Enhanced 99Tc retention in glass waste form using Tc(IV)-incorporated Fe minerals

Abstract

Technetium (Tc-99) immobilization by doping into iron oxide mineral phases may alleviate the problems with Tc volatility during vitrification of nuclear waste. Because reduced Tc, Tc(IV), substitutes for Fe(III) in the crystal structure by a process of Tc reduction from Tc(VII) to Tc(IV) followed by co-precipitation of Fe oxide minerals, two Tc-incorporated Fe minerals (Tc-goethite and Tc-magnetite/maghemite) were prepared and tested for Tc retention in glass melt samples at temperatures between 600 and 1000 degrees C. After being cooled, the solid glass specimens prepared at different temperatures at 600, 800, and 1000 degrees C were analyzed for Tc oxidation state using Tc K-edge XANES. In most samples, Tc was partially (<60%) oxidized from Tc(IV) to Tc(VII) as the melt temperature increased up to 600 degrees C. However, most of Tc(IV) was completely (>95%) oxidized to Tc(VII) at temperature above 800 degrees C. Tc retention in glass melt samples prepared using Tc-incorporated Fe minerals were slightly higher (similar to 10%) than in glass prepared using KTcO4 because of limited and delayed Tc volatilization. (C) 2017 Elsevier B.V. All rights reserved.