Performance and hydration mechanism of MSWI FA-barium slag-based all-solid waste binder

Abstract

Barium slag (BS) and municipal solid waste incineration fly ash (MSWI FA) are hazardous wastes produced in large quantities, with heavy metals such as Ba, Pb, and Cr significantly exceeding acceptable levels, posing a threat to the ecological environment and living organisms. The development of technologies for the harmless disposal and resource utilization of hazardous waste is a current research focus. This study used BS, blast furnace slag (BFS), MSWI FA, and flue gas desulphurized (FGD) gypsum to replace cement in the preparation of solid waste-based binder. The results indicated that the optimal mass ratio was BS: BFS: FGD gypsum: MSWI FA = 14 %:56 %:20 %:10 %. The compressive strengths of the binder at 3, 7,and 28 days were 23.7 MPa, 30.76 MPa, and 38.65 MPa, respectively. Chinese standard HJ557–2010 was adopted to carry out heavy metal leaching experiment on raw materials, the immobilization efficiency of heavy metals Ba, Pb, and Cr were 99 %, 99 %, and 96 %, respectively, and the leachate toxicity was below the Class III groundwater limit. XRD, FT-IR, TG-DSC, XPS, SEM-EDS and other experimental methods were used to study the effect of BS content on the properties of cementable materials. An appropriate amount of BS hydrolyzes during hydration, releasing Ba²⁺ and OH⁻ ions, which activated the BFS, producing AFt and C–(A)–S–H gel. These products interweaved with material particles to fill the pore spaces, enhancing the binder’s mechanical strength and heavy metal immobilization capability. However, when excessive BS was added, the hydration products favored the formation of FS, leading to a decline in binder performance.