Ion waves in reactive porous media : coupling acidity and salinity transport through surface chemistry
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Transport behavior in groundwater systems is dominated by chemical interactions between aqueous species and the materials that compose the subsurface. The interfacial region between the solid and liquid phase is complex, both in its structure, and electrochemical behavior. Despite this difficulty, much effort has been extended towards a mechanistic understanding of the mineral surface. Such models have been extensively tested in batch settings. In contrast the transport literature is quite sparse. In the present study we extend well established mathematical techniques from chromatography to investigate the role of surface chemistry on the transport of ions in reactive porous media. Of particular importance is the coupled transport of salinity and acidity. Together these quantities determine the charging behavior, and therefore reactivity, of mineral surfaces. The work consists of both experimental and theoretical analyses of the acidity-salinity transport system through quartz sand. The results inform how the electrostatic behavior of the silica surface determines transport of charged species, with implications for a range of fields including CO₂ sequestration, colloid transport, and nuclear waste storage.