Impact of multicomponent ionic transport on pH fronts propagation in saturated porous media

Abstract

We investigate the propagation of pH fronts during multicomponent ionic transport in saturated porous media under flow-through conditions. By performing laboratory bench-scale experiments combined with numerical modeling, we show the important influence of Coulombic effects on proton transport in the presence of ionic admixtures. The experiments were performed in a quasi two-dimensional flowthrough setup under steady-state flow and transport conditions. Dilute solutions of hydrochloric acid with MgCl 2 (1:2 strong electrolyte) were used as tracer solutions to experimentally test the effect of electrochemical cross coupling on the migration of diffusive/dispersive pH fronts. We focus on two experimental scenarios, with different composition of tracer solutions, causing remarkably different effects on the propagation of the acidic fronts with relative differences in the penetration depth of pH fronts of 36% between the two scenarios and of 25% and 15% for each scenario with respect to the transport of ions at liberated state (i.e., without considering the charge effects). Also differences in the dilution of the distinct ions plumes up to 28% and 45% in experiment 1 and 2, respectively, were measured at the outflow of the flow-through system. The dilution of the pH plumes also changed considerably (26% relative difference) in the two flowthrough experiments only due to the different composition of the pore water solution and to the electrostatic coupling of the ions in the flow-through setups. Numerical transport simulations were performed to interpret the laboratory experiments. The simulations were based on a multicomponent ionic formulation accurately capturing the Coulombic interactions between the transported ions in the flow-through system. The results of purely forward simulations show a very good agreement with the high-resolution measurements performed at the outlet of the flow-through setup and confirms the importance of charge effects on pH transport in porous media.

Dynamics of calcium carbonate formation: Geochemical modeling of a two-step mechanism

“…It led to substantial pore blockage under all experimental conditions (Boyd et al, 2014;Yoon et al, 2015). It also appeared that the pore scale suits well to catch multicomponent transport mechanisms like Coulombic effects on transverse hydrodynamic dispersion, as studied by Rolle et al (2013a, b) and Muniruzzaman and Rolle (2015).…”

“…On the other hand, the results obtained for diffusion simulations (Appendix A) show that the microfluidic experimental device made of a single straight channel, as considered in the present study, cannot clearly bring multicomponent diffusion effects to light. This suggests that microfluidic devices with more complex structures, and thus non-zero tortuosity, must be used to catch multicomponent transport mechanisms like Coulombic effects on transverse hydrodynamic dispersion, as studied by Rolle et al (2013a, b) and Muniruzzaman and Rolle (2015). Conversely, these results mean that simply-structured microfluidic devices are well suited for studying chemical processes without the disturbance of complex transport-related phenomena.…”

Normal and Inverse Diffusive Isotope Fractionation of Deuterated Toluene and Benzene in Aqueous Systems

“…In the case of toluene, the deuterated isotopologue has a slightly lower diffusion coefficient and results in decreasing isotope ratios as the toluene species diffuse towards the pure gel medium. 42 This parameterization of transverse dispersion has been tested for solute transport in similar quasi 2-D systems [43][44][45] and verified in pore-scale studies [46][47] and fully three-dimensional flow-through experiments. 38 The essential feature of Eq.…”

Nernst‐Planck‐based Description of Transport, Coulombic Interactions, and Geochemical Reactions in Porous Media: Modeling Approach and Benchmark Experiments

“…HCl plumes (pH∼4) in different solutions with MgCl 2 were used to test the effect of electrochemical cross coupling on the migration of diffusive/dispersive pH fronts. Details on the flow‐through experiments are given by Muniruzzaman and Rolle (). A similar scenario with the same geometry and boundary conditions is considered for transport of H 2 SO 4 in solution with MgSO 4 .…”