Key attributes of superfine tailings cemented paste backfill modified with nano-Al2O3: Mechanical properties, flowability, microstructure, and thermal decomposition characteristics

Cemented paste backfill (CPB) technology plays a crucial role in promoting sustainable mining practices by utilizing mine tailings for backfilling. However, the use of superfine tailings in CPB presents significant challenges. This study aims to optimize superfine tailings CPB (SCPB) performance by incorporating nano-Al2O3(NA) to enhance its mechanical and flowability properties. A series of experiments are conducted to investigate the rheological behavior, compressive strength, microstructure, and thermal stability of the SCPB modified with NA (NA-SCPB). The findings reveal that fresh NA-SCPB behaves as a non-Newtonian fluid, with its yield stress, apparent viscosity, and thixotropy increasing proportionally with NA content. The uniaxial compressive strength (UCS) of NA-SCPB initially rises with increasing NA content, reaching a peak at 1.5 % NA, where the UCS is enhanced by 30.9%, 25.6%, 15.8%, and 7.8% at 1, 3, 7, and 28 days, respectively, compared to the control. The influence of NA on early strength development is more pronounced than on long-term strength. The mechanism is attributed to the catalytic effect of NA on gypsum, which accelerates hydrolysis and increases the hydration reaction, leading to greater formation of hydration products. Thermal decomposition analysis further suggests that the AFt and C-(A)-S-H phases in NA-SCPB exhibit higher bond energies and a more stable structure, resulting in superior strength compared to traditional SCPB. This study demonstrates that NA is a promising additive for enhancing the performance of CPB, particularly in addressing the challenges posed by superfine tailings in mining operations.