Particle size distribution of coal gangue.

A new type of paste filling material was created using fluorogypsum, a byproduct of hydrofluoric acid, as the raw material to address the issue of the filling material’s high cost. The effects of five factors, including gangue, fly ash, fluorogypsum, lime content, and mass concentration on the physical and mechanical properties of filling material were also examined. In addition to analyzing slump and extension changes, the filler’s mineral composition and microstructure were examined using SEM and XRD examinations. The results show that the best ratio of the developed filling material was 1000g coal gangue, 300g fly ash, 300g fluorogypsum, and 50g lime and mass concentration is 78%, and its compressive strength can reach 4–5MPa at 28 days. Raw materials such as gangue and fly ash will have a certain influence on the mechanical properties of the filling material. The hydration products of the developed filling material prepared by XRD and SEM were ettringite, calcium sulfate dihydrate, and calcium silicate hydrate gel. The new fluorogypsum-based paste filling material can be used to consolidate loose rock strata and fill goaf. It solves the problem of disposal of industrial waste fluoropgypsum and also solves the problem of coal mine gangue stacking, which has a far-reaching influence on ecological environment management.