Redox-Active Electrodes Enable Selective Ammonium Recovery and Reuse for Rare Earth Mining

Abstract Rare earth element (REE) extraction from ion-adsorption deposits relies on ammonium (NH4+) assisted in situ leaching, yet the spent leachant is typically discarded as wastewater rather than recovered for reuse. Here, we report a redox-active electrosorption platform that selectively recovers NH4+ from REE tailings wastewater and enables its direct reuse in the leaching process, establishing a circular approach to nitrogen management. This platform employs nickel-substituted copper hexacyanoferrate as redox hosts for reversible ammonium storage. Nickel incorporation modifies the redox and ion-transport properties of CuHCF while improving framework stability. The resulting Cu0.8Ni0.2HCF redox-active electrode exhibits a high capacity of 82.6 mAh g–1, superior cycling durability (>90% retention after 30 h), and remarkable ammonium selectivity over Na+ (9.2), Ca2+ (19.3), Mg2+ (25.5), La3+ (38.5), and Y3+ (42.2). Multiscale characterizations and calculations support favorable NH4+ host–guest interactions and ion transport within the framework. The recovered ammonium is directly reused for ion-adsorption-type rare earth leaching with extraction performance comparable to fresh leachants. Life-cycle assessment and techno-economic analyses demonstrate reduced environmental footprint and favorable economic feasibility. This study established a redox-active electrosorption platform that shifts nitrogen management from a linear “treatment-discharge” model toward a circular “recovery-reuse” pathway.