Study on the strength improvement mechanism of fine-grained iron tailings cemented backfill after high temperature calcining

Abstract

Backfill has become an essential element of underground mining operations around the globe. However, a significant amount of fine-grained tailings can affect the consolidation performance and reduce the strength of backfill. It has been reported that mixing active materials with tailings, while calcining at high temperatures can enhance the gelling activity and strengthen the backfill. To examine the mechanism behind the strength improvement of fine-grained iron tailings cemented backfill following high-temperature calcination, various methods such as uniaxial compression test was used to measure the strength parameter, while laser particle size analysis, XRD and SEM analysis, and thermogravimetric analysis were used to provide a microscopic investigation. The results indicate that the uniaxial compressive strength (UCS) of the samples increased by 596.8 %, from 0.224 MPa to 1.561 MPa after when the tailings were calcine at 800 °C for 2 h and cured for 7 days. Among the mixed calcine groups, the 10 % red mud group showed the most significant effect with UCS of 3.138 MPa after 7 days of curing, showing a 101.0 % higher strength increase than the direct calcine group. Meanwhile, the 20 % red mud mixture showed the highest strength with a UCS of 5.407 MPa, showing a 246.4 % higher strength increase than the direct calcine group. This increase in strength is attributed to the high-temperature calcination, which improved the particle size and increased the number of particles beyond 25 μm. Additionally, the higher temperature calcination caused a dehydroxylation reaction of clinochlore and mica in the tailings, led to the destabilization of the layered chain structure and improved the activity of pozzolanic ash. Furthermore, with the increase of mixed red mud, the dehydroxylation reaction of aluminosilicates occurred at high temperature, and more N-A-S-H gels were generated in the hydration reaction. This created a more stable and compact structure with lower porosity and higher strength in the sample. The findings of this study provide a valuable insight into the large-scale backfill of fine-grained iron tailings in underground stope, as well as reducing the accumulation of fine-grained tailings on the surface.