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 similar to 7 wt% of substituted iodine was carried out at 200 degrees 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) x 10(-7), 2.6 (+/- 0.2) x 10(-7) and 2.4 (+/- 0.4) x 10(-5) g/m(2)/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. (C) 2018 Elsevier B.V. All rights reserved.