Rare earth recovery using metal–organic frameworks: advances, challenges, and future directions

The field of study of rare earth element (REE) adsorption by metal–organic frameworks (MOFs) has emerged relatively recently. Recovering REEs from industrial, mining, and end-of-life electronics recycling effluents offers a sustainable approach to mitigating their unrestricted release into the environment. MOFs, known for their exceptional porosity and modifiability, have demonstrated significant potential as sustainable and efficient adsorbents for REE recovery from aqueous environments. To propel the advancement of this promising technology, a review of the fragmented research conducted over the past decade on REE adsorption by MOFs has been undertaken. Functionalization and combination of MOFs have proven effective in enhancing adsorbent capacity, stability, adsorption rate, and reusability. Notably, the 3D-agaric-like core–shell U6N@ZIF-8-20 MOF, MOF-bonded silica amine and polymer, and phosphonic acid–functionalized ZIF-67@SiO2 MOF exhibited adsorption capacities of 341.0, 426.0, and 342.5 mg/g for Er3+, Y3+, and Ce3+, respectively. Eluents such as HCl, HNO3, and acetonitrile successfully achieved up to five adsorption–desorption cycles with minimal loss in adsorption efficiency. While MOFs are highly effective for REE adsorption, further advancements are needed in reducing equilibrium time, conducting fixed-bed column studies, and evaluating real-world wastewater to support their continued development.