Reversible cycling of Nd ion adsorption to the surface of an aqueous solution was implemented by using X-ray exposure to alter the equilibrium between Nd bound to DTPA dissolved in bulk water and Nd bound to a monolayer of DHDP on the surface of the aqueous solution. Similar results were obtained for Gd ions and shown in the SI. A simple model described the measured temporal variation of ion surface density for X-rays-on and X-rays-off conditions. The derived kinetic rates correspond to time scales on the order of hundreds of seconds. We suggest that these long time processes are most likely dominated by diffusion effects of either ions, radiolysis products, or DTPA, because other processes should be much faster. X-ray exposure effects on the DHDP monolayer at pH 3.0 were due indirectly to radiolysis of bulk water, but at pH 4.5 an X-ray exposure process independent of radiolysis effects, possibly due to ozone production, was present. X-ray exposure effects on DTPA were due either indirectly to radiolysis of bulk water or to direct exposure of DTPA.