Experimental strategy for acid-free plutonium recovery from assorted matrices: Non-aqueous leaching followed by selective solid phase extraction

Methodologies comprising usage of innocuous reagents, lower overall chemical inventory and simplification of process scheme for plutonium recovery from assorted matrices, solid as well as liquid, are key to establishing sustainability of the nuclear fuel cycle. The present study demonstrates, for the first-time, plutonium leaching from different refractory matrices: oxide, mixed oxide as well as simulated cellulosic waste using the benign halide anion free choline citrate - urea (1 : 2 mole ratio) based eutectic solvent (referred to as CU). This mineral acid and hydrofluoric acid-free, non-aqueous route of plutonium recovery with controlled infra-red heating yielded.93% efficiency. CU was diluted with biodegradable, less viscous propylene glycol (referred to as PG), which was chosen as the non-aqueous polar phase for facile solid phase extraction (SPE), which is a green alternative to liquid-liquid extraction owing to process simplification and solvent inventory reduction. Exclusive stabilization of tetravalent plutonium in the novel media, confirmed by ultraviolet-visible spectrophotometry and electrochemical methods, led to process simplification, eliminating any pre-extraction requirement for oxidation state adjustment. Extractant, di-2-ethyl hexyl phosphoric acid encapsulated polyether sulfone beads, prepared by phase inversion method, were employed for efficient SPE of plutonium (Distribution co-efficient, k(D)=950 +/- 6). Selectivity of non-aqueous SPE was found to be Pu(IV)>>UO22+> Am(III) vis-a-vis aqueous acid medium.

Automated summary

The use of benign reagents, simplification of the process scheme, and reduction of chemical inventory are crucial for the sustainable recovery of plutonium from various matrices. In this study, a non-aqueous route of plutonium recovery using a halide-free eutectic solvent called CU was demonstrated for the first time. The use of biodegradable propylene glycol as a polar phase for solid phase extraction (SPE) further simplified the process and reduced solvent inventory. The encapsulated polyether sulfone beads containing di-2-ethyl hexyl phosphoric acid were effective for SPE of plutonium.