Resource utilisation of hazardous aluminium dross and coal gangue for fibre-reinforced cemented foam backfill

Abstract

The resource utilisation of hazardous aluminium dross and coal gangue for fibre-reinforced cemented foam backfill can enhance the stability of filling stopes and address environmental issues. Herein, aluminium dross was first co-calcined with quicklime at 800°C, 950°C and 1100°C to prepare modified foaming agents, and their phase transformations during calcination were analysed. Next, the calcined mixes, cement, coal gangue and fibres were employed to prepare the samples. The expansion ratio and hydration evolution—as well as the strength, deformation and heavy metal–leaching behaviours—of the fibre-reinforced cemented foam backfill were comprehensively investigated. Experimental results reveal that partial elemental Al in raw aluminium dross becomes active in the C12A7 and CA2 forms, which enhances the hydration reactivity of the calcined mixes. The efficient denitrification achieved at 1100°C is because of the coupled effects of quicklime dispersion and high-temperature calcination. The grindability of the calcined mixes initially improves and subsequently worsens with increasing calcination temperature, which is related to the Al2O3 crystallinity. Active Al in the calcined mixes is conducive to hydration at an early age, leading to the generation of larger quantities of Hc/Mc and the AH3 gel and a smaller amount of portlandite. Owing to the coupled effects of the porous structure and fibre reinforcement, the fibre-reinforced cemented foam backfill exhibits good mechanical performance and large plastic deformation. Furthermore, the M1-10, M2-10 and M2-30 samples possessing an expansion ratio of 4%–10 %, a compressive strength of >3 MPa and a good ability to stabilise heavy metals are excellent choices for the practical application of foam backfill technology in mining engineering.