The use of organophosphorus extractants in f-element separations

Jenifer Claire Braley

doi:10.7273/000006172

Used nuclear fuel reprocessing has been typically performed using solvent extraction. Different organic extractants have been developed containing nitrogen, sulfur and phosphorus; however, the only current reprocessing separation (PUREX) applied at a large scale utilizes trinbutyl phosphate, an organophosphorus extractant. The lower impact of radiolysis on reagent lifetime is one reason organophosphorus extractants have seen such success in used fuel separations. This dissertation will focus on defining several applications of organophosphorus extractants to manage used fuel, using solvent extraction and extraction chromatographic separations. The first application will focus on the development of a sludge phase minimization process to be employed at Hanford’s Waste Treatment Plant. The localization of actinides in the sludge phase makes minimizing the volume of waste produced particularly important. Aggressive acidic or oxidative scrubs have been proposed; however, undesired transuranic radionuclide migration from the solid sludge to the acidic waste stream is possible. A contaminated acidic waste stream would require cleanup prior to disposal. An extraction chromatographic decontamination has been proposed using trinbutyl phosphate or trinoctyl phosphine oxide impregnated resins. Results indicate that successful removal of Eu, U, Np and Pu from the vi aluminum and chromium aqueous phase is possible. An extension of these studies was initiated by examining the uptake capabilities of a resin with covalently bound phosphate moieties. The resins were ultimately determined highly susceptible to acidic degradation. The second issue addressed by the use of organphosphorus extractants is the separation of trivalent lanthanides from trivalent actinides using organophosphorus acids in the TALSPEAK (Trivalent Actinide Lanthanide Separation by Phosphorus reagent Extraction from Aqueous Komplexes) process. Much circumstantial support exists for the aggregation of extractant molecules in the organic phase (a precursor to third phase formation). To address the possibilities of third phase formation, variations of TALSPEAK using extraction chromatography or an organophosphonic acid were developed. Results show chromatographic Am/Ln separations were comparable to separations performed using solvent extraction. Studies indicate the phosphonic acid is capable of providing a separation of comparable quality to “classical” TALSPEAK, but may be less prone to aggregation.

The use of organophosphorus extractants in f-element separations

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