Heavy metal fixing and heat resistance abilities of coal fly ash-waste glass based geopolymers by hydrothermal hot pressing

Abstract

Hydrothermal hot pressing (HHP) was used to prepare high compressive strength fly ash-wasted glasses based geopolymers, which was subject to thermal analysis and the test of heat resistance as well as heavy metal solidification. Results showed that the geopolymers had good efficiency of encapsulating and fixing heavy metals. As for heavy metal element like Cu, Zn, Cd and Pb, the fixed efficiency reach at least 95%. Heat resistance test showed that the most mass-loss ratio of geopolymers was below 11.04% and the compressive strength was more than 55.27 MPa when it was calcined at 200–1000 °C for 2 h. During the calcining, geopolymers had gone through several main processes, including the evaporation of the free water, the bound water and constitutional water, the decomposition of carbonate, combustion of carbon, and crystallization reaction. XRD and FT-IR analysis showed that when calcined at 1000 °C, there produced several new crystallization phases with good heat resistance, including nepheline, kyanite, sillimanite. The improvement of this work does not only reflect that the hydrothermal hot pressing is featured by simple procedures, easy automation, timesaving and low cost, and also provide a long-term goal project, which could meet both demands: utilizing solid waste, saving resources and protecting the environment.