Time dependent zero valent iron oxidation and the reductive removal of pertechnetate at variable pH

• Published in: Journal of hazardous materials 2022-02, Vol.424 (Pt B), p.127400-127400, Article 127400
• Main Authors: Kandel, Shambhu, Katsenovich, Yelena P., Boglaienko, Daria, Emerson, Hilary P., Levitskaia, Tatiana G.
• Format: Article
• Language: English
• Subjects: Hydrogen-Ion Concentration; Iron; Iron oxides; Oxidation-Reduction; Sodium Pertechnetate Tc 99m; Sulfate; Sulfates; Technetium-99; Zero valent iron
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2021.127400

Elemental iron Fe0 is a promising reductant for removal of radioactive technetium-99 (Tc) from complex aqueous waste streams that contain sulfate, halides, and other inorganic anions generated during processing of legacy radioactive waste. The impact of sulfate on the kinetics of oxidation and reduction capacity of Fe0 in the presence of Tc has not been examined. We investigated the oxidative transformation of Fe0 and reductive removal of TcO4- in 0.1 M Na2SO4 as a function of initial pH (i.e., pHi 4, 7, and 10) under aerobic conditions up to 30 days. Tc reduction was the fastest at pHi 7 and slowest at pHi 10 (Tc reduction rate pHi 7 > 4 > 10). Aqueous fraction of Tc was measured at 0.4% at pHi 7 within 6 h, whereas ≥ 97% of Tc was removed from solutions at pHi of 4 and 10 within 24 h. Solid phase characterization showed that magnetite was the only oxidized crystalline phase for the first 6 h regardless of initial pH. Lepidocrocite was the most abundant oxidized product for pHi 10 after 5 days, but was not observed at pH of 4 or 7. [Display omitted] •Fe0 quantitatively removes Tc7+ from aqueous sulfate solutions at pH 4-10 under aerobic conditions.•Tc7+ reductive removal followed first-order kinetics depending on initial pH (7 > 4 > 10).•Fe0 oxidation rates were dependent on initial pH (4 > 7 > 10).•Initial pH governed the nature of the formed iron oxide phases.•Oxidation of Fe0 was inhibited in presence of Tc7+.