On the existence of AgM9(VO4)6I (M = Ba, Pb)

Abstract

The syntheses of the reported compounds AgM₉(VO₄)₆I (M = Ba, Pb) were reinvestigated. Stoichiometric amounts of AgI with either M₃(VO₄)₂ (M = Ba, Pb) or PbO and V₂O₅ were reacted in the solid-state at elevated temperatures in air or in flame-sealed quartz vessels. The resulting products were characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, and thermal analyses. Results show that, for all reaction conditions, the target AgM₉(VO₄)₆I (M = Ba, Pb) phases could not be isolated. Instead, heterogeneous phase distributions of primarily M₃(VO₄)₂ (M = Ba, Pb) and AgI were obtained. These findings demonstrate that AgI incorporation into single phase, iodine-deficient apatite derivatives for the immobilization of iodine-129 are not feasible under such conditions. This conclusion is important for the conditioning of iodine-129 in advanced reprocessing flowsheets, where iodine is typically sequestered as AgI.