Factors affecting the hydrothermal synthesis and durability of pollucite. Towards the practical radioactive Cs immobilization

Hydrothermal synthesis of pollucite by investigating the experimental parameters of heating time, alkalinity, additional Na⁺ and Ca²⁺, Cs⁺-Na⁺ and Cs⁺-K⁺ replacement, at basic bulk composition of Cs₂O:Al₂O₃:4SiO₂:111H₂O was conducted, and ion exchange behavior of the synthesized pollucite was discussed. Results showed that alkaline (OH^-) was a key factor governing the formation of pollucite, where additional alkali was necessary for practical soil decontamination. Pollucite structure was stable under the coexistence or replacement of other cations, and Cs₂O content was reduced partly by the co-crystallization of other metal ions. Under the surrounding of K⁺ or Na⁺, 14-17 mol% Cs⁺ in pollucite released from pollucite (220 °C), and there was a strict selectivity between ANA minerals and specific cations. For the harmless management of real radioactive Cs polluted soil, it is necessary to give careful evaluation on the immobilization ability of pollucite under the influence of other metal ions. (author)