A host of methods have been applied over the years to develop a molecular-level understanding of key chemical reactions at the surface-solution interface from macroscopic adsorption isotherms and potentiometric titration measurements, to more recent molecular spectroscopy and synchrotron-based techniques. Yet among the hundreds of studies conducted and published in relation to mineral/solution interfaces, very few deal with the thermodynamics of interfacial reactions. Although numerous studies have utilized spectroscopic observations and quantum chemical calculations to base surface complexation models on mechanistic considerations, the resulting models are not well constrained energetically, i.e. there is no analysis specific to the enthalpy of the systems modeled. Sorption thermodynamic parameters have been traditionally determined from sorption isotherms.Calorimetry, in both flow and titration mode, provides an excellent alternative to isotherm-derived energetics. The synergy between spectroscopic methods and calorimetry can improve our understanding of surface reactions and the formulation of surface complexation models by providing thermodynamic constraints and additional information on outer sphere complexation that is difficult to detect when inner sphere complexes predominate. This study will illustrate this synergy for two model systems: sulfate on goethite and chromate on ferrihydrite and hematite.

Integrated approach to study surface reactions using spectroscopy and calorimetry

249th National Meeting (2015)

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