Recycling of superalloys: circular strategies for critical mineral supply chain resilience

Superalloys are indispensable in aerospace, energy, and defense applications due to their exceptional resistance to heat, stress, and oxidation. These alloys typically contain a nickel matrix alloyed with critical elements such as rhenium, tantalum, and tungsten. Growing demand for such elements underscores the urgency of developing effective recycling strategies. However, recycling superalloys remains challenging due to complex chemistries and strong resistance to chemical and thermal breakdown. This review provides a critical synthesis of current and emerging recycling pathways. Pyrometallurgical routes rely on energy-intensive remelting of spent alloys with virgin metals, reaching 88–97% of nickel recovery, while hydrometallurgy employs acid-alkali leaching and separation/purification steps that often require extensive pre-milling and long processing times, achieving 92–99% extraction for rhenium, nickel, and cobalt, as well as precipitation efficiencies of 95–99% for cobalt and nickel oxalate salts. Hybrid pyro–hydro approaches integrate processes such as oxidative roasting or alkali calcination with subsequent leaching and purification, obtaining 95% nickel leaching in the first leaching step and 99% rhenium leaching in the second step after reacting superalloy with aluminum granules at 1500°C. Moving beyond a descriptive catalogue of these methods, this review identifies the fundamental thermodynamic bottlenecks, such as element cross-contamination and phase stability, that limit commercial scalability. We evaluate emerging technologies, including electrochemical methods, membrane separations, deep eutectic solvents, and ionic liquids, as high-selectivity alternatives. By mapping these innovations onto current industrial gaps, this work provides a forward-looking roadmap to guide activities toward a more sustainable and efficient circular supply chain for high-performance materials.