High-value utilization of modified magnesium slag solid waste and its application as a low-carbon cement admixture

A large amount of magnesium slag solid waste, insufficient comprehensive disposal capacity, high disposal costs, and uncertain environmental stability hinder the low-carbon, green, and sustainable development of magnesium and magnesium alloy smelting. Therefore, this study proposed a high-quality, large-scale, and industrialized disposal method for modified magnesium slag (MMS). Through relevant experimental tests and microscopic characterization methods (physical and chemical performance, hydration heat, resistivity, and microstructure tests), the physical and chemical properties, curing mechanism, and social benefits of MMS low-grade magnesium slag were investigated. The physical and chemical properties, curing mechanism, and social benefits of modified magnesium slag low-carbon Portland cement (MMSPC) produced by MMS as a cement admixture were elucidated. The results showed that (1) the physical and chemical properties of MMSPC met the requirements of the GB 175-2007 "General Portland Cement" standard. (2) A significant difference was observed in the early hydration heat release of fresh MMSPC slurry, confirming a hydration composite effect between MMS and clinker, which was also the key reaction mechanism of MMS replacing clinker to produce MMSPC. (3) The resistivity of MMSPC increased, decreased, and then increased with time, which was mainly controlled by the settling of the aggregate, the dissolution of the binder, and the hydration reaction of the system. However, the variation in resistivity with time and value was influenced by the mixing ratio of the system. (4) MMSPC could also offer certain environmental and economic benefits. Carbon emissions per ton of cement produced were reduced by 7.95%, and the total cost per ton of cement produced was reduced by more than 10%. This study provided a theoretical basis for the high-value disposal of MMS and the reduction of carbon emissions in the cement industry.