Application of molten iron desulfurization slag to replace steel slag as an alkaline component in solid waste-based cementitious materials

Desulfurization slag (DS), generated from molten iron pre-desulfurization process, has a high alkalinity that may cause seriously environmental issues. To solve the DS-disposal problem, this research proposes a new type of cementitious material composited of DS, ground granulated blast furnace slag (GGBS), steel slag (SS), and flue gas desulfurization gypsum (FGDG). The effects of DS on cementitious material were studied by testing the working performance indexes such as mortar fluidity and compressive strength, and the microscopic analysis such as XRD, TG and SEM. The results show that DS reduces the fluidity of the mortar, and significantly improves compressive strength of 3 days. The optimal ratio of DS/SS ratio in the GGBS–SS–DS–FGDG cementitious material is 1.0, and its compressive strength of 3 days and 28 days reached 24.6 and 52 MPa, respectively. The 3 days’ compressive strength of GGBS-SS-DS-FGDG is 748% higher than that of GGBS–SS–FGDG. The high alkalinity of DS promotes the dissociation of GGBS, and enhances the early hydration rate, which shortened the hydration induction period, and enhanced the cumulative released heat. Also, DS promotes the formation of ettringite (AFt) and increases the polymerization degree of the C–(A)–S–H gel at early stage. However, cementitious material containing DS has high porosity, which can be offset by the gel pores generated by SS. In summary, the GGBS–SS–DS–FGDG as a cementitious material with low carbon emission may be used to replace cement. The results of this paper can guide the large-scale and comprehensive utilization of DS with other solid waste.