Iodine local environment in high pressure borosilicate glasses: An X-ray photoelectron spectroscopy and X-ray absorption spectroscopy investigation

• Published in: Journal of nuclear materials Vol. 553; p. 153050
• Main Authors: Morizet, Yann, Jolivet, Valentin, Trcera, Nicolas, Suzuki-Muresan, Tomo, Hamon, Jonathan
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-09-2021; Elsevier BV; Elsevier
• Subjects: Absorption spectroscopy; Borosilicate glass; Coexistence; Coordination numbers; Dissolution; High pressure; Iodides; Iodine; Iodine dissolution mechanism; Iodine isotopes; Nuclear waste glasses; Photoelectron spectroscopy; Photoelectrons; Physics; Radioactive wastes; Radioisotopes; Speciation; Species; Spectrum analysis; X ray absorption; X ray photoelectron spectroscopy; X-ray absorption spectroscopy; Nuclear waste glasses; Iodine dissolution mechanism; X-ray absorption spectroscopy; X-ray photoelectron spectroscopy
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2021.153050

•Iodine is dissolved as iodide (I−) in high pressure borosilicate glasses.•Both alkali and alkaline-earth cations act as a charge compensator to I− species.•The absence of iodate (I5+) suggests that there is a complex interplay between I− species and oxygen species within the glass structure.
The 129I radioactive isotope is a by-product of nuclear plants activity. Owing to its strong volatility, there is currently no ideal protocol to immobilize 129I in nuclear waste borosilicate glasses. Recently, we have proposed the use of high-pressure syntheses to dissolve iodine in various glass compositions; however, I speciation and dissolution mechanism could not be determined.
We have adopted an approach combining X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) methods to determine I speciation and molecular environment in glasses containing from 0.5 to 2.5 mol.% I. The XPS spectra reveal that I is mostly dissolved as iodide (>85% I−) with a small proportion of elemental iodine (<15% I0) and the absence of iodate species (I5+). For borosilicate glasses, the XAS results and subsequent spectrum simulations suggested that Na and Ca are involved in the I− vicinity with averaged derived coordination number (CN) of 3.6 and 2.0 and bond length to the nearest neighbour (rX-I) 2.98 and 2.85 Å, respectively. These results suggest that the coexistence of both I− and I5+ species is not requested for electric neutrality but instead, we explain the I speciation by the possible interplay with oxygen species from the borosilicate matrix. In addition, the results imply that the borosilicate network is affected by the I dissolution.