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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Developing a one-step, acid-free microbial process to recover and separate REE (CRADA Final Report)

The project aimed to develop and test microbial strains for increased bioleaching, bioconcentration, and/or bioaccumulation of REEs, and for enhanced separation of REEs from other metals and of individual REEs from one another. The team secured and tested unconventional REE feedstocks to evaluate strains/processes for bioleaching, bioconcentration, and bioaccumulation, including but not limited to wastewater, geothermal brines, red mud, and electronic waste. purified and chemically analyzed REE granules from the microbial platform; determined metabolite and biosynthetic impacts of growth with REEs and the composition of extracellular material(s) produced by platform strains; optimized the growth process with alternative carbon feedstocks to reduce the cost of the fermentation process; and scaled the process from 1 mL to 10 L.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Multi-Sourced Collaboration for the Production and Refining of Rare Elements and Critical Metals (Final Technical Report)

The project objective was to develop a feasible and cost-effective method for recovering rare earth elements (REEs) and critical materials (CMs) from coal and coal byproducts, resulting in high-purity individually separated REEs and CMs. The targeted REEs included Y, Pr, Nd, Gd, Dy, and Sm, with a purity of over 99.5%, while the CMs included Co, Mn, Ga, Sr, Li, Ni, Zn, and Ge, with a purity of over 90%. The project aimed to design a prototype facility capable of producing 1-3 tonnes/day of high-purity REO mixes. The work was divided into four designated circuits: 1) REE extraction and concentration, 2) REE separation and purification, 3) RE metal production, and 4) CM production. To achieve these goals, the project involved 11 tasks, including technology reviews, research, process flow diagram development, mass balance estimation, and preliminary technical-economic analysis. The project team included researchers from the University of Kentucky, University of Alabama and Virginia Tech as well as process specialists from Argonne National Laboratory. MP Materials provided technical support regarding rare earth markets and processing while Alliance Coal performed resource assessment. The project included a market analysis for Nd/Pr, Tb, Dy, Gd, Y, Co, Mn, Li, Sr, Ga, Ni, Zn, and Ge. These analyses provided insights into the supply and demand trends as well as historic and future projections of market price relative to purity requirements for these elements. Two coal resources were selected for the project: the West Kentucky No. 13 (Baker) Seam and an undisclosed lignite resource in the Illinois coal basin. The estimated quantities of REEs in these resources were calculated based on production samples and drilling data. It was estimated that there is adequate supply for an operation producing one metric ton daily of higher purity mixed rare earth oxides (MREO) for approximately 20 years at a site located in western Kentucky. In Circuit 1, project data was obtained from a pilot heap leach and REE concentration facility. It was concluded that the existing circuit, which generated a MREO concentrate, two types of CM mixed products, and Li- and Sr-containing waters, would be suitable feed for circuits 2-4. Data from the first-of-its-kind coal coarse refuse heap leach pilot pad played a crucial role in estimating reliable elemental concentrations of the pregnant leaching solution (PLS). The average total REE concentration in the PLS was found to be 28.6 ppm. In Circuit 2, several concepts were explored including a novel process referred to as solvent-assisted chromatography (SAC). This concept involved a novel columnar reactor that incorporated multiple mixer/settlers, thereby enabling the operation of counter-flowing aqueous and organic phases. Unfortunately, due to project time constraints, a complete fundamental modeling analysis could not be completed to fully evaluate the technology. Molten salt electrowinning was considered as an alternative for circuit 3 following circuit 2 purification circuit utilizing the novel SAC process. A mass and energy balance of Nd reduction to metal in a fluoride containing molten salt electrolyte was conducted. Comparisons were made with the current state of Asian molten salt electrorefining, and potential improvements in siphoning rare earth metals (REM) from the reactor were presented. A cost estimate was performed for the production of 1 tonne per day, which yielded a total of $2.29 million for the nine electrowinning (EW) cells required. The selected option for circuits 2 and 3 was a plasma distillation process, which initially separates rare earth elements (REEs) from other elements. This is followed by selective electrowinning in various ionic liquids. The selection was made on the basis of thermodynamic modeling and experimental data previously published by a project partner. The combination offers an innovative approach to integrated refining and RE metal production. For Circuit 4, an extensive literature review was conducted for the processing of the CMs. The ultimate decision was to utilize a combined plasma and ionic liquid process as well to produce individual high-purity concentrates of Zn, Ni, Co, Mn, and Mg. A separate flowsheet for Li and Sr was recommended, which would yield carbonates of these elements. Due to the lack of suitable experimental data at this time, a process recommendation could not be provided but several methods have been proposed for consideration. Lastly, a techno-economic analysis (TEA) was conducted to assess the effectiveness of the proposed process for further investigation. The TEA results revealed a capital expense (CapEx) of $737 million and an annual operational expense (OpEx) of $220 million. Due to the selected elements, the hypothetical heap leach pad can produce 1 metric tonne per day of REO equivalent, but a conscious decision was made to only treat targeted REEs, resulting in the production of 0.4 metric tonne of REM. An estimated annual revenue of $90.87 million was projected based on standard market pricing information provided by the funding agency. During the TEA, ten different modules were evaluated for costing purposes. The precipitation circuit was identified as the largest single operational expense, followed by the Mg/Mn process due to the amount of treated metal. In terms of capital expenditures, the heap leach process incurred the highest cost, followed by the Mg/Mn process. The scalability of the plasma process is a crucial consideration since the reactors cannot be scaled beyond the largest demonstrated size due to their reliance on surface area of the slag and vapor phase. The purity estimate for the REEs are generally 98%±2% to produce a metal. The purity level being lower than the project objective was due to the lack of specific experimental data needed to tighten the tolerance of the estimates. Based on literature and previous experience, the CMs are estimated as follows; Ga (95%+, metal), Sr (95%+, carbonate), Li (95%+, carbonate), Ni (98%±2%, metal), Zn (95%+, metal sponge), Ge (95%+, metal), Co (98%±2%, metal), and Mn (98%±2%, metal).

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2026

Ion-Specific Precipitation of Extractants Enables Rare-Earth Separation and Wastewater Remediation from Solvent Extraction of Critical Elements

The increasing demand for rare-earth elements (REEs) necessitates sustainable recovery strategies, particularly from secondary sources, such as electronic waste. Solvent extraction is the primary industrial method for REE separation; however, the unintentional dissolution of extractants into wastewater poses serious environmental risks, leading to organic contamination and process inefficiencies. Existing wastewater treatment methods struggle to remove these persistent pollutants, underscoring the need for innovative recovery approaches. Herein, we present a ligand-mediated precipitation strategy that simultaneously recovers REEs and removes dissolved extractants from solvent extraction wastewater. We show that residual extractants in the aqueous phase can selectively bind REEs, inducing their precipitation while leaving transition metals in solution. By integrating FTIR spectroscopy, EDS, XPS, EXAFS, and SAXS, we elucidate the mechanism of ion-specific precipitation and the local coordination environment of metal ions in the precipitate. Importantly, we demonstrate that the precipitated extractants can be efficiently recovered and reused, providing a closed-loop solution that enhances sustainability. Applying this method to leachates from samarium–cobalt (Sm–Co) and neodymium–iron–boron (NdFeB) mixed magnets, we achieve highly selective REE precipitation under mild conditions, demonstrating a scalable and cost-effective pathway for REE recovery, wastewater purification, and extractant recycling. In conclusion, by integrating element-specific ligand-mediated precipitation with extractant reuse, this work offers a transformative approach to REE separation that reduces the environmental impact while improving resource efficiency.

E-waste↗
DOE OSTI2022

Recent advances in the global rare-earth supply chain

The current global rare-earth element (REE) supply chain is highly imbalanced and tightly controlled by just a few countries. Such an imbalance of the critical metals supply chain poses a significant challenge to the energy-transition strategies and the national security of many countries. As such, this issue of MRS Bulletin delves into the materials science aspects of the REE supply chain, including fundamental REE mineralogy, REE separation and extraction, REE mining economics, the environmental impacts of REE mining and processing, and circular economy potential for REEs. This issue of MRS Bulletin is meant to inform the materials science community of some of the constraints on REE production from the mining of ore deposits, through processing technologies, and then finally, the possibility of recycling.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2025

X-ray absorption spectroscopy of lanmodulin-derived peptides bound to rare earth elements

A sustainable and robust supply chain of rare earth elements (REEs) is necessary to meet our consumer, national security and clean energy goals. However, current intra-REE separation technologies (e.g. solvent extraction) are costly and carry a heavy environmental burden. Therefore, the development of new aqueous based ligands that are selective for individual REEs will be integral in future REE production systems. To develop these ligands, an understanding of how ligand coordination structure relates to selectivity is imperative. We used X-ray absorption spectroscopy (XAS) to observe the local structure around four lanthanide (Ln) ions (La, Ce, Pr and Nd) complexed by water and several relevant chelating ligands [lanmodulin EF-hand 1 peptides (LanM1), ethyl­enedi­amine­tetra­acetic acid (EDTA), amino­tris­(methyl­ene­phospho­nic acid) (ATMP) and citric acid]. To collect these liquid-phase XAS spectra, we developed a new flow cell that prevents bubble interference and beam damage to the samples. In the X-ray absorption near-edge structure (XANES), we observed energy shifts in the white line, white line broadening and differences in the white line intensity of different Ln–ligand complexes between ligands. In the extended X-ray absorption fine structure (EXAFS), we distinguished differences in peak intensity and distance between coordinating ligands. Differences in the local coordination structure between Ln–LanM1 peptide complexes were more subtle compared with the other ligands (La–water, La–EDTA, La–ATMP and La–citric acid complexes). Further XANES and EXAFS studies, in combination with modelling and other techniques, could greatly improve our structural knowledge of how these aqueous ligands bind Ln ions and how they can be used to design more selective ligands for more efficient and sustainable REE separations.

EDTA↗
DOE OSTI2026

Microchannel-based Membrane-less Extraction of Li from Unconventional Lithium Sources & the Separation of REE

This final report provides an overview of the Project's entire duration, covering July 1, 2021 to December 31, 2023. It primarily focuses on the achievements, technological developments, and unique challenges the team faced while working on separating and extracting Lithium from produced waters. The project's primary aim was to create an integrated, high-throughput, membrane-less, and modular microfluidic platform that could extract Lithium from unconventional sources. We have successfully met all goals and milestones envisioned in the SOPO document. The most critical primary milestones, including the Go-No-Go milestone (refer to the Gantt chart in the Appendices), were successfully accomplished. We demonstrated phase separation (>90%) and extraction (>85%) performance in the MPSE using synthetic, and representative produced water composition feed at 50 ml/min total flow through MPSE 36. We have also performed a parametric study of the MPSE operations, beyond the scope of SOPO, exploring operating conditions of current and broader interest. The extended investigation of operational parameters is concurrent with our efforts to seek further development of the MPSE technology beyond the scope of the Project. Along these lines of development, we have made efforts to be responsive to DOE calls for technological developments of other types of resources (beyond PW) for the recovery of Critical Materials and higher TRL development (beyond TRL 4). During the work on this Project, we developed and implemented three innovative technical approaches that emerged from our efforts to successfully meet the Project milestones. The innovative & original technical approaches developed and implemented in this Project are now the contributions to process engineering that could be clearly credited to the Project. First, Convergent Design Approach is a comprehensive feedforward & feedback loop of four design phases: i) design for functionality, ii) design for manufacturing, iii) design for sustainability, and iv) design for market. Next was Process Intensification. A major aim of this Project was to create an innovative phase separation & extraction microscale-based technology for Li separation – thus the words microchannel-based in the Project title. A microscale-based technology is intrinsically in the center of the Process Intensification domain as defined by its unique principles. Therefore, Process Intensification was implicitly envisioned in the Project’s SOPO. Lastly, Time Scale Analysis is a novel tool for discovering the needs and directions of Process Intensification implementations in any process technology. This Project is fully credited for developing and implementing the three novel technical approaches mentioned above. These are general contributions to process engineering that emerged from this Project. Beyond the original SOPO scope, the OSU-U.Pitt research group utilized a Convergent Design methodology, integrating first-principles mathematical modeling with experimental validation on the Minimum Development Vehicle. By creating these Digital Twins, the team rapidly assessed manufacturing iterations to support TEA analysis. This framework further enabled the development of advanced Surface Modification Techniques, where hydrophobic and oleophobic coating strategies were optimized via Digital Twin tools and validated through rigorous 100-hour longevity testing. TEA Analysis: The closing efforts of this Project were focused on the TEA analysis. TEA analysis had two primary functions: i) enabling critical assessments of design variations withing 10 the Concurrent Design Approach, thus enabling evolution of the MPSE design to reach faster- better-cheaper alternatives; and ii) to create a bridge between the accomplishments of this Project and future projects of higher TRL, beyond TRL 6 level. It is important to note that the TEA model created in the Project stirred the technological solutions for the recovery of critical materials toward a vision of a very profitable modular plant that has unique zero-waste water discharge signature. More importantly, thanks to our experimental performance data and conservative assumptions, the TEA model predicts minimal technological and investment risks. Low cost of a modular unit of a nominal capacity of [1000 tons of Li 2 CO 3 /year] positions the MPSE based technology within the reach of community investors, thus offering a paradigm shift in the development of critical technologies. The project successfully navigated two primary challenges: solvent selection and manufacturing adaptation. Restricted by the SOPO to existing literature for lithium recovery, the team identified a critical need for a "material excellence program" to develop next-generation solvents, eventually concluding with a preliminary investigation into promising Ionic Liquids (ILs). Simultaneously, COVID-19 supply chain disruptions forced a pivot from traditional manufacturing to advanced additive methods at ATAMI-OSU. By transitioning from stainless steel to 3D-printed polymer substrates, the team achieved a transformative three-order-of- magnitude reduction in manufacturing costs and compressed prototyping timelines from several months to just two days. The MPSE technology offers significant energy, environmental, and economic advantages by overcoming the traditional bottlenecks of phase-separation hardware and contactor size. Unlike conventional mixer-settlers or membrane-based systems, MPSE operates without moving parts or fouling-prone membranes, achieving robust performance even with challenging, viscous, or particulate-heavy feeds. Key performance metrics include an energy intensity reduction of 5–50x (3–40 kJ/m 3 ) compared to incumbent technologies and a dramatic reduction of processing time to under 60 seconds, which drastically reduces the physical plant footprint. These technical efficiencies translate into superior economic outcomes; for a 100 t/year Li 2 CO 3 facility, implementing MPSE is projected to nearly halve contactor CAPEX (from $\$$6.08M to $\$$3.01M) and significantly increase the project's Net Present Value (NPV), derisking new investment and enabling distributed critical-mineral processing configurations. The commercialization of MPSE technology is being spearheaded by Vigsur Dynamics Inc., which has adopted a structured, parallel approach to technical and business development since its formation in January 2026. Following extensive customer discovery and engagement with the Oregon State University accelerator, Vigsur Dynamics is working to establish a business model that transitions from pilot demonstrations to modular hardware sales, ultimately aiming for a "build-own-operate" service strategy. Current technical milestones—including 100 hours of continuous operation, superior energy efficiency, and successful 6-unit modular scale-up— provide a foundation for this transition. Backed by ongoing IP licensing and a growing network of industrial and venture advisors, the company is actively de-risking the platform to replace conventional mixer-settler systems in the critical minerals market.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

The Coordination Chemistry and Stoichiometry of Extracted Diglycolamide Complexes of Lanthanides in Extraction Chromatography Materials

Industrial rare earth element (REE) separations predominantly utilize solvent extraction processes tailored toward conventional resources such as bastnäsite, monazite, and ion adsorption clays. Advances in diglycolamide (DGA) chemistry have shown effective extraction characteristics for REE separations. However, limitations associated with traditional DGA solvent extraction techniques, such as third-phase formation and gelling, have hindered commercial viability. By supporting DGA extractants on porous resins such as polystyrene divinyl benzene (PS-DVB), the desirable combination of solvent extraction selectivity and ease of operation of sorbent columns can be achieved. To design a low-cost model for such solid-supported DGAs, extraction characteristics as influenced by the underlying coordination chemistry must be explored to achieve efficient functional systems. Within this study, we report novel DGA resin materials, each incorporating one of the DGAs N,N,N’,N’-tetra-(1-octyl)-3-oxapentane-1,5-diamide (TODGA), N,N'-dimethyl-N,N'-dioctyl-3-oxapentane-1,5-diamide (DMDODGA), and 2,2'-oxybis(1-(3-(((2-ethylhexyl)thio)methyl)-4-methylpyrrolidin-1-yl)ethan-1-one) (DEHPDGA). The affinity of DGAs across the lanthanide (Ln) series was evaluated for both hydrochloric acid and nitric acid media with varying Ln feed concentrations to study distribution ratios and loading characteristics. Focusing on dysprosium, extended X-Ray Absorption Fine Structure (EXAFS) and density functional theory (DFT) calculations were also utilized to explore coordination chemistry and their effects on ligand performance. The general trend for both acid media resulted in DMDODGA having the highest extraction strength of all three DGAs at varying acid concentrations. Coordination-chemistry analysis supported by loading data, DFT calculations, and EXAFS results under forced loading conditions posited less than the expected 3:1 ligand-to-metal coordination.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Insights into coordination and ligand trends of lanthanide complexes from the Cambridge Structural Database

Abstract Understanding lanthanide coordination chemistry can help develop new ligands for more efficient separation of lanthanides for critical materials needs. The Cambridge Structural Database (CSD) contains tens of thousands of single crystal structures of lanthanide complexes that can serve as a training ground for both fundamental chemical insights and future machine learning and generative artificial intelligence models. This work aims to understand the currently available structures of lanthanide complexes in CSD by analyzing the coordination shell, donor types, and ligand types, from the perspective of rare-earth element (REE) separations. We obtain four sets of lanthanide complexes from CSD: Subset 1, all Ln-containing complexes (49472 structures); Subset 2, mononuclear Ln complexes (27858 structures); Subset 3, mononuclear Ln complexes without cyclopentadienyl ligands (Cp) (26156 structures); Subset 4, Ln complexes with at least one 1,10-phenanthroline (phen) or its derivative as a coordinating ligand (2226 structures). The subsequent analysis of lanthanide complexes in these subsets examines the trends in coordination numbers and first shell distances as well as identifies and characterizes the ligands and donor groups. In addition, examples of Ln-complexes with commercially available complexants and phen-based ligands are interrogated in detail. This systematic investigation lays the groundwork for future data-driven ligand designs for REE separations based on the structural insights into the lanthanide coordination chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

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. Here, 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.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Rare earth ion transport and selectivity in large diameter nanotube porins

Selective separation of rare earth elements (REEs) in nanoporous media is very challenging due to the similar physicochemical properties of trivalent lanthanide ions. In this work, we systematically investigate the transport and selectivity of REE 3+ ions through two model nanofluidic channels: 1.5 nm diameter carbon nanotube porins (wCNTPs) and 2.1 nm diameter boron nitride nanotube porins (BNNTPs). Using a fluorescence-based vesicle assay, we find that while wCNTPs show almost no differential selectivity across the lanthanide series, a behavior consistent with bulk-dominant transport through their moderately-confined channels with chemically inert, hydrophobic walls. In contrast, BNNTPs exhibit nearly an order of magnitude higher permeability and significant differential selectivity, following a volcano-shaped trend with Eu 3+ ions showing the highest permeability. We attribute this enhanced performance to the high negative surface charge of BNNTPs, which facilitates a surface-dominated transport mechanism where ion migration within the electric double layer becomes the primary contributor to conductance. These results elucidate the distinct roles of surface charge in nanoscale confinement and provide critical design rules for the development of future membranes tailored for efficient REE separations.

Materials science↗
DOE OSTI2024

Exploring the Structural Behavior of Hydrophilic Diglycolamide Complexes with the Lanthanides and Actinides

In the ongoing effort to meet the anticipated rise in energy demand while maintaining the full-scale abandonment of natural gas and coal, a substantial shift in our considerations of green energy is required through the wider adoption of nuclear power. However, the advantages of nuclear power are hindered by the challenges of safely managing nuclear waste. Hydrophilic diglycolamides (DGA) ligands have been explored for use as stripping agents in various lanthanide and actinide partitioning processes. Additionally, the separation of lanthanide fission products and transplutonic actinides can serve multifaceted advantages in that the separation neutron poisoning rare earth element (REE) fission products from minor actinides from used nuclear fuel (UNF) can be mutually beneficial to the fundamental research behind REE separations and UNF separations. With this in mind, understanding the bonding differences between the Ln3+ and An3+ ions as a function of DGA structure, such as varying the alkyl groups on each of the amide functional groups, has an influence on the molecule’s selectivity and solubility and whose changes in molecular architecture also impact the radiolytic behavior of these molecules. As such, crystal structures of (Y3+, La-Lu3+, excl. Pm, Pu3+/4+, Am3+, Bk3+, and Cf3+) with hydrophilic diglycolamides show the systematic progression, and changes in coordination habits, as a function of a f-element ions. These coordination complexes see a consistent decrease in bond lengths and changes in the coordination environment while traversing across the f-elements, owing to the effects of the lanthanide contraction as well as local geometry around the metal centers. Direct comparisons of lanthanide with actinide DGA structures display both striking similarities in coordination with earlier actinides of Pu and Am, while later actinides of Bk and Cf display a complete breakdown of these observed trends. This work has also presented the rare opportunity to study homoleptic DGA compounds across multiple oxidation states have provided insight into their nuanced differences in structural chemistry.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2024

Impacts of Neodymium Complexation on Radiolysis of Tetramethyl Diglycolamide (TMDGA) in Aqueous Solutions

Hydrophilic diglycolamides (DGA) ligands have been explored for use as stripping agents in various lanthanide and actinide partitioning processes.1 The separation of lanthanide fission products and transplutonic actinides can serve multifaceted advantages, in that the separation of neutron poisoning rare earth element (REE) fission products from the minor actinides in used nuclear fuel (UNF) can be mutually beneficial to the fundamental research behind REE separations and UNF separations. Considerable efforts have been devoted to understanding the radiation chemistry of hydrophilic DGAs. However, recent studies with lipophilic DGAs have shown that metal ion complexation can promote significant changes in their radiolytic susceptibility.2,3 These effects have been attributed to various parameters, including delocalization of electron density, the presence of radiolytically more susceptible counter ions, and steric hindrance. As such, it is pivotal for these complexation effects to be more thoroughly probed to establish mechanistic knowledge for their effects on hydrophilic DGA molecules. Here we present a time-resolved electron pulse and accumulated gamma dose irradiation study on neodymium ion complexes of tetramethyl diglycolamide (TMDGA) under aqueous solution conditions. References (1) Rostaing, C.; Poinssot, C.; Warin, D.; Baron, P.; Lorrain, B. Development and Validation of the EXAm Separation Process for Single Am Recycling. Procedia Chem. 2012, 7, 367–373. https://doi.org/doi: 10.1016/j.proche.2012.10.057. (2) Horne, G. P.; Conrad, J. K.; McLachlan, J. R.; Rotermund, B. M.; Cook, A. R.; Celis-Barros, C.; Mezyk, S. P. Impact of Lanthanide Complexation and Temperature on the Chemical Reactivity of N,N,N’,N’-Tetraoctyl Diglycolamide (TODGA) with the Dodecane Radical Cation. Phys. Chem. Chem. Phys. 2023, Under Review. (3) Kimberlin, A.; Saint-Louis, G.; Guillaumont, D.; Camès, B.; Guilbaud, P.; Berthon, L. Effect of Metal Complexation on Diglycolamide Radiolysis: A Comparison between Ex Situ Gamma and in Situ Alpha Irradiation. Phys. Chem. Chem. Phys. PCCP 2022, 24 (16), 9213–9228. https://doi.org/10.1039/d1cp05731f.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

Impact of organic acids on extraction of rare earth elements: Mechanisms and optimization

Organic acids are increasingly recognized as an environmentally friendly and efficient selective leaching agent of critical minerals. However, their impact on subsequent extraction processes remains unclear. This study investigates the extraction behavior of rare earth elements (REEs), representative of critical minerals, in the presence of various organic acids, including citric acid, maleic acid, malonic acid, DL-malic acid, L(+)-tartaric acid, and L-ascorbic acid. The results show that organic acids slightly reduce the extraction of REEs but greatly increase the extraction of aluminum (Al³⁺), making it harder to separate REEs from other elements. To avoid this, it is best to keep organic acid concentrations as low as possible in practical applications. However, by optimizing extraction conditions, these negative effects can be minimized. Specifically, adjusting the contact time between solutions allows for efficient REE extraction while limiting unwanted aluminum extraction. Among the acids tested, malonic acid and L(+)-tartaric acid were found to be the most effective for selectively extracting REEs. Mechanistically, organic acids are likely to form complexes with REEs and D2EHPA during extraction, except for Y (III), offering practical guidelines for optimizing REE recovery. Beyond extraction, this study also highlights a way to recover organic acids by precipitating REEs from stripping solutions using oxalic acid, which adds both environmental and economic benefits. Furthermore, these findings provide useful insights for optimizing REE recovery and offer a reference for extracting other critical minerals from solutions containing organic acids.

D2EHPA↗
DOE OSTI2021

Influence of the Anionic Zinc-Adeninate Metal–Organic Framework Structure on the Luminescent Detection of Rare Earth Ions in Aqueous Streams

Rare earth elements (REEs) are critical to numerous technologies; however, a combination of increasing demand, environmental concerns, and monopolistic marketplace conditions has spurred interest in boosting the domestic REE production from sources such as coal utilization byproducts. The economic viability of this approach requires rapid, inexpensive, and sensitive analytical techniques capable of characterizing the REE content during resource exploration and downstream REE processing (e.g., analyzing REE separation, concentration, and purification production steps). Luminescence-based sensors are attractive because many REEs may be sensitized to produce element-specific emission. Hence, a single material may simultaneously detect and distinguish multiple REEs. Metal–organic frameworks (MOFs) can sensitize multiple REEs, but their viability has been hindered by sensitivity and selectivity challenges. Understanding how the MOF structure impacts the REE sensing efficacy is critical to the rational design of new sensors. Here, we evaluate the sensing performance of seven different anionic zinc-adeninate MOFs with different organic linkers and/or structures for the visible-emitting REEs Tb, Dy, Sm, and Eu. The choice of a linker determines which REEs are sensitized and significantly influences their sensitivity and selectivity against competing species (here, Fe(II) and HCl). For a given linker, structural changes to the MOF can further fine-tune the performance. The MOFs produce some of the lowest detection limits (sub-10 ppb for Tb) reported for the aqueous sensitization-based REE detection. Importantly, the most selective MOFs demonstrated the ability to sensitize the REE signal at sub-ppm levels in a REE-spiked acid mine drainage matrix, highlighting their potential for use in real-world sensing applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Functionalized Mesoporous Carbon Materials for Effective Recovery of Rare Earth Elements from NdFeB Magnet Scrap

The increasing demand and high dependence on international supplies of rare earth elements (REEs) have prompted the US to explore alternative resources and sustainable technologies for domestic REE production. One potential resource is the secondary electronic and industrial wastes at DoD complexes and across the US. These hazardous wastes require high costs for the maintenance and remediation, but their high-REE contents offer unique opportunities for REE recovery. Current hydrometallurgical technologies for REE extraction are energy intensive and costly, with low REE recovery efficiency and the generation of hazardous secondary wastes. Thus, it is crucial to develop high efficiency and environmental-friendly technologies for REE extraction and recovery from the secondary wastes. This project aims to develop novel functionalized mesoporous carbon materials for effective recovery of REEs from NdFeB magnet scrap. The proposed novel functionalized materials will be applied in a solid-liquid separation platform that can effectively extract, recover and separate REEs from NdFeB magnet scrap (the current focus), but also from other secondary electronic/industrial wastes in the future, minimize the generation of secondary hazardous wastes, and offset the management costs for existing waste streams.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Technology Development and Integration for Volume Production of High Purity Rare Earth Metals from Phosphate Processing

Under this project and in collaboration with Pacific Northwest National Laboratory (PNNL), Oak Ridge National Laboratory (ORNL), Florida International University (FIU), and Mosaic, the FIPR Institute successfully developed and demonstrated on laboratory batch scale a complete processing technology for production of high-purity rare earth elements (REE) in the form of mixed rare earth oxides (MREO) and rare earth metals (REM) using phosphoric acid sludge (a byproduct from phosphate mining) as the REE feedstock. Based on the research results, a technical research plan has been developed with expanded team members to elevate the technology readiness level (TRL) of the subject technology from 4 to 6 by conducting continuous testing of the processing flowsheet with the ultimate goal of producing about 900 tons per year of REM using the phosphate mining byproduct. Those 900 tons of REM would contain approximately 180 tons of Y, 120 tons of Nd, 50 tons of Gd, 37 tons of Dy, 33 tons of Sm, and 31 tons of Pr, meeting the US demand of roughly 39%, 6%, 42%, 48%, 101% and 7% for these elements, respectively. The advanced technologies for REE separation and purification involves three technology companies: K-Technologies, Inc. would test their continuous-ion-exchange/continuous-ion chromatography technologies on both the REE leachate and solvent extraction concentrate for 4 production of high-purity individual or binary REM. Rare Earth Salts would test their innovative electrochemical technology on the REE leachate or re-dissolved MREO in dilute acid for production of high-purity individual or binary REM. Rare Earth Technologies, Inc. would evaluate their advanced chromatographic separation technology on the dissolved MREO product for production of high-purity individual or binary REM.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Protein-based approach for high-purity Sc, Y, and grouped lanthanide separation

Rare earth elements (REEs: Sc, Y, La- Lu) are irreplaceable components in many clean energy and consumer technologies. However, the extraction and subsequent separation of individual REEs from ore-based feedstocks remains a significant economic and environmental challenge. Here in this work, we investigated the intra-REE separation potential of lanmodulin (LanM), a natural protein from Methylorubrum extorquens that has emerged as a sustainable potential alternative to conventional solvent extraction-based separation. By determining the intra-REE selectivity of immobilized LanM and systematically testing pH-based and small chelator-based (i.e., citrate and malonate) desorption processes, we established the framework and methodology for achieving select individual and grouped REE separations from a mixed REE feedstock. We show that Sc forms the tightest complex with LanM among REEs but can be readily and selectively desorbed using malonate to generate high-purity Sc (>99 % purity, >99 % yield) in a single adsorption/desorption cycle. We further show that the intrinsic REE selectivity of LanM is sufficient to achieve heavy REE (HREE) separation from light and middle REEs (L-MREEs), yielding an yttrium-enriched product. This separation effect is further magnified by pairing LanM’s unique M-LREE preference with a HREE-preferring chelator in the desorption process, which enriches HREE and MREE fractions relative to low value, abundant La/Ce. Finally, by combining pH- and citrate-based desorption processes in a two-cycle separation scheme, we demonstrate the generation of fractions highly enriched in Y, Gd-Lu, Pr-Eu, and La-Ce. Collectively, these data support the application of a LanM-based approach for achieving impactful REE separations from mixed REE feedstocks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗