Understanding the mechanism of uranium removal from groundwater by zero-valent iron using X-ray photoelectron spectroscopy

The contaminant of most concern in groundwater at the Oak Ridge Y-12 Plant's Bear Creek Valley Characterization Area is soluble uranium. The removal mechanism of soluble uranium from groundwater by zero-valent iron (ZVI, Fe-0) was investigated. X-ray photoelectron spectroscopy (XPS, ESCA) was used to determine the uranium oxidation state at the Fe-0 or iron oxide surface. Product speciation and relative reaction kinetics for the removal of soluble uranium under aerobic and anaerobic conditions with ZVI are presented. Under aerobic conditions, U6+ is rapidly and strongly sorbed to hydrous ferric oxide particulates ("rust"), whereas U6+ is slowly and incompletely reduced to U4+ under anaerobic conditions.