Uranyl(VI) carbonate complex formation:: Validation of the Ca2UO2(CO3)3(aq.) species
Uranyl(VI) carbonate complex formation:: Validation of the Ca2UO2(CO3)3(aq.) species
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DOI：
10.1524/ract.2001.89.8.511
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发表时间：
2001-01-01
影响因子：
1.8
通讯作者：
Nitsche, H
中科院分区：
文献类型：
--
作者：
Bernhard, G;Geipel, G;Nitsche, H
我们最近在铀矿开采相关水体[1]中发现了一种中性的三碳酸铀酰二钙络合物Ca2UO2(CO3)(3)（aq.）。我们现在报告使用时间分辨激光诱导荧光光谱（TRLFS）物种检测的两种分析方法进一步验证该配合物的化学计量学和形成常数：i)用钙离子滴定非荧光三碳酸铀酰配合物溶液，并通过TRLFS定量测定产生的荧光钙配合物；ii)通过与EDTA（4-）的竞争性钙络合作用改变复合物中钙浓度。两种方法的对数（荧光强度）与对数[Ca2+]的斜率分析表明，两个钙离子结合形成络合物CaUO2(CO3)(3)（aq.）。两种独立方法确定的地层常数分别为：1)对数β度(213)= 30.45 +/- 0.35;2)对数β度(213)= 30.77 +/- 0.25。在激光诱导光声光谱（LIPAS）中观察到UO2(CO3)(3)（4-）配合物与Ca2UO2(CO3)3（aq.）配合物之间存在0.35 nm的色时偏移，为碳酸铀酰钙配合物的形成提供了额外的证据。在含钙和不含钙的碳酸铀溶液中，铀的L-II和l - iii边缘的EXAFS光谱没有显著差异。通过加入U-Ca壳层，获得了与Ca2UO2(CO3)3（aq）配合物的EXAFS更合适的结构。根据溶液中Ca2UO2(CO3)3（aq.）的EXAFS与天然矿物李氏褐铁矿的相似性，我们得出结论，钙原子可能在溶液配合物和固体中处于相同的位置。这一复合物对富钙铀矿相关水域pH值从6到10范围内铀的形态有相当大的影响。
We recently discovered a neutral dicalcium uranyl tricarbonate complex, Ca2UO2(CO3)(3)(aq.), in uranium mining related waters [1]. We are now reporting a further validation of the stoichiometry and the formation constant of this complex using two analytical approaches with time-resolved laser-induced fluorescence spectroscopy (TRLFS) species detection: i) titration of a non-fluorescent uranyl tricarbonate complex solution with calcium ions, and quantitative determination of the produced fluorescent calcium complex via TRLFS; and ii) variation of the calcium concentration in the complex by competitive calcium complexation with EDTA(4-).Slope analysis of the log (fluorescence intensity) versus log [Ca2+] with both methods have shown that two calcium ions are bound to form the complex CaUO2(CO3)(3)(aq.). The formation constants determined from the two independent methods are: i) log beta degrees (213) = 30.45 +/- 0.35 and ii) log beta degrees (213) = 30.77 +/- 0.25.A bathochrorne shift of 0.35 nm between the UO2(CO3)(3)(4-) complex and the Ca2UO2(CO3)3(aq.) complex is observed in the laser-induced photoacoustic spectrum (LIPAS), giving additional evidence for the formation of the calcium uranyl carbonate complex.EXAFS spectra at the L-II and L-III-edges of uranium in uranyl carbonate solutions with and without calcium do not differ significantly. A somewhat better fit to the EXAFS of the Ca2UO2(CO3)3(aq.) complex is obtained by including the U-Ca shell. From the similarities between the EXAFS of the Ca2UO2(CO3)3(aq.) species in solution and the natural mineral liebigite, we conclude that the calcium atoms are likely to be in the same positions both in the solution complex and in the solid.This complex influences considerably the speciation of uranium in the pH region from 6 to 10 in calcium-rich uranium-mining-related waters.