Highlights
- Comprehensive review reveals metal-organic frameworks (MOFs) demonstrate exceptional rare earth element adsorption capacities up to 426 mg/g.
- MOF technologies show high selectivity, rapid equilibrium times, and reusability across multiple adsorption-desorption cycles.
- Despite promising results, scaling from laboratory research to industrial application remains a critical challenge requiring integrated research approaches.
Clint Sutherland of the University of Trinidad and Tobago authored this comprehensive 2025 review article (opens in a new tab), which evaluates the use of metal–organic frameworks (MOFs) for rare earth element (REE) recovery from aqueous solutions. The central hypothesis is that functionalized and composite MOFs offer superior adsorption performance and selectivity for REEs, positioning them as promising candidates for sustainable recovery technologies. Sutherland conducted a narrative review of experimental studies published between 2014 and 2024, selecting only laboratory-based research involving REE adsorption from water using MOFs. The review collates findings on adsorption performance, mechanisms, regeneration, and upscaling potential, emphasizing functionalized MOFs’ ability to outperform conventional adsorbents.
Findings
The review found (opens in a new tab) that MOFs, especially composites like U6N@ZIF-8-20, MIL-101(Cr)-SMA-ED-PMG, and P-MNPC@SiO₂, demonstrated exceptional adsorption capacities—up to 426 mg/g for Y³⁺—and high selectivity in the presence of competing ions. Notably, rapid equilibrium times (as low as 10 minutes) and excellent reusability through up to five adsorption-desorption cycles were achieved using eluents like HCl, HNO₃, and acetonitrile.
Mechanistically, MOF adsorption is dominated by electrostatic attraction and chemical coordination, often optimized by tailoring functional groups like amine, carboxyl, and phosphonic acid moieties. In nearly all studies, adsorption kinetics conformed to Langmuir and pseudo-second-order models, suggesting monolayer chemisorption as the dominant pathway.
Limitations
Limitations include the predominance of small-scale, single-ion batch studies using synthetic solutions, which fail to simulate real industrial effluents. Long-term stability, oxidation-reduction interactions, and fixed-bed column studies remain largely unexplored. Regeneration performance, though promising for some MOFs, showed significant efficiency loss after repeated use for others (e.g., HKUST-1 with 90% loss by the third cycle). Additionally, practical issues related to nanoparticle handling, pressure drop in flow systems, and safe disposal of spent MOFs have not been adequately addressed. Comprehensive economic analyses remain rare, with only one cited study estimating cost-effective REE recovery from wastewater.
Implications
MOFs represent a cutting-edge technology for environmentally responsible REE recovery, boasting high adsorption capacities, selectivity, and reusability. However, the field requires urgent scaling up through real-world application studies, cost-benefit modeling, and fixed-bed column designs. Advancing MOFs from lab-scale curiosity to industrial solutions demands integrated research that encompasses engineering, environmental, and economic dimensions. As geopolitical tensions intensify around critical minerals, MOFs could play a central role—if backed by investment in applied research and infrastructure.
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