Hexavalent Americium Recovery Using Copper(III) Periodate

Abstract

Separation of americium from the lanthanides is considered one of the most difficult separation steps in closing the nuclear fuel cycle. One approach to this separation could involve oxidizing americium to the hexavalent state to form a linear dioxo cation while the lanthanides remain as trivalent ions. This work considers aqueous soluble Cu periodate as an oxidant under molar nitric acid conditions to separate hexavalent Am with diamyl amylphosphonate (DAAP) in n-dodecane. Initial studies assessed the kinetics of Cu periodate autoreduction in acidic media to aid in development of the solvent extraction system. Following characterization of the Cu periodate oxidant, solvent extraction studies optimized the recovery of Am from varied nitric acid media and in the presence of other fission product, or fission product surrogate, species. Short aqueous/organic contact times encouraged successful recovery of Am (distribution values as high as 2) from nitric acid media in the absence of redox active fission products. In the presence of a post-plutonium uranium redox extraction (post-PUREX) simulant aqueous feed, precipitation of tetravalent species (Ce, Ru, Zr) occurred and the distribution values of Am were suppressed, suggesting some oxidizing capacity of the Cu periodate is significantly consumed by other redox active metals in the simulant. The manuscript demonstrates Cu periodate as a potentially viable oxidant for Am oxidation and recovery and notes the consumption of oxidizing capacity observed in the presence of the post-PUREX simulant feed will need to be addressed for any approach seeking to oxidize Am for separations relevant to the nuclear fuel cycle.

Ultrafiltration separation of nanoscale Am(VI)-polyoxometalate clusters from lanthanides

“…The rejection coefficient of Eu 3+ is low at 1.3%. These results give rise to a Am(VI)/Eu(III) separation factor of 873 that is significantly higher than those of all other americium oxidation associated separation techniques [20][21][22][23][24][25][26][27] (Fig. 4c).…”

Chemical Understanding of Actinide Separations

“…A group actinide(VI) extraction seeks to oxidize U, Np, Pu, and Am to the 6+ oxidation state and extract all four actinides into an organic phase as their respective actinyl cations by a solvating ligand or by a cocrystallization method. [53][54][55][56][57][58][59][60] The primary challenge in the group actinide(VI) extraction concept is oxidizing americium(III) to the 6+ oxidation state. An Am(VI)/Am(III) redox potential of 1.68 V vs. SCE requires strong oxidizers to generate the americyl cation).…”

“…Solvent extraction of AmO2 2+ oxidized by Cu 3+ periodate was demonstrated with DAAP and monoamide ligands. 56,58,59 Although separation by 1 M DAAP was achieved, short contact times less than 10 seconds were required. 56,58 Distribution values decreased with extended contact times.…”

“…56,58,59 Although separation by 1 M DAAP was achieved, short contact times less than 10 seconds were required. 56,58 Distribution values decreased with extended contact times. The trend was observed both in NaBiO3 and Cu 3+ periodate oxidation schemes.…”

Oxidation and extraction of Am(VI) using a monoamidic extractant in 3D printed centrifugal contactors

“…The standard potential for the Am(III)/Am(VI) redox couple under acidic conditions is about 1.7 V, and thus strong oxidizing agents are required [1,11]. Several oxidants have been explored including peroxydisulfate [12,13], copper(III) periodate [14,15], electrochemical techniques [16], and sodium bismuthate [5][6][7][8]17]. Once oxidized the Am(VI) exists as the americyl AmO 2 2+ ion and behaves similarly to the other hexavalent actinyl cations.…”