Immobilization of simulated 137CsCl using metakaolin based geopolymers obtained by hybrid hydrothermal-sintering processes

A hydrothermal-sintering process for metakaolin-based geopolymers was exploited to immobilize simulated 137CsCl. Pollucite phase is easily formed from geopolymers containing NaOH under 200 ℃ hydrothermal conditions. An additional 1200 ℃-sintering process step not only retained the pollucite phase in the sintered geopolymers, but also increased the density of the microstructures. The leached ion fraction from the geopolymers prepared using the hybrid hydrothermal-sintering process was obviously lower than that of geopolymers prepared using only the 200 ℃ hydrothermal processing steps. Especially, the hybrid hydrothermal-sintering process lowered the Cs+ volatilization during sintering due to the presence of the pollucite phase precursor in the geopolymers.