The Influence of Glass Composition on Iodine Solubility
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.665
The Influence of Glass Composition on Iodine Solubility Maria Rita Cicconi1, Eric Pili2, Lucie Grousset1, Daniel R. Neuville1 1 Institut de Physique du Globe de Paris, Géomatériaux, CNRS-UMR7154, Sorbonne Paris Cité, 1 rue Jussieu 75005 Paris cedex 05, France
2
CEA, DAM, DIF, F-91297 Arpajon, France
Abstract: Two glass series in the ternary systems K2O-B2O3-SiO2 (KBS) and Na2O-B2O3-SiO2 (NBS) were studied in order to identify the main factors influencing the solubility of iodine. We established that iodine incorporation is strongly linked to the bulk chemistry, i.e. the SiO2/(B2O3+SiO2) molar ratio, and to the physical properties of the glasses, and we assessed three different solubility limits. Iodine in Si-rich glasses has a low solubility (≤1 mol% I) regardless of the alkali ion present. On the contrary, in B-rich glasses, the solubility is five times higher than in Si-rich glasses for Na-glasses, and more than six times higher for Kglasses. The strong dependence of iodine solubility on the bulk chemistry is related to the adaptability of the glass network. Furthermore, our data suggest that iodine is stable with different redox states in the glasses here analyzed.
INTRODUCTION Iodine, the heaviest stable halogen element, benefitted from relatively few studies on its solubility in glass matrices compared to the lighter halogens [1]. However, the incorporation, dissolution and mobility of this ion is very important in many fields, ranging from Materials and Earth Sciences to Waste management. Iodine occurs in nature as iodide (I-), as the oxyanion iodate (IO3-) and rarely as elemental I (I2), respectively with oxidation states -I, +V and 0. The radioisotope 129I is of particular concern because it will be the main contributor to the radioactivity released by a geological repository site for nuclear wastes [2]. Furthermore, the iodine-xenon 131, 133, 135 decay chains are particularly important in the framework of the verification of the Comprehensive nuclear-Test-Ban Treaty (CTBT). Indeed, atmospheric radioxenon monitoring constitutes an important mean for the detection of underground nuclear explosions after transport to the subsurface [3–5].
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While the xenon source term in the nuclear cavity can be calculated, uncertainties persist regarding to what extend iodine may be trapped in magma inside the nuclear cavity [6]. Previous studies of iodine were mainly focused on the determination of iodine oxidation state and local surrounding in borosilicate waste glasses, and in cementitious wasteforms e.g. [7–9] because the assessment of the valence state is quite important when dealing with radionuclide. Indeed, beside the redox state of the environment, also physical and chemical form of the elements
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