A novel composite of layered double hydroxide/geopolymer for co-immobilization of Cs and SeO from aqueous solution.

Geopolymers are always considered as promising materials for the treatment of radioactive wastes. In order to extend the application of geopolymer to the immobilization of anionic species, a novel composite of layered double hydroxide/geopolymer (LDH/GEO) was synthesized and applied for cosorption of Cs and SeO. The ability of LDH/GEO to sorb Cs was maintained as that of pure GEO, even though the surface of geopolymer was homogeneously covered by the LDH platelets. The sorption of Cs onto LDH/GEO composite occurred via ion exchange, which was controlled by particle diffusion. It is different with Cs sorption onto pure GEO governed by film diffusion. Therefore, "Pocket diffusion" was proposed for the particle diffusion as the case of LDH/GEO because this kind of diffusion would be restricted in a certain distance around the ring entrance gate due to the amorphous essence of GEO. For SeO sorption by LDH/GEO, ion-exchange with the interlayer NO and surface sorption could be the main mechanisms. Importantly, the sorption speed of SeO achieved by LDH/GEO composite was much faster than that by pure LDH. In the binary system (Cs+ SeO), the sorption of Cs was slightly suppressed compared to the single system, which might be due to the formation of ion-pair complex of [CsSeO]. However, it did not have negative effect on the SeO sorption. In the presence of other cations or anions, the cosorption performances of Cs and SeO were satisfactorily obtained. Furthermore, the Cs and SeO sorption densities were superior to the previously reported values. The combined MgAl-LDH/geopolymer composite could be a promising material for the immobilization of Cs and SeO, and this work would provide guidance for the development of geopolymer-based materials for environmental applications.