A unified framework for rare earth recycling from secondary resources: process trade-offs and decision pathways

The critical role of rare earth elements (REEs) in advanced technologies has intensified concerns over supply security and the environmental footprint of primary extraction. Secondary resource recovery offers a theoretically sustainable alternative, yet practical recycling remains inefficient or absent for many waste streams, constrained by material heterogeneity, product design, and fundamental process limitations. This review examines representative REE-containing secondary resources, evaluates their realistic recycling potential, and critically assesses current recycling strategies. Hydrometallurgical and pyrometallurgical approaches are discussed within a unified framework that distinguishes pre-separation (conversion and conditioning of complex matrices) from downstream separation and refining, enabling a clearer comparison across different technological routes. Beyond 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, explaining why no universal strategy exists and why laboratory success often fails at industrial scale. Key development trajectories are identified, including clean pre-separation, advanced hydrometallurgy, and hybrid systems integrating robustness with selectivity. By framing REE recycling as a strategic component of resource governance rather than an end-of-pipe solution, this work provides a foundation for advancing a circular rare earth economy.