To explore the microstructure evolution of oolitic hematite during microwave fluidization roasting, COMSOL multiphysics and scanning electron microscopy (SEM)–energy-dispersive spectrometry (EDS) were used to simulate and explore the microstructure evolution. The simulation results indicated that with the extension of microwave heating time and the increase of microwave power, the surface temperature in the particle model progressively increased, and the heating rate of hematite was the fastest, followed by quartz and apatite; simultaneously, the temperature stress and difference between the three mineral interfaces in the model were increased. The SEM–EDS results illustrated that there were microcracks at the interface between iron minerals and gangue minerals, such as quartz and apatite, and the microcracks were more obvious at the interface between iron minerals and quartz minerals. With the extension of microwave treatment time, the microcracks were gradually extended and expanded inward along the outer edge of oolitic and gradually formed in the core of the oolitic structure. Appropriately increasing the roasting temperature, prolonging the roasting time, and increasing the CO concentration made the particle surface more loose and rough, and produced more cracks and pores, while the ore surface presented a honeycomb morphology.

Adjacent, multi-working face mining can expand the range of disturbed overburden, increasing the risk of triggering roof water inrush, which threatens the safe operation of coal mines. In this paper, we propose a risk identification method for roof water inrush under multi-working face mining conditions based on the theory of Key Strata and Full Mining Disturbance. Firstly, the key strata of the overburden are determined based on lithological and structural data from exploration boreholes. A formula is then derived to calculate the critical dimension (L) of the working face that could induce a fracture in the key stratum. The relationship between L and the combined width of the preceding and adjacent working faces is analyzed to assess whether the key stratum is fractured and how it affects the preceding working face. Finally, the height of the water-conducting fracture zone is predicted. The impact of repeated disturbances from multi-working face mining is evaluated to determine whether the height of the water-conducting fracture zone in the preceding working face increases, thereby enabling risk identification for roof water inrush under multi-working face mining conditions. Taking the multi-working faces of the Banji Coal Mine in Anhui Province as a case study, the predicted height of the water-conducting fracture zone is 60 m, with no risk of delayed roof water inrush in the preceding working face. Both numerical simulation results and field measurements of the development height of the water-conducting fracture zone confirm the effectiveness of this method. It is capable of accurately predicting the development height of the water-conducting fracture zone under multi-working face mining conditions and identifying the associated risk of roof water inrush, thus providing a valuable reference for ensuring safe mining operations in multi-working face mining conditions.