Geopolymer-based beads for adsorption purposes

Adsorption is considered as one of the most easy and effective techniques for different aims and alternative and low cost adsorbents, obtained by simple processes, are always researched. Beads and spheres have lately received attention for their potential use as adsorbents, thanks to the good mobility, high packing density, ease of separation and reuse after regeneration. Therefore, geopolymer-based spheres were produced exploiting spherification processes in order to obtain millimeter-size porous beads useful for adsorption purposes. The processes were established on the formulation of different geopolymer slurries based on the mixing of metakaolin with a potassium alkaline activating solution, and making use of an injection-solidification method in different mediums, i.e. polyethylene glycol or liquid nitrogen, to produce the beads. Furthermore, geopolymer slurries were mixed with a solution of sodium alginate and then dropped off in a hot CaCl2 solution to obtain beads by means of a ionotropic gelation. An hybridization of the material (inorganic+organic), able to improve the adsorption properties, was obtained. The production process parameters were deeply investigated and the most performing spheres were selected and characterized in term of morphology, macro- and microstructure, composition-stoichiometry, porosity distribution and specific surface area together with the adsorption properties towards, for example, organic dyes.