Impact of various reductants on Pu(iii) stability in the organic phase and its distribution ratio in a biphasic system

Abstract

Plutonium–uranium extraction (PUREX) reprocessing relies on stabilizing Pu(III) to enable effective U/Pu separation. This study compares four reductants – N,N-dimethylhydroxylamine (DMHAN), hydroxylammonium nitrate (HAN), monomethyl hydrazine (MMH), and hydrazine (N₂H₄) – for their ability to preserve Pu in the trivalent state (Pu(III)) and thereby minimize its distribution to the organic phase in a TBP (tributyl phosphate)–HNO₃ biphasic system. Optimizing reductant choice is essential for process safety (preventing Pu(III) re-oxidation and exothermic side reactions) and efficiency (maximizing Pu stripping from the organic phase). Experimental results across varying nitric acid concentrations show that Pu(III) stability and low distribution ratios are best achieved using DMHAN, especially when paired with a nitrite scavenger (e.g., MMH), sustaining Pu(III) even at high acidity. In contrast, hydrazine and HAN provided comparatively less Pu(III) stabilization under strong acid conditions. In conclusion, the DMHAN–MMH combination offered superior performance, ensuring safer operation and more efficient Pu(III) retention for improved PUREX partitioning.