Date of Award
Master of Science (MS)
Several wetlands throughout The United States are known to have attenuated significant concentrations of uranium. A recent study culminating fifty years of contaminant monitoring has indicated that uranium present in a wetland within the Savannah River Site is predominantly immobile. Previous works have demonstrated that iron cycling, organic carbon concentrations, and the sharp boundaries between anoxic and oxic zones (present in the hyporheic zones of gaining streams) substantially impact the transport of contaminants in wetlands, but the mechanisms preventing the movement of uranium at the Savannah River Site are not fully understood. However, this wetland is known to be enriched in iron and natural organic matter and both of these constituents can influence the mobility of uranium.The objective of this work was to understand the influence of organic ligand concentration (citrate was selected as a surrogate ligand in this work) on the transport of iron and uranium through the hyporheic zone under gaining stream conditions. Observations of the impact of the ligand concentration on the oxidation of ferrous to ferric iron, the precipitation of iron (hydr)oxides, and the stability of iron particles in solution in a lab scale hyporheic zone provided insight into the transport of iron and uranium. To accomplish this objective, it was imperative to build a 2D tank representative of the hyporheic zone under gaining stream conditions, construct an apparatus capable of delivering anoxic solutions to a 2D tank, and devise an image analysis system to determine the concentrations of iron (hydr)oxide precipitates distributed throughout the sediment layer of the 2D tank. Observations made during this study indicate that the treatment of sodium citrate present in the system impacted the distribution of iron and uranium between the sediment layer, overlying water, and on top of the sediment surface. Higher concentrations of sodium citrate were able to increase the normalized concentrations of iron and uranium in the overlying waters and prevent the precipitation of iron (hydr)oxides in the sediment layer. Lower concentrations of sodium citrate yielded lower normalized concentrations of iron and uranium in the overlying water and were not able to prevent the precipitation of iron (hydr)oxides in the sediment layer. This evidence suggests that higher concentrations of sodium citrate were able to increase the mobility of iron and uranium.
Williams, Reid, "Transport and Precipitation of Iron and Uranium in a Lab Scale Model Riparian Zone" (2021). All Theses. 3602.