Facile low temperature solid state synthesis of iodoapatite by high-energy ball milling

Abstract

The apatite structure-type has been proposed as a potential waste form for the immobilization of long-lived fission products, such as I-129; however, it is difficult to synthesize iodoapatite without significant iodine loss due to its high volatility. In this study, we report a facile low temperature (∼50 °C) solid-state method for successfully synthesizing lead-vanadate iodoapatite by high-energy ball milling (HEBM) of constituent compounds: PbI₂, PbO and V₂O₅. As-milled iodoapatite is in the form of an amorphous matrix embedded with nanocrystals and can be readily crystallized by subsequent thermal annealing at a low temperature of 200 °C with minimal iodine loss. Rietveld refinement of the X-ray diffraction patterns indicates that the thermally-annealed iodoapatite is iodine deficient with an iodine concentration of ∼4.2 at%. Thermal gravimetric analysis (TGA) indicates that low temperature annealing greatly improves the thermal stability and iodine confinement. This novel approach, using HEBM and thermal annealing, is a very promising method for synthesizing advanced materials that can confine highly volatile radionuclides, such as I-129, which pose significant challenges for the successful disposal of high-level nuclear waste.