Properties of modified superfine tailings cemented paste backfill: Effects of mixing time and Al2O3 dosage

As world advances towards goals of "carbon peak" and "carbon neutrality", tailings filling has become an important direction for the construction of green and low-carbon mines. Mixing time has an important effect on the performance of tailings filling slurry and filling body. This research explores the mechanism of mixing time on mechanical properties, slurry fluidity and microstructure of superfine tailing cemented paste backfill (SCPB) under conditions of different nano-Al2O3 (NA) dosage. The results show that prolonging mixing time causes the slurry fluidity to increase and then decrease or increase and then gradually stabilize with different NA dosages, while the uniaxial compressive strength (UCS) increases and then decreases. When the NA dosage are 0%, 1%, 2% and 3%, the mixing time that optimizes fluidity and strength are 5 min, 5 min, 9 min and 11 min, respectively. Both mixing time and NA dosage have significant effects on the early strength of SCPB. The UCS of SCPB increases and then decreases with the increase of NA dosage, and reaches the highest at 2% NA dosage at different curing time. Taking into account the microscopic test results, it can be seen that the hydrolysis degree of C3S and gypsum is higher under the ideal mixing time, which can generate more hydration products such as C -SH and AFt. Meanwhile, NA dissolves and releases reactive Al and Al(OH)4- in alkaline conditions to take part in the hydration reaction, generating alumina hydrate, AFt, and C -(A) -S -H, thus further improving the quantity of hydration products generated and decreasing porosity in the microstructure of SCPB, and thus improving the strength of SCPB. The findings offer reference for improving utilization of superfine tailings and effective backfilling.