Abstract:

Strategic critical metals， such as rare earths and dispersed metals， are indispensable key raw materials for high-tech industries， including new energy and electronics. Although China is rich in mineral resources （especially rare earth minerals）， the supply has always been a concern due to extremely uneven distribution and the significant environmental pressures caused by the mining process. At the same time， with the rapid development of related industries， the amount of waste equipment containing these metals （such as discarded batteries and used NdFeB magnets） and industrial wastewater has increased sharply. Therefore， efficiently recovering strategic critical metals from secondary resources is of great importance. Among various recovery processes， solvent extraction and precipitation methods have been widely applied in systems with conventional concentrations and relatively simple components due to their mature technology and relatively high separation efficiency. However， these methods face challenges such as low efficiency， poor selectivity， and high environmental burden when treating low-concentration， multi-component systems. Adsorption methods， with their simple operation， low energy consumption， and environmentally friendly characteristics， have become one of the most promising methods for recovering and processing strategic critical metals in extreme industrial systems. By designing or selecting specific adsorbent materials （such as ion-imprinted polymers， functionalized porous materials）， specific adsorption of target metal ions can be achieved， especially enabling efficient separation of desired metals in complex multi-metal solutions. However， this method demands higher requirements for the performance and stability of the adsorbents. Therefore， developing novel adsorbent materials with high selectivity， high adsorption capacity， and environmental friendliness has become a key bottleneck that urgently needs to be overcome in this field. Covalent organic frameworks （COFs） are a fascinating class of crystalline porous organic materials constructed via strong covalent bonds from light elements including carbon， hydrogen， nitrogen， oxygen， and boron. COFs integrate multiple superior properties. They not only possess ultra-high specific surface areas and tunable pore sizes but also exhibit excellent structural designability. Their pore sizes can be adjusted from the nanometer scale to the angstrom level， allowing for the sieving of ions of different sizes through size exclusion effects. Moreover， the organic monomers of COFs contain abundant functional groups， enabling selective recovery based on differences in affinity for metal ions. At the same time， their fully organic frameworks endow numerous COFs with excellent stability in harsh environments such as acids and bases. Thanks to these unique characteristics， COFs have emerged as promising candidates for the highly selective and high-capacity recovery of critical metals in low-concentration， multi-component systems.This review systematically summarizes recent advances in the application of COFs for the recovery of rare earth and dispersed metals， with a focus on the introduction of specific functional groups through direct synthesis and post-modification strategies to achieve efficient recognition and capture of target metal ions. The performance of COFs in terms of adsorption capacity， selectivity， and cycling stability is outlined， and their adsorption mechanisms， as well as desorption and regeneration methods， are discussed. Finally， challenges in structural design， scalable synthesis， and environmental adaptability for practical applications are analyzed， and future research directions are proposed. This review aims to provide a reference for researchers in this field and to promote further development of COF materials in resource recovery applications.

Key words: covalent organic framework （COF）, synthesis, rare earth metals, dispersed metals, adsorption, recovery