Interactions of ions with charged particles are important in many geochemical systems. Adsorption and desorption of ions determine the bioavailability and transport of nutrients and toxic elements. Ion adsorption to colloids changes the effective charge of the particles,ultimately affecting their stability and transport in aqueous conditions. Precise description of these processes depends on a fundamental understanding of the interplay between the long-range electrostatic and the short-range hydration forces. Herein we present new experimental results on the interaction of Y3+ ions with the negatively-charged muscovite (001) surface to explore the role of strong ion-ion correlations and their impact on ion-mineral interactions. In-situ specular crystal truncation rod and resonant anomalous x-ray reflectivity measurements show that Y3+ adsorbs as three distinct species (inner-sphere, adsorbed outer-sphere, and extended outer-sphere). Uptake measurements show that the maximum Y3+ coverage exceeds by ~50% the amount needed to satisfy the muscovite surface charge in the absence of background electrolyte, but this overcompensation is largely suppressed in the presence of 0.1 mol/kg NaCl. The measured intrinsic standard-state Gibbs free energy for Y3+ adsorption (-36.9�0.9 kJ/mol) generally matches the value extrapolated from those determined previously for monovalent and divalent cations when the difference in electrostatic potential generated by the difference in adsorbed cation speciation is considered. These results provide new insight into the electrostatic-driven adsorption of ions at a charged surface and suggest the need for developing a more robust conceptual model for ion interactions at solid-water interfaces where ion hydration plays a critical role in determining the energetics, height, and coverage of adsorbed cations.

Adsorption of trivalent yttrium at the muscovite (001) - water interface

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.