Immobilization efficiency and mechanism of metal cations (Cd2+, Pb2+ and Zn2+) and anions (AsO43- and Cr2O72-) in wastes-based geopolymer

In this study, a composite geopolymer based on solid wastes (drinking water treatment residue (DWTR) and granulated blast furnace slag (GBFS)) were used in immobilization of heavy metals cations (Cd2+, Pb2+ and Zn2+) and anions (AsO43- and Cr2O72-). For evaluating the immobilization effect for heavy metals, the mechanical strength and leaching properties of geopolymers were investigated. Meanwhile, different characterization methods were used to research the immobilization mechanisms. The results indicated that the mechanical strength of geopolymers containing heavy metals was effectively improved by 37.11% with addition of DWTR. The stability of metals in geopolymer were increased and the release risk was decreased under the effect of DWTR. Characterization results verified the uniform distribution of heavy metals in geopolymer, and the adding of Pb2+, AsO43- and Cr2O72- caused the formation of crystalline phases. After the adding of heavy metals, the chemical environment change of Al 2p is more significant than Si 2p. Based on Si-29 and Al-27 MAS-NMR results, the different metals show various influences on the silicon and aluminum species in geopolymer matrix, and the strength of polymerized structure is mainly based on the Q(4)(mAl).