Structural changes of fly ash-based geopolymers induced by a large amount of lead

Abstract

Geopolymers has emerged as possible techological and environmentally solution for the effective immobilization of heavy metals and other toxic materials. In this paper, structural changes of geopolymers induced by large amount of lead (up to 30%) were examined. Geopolymers were synthesized by alkali activation of fly ash using sodium silicate with modulus 1.5 as alkali activator. Lead was added in the form of water-soluble salt - lead-nitrate, during the synthesis of geopolymers. Structural changes of geopolymers due to Pb addition were assessed by means of XRD and 29Si MAS NMR analysis. XRD analysis confirmed that the Pb addition led to the formation of new Pb-phases, which indicated that Pb formed chemical bonds with the geopolymers. 29Si MAS NMR analysis showed the increase of less condensed Q1 and Q2 structural units of geopolymers with Pb addition.