Abstract
Coulombic interactions between charged species in pore water and at surface/solution interfaces are of pivotal importance for multicomponent reactive transport in porous media. In this study, we investigate the impact of domain dimensionality on electrostatically coupled dispersion and surface-solution reactions during transport of acidic plumes and major ions in porous media.Column and quasi two-dimensional flow-through experiments were performed, with identical silica porous media and under the same advection-dominated conditions. Equal mass fluxes of different electrolyte solutions (i.e., HCl - pH ∼ 2.8, NaBr - 100 mM, HCl - pH ∼ 2.8 plus NaBr - 100 mM) were continuously injected in the 1-D and 2-D experiments and breakthrough curves of pH and major ions were measured at the outlet of the domains. The presence of pronounced ionic strength gradients in the transverse direction in the 2-D setup caused distinct retardation and transport behaviors of protons and major ions which were not observed in the one-dimensional column experiments. Furthermore, in the cases of salt electrolytes injection, considerably enhanced release of H+ (>61%) from the quartz surface was observed in the multidimensional system compared to the one-dimensional setup.Reactive transport modeling was performed to reproduce the experimental outcomes and to analyse the coupling between transport processes, based on the Nernst-Planck formulation of diffusive/dispersive fluxes and on surface complexation reactions at the solid-solution interface. Electrostatic interactions between Na+, Br−, and H+, and deprotonation of the quartz surface upon the formation of sodium outer-sphere complexes, are the primary controllers of the spatial and temporal features displayed by the pH and major ions measurements. The reactive transport simulations allowed us to interpret the experimental observations, to visualize the distribution and spatio-temporal evolution of dissolved and solid species, to identify a spatially heterogeneous zonation of Coulombic interactions with distinct behavior at the fringe and core of the injected plumes in the multidimensional setup, and to quantify the different components of the Nerst-Planck fluxes of the charged solutes. This study demonstrates that the domain dimensionality directly affects electrostatic interactions between charged aqueous species in the pore water and surface complexation reactions at the solid-solution interface. The non-trivial effects of dimensionality on multicomponent ionic transport result in a significantly different behavior in 1-D and 2-D systems.
Highlights
Coulombic interactions between charged aqueous species and reactive processes such as dissolutionprecipitation and sorption mechanisms play key roles in the transport of solute plumes in porous media
We evaluated dimensionality effects on multicomponent ionic transport and surface complexation by comparing one-dimensional and quasi two-dimensional flow-through experiments performed in the same silica sand porous medium, under the same advection-dominated flow regimes, hydrochemistry, and injection conditions
Three different electrolyte solutions with sodium bromide and hydrochloric acid were continuously injected through the domain, and measurements of pH and major ions breakthrough curves were performed at the outlet of the setups
Summary
Coulombic interactions between charged aqueous species and reactive processes such as dissolutionprecipitation and sorption mechanisms play key roles in the transport of solute plumes in porous media. From the early work of Vinograd and McBain (1941), the role of coupled diffusive fluxes has been increasingly recognized for a variety of natural systems such as seawater ionic mixtures (Felmy and Weare, 1991), fluid-sediment interactions in hydrothermal circulation (Giambalvo et al, 2002), transport of major ions and charged contaminants (Liu et al, 2011; Muniruzzaman and Rolle, 2021), diffusion in clay rocks including potential repositories for nuclear waste storage (Appelo and Wersin, 2007; Appelo et al, 2008; Appelo et al 2010; Soler et al, 2019), uranyl diffusion, and displacement of stable and radiogenic isotopes (Druhan et al, 2015). Sorption-desorption mechanisms have been investigated for different types of reactive minerals, including iron and aluminum oxides (Fuller et al, 1996; Davis et al, 1998; Akai et al, 2004; Fukushi and Sverjensky, 2007; Johannesson and Neumann, 2013; Stolze et al, 2019a,b), clay minerals (Leroy and Revil, 2004; Leroy et al, 2006; Glaus et al, 2007; Appelo et al, 2010; Bourg et al, 2015; Tertre et al, 2015; Tournassat and Steefel, 2015; Gimmi and Alt-Epping, 2018; Muniruzzaman and Rolle, 2019; Glaus et al, 2020), and silica minerals (Stumpf et al, 2008; McNeece and Hesse, 2016, 2017; McNeece et al, 2018; Stolze et al, 2020)
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