PNNL

Abstract

Solid-phase characterization of several uranium contaminated sediments from the U.S. Department of Energy’s Hanford Site was used in conjunction with semi-selective extraction analyses and batch and column leach tests to identify the form of uranium in the samples. Results of scanning electron microscopy analyses indicated that the majority of the uranium in the most contaminated sediment was present as discrete uranium phases and possibly co-precipitates with carbonate and iron- and/or aluminum-oxide/hydroxide phases. Molecular probe techniques confirmed the presence of the uranyl ion; structural model fits of the sample spectra were consistent with uranophane, liebigite, and in one case, with a uranium-carbonate adsorption complex on the surface of an iron-(hydr)oxide. Uranium effluent concentrations failed to reach steady-state conditions during long-term column leach tests, indicating that the release of uranium from the sediments was controlled by multi-rate kinetic processes that could be attributed to the different forms of uranium in the samples.