Sorption of Trivalent Rare Earth Elements on Calcite

A unique surface-destabilizing effect of NaNO3 on calcite, one of the most abundant minerals on earth, has been studied on the molecular scale by X-ray reflectivity. Upon exposure to NO3- the crystal structure at the surface of the mineral is heavily destabilized, resulting in partial dissolution and the formation of an amorphous substrate layer at the interface. The effect extends more than 15 Å deep into the crystal, and changes the mineral water interface considerably. The influence upon the adsorption of the rare earth ion Y(III) reveals the change in interfacial reactivity that accompanies the reaction. Both inner-sphere and outer sphere sorption species can be identified by resonant anomalous X-ray reflectivity (RAXR) in the absence of NO3-, but both species were found to be desorbed quantitatively from the surface in its presence.