Further development of iodine immobilization technique by low temperature vitrification with BiPbO ₂I

The authors describe progress in the development of low temperature vitrification with BiPbO ₂I (BPI) as a promising immobilization technique by which Iodine-129 is recovered by BiPbO ₂NO ₃ to form BPI, and then solidified into a lead-boron-zinc glass matrix (PbO-B ₂O ₃-ZnO) using a low temperature vitrification process. The microscopic structure of BPI glass was analyzed by various analytical techniques, such as XRD (X-ray diffraction), NMR (nuclear magnetic resonance analysis), and XPS (X-ray photoelectron spectroscopy), using several types of glass samples. The results obtained provide structural information on key elements in BPI glass and can be applied for modeling the structure of the BPI glass, simulated by molecular dynamics. The previous work suggested that the leaching behavior of iodine from BPI glass depended upon the chemical conditions of the solution. Further leaching tests using solutions under varying conditions were carried out in order to predict mechanisms of iodine leaching. Normalized elemental mass loss values of iodine in simulated seawater and bentonite pore water are almost the same as those of boron, showing that iodine dissolves congruently with BPI glass, whereas iodine dissolves incongruently in Ca(OH) ₂ solutions of pH 9 and 11. To demonstrate the feasibility of the BPI vitrification process, recovery tests of iodine from spent iodine filters were conducted and a prototype melting furnace was developed for scale-up tests of glass sample. It was found that more than 95% of iodine can be recovered from the spent iodine filter and that the prototype furnace can produce approximately 0.5 liters of homogeneous glass.