Real - Time X - ray Absorption Spectroscopy of Uranium , Iron , and Manganese in 1 Contaminated Sediments During Bioreduction 2 Tetsu

11 The oxidation status of uranium in sediments is important because the solubility of this toxic and 12 radioactive element is much greater for U(VI) than for U(IV) species. Thus, redox manipulation 13 to promote precipitation of UO2 is receiving interest as a method to remediate U-contaminated 14 sediments. Presence of Fe and Mn oxides in sediments at much higher concentrations than U 15 requires understanding of their redox status as well. This study was conducted to determine 16 changes in oxidation states of U, Fe, and Mn in U-contaminated sediments from Oak Ridge 17 National Laboratory. Oxidation states of these elements were measured in real-time and 18 nondestructively using X-ray absorption spectroscopy, on sediment columns supplied with 19 synthetic groundwater containing organic carbon (OC, 0, 3, 10, 30 and 100 mM OC as lactate) 20 for over 400 days. In sediments supplied with OC ≥ 30 mM, 80% of the U was reduced to U(IV), 21 with transient reoxidation at about 150 days. Mn(III,IV) oxides were completely reduced to 22 Mn(II) in sediments infused with OC ≥ 3 mM. However, Fe remained largely unreduced in all 23