Solubility study of Tc(IV) in a granitic water
Solubility study of Tc(IV) in a granitic water
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Tc(IV) 在花岗岩水中的溶解度研究
DOI：
10.1524/ract.2007.95.9.523
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发表时间：
2007
影响因子：
1.8
通讯作者：
N. Maes
中科院分区：
文献类型：
--
作者：
D. J. Liu;J. Yao;B. Wang;C. Bruggeman;N. Maes
深部地质处置高放废物在大多数国家被认为是一种安全的处置方法。核废料中存在着大量的长寿命裂变产物99Tc，其在水溶液中的化学行为引起了人们的极大兴趣。在氧化条件下，锶以阴离子形式TcO_4·−存在，而在还原条件下，一般预测在深部地质储集库中将以TCO_2·nH_2O的形式存在。因此，在这些条件下，TC(IV)在还原地下水中的迁移性可能受到TCO2·nH2O的溶解度的限制。因此，研究TCO_2·nH_2O的溶解度是非常重要的。溶解度决定了放射性核素从废物形式中的释放，并被用作放射性废物储存库性能评估中放射性核素迁移分析的源项。用Sn2+还原纯钛酸根溶液制备了锶(IV)。在好氧和厌氧条件下，测定了Tc(IV)在模拟地下水和再蒸馏水中的溶解度。研究了溶液pH和CO32-−浓度对Tc(IV)溶解度的影响。用溶剂萃取法分离氧化和还原的氚，并用液体闪烁计数器计算~(99)Tc的β活度，从而周期性地测定溶液中总的锶和Tc(IV)的浓度。实验结果表明，在好氧条件下，模拟地下水和再蒸馏水中TC(IV)的氧化速率约为(1.49∼1.86)×10−9moL L−1D−1，而在厌氧条件下，模拟地下水和再蒸馏水中没有检测到Tc(IV)的氧化。在好氧或厌氧条件下，经离心或超滤后，TC(IV)在模拟地下水和再蒸馏水中的溶解度基本相同。在pH=2时，TC(IV)的溶解度随pH的降低而增加，在pH=11时随pH的升高而增加，在pH=11的范围内与pH无关。在pH=11时，Tc(IV)的浓度在10−8~10−9mol L−1的范围内。地球化学模拟显示，我们的实验结果与NEA TDB综述中的热力学常数之间有很好的一致性。这些数据可以用来估算在高放射性废物处置库的还原环境中，在溶解度限制的情况下，Tc(IV)的溶解度。
The deep geological disposal of the high level radioactive wastes is expected to be a safe disposal method in most countries. The long-lived fission product 99Tc is present in large quantities in nuclear wastes and its chemical behavior in aqueous solution is of considerable interest. Under oxidizing conditions technetium exists as the anionic species TcO4− whereas under the reducing conditions, expected to exist in a deep geological repository, it is generally predicted that technetium will be present as TcO2·nH2O. Hence, the mobility of Tc(IV) in reducing groundwater may be limited by the solubility of TcO2·nH2O under these conditions. Due to this fact it is important to investigate the solubility of TcO2·nH2O. The solubility determines the release of radionuclides from waste form and is used as a source term in radionuclide migration analysis in performance assessment of radioactive waste repository. Technetium(IV) was prepared by reduction of a technetate solution with Sn2+. The solubility of Tc(IV) has been determined in simulated groundwater and redistilled water under aerobic and anaerobic conditions. The effects of pH and CO32− concentration of solution on solubility of Tc(IV) were studied. The concentration of total technetium and Tc(IV) species in the solutions were periodically determined by separating the oxidized and reduced technetium species using a solvent extraction procedure and counting the beta activity of the 99Tc with a liquid scintillation counter. The experimental results show that the rate of oxidation of Tc(IV) in simulated groundwater and redistilled water is about (1.49∼1.86)×10−9mol L−1d−1 under aerobic conditions, while no Tc(IV) oxidation was detected in simulated groundwater and redistilled water under anaerobic conditions. Under aerobic or anaerobic conditions the solubility of Tc(IV) in simulated groundwater and redistilled water is equal on the whole after centrifugation or ultrafiltration. The solubility of Tc(IV) increases with the decrease of pH at pH<2, increases with the increase of pH at pH>11 and is pH independent in the range 2<pH<11. The concentrations of Tc(IV) species were in the range of 10−8 to 10−9mol L−1 at 2<pH<11. The solubility of Tc(IV) slightly increases with increasing the increase of CO32− concentration. Geochemical modelling showed a good agreement between our experimental results and thermodynamic constants from the NEA TDB review. These data could be used to estimate the Tc(IV) solubility for cases where solubility limits transport of technetium in reducing environments of high-level waste repositories.