Immobilization of simulated radioactive CsCl by hydrothermal synthesis for molten salt waste disposal

In this study, the pollucite solidified form was hydrothermally synthesized by metakaolin, non-radioactive CsCl, and NaOH to immobilize CsCl in the radioactive molten salt waste. At 200 °C, the immobilization ratio of Cs increased with the enhancement of reaction system alkalinity by NaOH, but it was also accompanied by the formation of sodalite. Excessive Si was adverse to the crystallization of the solidified form. In addition, the proportion of Cs in the solidified form was constrained by the substitution competition between Cs + and Na + , which was affected by reaction time. The nucleation and growth of pollucite mainly occurs from 2 to 4 h, and the CsCl immobilization ratio could reach 36.27 wt .% at 6 h. The thermal weight loss rate of the solidified form within 1000 °C was less than 4 wt .%, and the normalized leaching rate of Cs was 5.05 × 10 –5  g m −2  d −1 for 14 d, showing reliable thermal stability and chemical durability. Graphical abstract