Efficient in situ reduction and recovery of neptunium(V) using redox-functionalized deep eutectic solvents

Area of Science:

• Nuclear Chemistry
• Materials Science
• Chemical Engineering

Background:

• Neptunium (Np) separation is crucial for nuclear waste reprocessing.
• Conventional methods struggle with efficient Np(V) capture.
• Developing advanced solvents is key for nuclear fuel cycles.

Purpose of the Study:

• Design and synthesize novel hydrophobic deep eutectic solvents (DESs) for Np(V) recovery.
• Investigate the in situ reduction and extraction mechanism of Np(V) using DESs.
• Evaluate the performance of DESs under various challenging conditions relevant to nuclear waste.

Main Methods:

• Synthesized three DESs using tri-n-octylphosphine oxide (TOPO) and dihydroxybenzene isomers (catechol, resorcinol, hydroquinone).
• Performed liquid-liquid extraction experiments to determine Np(V) distribution ratios and reduction efficiency.
• Conducted mechanistic studies to elucidate the coordination-driven reduction process.
• Assessed DES stability under high salinity, wide temperature ranges, and gamma irradiation.

Main Results:

• The TOPO-CC DES system demonstrated outstanding Np(V) extraction (D_Np up to 85) across a wide acidity range (10^-3 to 2.0 M HNO3).
• Achieved over 98% in situ reduction of Np(V) to Np(IV) within 5 minutes.
• The extraction follows a "coordination-driven reduction" mechanism involving TOPO and dihydroxybenzene.
• The DES system showed stable performance in high salinity, varying temperatures, and significant gamma irradiation (up to 60 kGy).

Conclusions:

• Developed an integrated "coordination-reduction-extraction" process using functionalized DESs for efficient Np(V) recovery.
• The TOPO-CC DES offers a promising green and efficient strategy for Np separation in advanced nuclear fuel cycles.
• This research provides a foundation for applying tailored DESs in nuclear waste management and reprocessing.