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Liquid radioactive waste is produced in the nuclear industry and has to be treated to firstly minimize their impact on environment and secondly to propose an ultimate confinement matrix. One way to decontaminate these waste is to synthesize inorganic monolithic filters that are less sensitive to radiolysis phenomena than organic ones. Geopolymer cements are good candidates to fulfill these specifications since intrinsically they are mesoporous with high specific surface area [1] and compatible with specific grafting agents which allow to trap selectively radionucleides of interest (especially the cesium) [2]. For this purpose, a monolithic geopolymer with good mechanical resistance and hierarchical porous network (tailored open macroporosity) was synthesized. From this geopolymer foam, the precipitation of copper hexacyanoferrate into the porous network has been performed in order to trap selectively the cesium. The functionalized foams were characterized and the trapping capacity of Cs was assessed. After having determined the sorption kinetics, sorption isotherms were performed and the maximum sorption capacity, Q = 120 mg/g, was measured. Tests in a radioactive environment were also carried out in order to validate the performance of the material in real conditions (traces of Cs in fresh water). The results show that the functionalized material is capable of selectively trapping Cs with a distribution coefficient Kd of 2.37 10 5 ml/g. The results demonstrate remarkable potential of this innovative material for Cs removal from liquid nuclear waste.

Fire resistance performance is one of the most important requirements in geological storage conditions in order to improve the resistance of storage packages to high thermal constraints (in the case of a fire for example). With the need to develop new fire-resistant materials, the aim of the present study was to develop fire-resistant geopolymer binders based on Callovo-Oxfordian (COx) argillite. Two types of kaolin with different degrees of purity were mixed with argillite in various proportions. These mixtures were calcined at 600 or 750°C. In order to assess the fire resistance of activated materials, thermal treatment at 1000°C was performed. The compressive strength and mineralogical composition of the samples were investigated before and after heat treatment. The results showed that the addition of argillite improved significantly the thermomechanical properties of kaolin-based geopolymers containing impurities, especially the mixture containing 67% argillite and calcined at 750°C. This phenomenon was not observed for the pure-kaolin geopolymer. Improvement of fire resistance was due to the formation in situ of leucite and zeolite-type phases (KAlSi2O6 and KAlSiO4) and of wollastonite (CaSiO3) at high temperature, which is linked to the Ca available in the raw materials.

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