Organic and Aqueous Redox Speciation of Cu(III) Periodate Oxidized Transuranium Actinides

• Published in: Industrial & engineering chemistry research 2018-01, Vol.57 (4), p.1277-1283
• Main Authors: McCann, Kevin, Sinkov, Sergey I, Lumetta, Gregg J, Shafer, Jenifer C
• Format: Article
• Language: English
• Subjects: americium; copper(III); DAAP
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/acs.iecr.7b04158

A hexavalent group actinide separation process could streamline used nuclear fuel recycling and waste management. The limiting factor to such a process compatible with current fuel dissolution practices is obtaining and maintaining hexavalent Am, AmO2 2+, in molar nitric acid because of the high reduction potential of the Am­(VI)/Am­(III) couple (1.68 V vs SCE). Two strong oxidants, sodium bismuthate and Cu3+ periodate, have demonstrated quantitative oxidation of Am under molar acid conditions, and better than 50% recovery by diamyl amylphosphonate (DAAP) is possible under these same conditions. This work considers the use of Cu3+ periodate to oxidize Np­(V) to Np­(VI) and Pu­(IV) to Pu­(VI) and to recover these elements by extraction with DAAP. A metal:oxidant ratio of 1:1.2 and 1:3 was necessary to quantitatively oxidize Np­(V) and Pu­(IV), respectively, to the hexavalent state. Extraction of hexavalent Np, Pu, and Am by 1 M DAAP in n-dodecane was measured using ultraviolet–visible (PuO2 2+, AmO2 2+) and near-infrared (NpO2 2+) spectroscopy. Distribution values of AmO2 2+ were found to match previous tracer level studies. The organic phase spectra of Np, Pu, and Am are presented, and molar absorptivities are calculated for characteristic peaks. Hexavalent Pu was found to be stable in the organic phase, while NpO2 2+ showed some reduction to NpO2 +; Am was present as Am3+, AmO2 +, and AmO2 2+ species in aqueous and organic phases during the extraction experiments. These results demonstrate, for the first time, the ability to recover macroscopic amounts of americium that would be present during fuel reprocessing and are the first characterization of Am organic phase oxidation state speciation relevant to a hexavalent group actinide separation process under acidic conditions.