Mechanistic Insights into Molybdenum–Iron-Catalyzed Neptunium Reduction and Extraction

Neptunium (Np), as a critically regarded actinide in nuclear waste, is of great significance for environmental hazard mitigation and the resource-oriented management of nuclear waste. The reduction of Np(V) to Np(IV) represents a pivotal step toward efficient Np recovery. However, this process is profoundly influenced by the intricate redox chemistry of Np itself and the diverse concomitant fission products in spent nuclear fuel, with the underlying mechanistic details remaining inadequately elucidated. In this study, we demonstrated that molybdenum (Mo) and iron (Fe) dramatically accelerated the reduction rate of Np(V) by approximately 2 × 104-fold. Additionally, by integrating analytical techniques including absorption spectroscopy, stopped-flow spectroscopy, inductively coupled plasma–mass spectrometry, and solvent extraction, we deciphered the electron transfer interactions between Mo and Fe, as well as their synergistic catalytic mechanism in driving the Np(V)–Np(IV) conversion. This study not only advances the fundamental understanding of Np redox chemistry in complex nuclear waste matrices but also offers technical support for optimizing nuclear waste treatment protocols.