Quantitative mineral determinations of industrial coal ash

The majority of coal ash generated by electric utilities and power plants of industrial manufacturers is disposed of in landfills; the remainder is used primarily as admixtures in construction materials. Predictive computer models used to assess the environmental impact of disposal or utilization need quantitative information on ash composition and mineralogy. Typically, compositions are reported as elemental concentrations, but this data does not indicate the mineral or glass (amorphous) phases in which the elements are contained. Such phases affect the leaching mechanisms and rates. X-ray diffraction and scanning electron microscopy combined with energy dispersive X-ray spectrometry, common methods for qualitative mineral identification and particle characterization, were used to quantify coal ash mineral compositions. Samples of industrial coal ash from a stoker boiler and a fluidized bed combustion (FBC) system were analyzed and the results were compared to those for a standard sample of coal ash from the National Institute of Standards and Testing (NIST1633a). The results show that the stoker-boiler ash is similar in composition to the NIST sample. Mullite (AI6Si2O13) dominates the composition of the crystalline fraction and silica (SiO2,) dominates the composition of the amorphous fraction. The FBC ash contains the same minerals, but with large proportions of calcium-based phases: anhydrite (CaSO4), lime (CaO), calcite (CaCO3), and portlandite (Ga(OH)2). © Taylor and Francis Group, LLC