Unified framework for recycling rare earth elements from secondary resources: Process trade-offs and decision pathways

The critical role of rare earth elements (REEs) in advanced technologies has intensified concerns regarding supply security and the environmental impacts of primary extraction. Recovery of REEs from secondary resources offers a theoretically sustainable alternative; however, its practical application remains limited for many waste streams due to material heterogeneity, product design complexity, and inherent process constraints. This review examines representative REE-containing secondary resources, evaluates their practical recycling potential, and critically assesses current recycling strategies. Hydrometallurgical and pyrometallurgical approaches are discussed within a unified framework that separates preseparation (conversion and conditioning of complex matrices) from downstream separation and refining, enabling a clear comparison of different technological routes. Beyond the method-level comparison, we highlight the intrinsic trade-offs that govern recycling viability-selectivity versus robustness, chemical intensity versus scalability, and recovery efficiency versus environmental impact. We further explain why no universal strategy exists and why laboratory success often fails at the industrial scale. Key development pathways are identified, including clean preseparation, advanced hydrometallurgy, and hybrid systems that integrate robustness with selectivity. By framing REE recycling as a strategic component of resource governance rather than an end-of-pipe solution, this study provides a foundation for advancing a circular rare earth economy.