Real-time observations can provide direct insights into reaction processes at mineral – water interfaces. Temporal variations in the speciation and coverage of Rb+ adsorbed at the muscovite (001) – water interface were monitored during its exchange with competing ion Na+ using time-resolved resonant anomalous X-ray reflectivity. The Rb+ desorption experiments revealed a stepwise desorption process in which thermodynamically stable inner-sphere Rb+ species transformed to less stable outer-sphere Rb+ species before desorption from the interface. In contrast, the adsorption of Rb+ appeared to proceed directly to the dominant inner-sphere species within the experimental time resolution (~1 sec). The variations in Rb+ coverage during ion exchange at temperatures from 9 to 55 °C showed that Rb+ desorption was significantly slower than adsorption. This difference in reaction rate results from both a larger activation energy (by ~5 kJ/mol) and a smaller pre-exponential factor (by more than three orders of magnitude) for desorption.

Real-time observations of Rb+/Na+ exchange processes at the muscovite (001) – water interface

253rd National Meeting (2017)

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