Sintering of metakaolin‐based Na/Ca‐geopolymers and their immobilization of Cs

Abstract

AbstractMetakaolin‐based Na/Ca‐geopolymers with a designed composition close to feldspar were used as precursors of Cs immobilization form materials. The sintering behaviors of geopolymers and their sintered materials' immobilization of Cs ions were investigated; the results indicated that the major phases of sintered geopolymers are plagioclase feldspars and feldspathoid. With the addition of Cs to the geopolymers, Cs‐leucite phase and caesium silicates were formed at 1150°C and 1170°C, respectively. It was found that Cs addition can slightly decrease the sintering temperature of geopolymers and make the grains finer. In addition, in order to reduce the volatilization of Cs ions during sintering, sintering temperatures of Cs‐geopolymer were further decreased to 850°C by introducing B2O3. After the geopolymer and Cs‐geopolymer were sintered using a low‐temperature liquid‐phase process, they remained structurally plagioclase feldspars and feldspathoid. Leaching on Product Consistency Test indicates that the leaching concentrations of Cs‐geopolymer samples sintered at higher temperatures are lower than those of samples sintered at lower temperatures. Thus, the increased volatilization of Cs ions at the higher temperatures and the formation of Cs‐leucite phase and caesium silicates can lead to the decrease of leaching concentrations in leachates. Therefore, low sintering temperatures and the fabrication of Cs crystalline ceramics are the key factors toward improving the immobilization of Cs ions.