic Phase Ligands in the ALSEP Process

ABSTRACT Organic solutions comprising the Actinide Lanthanide Separation Process (ALSEP) solvent consisting of 0.5 M 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and 0.05 M N,N,N’,N’-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) in n-dodecane were subjected to low LET and high LET irradiation before and after equilibration with an aqueous phase of 3 M HNO3. Degradation dose constants revealed greater ligand degradation due to gamma irradiation than alpha irradiation for both ligands. Furthermore, equilibration with nitric acid did not have a significant impact on ligand degradation for either irradiation source. Identified degradation products were similar for both gamma and alpha irradiation and occurred mostly through the rupture of the N–Ccarbonyl and C–Oether bonds for T2EHDGA and the C–Oether bond in HEH[EHP]. Acid contact appears to alter the degradation pathway by favoring the formation of higher molecular weight recombination products. Mixed T2EHDGA-HEH[EHP]-NO3 complexes were formed with Nd(III) after extraction from 3 M HNO3, and low LET gamma irradiation of the Nd(III) loaded organic solution produced similar degradation products as the organic solution absent of Nd(III). Interestingly, and likely due to the greater radiolytic susceptibility of T2EHDGA than HEH[EHP], a HEH[EHP]-Nd(III) complex appears to form as the T2EHDGA degrades with increasing absorbed dose.

Green Approach for Rare Earth Element (REE) Recovery from Coal Fly Ash.

Due to the growing demands of rare earth elements (REEs) and the vulnerability of REEs to potential supply disruption, there have been increasing interests in recovering REEs from waste streams such as coal fly ash (CFA). Meanwhile, CFA as a large industrial waste stream in the United States (U.S.) poses significant environmental and economic burdens. Recovery of REEs from CFA is a promising solution to the REE scarcity issue and also brings opportunities for CFA management. This study demonstrates a green system for REE recovery from Class F and C CFA that consists of three modules: REE leaching using citrate, REE separation and concentration using oxalate, and zeolite synthesis using secondary wastes from Modules I and II. In Module I, ∼10 and 60% REEs were leached from the Class F and C CFA samples, respectively, using citrate at pH 4. In Module II, the addition of oxalate selectively precipitated and concentrated REEs from the leachate via the formation of weddellite (CaC2O4·2H2O), while other trace metals remained in solution. In Module III, zeolite was synthesized using wastes from Modules I and II. This study is characterized by the successful recovery of REEs and upcycling of secondary wastes, which addresses both REE recovery and CFA management challenges.

Chromatographic Separation of Rare Earth Elements as MGDA Complexes on Anion Exchange Resins

Chromatographic separation of rare earth elements (REE) as anionic complexes with chelating aminopolycarboxylate ligand methylglycine N,N-diacetate (MGDA) was studied experimentally. A synthetic mixture of La, Nd, and Eu were used to model a REE mixture obtained from processed secondary sources such as phosphogypsum (PG). In the REE extraction from PG, the REEs can be recovered with MGDA to obtain the REE–MGDA mixture. Three strong base anion exchange resins (Dowex 1X8, IRA-402, and IRA-410) were used as the separation materials. Successful separation of the REEs by elution with dilute HNO3 and HCl was attributed to differences in the stabilities of the REE–MGDA complexes. The pKa values of the complexes were determined by titration to be 3.81, 3.25, and 2.96 for La, Nd, and Eu, respectively. Fractionation of the ternary La-Nd-Eu mixture (with a 1:1:1 mole ratio) were studied. La was recovered at approximately 80% purity and 80% yield, but strong trade-offs between the yield and the purity of Nd and Eu must be made. Chromatographic separation was found to be an efficient process option, considering its simplicity and the recovery of several product fractions. The initial process design offers a promising starting point for investigating more advanced process configurations for the efficient recovery of pure REE from phosphogypsum.

Adsorption of rare earth elements in carboxylated mesoporous carbon

The separation of Rare Earth Elements (REEs) from various non-conventional sources is critically important to maintain the supply–demand balance of REEs in the western world. In this research, we have investigated coal Fly Ash (CFA) as the non-conventional source of REEs. In order to recover REEs, we have synthesized carboxylate-functionalized mesoporous carbon (CMC) to harness the chelation-induced adsorption of REEs. These adsorbents were characterized with pore textural properties, FTIR spectroscopy, and SEM-EDX mapping. In the initial study with single-component La(III) Dy(III) and Lu(III), it was revealed that CMC can adsorb those REEs 2–4 times more than that of pristine mesoporous carbon confirming the effective role of the carboxylate group in the REE separation. Furthermore, the affiliation of the carboxylate group towards heavier REEs (Lu > Dy > La, when present is equal amounts) provides an added benefit of this adsorbent owing to the high demand for heavier REEs in the technology sectors. The leachate solution produced from CFA contained sixteen REEs in the range of 50–200 ppb for most of the REEs. It was revealed that CMC can extract 80–90% of all the REEs thereby further confirming the success of the CMC as an effective REE sorbent. Three successive cycles of adsorption and desorption of REEs with the same CMC revealed the consistent adsorption capacity of REEs. In-situ X-ray Absorption Near Edge Spectroscopy (XANES) analysis confirmed the + 3 oxidation states of La, Dy, and Lu within CMC. In-situ Extended X-ray Absorption Fine Structure (EXAFS) analysis revealed the shortening of mean La-O, Dy-O, and Lu-O bond distance by 0.03–0.05 Å thereby confirming the coordination of these REEs with carboxylate groups present on CMC.

Solvent extraction in non-ideal eutectic solvents – Application towards lanthanide separation

Hydrophobic eutectic solvents (HES) emerged as promising substitutes to the conventional organic phase used in the solvent extraction (SX) of metal ions due to the avoidance of diluents and the suppression of third-phase manifestation. However, HES present a highly structured liquid phase defined by hydrogen-bonded interactions such that intercomponent interactions are expected to play a greater role in SX using HES compared to a diluted extractant solution. In this work, the extraction of lanthanides from nitrate media by the non-ideal solvent composed of decanoic acid (C10OOH) and trioctylphosphine oxide (TOPO) was determined as a function of the lanthanide cation selection, HES molar fraction, HNO3 concentration, and temperature. Through the systematic variation of these parameters, the delicate balance between complexation and solvent reorganisation and its influence on the extraction and metal selectivity is determined by metal partition experiments, time resolved fluorescence and Raman spectroscopy, and small-angle X-ray scattering (SAXS). A compromise between maximum Ln3+ loading and selectivity was observed, driven by the variation in the quantity of weakly H-bonded TOPO and the change in the configurational entropy of the mixture. All results point towards the need to explicitly consider the HES phase structuration and its compositional changes with solute co-extraction on the Ln3+ extraction as no change in the extracted complex speciation was observed across all tested conditions. The C10OOH + TOPO was used as a model system due as lanthanide extraction using TOPO and carboxylic extractants is well described whilst the phase diagram and properties of the eutectic are reported. Nevertheless, the derived conclusions are translatable to other systems and can help guide the design and application of possible HES combinations for SX.

Separation of niobium and rare earths from Fe-Nb-RE associated ultra-low-grade tailings using super gravity

Bayan Obo tailings is unique polymetallic resource associated with iron, niobium (Nb) and rare earths (REEs). However, conventional extraction processes are not economically viable for Nb and REEs due to their low-grade nature. To overcome this challenge, a new approach was employed in this study. The Fe-Nb-RE associated tailings were first reduced and iron-slag was separated at low temperatures under super gravity. This process transformed Nb and REEs into a Nb/REEs-rich phase in the primary enriched slag, which was then separated from the slag by super gravity to obtain a high-grade enriched sample. The end result was a sample with Nb2O5 and RE2O3 mass fractions of up to 24.98 wt% and 30.01 wt%, respectively. This process successfully concentrated Nb and REEs from associated elemental impurities and gangue minerals in the Fe-Nb-RE associated ultra-low-grade tailings, making extraction easier, optimizing subsequent leaching/dissolution, and reducing the number of steps and material flows required in the downstream hydrometallurgical extraction.

Theoretical Insights into the Selectivity of Hydrophilic Sulfonated and Phosphorylated Ligands to Am(III) and Eu(III) Ions.

The separation of lanthanides and actinides has attracted great attention in spent nuclear fuel reprocessing up to date. In addition, liquid-liquid extraction is a feasible and useful way to separate An(III) from Ln(III) based on their relative solubilities in two different immiscible liquids. The hydrophilic bipyridine- and phenanthroline-based nitrogen-chelating ligands show excellent performance in separation of Am(III) and Eu(III) as reported previously. To profoundly explore the separation mechanism, herein, we first of all designed four hydrophilic sulfonated and phosphorylated ligands L1, L2, L3, and L4 based on the bipyridine and phenanthroline backbones. In addition, we studied the structures of these ligands and their neutral complexes [ML(NO3)3] (M = Am, Eu) as well as the thermodynamic properties of complexing reactions through the scalar relativistic density functional theory. According to the changes of the Gibbs free energy for the back-extraction reactions, the phenanthroline-based ligands L2 and L4 have stronger complexing capacity for both Am(III) and Eu(III) ions while the phosphorylated ligand L3 with the bipyridine framework has the highest Am(III)/Eu(III) selectivity. In addition, the charge decomposition analysis revealed a higher degree of charge transfer from the ligand to Am(III), suggesting stronger donor-acceptor interactions in the Am(III) complexes. This study can provide theoretical insights into the separation of actinide(III)/lanthanide(III) using hydrophilic sulfonated and phosphorylated N-donor ligands.

Separation of Rare Earth Elements from Phosphogypsum Obtained from the Processing of Apatite Concentrate from the Chadormalu Mine by Acid Leaching

Separation of Rare Earth Elements from Phosphogypsum Obtained from the Processing of Apatite Concentrate from the Chadormalu Mine by Acid Leaching

Adsorption of La3+ onto trifluoroacetic acid modified UiO-66-COOH: Adsorption mechanism and application

The application of metal organic frameworks (MOFs) for the recovery of low concentrations of rare-earth elements (REEs) has attracted increasing attention due to the precious value of REEs resources. In this study, UiO-66-COOH was modified by trifluoroacetic acid (TFA) to not only promote material crystallization and the pore structure verified by XRD and SEM characterization, but successfully enhance its adsorption capacity and achieve perfect selectivity for Lanthanum ion (La3+). The adsorption capacity for UiO-66-COOH-24TFA was increased by 58% compared to unmodified material. The adsorption mechanism and application were comprehensively investigated. By adsorption kinetics, isotherm and thermodynamic studies, it was found that the adsorption process mainly exhibited monolayer adsorption with spontaneous endothermic-chemisorption characteristics, and –COOH of the modified materials (UiO-66-COOH-24TFA) played an important role, which was confirmed by XPS. Moreover, UiO-66-COOH-24TFA was applied to REEs actual wastewater by successive six-stage adsorption process, where the overall recovery rate on La3+ reached 94.1% under the coexisting conditions of multiple ions. The application of this acid modified material in the field of the separation and recovery of REEs is of great promise.