Geopolymer Beads and Applications

Geopolymer-based beads were produced exploiting spherification processes in order to obtain millimeter-size porous beads useful for adsorption purposes. Adsorbents in form of beads offer some advantages as a good mobility, high packing density, ease of separation and reuse after regeneration. Furthermore, adsorption is considered one of the easiest and most effective techniques and alternative and low cost adsorbents, obtained by simple processes, are always researched. For these reasons, starting from different mixtures, obtained from metakaolin and potassium silicate solutions, geopolymer-based beads were formed through an injection-solidification method in different media: polyethylene glycol, liquid nitrogen and calcium chloride (using the ionotropic gelation of the alginate added to the mixture). The optimization of the processes allowed to obtain reproducible, round and mechanically resistant beads. The beads were characterized in term of morphology, macro- and microstructure, composition-stoichiometry, porosity distribution and specific surface area. Adsorption tests were carried out using dyes with different concentration and attempts to promote adsorption were made formulating composite beads containing hydrotalcite or TiO2 (exploiting its photodegradation effect).