The current understanding of elementary reactions at mineral-water interfaces derives in large part from direct in situ observations of mineral surface and interfacial water structures and the distribution of adsorbed and incorporated ions, as well as growth and dissolution processes. This understanding was developed mainly from probing ideally flat surfaces in the presence of excess aqueous electrolyte to characterize the intrinsic reactivity of these systems. Here, we present recent work revealing how the nature of interfacial reactions can be strongly modified by extrinsic factors, specifically the shape and size of the reacting mineral and the advective-diffusive transport of ions to the reacting surface. This is illustrated through studies of calcite surface reactivity with metal-(e.g., Pb, Cd)-containing solutions that are under-saturated with respect to calcite. Unlike the limited reactivity found in calcite-saturated solutions, these reactions lead to dramatic morphological changes to the calcite interfacial topography, along with complex and spatially-variable deposition of adsorbed Pb and cerussite (PbCO3), and the eventual replacement of calcite by cerussite. The observed reactions are expected to provide important tests of dynamic reactive transport models that are crucial for understanding analogous reactions in natural geological media.

Understanding extrinsic controls to mineral water interfacial reactivity

ACS Spring Meeting 2021

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