Partitioning of U(VI) and Eu(III) between Acidic Aqueous Al(NO₃)₃and Tributyl Phosphate in n‐Dodecane

Abstract

The preferred approach to removing Al from Hanford tank sludges, based on aqueous alkaline leaching, often does not achieve complete success. Previous laboratory investigations on the treatment of Hanford tank sludge simulant samples indicate that an acidic scrub can enhance the dissolution of Al from various sludge matrices. If acidic leaching was deployed to enhance removal of tank waste residues, the resulting acidic Al(NO 3 ) 3 leachate solution could contain measurable amounts of solubilized transuranic elements and so would demand treatment prior to disposal. In this study, a liquid-liquid extraction system for the decontamination of the HNO 3 /Al(NO 3 ) 3 aqueous leachate by contact with 60% v/v tributyl phosphate (TBP)/n-dodecane organic solution has been examined. The partitioning of U and Eu between the TBP phase and solutions of varying [HNO 3 ] and [Al(NO 3 ) 3 ] containing small amounts of Cr or ascorbic acid have been investigated. . The results indicate that .99% of both species could be removed from the aqueous phase using such a process.

Influence of Light and Temperature on the Extractability of Cerium(IV) as a Surrogate of Plutonium(IV) and its Effect on the Simulation of an Accidental Fire in the PUREX Process

“…The dissociation of CAN by photolysis into cerium­(III) and a nitrate radical was previously studied by the group of Baciocchi. , However, this mechanism seems unlikely in our case, since nitrate radical formation occurs only by flash photolysis. Previous studies with highly oxidizing americium­(VI) ( E 0 AmO 2 2+ /AmO 2 + = 1.62 V) or chromium­(VI) ( E 0 HCrO 4 – /Cr 3+ = 1.35 V) have shown that the organic TBP/diluent mixture seems to play a reducing role toward both elements in such an extraction medium. − In fact, the standard potential of the redox couple Ce­(IV)–TBP/Ce­(III)–TBP was evaluated to be between E 0 = 1.356 V and E 0 = 1.416 V vs Ag/AgCl depending on the concentration of cerium­(IV), further emphasizing the oxidative power of cerium­(IV). Thus, it appears that the Ce­(IV)–TBP complexes react with solvent molecules, yielding cerium­(III) that is quickly back-extracted to the aqueous phase.…”