Evaluation of waste powder from open pit mines as supplementary cementitious material: Crystal structure and hydration characteristics

The effective utilization of mineral resources and the sustainable management of solid waste from open-pit mines have gained significant attention in recent years. In this study, the feasibility of using open-pit mine waste powder (OMWP) as a supplementary cementitious material (SCM) was investigated, and the crystal structure and hydration characteristics were evaluated using various characterization methods. The activity index of OMWPs was analyzed after mechanical activation using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDS). The results showed that mechanical activation reduced the crystallinity and elemental surface bonding energy of OMWPs, while vibration extended the chemical bond without breaking and forming it. The optimal fineness and reactivity were achieved after 20 min of grinding. Moreover, substituting 10% of cement with mechanically activated OMWP increased the compressive strength of mortar at all curing ages, which was attributed to the increased amount of calcium silicate hydrate (C-S-H) gel, decreased calcium hydroxide (CH) and reduced porosity as determined by thermogravimetric-differential scanning calorimetry (TG-DSC) and mercury intrusion porosimetry (MIP). In addition, the microstructure of the mortar was improved due to the filling of pores by unhydrated OMWP particles, which resulted in a microaggregate effect. These results demonstrate the potential of OMWP as a valuable resource for cement production with environmental and economic benefits. This research provides the foundation for OMWP resource exploitation and the long-term development of mining operations.