Uranium(VI) complexation by humic acid under neutral pH conditions studied by laser-induced fluorescence spectroscopy
Uranium(VI) complexation by humic acid under neutral pH conditions studied by laser-induced fluorescence spectroscopy
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DOI：
10.1524/ract.2007.95.2.103
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发表时间：
2007
影响因子：
1.8
通讯作者：
S. Sachs;V. Brendler;G. Geipel
中科院分区：
文献类型：
--
作者：
S. Sachs;V. Brendler;G. Geipel
研究了pH为7时，在排除CO2的条件下U（VI）与Aldrich腐殖酸（HA）的络合作用。利用时间分辨激光诱导荧光光谱（TRLFS）和超快脉冲TRLFS（fs-TRLFS）两种独立的激光诱导光谱方法，研究了UO_2 OH ~+与HA反应生成的三元单羟基腐植酸U（VI）配合物UO_2（OH）HA（I）。假设HA的所有质子交换官能团都能参与络合物的形成，则UO_2（OH）HA（I）的平均稳定常数为6.58 ± 0.24。或者，基于金属离子电荷中和模型评价分析数据，得到络合常数为6.95 ± 0.10，负载容量为0.76 ± 0.28。从未水解的UO_（22+）离子出发，计算出U（VI）与HA的总络合常数logβ_（0.1）M = 14.89 ± 0.54。该值与文献数据非常吻合。考虑到UO_2（OH）HA（I）络合物的存在，重新计算了HA存在下U（VI）的形态。结果表明，UO_2（OH）HA（I）的形成对铀（VI）在环境pH值范围内的分布有重要影响。因此，U（VI）在天然含水层系统中的流动性可能会增强。
The complexation of U(VI) with Aldrich humic acid (HA) was studied at pH 7 under exclusion of CO2. Using two independent laser-induced spectroscopic methods, time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrafast pulses (fs-TRLFS), the formation of the ternary U(VI) mono hydroxo humate complex UO2(OH)HA(I) by reaction of UO2OH+ with HA was studied. Assuming that all proton exchanging functional groups of the HA are able to contribute to the complex formation, a mean stability constant of 6.58 ± 0.24 was derived for UO2(OH)HA(I). Alternatively, the analytical data were evaluated based on the metal ion charge neutralization model resulting in a complexation constant of 6.95 ± 0.10 and a loading capacity of 0.76 ± 0.28. An overall complexation constant of logβ0.1M = 14.89 ± 0.54 was calculated for the total reaction of U(VI) with HA starting from the non-hydrolyzed UO22+ ion. This value agrees very well with literature data. Taking into account the UO2(OH)HA(I) complex, the speciation of U(VI) in presence of HA was recalculated. It was found, that the formation of UO2(OH)HA(I) can significantly influence the U(VI) distribution in the environmentally relevant pH region. As a consequence, the mobility of U(VI) in natural aquifer systems could be enhanced.