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

Abstract

The synthesis of a palladium-containing iodovanadinite derivative, hypothetically "PdPb9(VO4)(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(VO4)(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 degrees 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(VO4)(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(VO4)(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.