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INCORPORATION OF RADIOACTIVE CONTAMINANTS INTO PYROAURITE-LIKE PHASES BY ELECTROCHEMICAL SYNTHESIS

Y. Roh^1,, S.Y. Lee², M.P. Elless³ and J.E. Foss¹

¹ Department of Plant and Soil Sciences, The University of Tennessee, Knoxville, Tennessee 37996, USA
² Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
³ Edenspace System Corporation, Reston, Virginia 20191, USA

E-mail of corresponding author: rohy{at}ornl.gov

During electrochemical remediation of radionuclide, ²³⁵U, ²³⁸U, and ⁹⁹Tc-contaminated aqueoussolutions, pyroaurite-like phases, ideally [M(II)M(III)(OH)₁₆CO₃·4H₂O] where M = Fe, were synthesized following coprecipitation with iron from metal iron electrodes. The effect of radionuclides on the transformation of amorphous precipitates to crystalline pyroaurite-like phases was investigated using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray analysis, Fourier-transform infrared (FTIR) spectroscopy, and fluorescence spectroscopy. The synthetic iron carbonate hydroxide phases showed primary XRD peaks at 0.7 and 0.35 nm and FTIR spectra that indicated the presence of a brucite-like sheet structure with carbonate anions occupying the interlayer. Divalent and trivalent iron, eroded from the electrode, occupies the octahedral sites of the brucite-like sheets. The carbonate anions in the interlayer balance the excess positive charge from isomorphous substitution of the Fe²⁺ or Fe³⁺ by reduced uranium (U⁴⁺) and technetium (Tc⁴⁺). Because of the lower solubility associated with crystalline phases than amorphous phases, incorporation of radioactive contaminants into pyroaurite-like phases by electrochemical syntheses represents a more effective approach for removing U and Tc from contaminated aqueous solutions than traditional technologies.

Key Words: Coprecipitation • Groundwater Remediation • Pyroaurite • Technetium • Uranium • Zero-Valent Iron

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