Research Progress in the Application of Novel Hydroxamic Acid Collectors for the Beneficiation of Rare−earth Minerals

Rare earth elements (REEs) serve as critical strategic resources with irreplaceable core application value in fields such as renewable energy and advanced manufacturing. Froth flotation is the most widely employed separation technology for REE minerals, where the selection of collectors is the pivotal step, directly determining the separation efficiency and resource utilization. This review summarizes recent advances in novel hydroxamic acid collectors. For alkyl hydroxamic acids, performance in bastnaesite flotation has been significantly enhanced through strategies including introducing amino/amide groups via flexible aliphatic chain modification, hybridizing sulfur-nitrogen functional groups, constructing di-hydroxamic acid headgroups, and optimizing alkyl chain structures. For aromatic hydroxamic acids, modifications such as incorporating heterocycles, olefin groups, or halogen atoms into the rigid aromatic framework, or forming di-hydroxamic acid structures for multidentate chelation with REE ions, have been employed to improve collecting capability and selectivity, with performance notably influenced by steric hindrance and synergistic effects with depressants. Nevertheless, current research exhibits notable limitations, including a predominant focus on bastnaesite, insufficient suppression of key gangue minerals, and a lack of industrial validation. Future research should extend the application studies to other rare earth minerals such as monazite and xenotime; integrate the structural advantages of both alkyl and aromatic types to design comprehensive collectors; develop low-cost and environmentally friendly synthetic routes; and investigate the synergistic mechanisms with regulators in complex pulp systems to promote industrial applications.