Synthesis of lead vanadate iodoapatite utilizing dry mechanochemical process

For consolidation and subsequent deep geological repository of radioactive 129I, a novel synthesis method of iodine-bearing lead vanadate apatite Pb10(VO4)6I2 was developed. In order to reduce the reaction temperature, a dry mechanochemical process was applied and iodoapatite was successfully synthesized without heating. Calcining the as-synthesized low crystalline specimen at 300 °C gave a single-phase with high crystallinity. The obtained powder was consolidated by hot-press sintering at 400 °C under uniaxial pressure of 90 MPa and submitted to leach tests by immersion into pure water at room temperature. The normalized leach rate of iodine on the first day was about 2.6 × 10−1 g m−2 d−1. After 56 days of immersion, the iodine leach rate was reduced to less than 1/30 of the initial rate in newly changed water. Iodoapatite specimens in which part of VO43− was substituted with PO43−, Pb10(VO4)4.8(PO4)1.2I2, were also synthesized by the same method.