An in-situ X-ray absorption spectroelectrochemical study of the electroreduction of uranium ions in HCl, HNO3, and Na2CO3 solutions
An in-situ X-ray absorption spectroelectrochemical study of the electroreduction of uranium ions in HCl, HNO3, and Na2CO3 solutions
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DOI：
10.1515/ract-2015-2436
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发表时间：
2016-01
影响因子：
1.8
通讯作者：
A. Uehara;T. Fujii;H. Yamana;Y. Okamoto
中科院分区：
文献类型：
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作者：
A. Uehara;T. Fujii;H. Yamana;Y. Okamoto
摘要研制了一种用于现场X射线吸收光谱分析的光谱电化学池。在电解质溶液中的电化学还原过程中，监测的XAS光谱的铀LIII边缘。用恒电流电解法从六价铀UO 22+在1 mol dm-3（M）盐酸溶液中制备了四价铀U 4+，并对其扩展X射线吸收精细结构（EXAFS）进行了分析。根据具有径向结构函数的线性UO_（22+）单元U-O_（ax）键中两个轴向氧原子的信号强度，计算了电解过程中五价铀（UO_（22+））还原生成的UO_（22+）和U_（4+）的浓度比。在1 M HCl中的UO 22 +/U4+电对的表观氧化还原电位基于使用UO 22+和U4+的浓度的Nernst方程来确定。电极电位接近于以前报道的UO_（22+）/UO_（2+）电偶的形式电位。该结果表明，在电极处电化学形成的UO 2+在本体溶液中发生电化学反应以形成UO 22+和U4+。还进行了UO_（22+）在0.1M硝酸中的原位XAS。形成的U4+被溶液中存在的NO3-部分再氧化为UO 22+。在本体电解过程中，在1 M碳酸钠溶液中通过原位XAS观察到UO 2+碳酸根络合物的形成。由于UO ~（2 2+）还原为UO ~（2+）碳酸根络合物，X射线吸收近边结构（XANES）谱的边跳从17.164 keV移至17.163 keV，CO ~（3 2-）的U-O_（ax）和U-O键距分别从1.78增至1.88 μ m和2.42增至2.53 μ m。
Abstract A spectroelectrochemical cell was fabricated for in-situ X-ray absorption spectroscopy (in-situ XAS). The XAS spectra of the uranium LIII edge were monitored in electrolyte solutions during the electrochemical reduction. Tetravalent uranium, U4+, in 1 mol dm–3 (M) hydrochloric acid (HCl) was electrochemically prepared from hexavalent uranium, UO22+, by constant current electrolysis, and the extended X-ray absorption fine structure (EXAFS) was analyzed. The concentration ratio of UO22+ and U4+, which were formed via the disproportionation of pentavalent uranium, UO2+, during the electrolysis, were calculated based on the intensity of the signal for the two axial oxygen atoms in the linear UO22+ unit, the U–Oax, bond that had a radial structural function. The apparent redox potential of the UO22+/U4+ couple in 1 M HCl was determined based on the Nernst equation using the concentrations of UO22+ and U4+. The electrode potential was shown to be close to the formal potential of the UO22+/UO2+ couple as reported previously. This result indicates that the UO2+ that was formed electrochemically at the electrode disproportionated to form UO22+ and U4+ in the bulk solution. The in-situ XAS of UO22+ in 0.1 M nitric acid was also performed. The U4+ that formed was partially re-oxidized to UO22+ by the NO3– present in the solution. The formation of the UO2+ carbonato complex was observed by in-situ XAS in a 1 M sodium carbonate solution during the bulk electrolysis. The edge jump of the X-ray absorption near edge structure (XANES) spectrum shifted from 17.164 to 17.163 keV, and the bond distances of U–Oax and U–O for CO32– increased from 1.78 to 1.88 Å and from 2.42 to 2.53 Å, respectively, because of the reduction of the UO22+ to the UO2+ carbonato complex.