NO₂-mediated voloxidation for iodine separation from cesium iodide surrogates

Heterogeneous NO₂-mediated oxidation of uranium, also known as advanced voloxidation, is a proposed head-end reprocessing method for used nuclear fuel. An advantage of advanced voloxidation is the removal of volatile fission products, which complicate downstream separation and containment challenges leading to increased processing economics. Iodine, one of the volatile species of interest, has exhibited varied results in this process. Using CsI as a surrogate material, this work mimics the effect of NO₂-based voloxidation on iodine and sheds light on the factors that influence the solid–gas phase reaction. Solid-state analysis using Fourier transform infrared attenuated total reflectance spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy confirmed the conversion of CsI to CsNO₃. Iodine separation ranged from 46% to 100% across multiple tests. Iodine separation was most effective when multiple recharges of NO₂ were administered. At the bench scale, liberating iodine from CsI appears to occur within 1 h, but the presence of surface H₂O and the composition of the NO_x reagent mixtures greatly influence its success.