Hydrothermal conversion of Cs-polluted soil into pollucite for Cs immobilization

Abstract

To deal with the treatment of huge amounts of Cs-polluted soil from the first nuclear power plant in Fukushima (Japan), a low temperature hydrothermal technology has been developed to convert polluted soil into pollucite for the in-situ immobilization of Cs. The results show that pollucite could be synthesized with a wide range of Cs content using a short curing time (2 h) or low curing temperature (160 °C). However, a higher curing temperature or a longer curing time seems to favor the formation of more pollucite. With the addition of Ca(OH)2, a tough pollucite body could be synthesized, and the strength enhancement is mainly due to calcium silicate hydrate (C-S-H) formation. This also suggests that the hydrothermal technology has great potential for the direct immobilization of polluted Cs with a tough synthesized pollucite body, similar to cement or glass solidification of nuclear waste. The extended X-ray absorption fine structure (EXAFS) results reveal that the polluted Cs is immobilized into the structure of the synthesized pollucite rather than physically adsorbed in the pores. The leaching test results show that the amount of Cs leached from the synthesized specimens is very low (2.43 × 10−3 g·m−2·d−1 and 6.46 × 10−4 g·m−2·d−1), even lower than that of the reference hollandite-rich synroc (2.0 × 10−2 g·m−2·d−1). As such, the hydrothermal synthesis of pollucite using only Cs-polluted soil for immobilization of polluted Cs, may provide a new technology for the treatment of Cs-polluted soil.