May 4, 2011
Journal Article

Immobilization of 99-Technetium (VII) by Fe(II)-Goethite and Limited Reoxidation

Abstract

Synthesized goethite was successfully used with addition of Fe(II) to sequester Tc present in both deionized water and simulated off-gas scrubber waste solutions. Pertechnetate concentration in solution decreased immediately when the pH was raised above 7 by addition of sodium hydroxide. Removal of Tc(VII) from solution occurred most likely as a result of heterogeneous surface-catalyzed reduction to Tc(IV) and subsequent co-precipitation onto the goethite. The final Tc-bearing solid was identified as goethite-dominated Fe(III)-(oxy)hydroxide based on XRD analysis, confirming the widespread observation of its characteristic acicular habit by TEM/SEM images. Analysis of the solid precipitate by XAFS showed that the dominant oxidation state of Tc was Tc(IV) and was in octahedral coordination with Tc-O, Fe-O, and Tc-Fe bond distances that are consistent with direct substitution of Tc for Fe in the goethite structure. In some experiments the final Tc-goethite product was subsequently armored with additional layers of freshly precipitated goethite. Successful incorporation of Tc(IV) within the goethite mineral lattice and subsequent goethite armoring can limit re-oxidation of Tc(IV) and its subsequent release from Tc-goethite waste forms, even when the final product is placed in oxidizing environments that typify shallow waste burial facilities.

Revised: June 27, 2011 | Published: May 4, 2011

Citation

Um W., H. Chang, J.P. Icenhower, W.W. Lukens, R.J. Serne, N. Qafoku, and J.H. Westsik, et al. 2011. Immobilization of 99-Technetium (VII) by Fe(II)-Goethite and Limited Reoxidation. Environmental Science & Technology 45, no. 11:4904-4913. PNNL-SA-72463. doi:10.1021/es104343p