Cold sintering and durability of iodate-substituted calcium hydroxyapatite (IO-HAp) for the immobilization of radioiodine

Abstract Cold sintering of iodine-hosted calcium hydroxyapatite was investigated for the development of a durable matrix for radioiodine immobilization. Single-phase, nano-crystalline, iodate-substituted calcium hydroxyapatite (IO-HAp) was synthesized by a wet precipitation method and sintering of the dried IO-HAp powder containing ∼7 wt% of substituted iodine was carried out at 200 °C under a uniaxial pressure of 500 MPa. It was demonstrated that a sintered relative density of 96.8% can be achieved without affecting the iodate nature of the substituted iodine. A product consistency test of the sintered samples was also carried out under a standard condition. The normalized leaching rates of Ca, P and I after seven days were 6.9 (±0.5) × 10−7, 2.6 (±0.2) × 10−7 and 2.4 (±0.4) × 10−5 g/m2/d, respectively, providing evidence of the durability of the cold sintered matrix and promise of using the cold sintering process for the conditioning of volatile element-bearing radioactive waste into solid waste forms.