Stockmann M, Fritsch K, Bok F, Fernandes M Marques, Baeyens B, Steudtner R, Müller K, Nebelung C, Brendler V, Stumpf T, Schmeide K
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Bautzner Landstr. 400, 01328 Dresden, Germany.
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Bautzner Landstr. 400, 01328 Dresden, Germany.
Sci Total Environ. 2022 Feb 1;806(Pt 2):150653. doi: 10.1016/j.scitotenv.2021.150653. Epub 2021 Sep 28.
The influence of ionic strength up to 3 mol kg (background electrolytes NaCl or CaCl) on U(VI) sorption onto montmorillonite was investigated as function of pH in absence and presence of CO. A multi-method approach combined batch sorption experiments with spectroscopic methods (time-resolved laser-induced fluorescence spectroscopy (TRLFS) and in situ attenuated total reflection Fourier-transform infrared spectroscopy (ATR FT-IR)). In the absence of atmospheric carbonate, U(VI) sorption was nearly 99% above pH 6 in both NaCl and CaCl and no significant effect of ionic strength was found. At lower pH, cation exchange was strongly reduced with increasing ionic strength. In the presence of carbonate, U(VI) sorption was reduced above pH 7.5 in NaCl and pH 6 in CaCl system due to formation of aqueous UO(CO) and CaUO(CO) complexes, respectively, as verified by TRLFS. A significant ionic strength effect was observed due to the formation of CaUO(CO), which strongly decreases U(VI) sorption with increasing ionic strength. The joint analysis of determined sorption data together with literature data (giving a total of 213 experimental data points) allowed to derive a consistent set of surface complexation reactions and constants based on the 2SPNE SC/CE approach, yielding log K° = 2.42 ± 0.04, log K° = -4.49 ± 0.7, and log K° = -20.5 ± 0.4. Ternary uranyl carbonate surface complexes were not required to describe the data. With this reduced set of surface complexes, an improved robust sorption model was obtained covering a broad variety of geochemical settings over wide ranges of ionic strengths and groundwater compositions, which subsequently was validated by an independent original dataset. This model improves the understanding of U(VI) retention by clay minerals and enables now predictive modeling of U(VI) sorption processes in complex clay rich natural environments.
研究了高达3 mol/kg（背景电解质为NaCl或CaCl₂）的离子强度对蒙脱石吸附U(VI)的影响，考察了有无CO₂时其随pH值的变化情况。采用多方法联用，将批量吸附实验与光谱方法（时间分辨激光诱导荧光光谱法（TRLFS）和原位衰减全反射傅里叶变换红外光谱法（ATR FT-IR））相结合。在没有大气碳酸盐的情况下，在NaCl和CaCl₂体系中，pH值高于6时U(VI)的吸附率接近99%，且未发现离子强度有显著影响。在较低pH值下，随着离子强度的增加，阳离子交换作用显著减弱。在有碳酸盐存在的情况下，由于分别形成了UO₂(CO₃)₂²⁻和CaUO₂(CO₃)₂²⁻水合络合物，在NaCl体系中pH值高于7.5时以及在CaCl₂体系中pH值高于6时，U(VI)的吸附作用减弱，这已通过TRLFS得到证实。由于形成了CaUO₂(CO₃)₂²⁻，观察到显著的离子强度效应，随着离子强度的增加，U(VI)的吸附作用强烈降低。将测定的吸附数据与文献数据（共213个实验数据点）进行联合分析，基于2SPNE SC/CE方法得出了一组一致的表面络合反应和常数，得到log K° = 2.42 ± 0.04、log K° = -4.49 ± 0.7和log K° = -20.5 ± 0.4。描述这些数据不需要三元碳酸铀酰表面络合物。利用这一简化的表面络合物集，获得了一个改进的稳健吸附模型，该模型涵盖了广泛的地球化学环境，包括不同的离子强度和地下水成分范围，随后通过一个独立原始数据集进行了验证。该模型增进了对粘土矿物对U(VI)保留作用的理解，现在能够对复杂富含粘土的自然环境中U(VI)的吸附过程进行预测建模。
