Solvent-extraction and ion-exchange separation of heavy rare-earth elements (dysprosium, terbium, samarium) from mixed concentrates. The narrow upstream chokepoint that determines whether NdFeB sintered magnets keep their coercivity at humanoid joint and EV traction temperatures. Distinct from light-RE separation in that the cascade requires far more stages, China holds ~90% of global capacity, and the metallization step that follows uses different alloy chemistry.