Influence of ethylenediaminetetraacetic acid on the long-term oxidation state distribution of plutonium. (July 2021)

• Record Type: Journal Article
• Authors: DiBlasi, Nicole A.; Yalçintas, Ezgi; Stanley, Floyd E.; Reed, Donald T.; Hixon, Amy E.
• Is Part Of: Chemosphere. Volume 274(2021)
• Publication Date: 2021-07
• Subjects: Plutonium -- Redox -- EDTA -- Radioactive waste disposal; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2021.129741
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: Spectrophotometry was used to study the effect of EDTA on plutonium oxidation state distribution as a function of time, pH, and ligand-to-metal ratio (L/M) under anoxic conditions. Novel Pu(V)-EDTA absorption bands were identified at 571, 993, 1105, and 1150 nm with molar absorption coefficients of 15 ± 1, 6 ± 1, 10 ± 1, and 10 ± 1 cm −1 M −1, respectively. Pu(V)-EDTA spectral changes occurred at L/M < 1, indicating only Pu V O2 (EDTA) 3- formed with logK = 3.6 ± 0.3. Time-resolved experiments showed EDTA drastically increased the Pu(V/VI) reduction rate, which we propose is driven by amine lone-pair electron donation and the oxidative decarboxylation of EDTA. Oxidation of Pu(III)-EDTA to Pu(IV)-EDTA occurred on a slower time scale (110–237 days) than previously reported (<15 min) and is hypothesized to be radiolysis driven. Pu(V/VI)-EDTA and Pu(III)-EDTA both approached Pu(IV)-EDTA stabilization over time, yet Pu(V/VI)-EDTA solubility data was ≥ 1.0 log10 units higher than predicted by Pu(IV)-EDTA solubility models, indicating that current thermodynamic models are incomplete. Ultimately, the data show EDTA preferentially stabilizes Pu(IV) over time regardless of initial oxidation state, but Pu(V)-EDTA can persist under environmentally-relevant conditions, emphasizing the need to continue investigating redox reactions, speciation, and behavior of these complexes to support the transuranic waste disposal and surface remediation/containment efforts. Highlights: Pu(V)-EDTA exhibits unique absorption bands at 571, 993, 1105, and 1150 nm. Pu(V)-EDTA spectrophotometry as a function of [EDTA] indicates formation of only 1:1 complexes. EDTA increases the rate of Pu(V/VI) reduction to stable Pu(IV)-EDTA complex(es). Pu(III) can persist much longer than expected in the presence of EDTA (110 days).