Incorporation of radioactive contaminants into pyroaurite-like phases by electrochemical synthesis

During electrochemical remediation of radionuclide, U-235, U-228, and Tc-99 -contaminated aqueous solutions, pyroaurite-like phases, ideally [M(II)M(II I)(OH)(16)CO3. 4H(2)O] where M = Fe, were synthesized following coprecipita tion with iron from metal iron electrodes. The effect of radionuclides on t he transformation of amorphous precipitates to crystalline pyroaurite-like phases was investigated using X-ray diffraction (XRD), scanning electron mi croscopy with energy dispersive X-ray analysis, Fourier-transform infrared (FTIR) spectroscopy, and fluorescence spectroscopy. The synthetic iron carb onate 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, er oded 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 wi th crystalline phases than amorphous phases, incorporation of radioactive c ontaminants into pyroaurite-like phases by electrochemical syntheses repres ents a more effective approach for removing U and Tc from contaminated aque ous solutions than traditional technologies.