Porous glass-ceramics from alkali activation and sinter-crystallization of mixtures of waste glass and residues from plasma processing of municipal solid waste

Alkali-activated aqueous slurries of fine glass powders, mostly deriving from the plasma processing of municipal solid waste ('Plasmastone'), were found to undergo progressive hardening at low temperature (75 degrees C) owing to the formation of C-S-H (calcium silicate hydrate) gels. Before complete setting, slurries could be easily foamed by vigorous mechanical stirring, with the help of a surfactant; finally, the resulting open-celled structure could be 'frozen' by a subsequent sintering treatment, with crystallization of Ca-Fe silicates. The densification of the struts upon firing was enhanced by mixing Plasmastone with up to 30 wt% recycled glasses and increasing the firing temperature from 800 to 1000 degrees C. A total porosity exceeding 75 vol%, comprising both well-interconnected macro- and micro-sized pores on cell walls, was accompanied by good compressive strength, well above 1 MPa. The stabilization of pollutants generally increased with increasing firing temperature and glass content, with some exceptions; no practical leaching was observed from samples deriving from Plasmastone combined with 30 wt% boro-aluminosilicate glass from the recycling of pharmaceutical vials.