Removal of cesium and strontium ions from aqueous solutions using metakaolin based geopolymers

The aim of presented work was to synthesize geopolymers based on the metakaolin and to determine their adsorption capability in the process of cesium and strontium ions removal from the aqueous solutions. New approaches were proposed for obtaining the two samples of geopolymers in techologically suitable forms. Morphology of materials was investigated by means of X-ray fluorescence analysis (XRF), low-temperature nitrogen adsorption/desorption and scanning electron microscopic studies (SEM). As it follow from the data of XRF analysis, SiO2 and Al2O3 oxides found to be the major components in all samples investigated (~ 54–84 wt. %). As was determined by SEM studies, geopolymers consisted from nanosized particles, amorphous geopolymers binder and unreacted kaolin. It has been found that all samples involve the mesopores with approx. 1–40 nm radii. The greatest specific surface area calculated by the Brunauer-Emmet-Teller (BET) method had the sample obtained in the forms of spherical rods (SBET = 88 m2/g) that about 10 times greater than for initial kaolin taken for synthesis. The ion exchange capacities of materials in the process of Cu2+, Cs+ and Sr2+ removal from water solution were determined and it was found that these properties depends on the method of materials obtaining. Data showed that the geopolymers were more effective for removal the desired ions than initial kaolin. The greatest adsorption capacity towards cesium ions was received on the samples obtained in forms of pyramids and was reached 1.75 mmol/g. Experimental data were fitted into the Langmuir models and the main Langmuir constants were calculated. When analysing the data of investigation with comparing the literature data it was noted that geopolymers obtained can be used in adsorption technology for purification of water from radionuclides as technologically suitable sorbents.