Department of Civil & Environmental Engineering & Earth Sciences, University of Notre Dame, 301 Stinson-Remick Hall, Notre Dame, IN, 46556, USA; Los Alamos National Laboratory, 1400 University Dr., Carlsbad, NM, 88220, USA.
Los Alamos National Laboratory, 1400 University Dr., Carlsbad, NM, 88220, USA.
Chemosphere. 2021 Jul;274:129741. doi: 10.1016/j.chemosphere.2021.129741. Epub 2021 Jan 25.
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 cmM, respectively. Pu(V)-EDTA spectral changes occurred at L/M < 1, indicating only PuO(EDTA) 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 log 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.
分光光度法被用于研究在缺氧条件下，EDTA 对钚氧化态分布的影响，该影响与时间、pH 值和配体与金属的比例（L/M）有关。在 571、993、1105 和 1150nm 处识别到了新的 Pu(V)-EDTA 吸收带，摩尔消光系数分别为 15±1、6±1、10±1 和 10±1cmM。当 L/M<1 时，Pu(V)-EDTA 光谱发生变化，表明仅形成了 PuO(EDTA)，logK=3.6±0.3。时间分辨实验表明 EDTA 大大增加了 Pu(V/VI)的还原速率，我们提出这是由胺孤对电子的供体和 EDTA 的氧化脱羧作用驱动的。Pu(III)-EDTA 氧化为 Pu(IV)-EDTA 的时间尺度比以前报道的（<15 分钟）要慢（110-237 天），并假设是由辐射分解驱动的。随着时间的推移，Pu(V/VI)-EDTA 和 Pu(III)-EDTA 都趋向于 Pu(IV)-EDTA 的稳定，但 Pu(V/VI)-EDTA 的溶解度数据比 Pu(IV)-EDTA 溶解度模型预测的高出≥1.0 个对数单位，这表明当前的热力学模型不完整。最终，数据表明 EDTA 优先随着时间的推移稳定 Pu(IV)，但无论初始氧化态如何，Pu(V)-EDTA 都可以在环境相关条件下持续存在，这强调了需要继续研究这些配合物的氧化还原反应、形态和行为，以支持放射性废物处置和表面修复/封存工作。
