Iron Oxide Waste Form for Stabilizing 99Tc

Abstract Crystals of goethite were synthesized with reduced technetium [ 99 Tc(IV)] incorporated within the solid lattice. The presence of 99 Tc(IV) as a substituting cation in the matrix and “armoring” by an additional layer of precipitated goethite isolated the reduced 99 Tc(IV) from oxidizing agents. These products were used to make monolithic pellets to quantify an effective diffusion coefficient for 99 Tc from goethite waste form contacted with a synthetic Hanford IDF (Integrated Disposal Facility) pore water solution (pH = 7.2 and I = 0.05 M) at room temperature for up to 120 days in static reactors. XANES analysis of the goethite solids recovered post-run demonstrated that the 99 Tc in the goethite crystals remains in the reduced 99 Tc(IV) state. The slow release of pertechnetate concentration with time in the static experiments with the monolith followed a square root of time dependence, consistent with diffusion control for 99 Tc release. An apparent diffusion coefficient of 6.15 × 10 −11  cm 2 /s was calculated for the 99 Tc–goethite pellet sample and the corresponding leaching index ( LI ) was 10.2. The results of this study indicate that technetium can be immobilized in a stable, low-cost Fe oxide matrix that is easy to fabricate and these findings can be useful in designing long-term solutions for nuclear waste disposal.