Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, Missouri 63130, United States.
Department of Environmental Science and Engineering, Fudan University, Shanghai 200438, China.
Environ Sci Technol. 2021 Jul 6;55(13):9352-9361. doi: 10.1021/acs.est.0c07491. Epub 2021 Jun 16.
Adsorption of uranium onto goethite is an important partitioning process that controls uranium mobility in subsurface environments, for which many different surface complexation models (SCMs) have been developed. While individual models can fit the data for which they are parameterized, many perform poorly when compared with experimental data covering a broader range of conditions. There is an imperative need to quantitatively evaluate the variations in the models and to develop a more robust model that can be used with more confidence across the wide range of conditions. We conducted an intercomparison and refinement of the SCMs based on a metadata analysis. By seeking the globally best fit to a composite dataset with wide ranges of pH, solid/sorbate ratios, and carbonate concentrations, we developed a series of models with different levels of complexity following a systematic roadmap. The goethite-uranyl-carbonate ternary surface complexes were required in every model. For the spectroscopically informed models, a triple-plane model was found to provide the best fit, but the performance of the double-layer model with bidentate goethite-uranyl and goethite-uranyl-carbonate complexes was also comparable. Nevertheless, the models that ignore the bidentate feature of uranyl surface complexation consistently performed poorly. The goodness of fitting for the models that ignore adsorption of carbonate and the charge distributions was not significantly compromised compared with that of their counterparts that considered those. This approach of model development for a large and varied dataset improved our understanding of U(VI)-goethite surface reactions and can lead to a path for generating a single set of reactions and equilibrium constants for including U(VI) adsorption onto goethite in reactive transport models.
针铁矿对铀的吸附是控制地下环境中铀迁移的重要分配过程，为此已经开发了许多不同的表面络合模型（SCM）。虽然个别模型可以拟合其参数化的数据，但与涵盖更广泛条件范围的实验数据相比，许多模型的性能都很差。因此，迫切需要定量评估模型的变化，并开发一种更稳健的模型，以便在更广泛的条件范围内更有信心地使用。我们通过元数据分析对 SCM 进行了对比和改进。通过寻求对具有广泛 pH 值、固/溶质比和碳酸盐浓度范围的复合数据集的全球最佳拟合，我们按照系统的路线图开发了一系列具有不同复杂程度的模型。每个模型都需要针铁矿-铀酰-碳酸盐三元表面络合物。对于基于光谱信息的模型，发现三平面模型提供了最佳拟合，但双层模型与双齿针铁矿-铀酰和针铁矿-铀酰-碳酸盐络合物的性能也相当。然而，忽略铀酰表面络合双齿特性的模型表现始终不佳。与考虑那些特性的模型相比，忽略碳酸盐吸附和电荷分布的模型的拟合优度并没有明显受到影响。这种针对大型和多样化数据集的模型开发方法提高了我们对 U(VI)-针铁矿表面反应的理解，并为在反应性传输模型中包含 U(VI)吸附到针铁矿的反应和平衡常数生成单一集合提供了途径。
