Functional Materials for Rare-Earth Element Recovery from Secondary Sources: A Mini Review of Adsorption-Based Strategies

Rare-earth elements (REEs) are vital to modern technologies, yet conventional mining and extraction methods pose environmental and geopolitical challenges. In response, increasing attention has been directed toward the recovery of REE from secondary sources, such as electronic waste, industrial wastewater, and mining residues. Among various separation techniques, adsorption has emerged as a promising alternative due to its operational simplicity, low cost, and potential for selective enrichment. This mini review summarizes recent advances in functional adsorbents for REE recovery, including clay minerals, zeolites, ion-exchange resins, carbon-based materials, metal–organic frameworks (MOFs), covalent organic frameworks (COFs), and biobased systems. Each material class is analyzed in terms of the adsorption mechanism, performance metrics, and current limitations. Clay minerals and zeolites offer low-cost options with moderate selectivity; carbon-based adsorbents are technically mature and tunable; ion-exchange resins combine high adsorption capacity, acid stability, and tunable selectivity through functionalization, making them among the most mature polymeric adsorbents for REE recovery; MOFs and COFs enable tailored binding but face challenges in stability and scalability; and lanmodulin (LanM)-based biosorbents exhibit outstanding selectivity and adaptability under harsh conditions, representing a promising yet still emerging strategy for REE recovery. Key future research priorities include validating adsorbents in real wastewater systems, improving regeneration and life-cycle performance, and exploring hybrid and waste-derived materials to advance sustainable REE recovery technologies.