Understanding the impact of wetting–drying cycles on iron oxides and associated radionuclide behavior is critical for managing contaminated environments, particularly legacy radioactive waste sites. Despite extensive research, knowledge gaps remain regarding the behavior of iron oxides and contaminants under field-relevant conditions. In this study, these gaps are addressed by investigating the transformations of ferrihydrite and goethite, as well as the mobility of contaminant analogs (Sr, Cs, and Nd), during six wetting–drying cycles in a replica trench at the Little Forest Legacy Site (LFLS). Synthetic ferrihydrite- and goethite-coated sands were deployed in permeable bags and subjected to alternating water-saturated (submerged) and air-exposed (drainage/partially drying) periods, which induced variable oxygen exposure and associated shifts in redox conditions. Results revealed limited transformations of ferrihydrite and goethite under the tested wetting–drying conditions, with ferrihydrite showing minor increases in crystallinity after prolonged submerged periods. Contaminant analogs exhibited distinctive behaviors: Sr remained predominantly mobile and Nd demonstrated strong structural incorporation into ferrihydrite, while Cs showed limited association with iron oxides, with its retention primarily controlled by clay minerals. Together, these contrasting behaviors highlight the selective role of iron oxides in controlling contaminant mobility, providing critical insights into iron oxide reactivity and the impact of iron oxide transformations on contaminant mobility during successive wetting–drying cycles in legacy waste environments.
Zhou et al. (Thu,) studied this question.