Pacific Northwest National Laboratory, RichlandWashington99354, United States.
Radiochemistry Program University of Nevada, Las Vegas, Las VegasNevada89154, United States.
Inorg Chem. 2023 Jan 16;62(2):792-801. doi: 10.1021/acs.inorgchem.2c03307. Epub 2022 Dec 30.
Organophosphorus extractants have been widely investigated for lanthanide recovery from ore and for application in the reprocessing of spent nuclear fuel, such as in Advanced TALSPEAK schemes. Determining the speciation of the extracted metal complex in the organic phase remains a significant challenge. A better understanding of the variability of HEH[EHP]-actinide complexes and the speciation of chelates for tetra- and hexavalent actinides can improve the predictability of actinide phase transfer in such biphasic systems. In this study, the extraction of Th(IV) and U(VI) from nitric acid media using HEH[EHP] in heptane is examined. The distribution ratio as a function of nitric acid concentration was quantified using UV-vis spectroscopy, and then the speciation of HEH[EHP]-metal complexes in the organic phase was investigated using Fourier transform infrared (FTIR) spectroscopy and low-temperature P nuclear magnetic resonance (NMR) spectroscopy. In addition to perturbation of the vibrational modes proximal to the phosphonic moiety in HEH[EHP] in the FTIR spectra, the appearance of a nitrate signal was found in the organic phase following extraction from the highest acidity conditions for U(VI). The P NMR spectra of the organic phase at a low temperature (-70 °C) exhibited a surprising number () of resonances ( ≥ 7 for Th(IV) and ≥ 11 for U(VI)), with the distribution between these resonances changing with the initial concentration of nitric acid in the aqueous phase. These results indicate that the compositions of the inner and outer spheres of the extracted actinides in the organic phase are more diverse than initially thought.
有机磷萃取剂已被广泛研究用于从矿石中回收镧系元素，以及应用于乏核燃料的后处理，例如在先进的 TALSPEAK 方案中。确定有机相中萃取金属络合物的形态仍然是一个重大挑战。更好地了解 HEH[EHP]-锕系元素络合物的可变性以及四价和六价锕系元素螯合物的形态，可以提高此类两相体系中锕系元素相转移的可预测性。在这项研究中，考察了用庚烷中的 HEH[EHP]从硝酸介质中萃取 Th(IV)和 U(VI)。使用紫外-可见光谱定量了分配比随硝酸浓度的变化，然后使用傅里叶变换红外（FTIR）光谱和低温 P 核磁共振（NMR）光谱研究了有机相中的 HEH[EHP]-金属络合物的形态。除了在 FTIR 光谱中 HEH[EHP]中靠近膦酸部分的振动模式受到干扰外，还发现从 U(VI)的最高酸度条件下萃取后，有机相中出现了硝酸盐信号。在低温（-70°C）下的有机相 P NMR 光谱显示出令人惊讶的多个共振（对于 Th(IV)≥7，对于 U(VI)≥11），这些共振之间的分布随水相初始硝酸浓度的变化而变化。这些结果表明，有机相中萃取的锕系元素的内球和外球的组成比最初想象的更加多样化。
