Chemical processes at naturally occurring mineral surfaces play important roles in the fate and transport of aqueous contaminants. However, characterizing sorption energetics is challenging, both from experimental and theoretical approaches. This is due to the inherent heterogeneity, as well as the structural complexity of surfaces and chemical complexity of ions in solution. A combined density functional theory (DFT) and thermodynamics modeling approach enables a molecular-level approach to interfacial processes of increasing complexity. The basis of the method is the partitioning of the chemical process into terms that are either purely calculable or purely related to experimental data. Using Nernst-based expressions for elementary steps of metal atoms going into the preferred aqueous speciation allows for analytical expressions that take into account changes in activity and pH, further bridging the model with experimental conditions. Here we report on extensions of DFT and thermodynamics modeling to the case of alkali metal sorption and exchange on hydrated quartz surfaces. We compare the model results to calorimetry measurements, and discuss trends in terms of ion size, charge, and speciation.

Systematic study of the effect of inner-sphere adsorption of alkali metals and alkaline Earth anions on the (101) α-quartz surface on dissolution energetics

ACS Spring Meeting 2021

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