Preparation and strength mechanism of slag-based mine backfill for low concentration ultra-fine tailings

High concentrated ultra-fine tailings have been cemented using various methods and used as the backfill ma-terial, whereas the suitable cementitious material formulations for the low concentrated ultra-fine tailings (LUFTs) with a solid content <= 55% have not been presented. For the purpose of utilizing the LUFTs in practice, this study presented a binder formulation for cementing the LUFTs; the cementitious material is alkali-sulfate -activated slag, and some amounts of ordinary Portland cement were added as a reinforcing agent to improve the properties of cemented LUFTs. The results showed that a binder with 61.3% GBFS, 20.0% cement, 15.1% anhydrite, and 0.5% alkaline activator (in which 50% for both quicklime and sodium metasilicate nine-hydrate), a binder to tailing ratio of 1:8, and a tailing slurry concentration of 55% exhibited the highest strengths in 3d, 7d and 28d, respectively 0.62 MPa, 0.93 MPa, and 1.41 MPa. Moreover, based on the XRD, TG, and SEM analysis, the compressive strength mainly originates from the reticular skeleton structure formed by the hydration product such as C-S-H gels and ettringite.