Synthesis and characterization of iodovanadinite using PdI 2, an iodine source for the immobilisation of radioiodine.

The synthesis of a palladium-containing iodovanadinite derivative, hypothetically "PdPb 9 (VO 4 ) 6 I 2 ", was attempted using PdI 2 as a source of iodine in searching for a novel waste form for radioiodine. Stoichiometric amounts of Pb 3 (VO 4 ) 2 and PdI 2 were batched and reacted at elevated temperatures in sealed vessels. Batched material was also subjected to high-energy ball-milling (HEBM) in order to reduce reaction time and the potential for iodine volatilization during subsequent reaction at 200-500 °C. The resulting products were characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, IR spectroscopy, thermal analysis and Pd K XANES. Results showed that PdI 2 can function as a sacrificial iodine source for the formation of iodovanadinite, prototypically Pb 10 (VO 4 ) 6 I 2 , however, the incorporation of Pd into this phase was not definitively observed. The sacrificial reaction mechanism involved the decomposition of PdI 2 to Pd metal and nascent I 2 , with the latter incorporated into the iodovanadinite Pb 10 (VO 4 ) 6 I 2 phase. In comparison to processing using standard solid state reaction techniques, the use of HEBM prior to high temperature reaction generates a more homogeneous end-product with better iodine retention for this system. Overall, the key novelty and importance of this work is in demonstrating a method for direct immobilisation of undissolved PdI 2 from nuclear fuel reprocessing, in a composite wasteform in which I-129 is immobilised within a durable iodovandinite ceramic, encapsulating Pd metal.