Direct visualization of <italic>f</italic>-block elements separation through electrically driven alloy phase transitions

Conventional electrolytic methods for separating chemically similar lanthanides (Ln) and actinides (An) are limited by thermodynamics and slow reaction kinetics, restricting their efficiency in rare-earth refining and nuclear fuel recycling. Herein, we report an electroextraction and oxidative back-extraction (EOB) strategy utilizing a LiCl-KCl-KAlCl4 molten salt that overcomes these limitations by leveraging divergent interfacial reactivity. The EOB process achieves an exceptional separation factor for Ln/An (> 1000), while simultaneously increasing the separation rate by at least one order of magnitude. Through in-situ synchrotron radiation X-ray micro-computed tomography (SR-μCT) and X-ray diffraction (SR-XRD), we capture selective oxidation-induced destabilization of Ln-Al alloys while actinides retain phase stability-directly visualizing the electrochemical alloy transition mechanism. This research redefines the separation of f-block elements in molten salt systems and introduces a multimodal approach to investigating transient interfacial phenomena that are usually inaccessible to conventional metallurgical diagnostics under extreme conditions.