Characterization of Indian Fly ashes for Mine Stowing

The objective of this study was to select the best fly ash material which can replace river bed sand to fill underground coal mine voids. To achieve the objectives, this study examined the suitability of seven numbers of Indian fly ashes for filling in the underground coal mine voids based on their physicochemical, morphological and mineralogical characteristics. The physical properties such as bulk density, specific gravity, particle size distribution, specific surface area, porosity, moisture content, pH etc. have been determined. The chemical and mineralogical properties were also determined in the laboratory by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray fluorescence (XRF) studies. From the chemical characterization it is found that the fly ash samples are enriched predominantly with silica (SiO2), alumina (Al2O3) and iron oxides (Fe2O3) along with a little amount of CaO and all the seven fly ash samples tested fall under the class F fly ash category. In addition to these, the fly ash samples also contain some trace elements in negligible amount. The mineral phases identified in the fly ash samples are quartz, mullite, magnetite, and hematite. The particle morphological analysis revealed that the fly ash particles are almost spherical in shape which would favor hydraulic pipeline transport to mine void filling areas. From the particle size and shape point of view the fly ashes tested may be considered as an alternative to conventional mine void filling material. Keywords— Fly ash, material characterization, mine void filling, specific gravity, density