Incorporation of Radioactive Contaminants into Pyroaurite-Like Phases by Electrochemical Synthesis

Y. Roh1, †, S.Y. Lee, 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
Present address: Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6038, USA E-mail of corresponding author: rohy@ornl.gov

Abstract: During electrochemical remediation of radionuclide, 235U, 238U, and 99Tc-contaminated aqueous solutions, 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

Clays and Clay Minerals; April 2000 v. 48; no. 2; p. 266-271; DOI: 10.1346/CCMN.2000.0480213
© 2000, The Clay Minerals Society
Clay Minerals Society (www.clays.org)