Title: Uranium Chemistry: A Materials Compatibility Challenge
The US Environmental Protection Agency (EPA) recently requested analysis of a civilian uranium milling and mining site for contamination to evaluate site remediation consideration.
Water and soil samples originating from the contaminated uranium milling and mining site were received at MCL to characterize the behavior of uranium in these phases and estimate site-specific partition coefficients for uranium. For groundwater samples, MCL determined the total uranium concentrations and soluble-uranium fraction, select water chemistry such as the total carbonate (alkalinity), and the net charge distribution (anion/cation) for complexed uranium. These parameters affect the solubility, speciation and mobility of uranium in groundwater and the subsequent interaction of uranium with soil solids. For soil samples, MCL determined the levels of total uranium and the fraction of total U that was reversibly bound by iron-containing minerals in the soil matrix. MCL also provided X-ray photoelectron spectroscopy (XPS) data to demonstrate that the uranium in the as-received soil samples was predominantly in a mixed-valent redox state, i.e., in a redox condition intermediate between U(VI) (generally the most soluble and mobile form of uranium in contact with groundwater systems) and U(IV) (a generally insoluble form of uranium found in, e.g., uraninite ore, UO2). In this respect, the average composition of uranium in the soil was similar to pitchblende (U3O8), another common, highly stable (low-solubility), uranium ore.
MCL’s analysis supported the EPA site remediation decisions.