Performance enhancement and environmental assessment of ultra-fine tailings mortars using waste-derived binders...

Recycling ultra-fine tailings (UFT) into backfill mortars provides a promising route for their massive utilization, thereby alleviating the environmental risks and land-use burdens associated with UFT stockpiling. However, the bonding efficiency of ordinary Portland cement (OPC) in UFT mortar is limited, and increasing the OPC content to meet strength requirements significantly increases costs and carbon emissions. In this study, arsenic-containing waste (AW) and calcium carbide residue (CCR) were used to synergistically activate ground granulated blast-furnace slag (GGBS) and oil shale residue (OSR), and novel waste-derived binders activated by alkali-sulfate were developed for UFT mortars to replace OPC. The rheological behavior, compressive strength, and microstructure of waste-derived mortars and OPC mortar were investigated, the activation mechanism of the waste-derived binders was clarified. The results showed that AW increased the yield stress and plastic viscosity of the fresh samples. When the AW/CCR ratio was 2:3, the compressive strengths of the waste-derived mortar at 7 and 28 days reached 0.596 MPa and 2.77 MPa, respectively, representing increases of 114.39% and 104.73% relative to the OPC mortar. Although these values were relatively low, they satisfied the strength requirements for non-structural backfill applications. The AW/CCR ratio modulated the amounts of calcium (alumino) silicate hydrate (C-(A)-S-H) and ettringite (AFt) formed, thereby influencing the strength evolution of the mortar. Meanwhile, the generated hydration products effectively immobilized As, Mn, Cu, and Zn, leading to markedly reduced leaching levels. Under conditions of a high water-to-binder mass ratio and high UFT content, the waste-derived mortars outperformed the OPC mortar in terms of cost, carbon emission, and embodied energy within the defined accounting boundary. This study provides a viable direction for the efficient green utilization of solid wastes and the strength optimization of non-structural UFT backfill mortars, offering important implications for environmental protection and sustainable development.