Leaching Behaviour of Heavy Metals from the Class C Fly Ash-Based Geopolymers

In this paper, leaching behavior of heavy metals from the class C fly ash (CFA)-based geopolymers were studied. The CFA-based geopolymers were prepared from CFA, flue gas desulfurization gypsum (FGDG), and water treatment residual (WTR). The extraction-leaching concentrations of heavy metals from CFA-based geopolymers were lower than their maximum concentration limits according to the U.S. environmental protection law. And the encapsulated and fixed ratios of heavy metals by the CFA-based geopolymers were 96.02~99.88 %. The dynamic real-time leaching concentration of Pb (II) were less than 1.1 µg / L, Cr (VI) less than 3.25 mg / L while Hg (II) less than 4.0 µg / L. Additionally, dynamic accumulated leaching concentrations were increased at the beginning of leaching process then kept stable. The leaching results indicated that the security of heavy metals in CFA-based geopolymer was safe.