PNNL

Abstract

Developing an understanding of the response of mineral/water interfaces to applied electric fields is central to detecting and interpreting signatures of interfacial processes in the subsurface. Here we focus density functional theory calculations on understanding K+ cation binding and diffusion across the (001) surface of orthoclase feldspar under various applied electric fields with and without surface hydration. The calculations reveal how water ligands labilize surface K+ cations for diffusion while also increasing their sensitivity to electric field effects on the binding energy at different surface sites. The calculations also show how the direction and strength of the electric field systematically affect surface cation mobility, sorption, and hydration behavior. Specifically, electric fields directed toward the surface increase the potassium binding energies, facilitate K+ diffusion across multiple binding sites, and increase the propensity of surface K+ ions to lose their hydration shells. The findings help fill a major knowledge gap into the impact of electric fields on mineral/water interface structure and dynamics more generally, featuring in this case a commonly found type of feldspar involved in a multitude of atmospheric and geochemical processes.