Department of Environmental Engineering, Technical University of Denmark, Miljøvej, Building 115, 2800 Kgs. Lyngby, Denmark; Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Department of Environmental Engineering, Technical University of Denmark, Miljøvej, Building 115, 2800 Kgs. Lyngby, Denmark.
J Contam Hydrol. 2022 Apr;246:103965. doi: 10.1016/j.jconhyd.2022.103965. Epub 2022 Feb 4.
Although mixing and surface complexation reactions are key processes for solute transport in porous media, their coupling has not been extensively investigated. In this work, we study the impact of mass-transfer limitations on heterogeneous reactions taking place at the solid-solution interface of a natural sandy porous medium under advection-dominated flow-through conditions. A comprehensive set of 36 column experiments with different grain sizes (0.64, 1.3 and 2.3 mm), seepage velocities (1, 30 and 90 m/day), and hydrochemical conditions were performed. The injection of NaBr solutions of different concentrations (1-100 mM) led to the release of protons via deprotonation reactions of the quartz surface. pH and solute concentration breakthrough curves were measured at the outlet of the columns and the propagation of pH fronts in the column setups was tracked inside the porous medium with non-invasive optode sensors. The experimental results show that the deprotonation of the reactive surfaces, resulting from their interactions with the injected ionic species, strongly depends on the hydrodynamic conditions and differs among the tested porous media despite their apparent similar surface properties. Reactive transport modeling was used to quantitatively interpret the experimental results and to analyze the effects of mass-transfer limited physical processes on surface complexation reactions, propagation of pH fronts, transport of major ions and spatio-temporal evolution of surface composition. A dual domain mass transfer formulation (DDMT) combined with a surface complexation model (SCM) allowed capturing the effects of incomplete mixing on the surface reactions and to reproduce the experimental observations collected in the experiments with high flow velocities. The SCM was parameterized with a single set of surface complexation parameters, accounting for the similar surface properties of the porous media, and was capable of describing the surface complexation mechanisms and their impact on the hydrochemistry over the large range of tested ionic strengths.
尽管混合和表面络合反应是多孔介质中溶质迁移的关键过程，但它们的耦合作用尚未得到广泛研究。在这项工作中，我们研究了在受对流主导的流动通过条件下，天然沙质多孔介质固-液界面上的非均相反应中传质限制的影响。我们进行了一组全面的 36 个柱实验，涉及不同的粒径（0.64、1.3 和 2.3 毫米）、渗流速度（1、30 和 90 米/天）和水文化学条件。注入不同浓度（1-100 毫摩尔）的 NaBr 溶液会导致石英表面的去质子化反应释放质子。在柱出口处测量 pH 值和溶质浓度的突破曲线，并使用非侵入式光纤传感器在多孔介质内部跟踪 pH 前沿在柱装置中的传播。实验结果表明，反应表面的去质子化作用，源自它们与注入离子物种的相互作用，强烈依赖于水动力条件，尽管测试的多孔介质具有明显相似的表面性质，但在不同的多孔介质中存在差异。反应性传输建模用于定量解释实验结果，并分析传质受限物理过程对表面络合反应、pH 前沿传播、主要离子传输以及表面组成的时空演化的影响。双域传质公式（DDMT）与表面络合模型（SCM）相结合，能够捕捉不完全混合对表面反应的影响，并重现高流速实验中收集的实验观察结果。SCM 用一组单一的表面络合参数进行参数化，这些参数考虑了多孔介质相似的表面性质，并能够描述表面络合机制及其对所测试离子强度范围内的水化学的影响。
