Porous iron material for TcO₄- and ReO₄- sequestration from groundwater under ambient oxic conditions

Technetium-99 (⁹⁹Tc) is a major contaminant at nuclear power plants and several US Department of Energy sites. Its most common aqueous species, pertechnetate (TcO₄^-), is very mobile in the environment, and currently there are no effective technologies for its sequestration. In this work, a porous iron (pFe) material was investigated for TcO₄^- and perrhenate (ReO₄^-) sequestration from artificial groundwater. The pFe was significantly more effective than granular iron for both TcO₄^- and ReO₄- sequestration under oxic conditions. The Tc removal capacity was 27.5 mg Tc/g pFe at pH ˜6.8, while the Re removal capacity was 23.9 mg Re/g pFe at pH ˜10.6. Tc K-edge XANES and EXAFS analyses indicated that the removed Tc species was 70-80% Tc(IV) that was likely incorporated into Fe corrosion products (i.e., Fe(OOH), Fe₃O₄) and 20-30% unreduced TcO₄^-. In contrast, the removed Re species was ReO₄^- only, without detectable Re(IV). In addition, the sequestered ReO₄^- was not extracted (<3%) by 0.1 M Na₂SO₄ and 1 M KI solution, which indicated that ReO₄^- and by chemical analogy, unreduced TcO₄^-, was likely incorporated into Fe corrosion products. This inexpensive pFe material may be applied to the sequestration and stabilization of ⁹⁹TcO₄^- from contaminated environments and nuclear waste streams.