Sulfhydryl-functionalized graphene oxide nanoparticles-adjusted ternary-reacted M−S−H cement achieves efficient solidification and stabilization of heavy metals and chloride salts in the municipal solid waste incineration fly ashes

The poor pozzolanic activity and high alkalinity of municipal solid waste incineration fly ashes (MSWI-FA) would deteriorate the stability of the MgO-SiO₂-H₂O (M-S-H) binder system, further inhibiting the treatment capacity of cement to wastes. In this study, sulfhydryl-functionalized graphene oxide nanoparticles (SFG) were synthesized and incorporated into the MSWI-FA-blended M-S-H (MSH-MSWI-FA) system to strengthen the solidification/stabilization (S/S) of both heavy metals (HMs) and chloride salts in the matrix and mechanical stability of cement. The linear increases in nanomaterials (from 0.5 % to 2.5 %) and MSH (from 40 % to 80 %) both decreased the concentrations of HMs and Cl anions leached from the solidified cubes in the MSH-MSWI-FA cementation. The least leaching concentration of Zn, Cu, Pb, Cd, Cr, and Cl were 0.0046 mg/L, 0.0032 mg/L, 0.014 mg/L, 0.00068 mg/L, 0.030 mg/L, and 0.36 g/L from the SFG-MSH-MSWI-FA cemented samples, respectively. The incorporation of graphene oxide nanoparticles (NGO) and SFG elevated the residual moieties of HMs, enhanced the mechanical strength and acid resistance, and improved the microstructural properties of MSH-MSWI-FA cementation. SFG played a more dominant role in the enhancement than NGO. Sulfhydryl-functionalization for nanomaterials intensifies the improvement process. The minerals including M-S-H, CaO-SiO₂-H₂O (C-S-H), and Phase-5 were formed in the MSH-MSWI-FA cement. Silica fume (SF), lightly burnt magnesia (CC-MgO), and MSWI-FA reacted with each other in a ternary system, which induced the self-alkali-activated cementation of C-S-H, M-S-H, and magnesium oxychloride (MOC) cement.