Immobilization of simulated An3+ in radioactive sludge via microwave sintering: Mechanism and performance

This study investigates the safe disposal of simulated radioactive sludge. Microwave sintering of silicate glass (SG) particles and simulated sludge is performed to prepare amorphous glass materials and oxy-apatite (AⅠxAⅡ10-x(SiO4)6O2) glass ceramics. The phase-evolution, microstructure, nucleation-growth mechanism, and chemical stability of the solidified products are systematically investigated. The optimum vitrification degree of the solidified product containing 60 wt.% SG particles in the radioactive sludge is achieved at 1200 ℃. Elements are uniformly distributed, and the final solid-solubility of Nd in the glass structure is 32 wt.%. For higher content, the Nd remained fixed at the AⅠ and AⅡ positions of an oxyapatite crystalline structure. The glass-ceramic material exhibited a high solid-solubility of Nd up to 40 wt.%. Furthermore, the normalized leaching rate of Nd was observed at a low level of 10−6 g·m−2·d−1 after 42 d. This study suggests a new processing method for the safe disposal of radioactive sludge.