Ion Adsorption and Desorption at the CaF(2)‐Water Interface Probed by Flow Experiments and Vibrational Spectroscopy

The dissolution of minerals in contact with water plays a crucial role in geochemistry. However, obtaining molecular insight into interfacial chemistry is challenging. Dissolution typically involves the release of ions from the surface, giving rise to a charged mineral surface. This charge affects the interfacial water arrangement, which can be investigated by surface‐specific vibrational Sum Frequency Generation (v‐SFG) spectroscopy. For the fluorite‐water interface, recent spectroscopic studies concluded that fluoride adsorption/desorption determines the surface charge, which contrasts zeta potential measurements assigning this role to the calcium ion. By combining v‐SFG spectroscopy and flow experiments with systematically suppressed dissolution, we uncover the interplay of dominant fluoride and weak calcium adsorption/desorption, resolving the controversy in the literature. We infer the calcium contribution to be orders of magnitude smaller, emphasizing the sensitivity of our approach.