Aqueous Synthesis of Technetium-Doped Titanium Dioxide by Direct Oxidation of Titanium Powder, a Precursor for Ceramic Nuclear Waste Forms

Journal Article · Sat Nov 18 00:00:00 EST 2017 · Chemistry of Materials

DOI:https://doi.org/10.1021/acs.chemmater.7b03567· OSTI ID:1482527

Lukens, Wayne W.  ^[1]; Saslow, Sarah A. ^[2]

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1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Technetium-99 (Tc) is a problematic fission product that complicates the long-term disposal of nuclear waste due to its long half-life, high fission yield, and the environmental mobility of pertechnetate, its stable form in aerobic environments. One approach to preventing Tc contamination is through incorporation into durable waste forms based on weathering-resistant minerals such as rutile (titanium dioxide). Here, the incorporation of technetium into titanium dioxide by means of simple, aqueous chemistry - direct oxidation of titanium powder in the presence of ammonium fluoride - is achieved. X-ray absorption fine structure spectroscopy and diffuse reflectance spectroscopy indicate that Tc(IV) replaces Ti(IV) within the structure. Rather than being incorporated as isolated Tc(IV) ions, Tc is present as pairs of edge-sharing Tc(IV) octahedra similar to molecular Tc(IV) complexes such as [(H₂EDTA)TcIV](μ-O)₂. Technetium-doped TiO₂ was suspended in deionized water under aerobic conditions, and the Tc leached under these conditions was followed for 8 months. The normalized release rate of Tc (LR_Tc) from the TiO₂ particles is low (3 × 10^-6g m^-2d^-1), which illustrates the potential utility of TiO₂ as waste form. However, the small size of the as-prepared TiO₂ nanoparticles results in an estimated retention of Tc of 10⁴ years, which is only a fraction of the half-life of Tc (2.1 × 10⁵ years).

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1482527
• Journal Information: Chemistry of Materials, Vol. 29, Issue 24; ISSN 0897-4756
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English