Iodine dissolution mechanisms in high-pressure aluminoborosilicate glasses and their relationship to oxygen speciation

Abstract

Incorporation of iodine(I) into high-pressure vitrified glasses appears to be a potential solution for the immobilization of ¹²⁹I radioisotopes. Under these conditions, I dissolution is strongly enhanced; however, the impact I dissolution has on the glass structure remains to be determined to assess the matrix durability. We have experimentally studied the change in I solubility and speciation in a series of sodium aluminoborosilicate glasses (Na₂O ranging from 10 to 40 mol%) held at 0.25 and 1.0 GPa and 1250 °C. As expected, the I solubility increases with pressure and with increasing Na₂O and is positively correlated with the glass optical basicity. The I speciation determined by XPS is changing with the initial loaded source of iodine (either I₂ or I₂O₅) with a predominant iodide form (I⁻) in the glass structure. The investigation of the oxygen environment in the I-bearing glasses using O 1s XPS revealed that I dissolution induces an apparent oxygen loss within the glass structure. This result is consistent with our current view on I dissolution mechanisms. Furthermore, the subsequent simulations of the O 1s XPS spectra suggest that I dissolution consumes non-bridging oxygen to form bridging oxygen. This change in the oxygen speciation points toward an increase in the glass durability, which is an important aspect for nuclear waste immobilization.