Biogeochemical cycling of uranium in a reduced aquifer
Résumé
Uranium transport in the aquifers is mainly controlled by its oxidation state, U(VI) being relatively mobile when U(IV) is relatively insoluble. Previous bioremediation studies have shown that adding electron donor to groundwater stimulates the activity of metal- and sulfate-reducing bacteria, which promotes U(VI) reduction in contaminated aquifers and immobilize U. However, studying U speciation in sediments biostimulated in the aquifers is challenging due to its low concentration. We have used in-well columns to obtain direct access to chemical and physical forms of U(IV), as well as Fe and S. We investigate the formation of U(IV) during early stages of a bioremediation experiment at the Old Rifle site, CO, from iron-reducing to sulfate-reducing conditions. X-ray absorption spectroscopy and microscopy were used to obtain information on Fe, S and U biogeochemical cycling. Chemical extractions of reduced sediments are also used to determine the rates of Fe(II) and U(IV) accumulation.