Multisolid waste collaborative production of aeolian sand-red mud-fly ash cemented paste backfill

This study proposed the novel idea of anaolian sand-red mud-fly ash cemented paste backfill (ARFCPB) to realize low-carbon backfill mining. This idea realizes large-scale disposal and resource utilization of red mud (RM) and fly ash (FA) solid wastes. The influence of the FA/RM mass ratio and mass concentration on the mechanism of action of ARFCPB was explored through comprehensive rheological performance, mechanical property, microscopic, and leaching toxicity tests. The results showed that the fresh ARFCPB slurry could be described by the Herschel–Bulkley model (R2 ≥ 0.964). As the FA/RM mass ratio increased, the ARFCPB slurry yield stress decreased, the thixotropy decreased, and the slump increased. This is because RM has a large specific surface area and an unsmooth surface, resulting in greater water absorption by RM than by FA. In addition, the uniaxial compressive strength (UCS) of ARFCPB can meet the needs of backfill mining with higher strength requirements. UCS first increases and then decreases with increasing FA/RM mass ratio, which is optimal when the mass ratio of FA to RM is 4. When the FA/RM mass ratio was 4, the UCSs of specimens A4 and B4 with mass concentrations of 78% and 80%, respectively, were 5.6 MPa and 6.4 MPa after 28 days of curing. The leaching results of heavy metal ions in group B4 meet the Class III groundwater standards and can be used for centralized drinking water sources and industrial and agricultural water. Considering the fluidity characteristics, mechanical properties, and leaching results, B4 was identified as the optimal formulation. Finally, the microstructure of the ARFCPB was studied using ultrasonic pulse velocity (UPV) and SEM. The results can contribute to clean production in the aluminum production industry, coal-fired power plants, and coal mines.