Recycling Rare Earth Elements Research Articles

Extraction of rare earth ions using thermomorphic ionic liquid: In situ spatial and temporal distribution combined with thermodynamic description

Homogeneous Liquid–Liquid Extraction (HLLE) provides a valuable opportunity for recycling Rare Earth Elements (REE) by circumventing the liquid–liquid interface and avoiding the problems linked to the high viscosity of ionic liquids (IL). For optimizing these processes with the ultimate goal of implementing them at the industrial scale, it is crucial to understand the mechanisms at play at various scales. In this study, we focused on the extraction of two REE elements, La(III) and Ce(III) with an HLLE system composed of the IL [Chol][TFSI], water and betaine as the extractant. We first established the phase diagram of [Chol][TFSI]/betaine/water using 1H nuclear magnetic resonance (NMR) spectroscopy. We then determined the efficiency E and distribution ratio D of the HLLE for different betaine concentrations. HLLE was modeled thermodynamically to access the most likely number of betaine molecules involved in the extraction process, which appears to be 2. Finally, we monitored in situ the extraction using X-ray Absorption Spectroscopy (XAS) at the K-edge of both lanthanum and cerium. It allowed us on one hand, to get some insight into the local environment around the REE, and on the other hand to measure the local concentration of REE at each position within the extraction system. In this latter process, we could evidence an accumulation of REE accumulates close to the liquid–liquid interface, a feature that was suggested by some recent simulations.

Synthesis and characteristics of Na-A zeolite from coal fly ash and application for adsorption of cerium(III)

Recycling rare earth elements (REEs) from waste is necessary for an environmentally sustainable reuse and wastewater management approach. Na-A zeolite was synthesized from coal fly ash (CFA) and applied for Ce3+ adsorption. Fourier transform infrared (FTIR) spectra show peaks at 790, 500 and 467 cm−1, which are bond vibrations of Si–O–Si, Si with Al–O and Si–O–. The surface area is 15.88 m2/g, with a pore size of 2.14 nm. SEM images show a cubic shape, which indicates the formation of zeolite. Field emission and energy disperse spectroscopy (EDS) shows the formation of Si, Al, Na, and O. Na-A zeolite was applied for Ce3+ adsorption. The optimum conditions for Ce3+ adsorption are 50 ppm concentration, 360 min, and pH 6. The maximum adsorption capacity is 176.49 mg/g. Based on the results, it is found that the adsorption of Ce3+ by Na-A zeolite is pseudo-second-order. The desorption test using HNO3 is more effective than using HCl and H2SO4. A desorption efficiency of 97.22 % is obtained at 4 cycles. Adsorption test using real sample wastewater demonstrates an adsorption efficiency of 83.35 %.

Microbial synthesized iron nanoparticles after recovering rare earth elements used for removing arsenic in mine groundwater

Recycling rare earth elements (REEs) from secondary sources such as mine wastewater has emerged as a sustainable economic strategy. In this study, microbial synthesized iron nanoparticles after the recovery of rare earth elements (FeNPs/REEs) have been used as an environmentally friendly material to remove arsenic from mine groundwater. The removal efficiencies of As(III) and As(V) were 94.5% and 96.0%, respectively, compared to that of As(III) (44.5%) and As(V) (66.5%) using only FeNPs. Indicated here is that the efficiency of FeNPs/REEs in removing arsenic was better than those of FeNPs. IC-AFS and XPS analysis showed that As(III) was partially oxidized to As(V) during the adsorption process via electron transfer. Electrochemical and BET indicated that FeNPs/REEs not only helped to expose more active sites but also the catalytic activity was enhanced. Meanwhile SEM-Mapping and FTIR demonstrated that arsenic was adsorbed onto the surface of FeNPs/REEs through complexation and ion exchange. Furthermore, Zeta potential analysis revealed electrostatic interactions between arsenic and FeNPs/REEs at pH = 6.0. Thus, the key physicochemical properties for the removal of As(III) and As(V) by FeNPs/REEs were statistically analyzed via Pearson correlation analysis, in order to understand the removal mechanism of arsenic involving surface complexation, oxidation, electrostatic and ion exchange. Finally, efficiency was consistently high in removing arsenic from mine groundwater using FeNPs/REEs with As (73.0%), Pb (76.0%), and Fe (36.0%). This study generates a new insight into FeNPs/REEs used in groundwater remediation.

Rare earth element recovery and aluminum-rich residue production from high alumina fly ash by alkali pre-desilication enhance the mechanochemical extraction process

Recycling rare earth elements (REEs) from coal fly ash by conventional acid leaching may generate large amounts of harmful waste acid, and the obtained acid residues have low utilization value. Accordingly, a green non-acid leaching approach for REE recovery and Al-rich residue production from high alumina fly ash (HAFA) was developed based on the alkali pre-desilication enhanced mechanochemical extraction process. REEs mainly existed in the chemically stable amorphous aluminosilicate glass phase of HAFA, which hindered the leaching of REEs. Thus, NaOH solution (150 g/L) was used to dissolve the glass phase and release REEs from the glass phase under a mild condition (80 °C, 2 h). The released REEs could be easily extracted by green EDTA during the mechanochemical extraction process. The extraction rates of La, Ce, Pr and Nd were about 82.03–88.71%, and valuable Al-rich residue (68.23% Al2O3 content and 2.51 Al/Si ratio) can be obtained when the mass ratio of the pre-desilication residue to EDTA, milling time, rotary speed, and liquid-solid ratio were 2:3, 2 h, 500 rpm, and 0.8, respectively. The used EDTA and REEs in the extracted solutions can be recycled by pH adjusting and organic solvent extraction. Thus, this study provides a new idea for green and high-value utilization of HAFA.

Recovery of rare earth elements from mine wastewater using biosynthesized reduced graphene oxide

Recycling rare earth elements (REEs) from sources of secondary waste such as REEs mine wastewater has emerged as a sustainable approach with both waste reuse and wastewater processing. In this study, green reduced graphene oxide (G-rGO) was prepared utilizing green tea extract with the advantages of being environmentally friendly, sustainable, and low cost. To understand how G-rGO functions, it was compared to commercial reduced graphene oxide (rGO), and the efficiencies in adsorbing Y(III) were 91.6% and 11.9%, respectively. This indicated there is a synergistic adsorption between the capping layer of G-rGO and rGO alone. G-rGO and rGO were characterized before and after exposure to Y(III). This comparison indicated that Y(III) was adsorbed on the surface of G-rGO through complexation and electrostatic interaction. The adsorption kinetics best fit the pseudo-second-order model and the Langmuir model isotherm model, with adsorption capacities of 24.54 mg g−1. A probable adsorption mechanism of Y(III) by G-rGO was proposed, involving electronic complexation, electrostatic adsorption and ion exchange. Furthermore, the adsorption efficiencies of G-rGO for Y(III), Ce(III) and Zn(II) in mine wastewater were 22.1%, 89.1% and 14.6%, respectively. These results demonstrate that G-rGO has great potential in the recovery of REEs from mine wastewater.

РІДКІСНОЗЕМЕЛЬНІ МЕТАЛИ ЯК КРИТИЧНА СИРОВИНА. КОРОТКИЙ ОГЛЯД

Rare earth metals REE is vital to modern technology and society and are among the most critical elements. The general physical properties of REE, the history of their discovery, the main natural resources and general applications are highlighted. The criteria by which REE belong to critical raw materials (deficit risk factor, economic importance) are considered. Europe, erbium and dysprosium have the highest vulnerability to supply constraints at the global level. The world's largest producer of REE by a wide margin from competitors is China (in 2021, about 168000 metric tons of rare earth oxides were mined). Ukraine has significant resources of rare earth metals, although it does not produce them. Here are known deposits of both traditional types associated with carbonates (Novo-Poltava) and Mariupolites (Oktyabrske) and non-traditional: rich zirconium and rare earth-zirconium ores of non-core siesites (Azov and Yastrebetske). Ores of most deposits of Ukraine belong to the poor, which are difficult to attract into operation. The structure of REE use has changed significantly over the past 20 years. If in the 90s of the twentieth century about one-third of resources were used for polishing glass and making ceramics, today this segment is occupied by permanent magnets of various applications. Rare earth magnets have become virtually indispensable in a wide range of strategic industries such as aerospace, automotive, electronic, medical and military industries. REE is actively used for high-efficiency engines of hybrid-electric vehicles and in wind power. Attention is focused on REE recycling technologies. Onlyabout 1% of RSM is processed from final products, and the rest is taken out of waste and removed from the material cycle. The main ways of recovery are hydrometallurgical and pyrometalurgical methods, as well as phytoextraction. Recycling rare earth elements from e-waste can significantly contribute to sustainability and environmental protection.

Separation and Recycling Potential of Rare Earth Elements from Energy Systems: Feed and Economic Viability Review

This review explores the potential of separating and recycling rare earth elements (REEs) from different energy conversion systems, such as wind turbines, electric vehicles batteries, or lighting devices. The REEs include 17 elements (with global production of 242 kilometric tons in 2020) that can be found abundantly in nature. However, they are expensive and complicated to extract and separate with many environmental challenges. The overall demand for REEs is continuously growing (with a 10% yearly increase) and it is quite clear that recycling has to be developed as a supply strategy in addition to conventional mining. However, the success of both mining and recycling depends on appropriate separation and processing technologies. The overall REE recycling situation today is very weak (only 2% of REEs are recovered by recycling processes compared with 90% for iron and steel). The biggest recycling potentials rely on the sectors of lamp phosphors (17%), permanent magnets (7%), and NiMH batteries (10%) mainly at the end-of-life stage of the products. The profitability of rare earth recycling mostly depends on the prices of the elements to accommodate the processing costs. Therefore, end-of-life REE recycling should focus on the most valuable and critical REEs. Thus, the relevant processes, feed, and economic viability warrant the detailed review as reported here.

Recovery of rare earth elements from electronic waste by diffusion dialysis

Recycling rare earth elements (REEs) contained in electronic waste is of utmost importance due to their ever-increasing use in the high-tech sector. In this context, the use of non-polluting techniques represents a real challenge for scientists. In this work, we demonstrated that a clean and energy-efficient process, diffusion dialysis, has great potential for the recovery of neodymium (Nd) and praseodymium (Pr), contained in the Nd-Fe-B magnets of end-of-life computer hard disk drives (HDDs). Four kinds of polymer membranes were prepared by blending cellulose triacetate (CTA) and polyethylenimine (PEI) with the addition of di-(2-ethylhexyl) phosphoric acid (D2EHPA), tridodecylamine (TDDA), trioctylamine (TOA) or trioctylphosphine oxide (TOPO). The membranes were first characterized by several techniques such as water uptake, contact angle, ATR-FTIR, SEM, XRD and zeta potential. They were further implemented in diffusion dialysis experiments in which diluted HDDs leachates were used as feed solutions. The relevance of the diffusion dialysis process for the recovery of REEs was demonstrated as it was possible to extract up to 15% of the boron by spontaneous diffusion through the CTA/PEI/TOA membrane in 6 h with a lab-scale cell operating in batch mode. All membranes were positively charged under the operating conditions and then, REEs (present mainly in the form of trivalent cations Nd3+ and Pr3+) were strongly rejected. A fairly good correlation was found between the membrane water uptake and boron transfer, with boric acid molecules passing more easily through the more hydrated membranes. The selectivity factor between boron and REEs resulted from the interplay between the membrane structure, its water uptake ability and surface charge. It was also found to be dependent on the leachate composition. The CTA/PEI/TDDA membrane was found to exhibit the greatest B/REE selectivity factors, with values reaching up to 3706 and 140 for Nd and Pr, respectively. The lower selectivity towards Pr was explained by the weaker Gibbs energy of hydration of Pr3+ cations compared with Nd3+.

Resource Recovery of Waste Nd–Fe–B Scrap: Effective Separation of Fe as High-Purity Hematite Nanoparticles

Recycling rare-earth elements from Nd magnet scrap (Nd–Fe–B scrap) is a highly economical process; however, its efficiency is low due to large portions of Fe impurity. In this study, the effective separation of Fe impurity from scrap was performed through an integrated nitric acid dissolution and hydrothermal route with the addition of fructose. Results showed that more than 99% of the scrap was dissolved in nitric acid, and after three dilutions that the Nd, Pr, Dy and Fe concentrations in the diluted acid were 9.01, 2.11, 0.37 and 10.53 g/L, respectively. After the acid was hydrothermally treated in the absence of fructose, only 81.8% Fe was removed as irregular hematite aggregates, whilst more than 98% rare-earth elements were retained. By adding fructose at an Mfructose/Mnitrate ratio of 0.2, 99.94% Fe was precipitated as hematite nanoparticles, and the loss of rare-earth elements was <2%. In the treated acid, the residual Fe was 6.3 mg/L, whilst Nd, Pr and Dy were 8.84, 2.07 and 0.36 g/L, respectively. Such composition was conducive for further recycling of high-purity rare-earth products with low Fe impurity. The generated hematite nanoparticles contained 67.92% Fe with a rare-earth element content of <1%. This value meets the general standard for commercial hematite active pharmaceutical ingredients. In this manner, a green process was developed for separating Fe from Nd–Fe–B scrap without producing secondary waste.

Comparison of Different Leaching Media and Their Effect on REEs Recovery from Spent Nd-Fe-B Magnets

Recycling rare-earth elements (REEs) from Nd-Fe-B magnet waste is an important step towards building a sustainable REE supply chain. In this study, two different processes were systematically investigated and compared. In the leaching stage, the effect of increasing H2SO4 or HCl concentrations were studied and it was determined that, although both can successfully promote REEs, B, Fe and Co leaching, HCl solutions extracted a wider range of metals. After leaching, the oxalate and double-sulfate precipitation methods were utilized to separate REEs from either HCl or H2SO4 leachates. Results suggest that, although > 99% REEs precipitation rates could be achieved with oxalate, the purity of REE-containing products is significantly affected by impurities like Fe and Co. In contrast, REE double-sulfate precipitation resulted in a product purity of > 99%; however, high levels of Na2SO4 (8 times the stoichiometric amount) were needed to achieve > 98% of REE precipitation.

Extraction of Rare Earth Elements from Chloride Media with Tetrabutyl Diglycolamide in 1-Octanol Modified Carbon Dioxide

Rare earth elements (REEs) are critical to our modern world. Recycling REEs from used products could help with potential supply issues. Extracting REEs from chloride media with tetrabutyl diglycolamide (TBDGA) in carbon dioxide could help recycle REEs with less waste than traditional solvents. Carbon dioxide as a solvent is inexpensive, inert, and reusable. Conditions for extraction of Eu from aqueous chloride media were optimized by varying moles percent of 1-octanol modifier, temperature, pressure, Eu concentration, TBDGA concentration, Cl− concentration, and HCl concentration. These optimized conditions were tested on a Y, Ce, Eu, Tb simulant material, REEs containing NdFeB magnets, and lighting phosphor material. The optimized conditions were found to be 23 °C, 24.1 MPa, 0.5 mol% 1-octanol, with an excess of TBDGA. At these conditions 95 ± 2% Eu was extracted from 8 M (mol/m3) HCl. Extraction from the mixed REE simulate material resulted in separation of Y, Eu, and Tb from the Ce which remained in the aqueous solution. The extraction on NdFeB magnet dissolved into 8 M HCl resulted in extraction of Pr, Nd, Dy, and Fe >97%. This results in a separation from B, Al, and Ni. Extraction from a trichromatic lighting phosphor leachate resulted in extraction of Y and Eu >93% and no extraction of Ba, Mg, and Al.

Recycling rare earth elements from waste cathode ray tube phosphors: Experimental study and mechanism analysis

In this work, we developed a clean and efficient process for recycling rare earth elements from waste CRT phosphors. A mixture of sulfuric acid and hydrogen peroxide was used for the oxidative leaching of the rare earth elements, and the leaching efficiencies of both Y and Eu reached 99% under the optimal leaching conditions: 3 M H2SO4, 4 vol.% H2O2, 55 °C, and 1 h. The S2− was oxidized to S0, which efficiently avoided the sulfur pollution produced by existing technologies. The green solvent ionic liquid [OMIm][PF6] and the extractant Cyanex272 were employed for the separation of the rare earths. The optimal extraction parameters were determined to be 0.2 mol/L H2SO4, 0.4 vol.% of Cyanex272 in the organic phase, a 10:1 A/O ratio, and an extraction time of 20 min at room temperature, under which, the individual extraction efficiencies of Y, Eu, Zn, and Al were 99%, 87, 8%, and 0%, respectively, and the separation factor of rare earth to Zn reached 593. Additionally, the extraction system could be recycled and reused by stripping. The mechanisms of the leaching and extraction process were also analyzed. Based on a kinetics study, the leaching process was found to follow the model of diffusion-control via the product layer, and the apparent activation energies for Y and Eu were calculated to be 75.86 kJ/mol and 77.06 kJ/mol, respectively. Meanwhile, a simulated leaching model based on diffusion through the solid S0 layer was established. The synergistic extraction mechanism was also discussed, and a cation exchange reaction was speculated to occur between the rare earth elements and Cyanex272. The findings in this study are expected to provide an effective and practical method for the recovery and reutilization of waste CRT phosphors.

Selective Extraction of Rare-Earth Elements from NdFeB Magnets by a Room-Temperature Electrolysis Pretreatment Step

NdFeB magnets are used in wind turbines and hybrid electric vehicles and are instrumental in progression toward a low-carbon economy. Recycling rare-earth elements (REEs) from NdFeB magnet waste is an important step toward building a sustainable REE supply chain. In this study, we describe an electrochemical process to selectively extract REEs from NdFeB magnet waste at room temperature. First, an electrolysis pretreatment step was performed to convert the elements present in the magnet waste into the respective hydroxides. A dual anode system was used where NdFeB magnet waste was taken as an anode along with an inert anode in an electrochemical reactor. The inert anode was used to ensure that iron in the magnet waste was converted into the Fe(III) form in the mixed hydroxides precipitate. Subsequently, the mixed hydroxides were leached with HCl. More than 97% of REEs and cobalt leached into the solution leaving iron in the residue. REEs were then selectively precipitated as rare-earth oxalates using oxal...

Novel Polyethylenimine–Acrylamide/SiO2 Hybrid Hydrogel Sorbent for Rare-Earth-Element Recycling from Aqueous Sources

Recycling rare earth elements (REEs) becomes increasingly important due to their supply vulnerability and increasing demands in industry, agriculture, and national security. Hybrid hydrogel sorbents were outstanding due to their high stability and selectivity. Organic-inorganic hybrid hydrogels were synthesized by thermo-polymerization of acrylamide onto PEI polymer chain with N,N’-methylene bisacrylamide as a crosslinker. The grafted network was evidenced by DRIFTS and XPS. The porous structure was observed by SEM. Crosslink degree, PEI grafting degree, and SiO2 concentration were studied to optimize the REEs adsorption. The pH value of the medium greatly affected REE adsorption capacity, where the nearly neutral conditions gave the strongest bonding of REEs to active sites. Moreover, kinetic studies showed that the rate-determining step of the adsorption process was chemical sorption, and that REE diffusion within micropores was the control step for, specifically, intraparticle diffusion. The adsorbents...

Mechanism and kinetics of the BaMgAl10O17:Eu2+ alkaline fusion reaction

Knowledge of the kinetics and mechanism of BaMgAl10O17:Eu2+ (BAM) fusion with sodium hydroxide will benefit recycling rare earth elements (REEs) from the waste phosphors. The reaction temperature range of 290–375 °C and the reaction mechanism were determined using X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Activation energy was determined by the four model-free methods, and calculated results showed that the Kissinger method value of 579.5 KJ/mol was close to the average value of the Kissinger-Akahira-Sunose (KAS) and the Flynn-Wall-Ozawa (FWO) methods of 563.5 kJ/mol. The calculated activation energy variation tendency versus conversion factor agreed with the proposed mechanism.

Recovery and separation of rare Earth elements using salmon milt.

Recycling rare earth elements (REEs) used in advanced materials such as Nd magnets is important for the efficient use of REE resources when the supply of several REEs is limited. In this work, the feasibility of using salmon milt for REE recovery and separation was examined, along with the identification of the binding site of REEs in salmon milt. Results showed that (i) salmon milt has a sufficiently high affinity to adsorb REEs and (ii) the adsorption capacity of the milt is 1.04 mEq/g, which is comparable with that of commercial cation exchange resin. Heavier REEs have higher affinity for milt. A comparison of stability constants and adsorption patterns of REEs discussed in the literature suggests that the phosphate is responsible for the adsorption of REE in milt. The results were supported by dysprosium (Dy) and lutetium (Lu) LIII-edge extended x-ray absorption fine structure (EXAFS) spectroscopy. The REE-P shell was identified for the second neighboring atom, which shows the importance of the phosphate site as REE binding sites. The comparison of REE adsorption pattern and EXAFS results between the milt system and other adsorbent systems (cellulose phosphate, Ln-resin, bacteria, and DNA-filter hybrid) revealed that the coordination number of phosphate is correlated with the slope of the REE pattern. The separation column loaded with milt was tested to separate REE for the practical use of salmon milt for the recovery and separation of REE. However, water did not flow through the column possibly because of the hydrophobicity of the milt. Thus, sequential adsorption–desorption approach using a batch-type method was applied for the separation of REE. As an example of the practical applications of REE separation, Nd and Fe(III) were successfully separated from a synthetic solution of Nd magnet waste by a batch-type method using salmon milt.

Scarcity of Rare Earth Elements

Rare earth elements (REEs) are important for green and a large variety of high-tech technologies and are, therefore, in high demand. As a result, supply with REEs is likely to be disrupted (the degree of depends on the REE) in the near future. The 17 REEs are divided into heavy and light REEs. Other critical elements besides REEs, identified by the European Commission, are also becoming less easily available. Although there is no deficiency in the earth's crust of rare earth oxides, the economic accessibility is limited. The increased demand for REEs, the decreasing export from China, and geopolitical concerns on availability contributed to the (re)opening of mines in Australia and the USA and other mines are slow to follow. As a result, short supply of particularly terbium, dysprosium, praseodymium, and neodymium is expected to be problematic for at least the short term, also because they cannot be substituted. Recycling REEs from electronic waste would be a solution, but so far there are hardly any established REE recycling methods. Decreasing the dependency on REEs, for example, by identifying possible replacements or increasing their efficient use, represents another possibility.

A Simple Assessment of the Global Long Term Supply of the Rare Earth Elements by Using a System Dynamics Model

Our simple dynamic-simulation model shows that the global supply of Rare Earth Elements is limited for meeting the future demands of new technologies. Unless improved recycling policies are adapted strategic elements may become scarce in the next half-century as a result of a “peak Rare Earths Elements” phenomenon. The model results also show that the market alone cannot solve the resource-inefficiency problem because the market’s instant and opportunistic nature impedes the long-term planning that is needed. Market mechanisms will only function if governments discourage wasteful practices by requiring recycling and long-term planning as conditions for the industry before the resource becomes too scarce. We conclude that technologies and industrial capacity for effectively recycling Rare Earth Elements will be in demand, and that effective recycling policy should be put in place soon to make the supply sustainable over the long-term (Less)