Abstract The coupled effects of pH and ionic strength impact a variety of geochemical processes in the subsurface. In this study, we investigate the interactions of H+ and major ions at the surface-solution interface of silica porous media under advection-dominated flow-through conditions. A series of 21 column experiments were performed by systematically injecting solutions of different pH and ionic strengths. Three types of porous media (i.e., two natural sands and quartz beads) were considered in order to explore differences in surface/solution interactions among quartz materials. Multiple lines of evidence were used to characterize the geochemical processes taking place during the flow-through experiments: (i) breakthrough curves of pH and major ions were measured at the column outlets; (ii) the natural sand surfaces were characterized by chemical extractions and scanning electron microscopy and the quartz structure was analyzed by XRD; (iii) reactive transport modeling was performed to quantitatively interpret the experimental results. We observed strong reactivity of the quartz surface characterized by significant release of protons when interacting with the major ions. The results also show significant differences in the quantity of protons emitted from the surfaces of the three silica porous media, as well as in the shape of the pH breakthrough curves. Reactive transport modeling was based on a multicomponent ionic transport formulation and on surface complexation description of the solid/solution interactions. The surface complexation model included the individual contributions of quartz and Fe/Al oxides present in the sand coatings with the component additive approach. For each medium, a single set of surface complexation parameters capable of reproducing the experimental dataset (i.e., 7 columns) was calibrated by parallelizing the simulations of the flow-through experiments. This approach allowed us to capture the pH and ionic species behavior within a large range of ionic strengths (i.e., [0–100] mM). The SCMs quantitatively show that H+ is released from quartz upon adsorption of Na+ and that the protonation of the oxides surfaces retards the pH front. Differences in acidity behavior between the silica surfaces seem to be primarily controlled by differences in surface topology, crystal structure of quartz and/or various presence of aluminosilicates. This study demonstrates that the reactivity and diversity of quartz surfaces in silica porous media and the complex interplay with oxide surfaces in the coatings control the transport of aqueous charged species in flow-through systems.

中文翻译：

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表面络合和静电相互作用对二氧化硅多孔介质中 pH 前沿传播的影响

摘要 pH 值和离子强度的耦合效应会影响地下的各种地球化学过程。在这项研究中，我们研究了 H+ 和主要离子在对流主导的流通条件下二氧化硅多孔介质的表面 - 溶液界面处的相互作用。通过系统地注入不同 pH 值和离子强度的溶液，进行了一系列 21 次柱实验。考虑了三种类型的多孔介质（即两种天然砂和石英珠），以探索石英材料之间表面/溶液相互作用的差异。使用多条证据来表征在流通实验期间发生的地球化学过程：(i) 在色谱柱出口测量 pH 值和主要离子的穿透曲线；(ii) 天然砂表面通过化学萃取和扫描电镜表征，并通过XRD分析石英结构；(iii) 进行了反应传输建模以定量解释实验结果。我们观察到石英表面的强烈反应性，其特征是与主要离子相互作用时质子的显着释放。结果还表明，从三种二氧化硅多孔介质表面发射的质子数量以及 pH 穿透曲线的形状存在显着差异。反应输运建模基于多组分离子输运公式和固/溶液相互作用的表面络合描述。表面络合模型包括砂涂层中存在的石英和 Fe/Al 氧化物的单独贡献，采用组分添加方法。对于每种介质，通过并行化流通实验的模拟来校准能够再现实验数据集（即，7 列）的单组表面络合参数。这种方法使我们能够在大范围的离子强度（即 [0–100] mM）内捕获 pH 值和离子种类行为。SCM 定量显示，H+ 在吸附 Na+ 时从石英中释放出来，并且氧化物表面的质子化延迟了 pH 前沿。二氧化硅表面之间酸性行为的差异似乎主要受表面拓扑结构、石英晶体结构和/或硅铝酸盐的各种存在差异的控制。