Aging Controls Colloidal Activated Carbon Mobilization from Saturated Sand Columns through Modulation of Energy Barriers

Colloidal activated carbon (CAC) is a promising material for in situ remediation of groundwater impacted by per- and polyfluoroalkyl substances (PFAS). However, long-term aging of CAC in the subsurface can trigger particle mobilization, threatening barrier integrity and increasing the risk of CAC-facilitated PFAS transport. Here, we systematically investigate how aging processes influence CAC mobilization from saturated porous media. CAC was subjected to physical, chemical (H2O2, Fenton, acid), and biological aging to mimic wet–dry cycling, oxidation, and biotic transformations relevant to soil–groundwater systems. Physicochemical characterization (surface charge and particle size) showed that most aging treatments increased CAC’s negative surface charge and structural fragility. These changes were accompanied by enhanced CAC mobilization in column experiments under stepwise salinity reduction (100 → 10 → 0.1 mM). In contrast, the slightly suppressed mobilization of Fenton-aged CAC suggests that dissolved Fe2+ interacts with CAC by neutralizing surface charge and forming iron oxide precipitates, decreasing electrostatic repulsion. Extended Derjaguin–Landau–Verwey–Overbeek (xDLVO) simulations captured how aging-induced changes in surface charge and particle size modify the mobilization energy barrier. These results reveal the critical role of aging in controlling CAC retention in in situ barriers and highlight the utility of interfacial interaction modeling for elucidating colloid mobilization mechanisms.