Over the past 20 years there have been remarkable changes in our understanding of sorption phenomena at mineral/aqueous solution interfaces. This new level of understanding is a direct result of improvements in experimental approaches to complex interfacial systems as well as in molecular-level theoretical approaches. For many years, idealized interfacial systems have been studied, typically involving relatively clean mineral surfaces and single types of adsorbate ions in solution. However, in complex natural systems, solid geomedia are often coated by natural organic matter (NOM) or microbial biofilms, resulting in dirty surfaces, which raises the question of how these coatings impact reactivity and reaction kinetics of sorption reactions. Recent long-period x-ray standing wave fluorescence yield studies of aqueous metal ion adsorption on metal oxide surfaces coated with natural organic matter as well as microbial biofilms have shown that these coatings reduce the rates of adsorption reactions, but they do not appear to change the relative reactivity of different metal oxide surfaces. Particle and pore sizes are also important variables in natural systems that impact adsorption processes. The impact of NOM coatings and particle size on the sorption of aqueous U(VI) in NOM-ferrihydrite systems will be discussed, based on recent U L-edge XAFS studies. Recent applications of Density Functional Theory to the sorption of Hg on a-Fe<sub>2</sub>O<sub>3</sub> will be used to illustrate the power of molecular-level quantum chemical approaches to understanding sorption processes. Collectively, these studies were designed to bridge the pressure, cleanliness, particle size, and complexity gaps that exist between classical UHV surface science studies of sorption processes and the highly complex sorption processes that occur in nature and in catalytic reactors.

Metal ion sorption at mineral/aqueous solution interfaces: Effects of complex coatings and particle/pore sizes

251st National Meeting (2016)

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