Comprehensive characterization of anthracite fly ash from a thermo-electric power plant and its potential environmental impact

Anthracite fly ash from a deactivated Portuguese thermo-electric power plant has been characterized to assess its relationship to the mineral matter in typical feed coal and the potential environmental impacts that might be caused by ash disposal.Several different aspects of the ash were characterized, including the petrographic and mineralogical composition, as well as the chemical composition of both the ash samples and their water leachates.Petrographic analysis demonstrates that the fly ash consists predominantly of glass, followed by char and crystalline mineral particles. SEM-EDX studies were used to complement this approach, revealing a mixture of different inorganic phases and unburnt organic matter. Quantitative XRD analysis further showed that amorphous material (or glass) is the main constituent (60–70%), followed by mullite, quartz, and traces of maghemite. Small proportions of kaolinite and illite also occur in some of the fly ash samples.According to their chemical composition, the fly ashes would be classified as sialic and are within the range of values shown by other European fly ash samples.Relatively low concentrations of elements in leachates from the fly ash could be due to enclosure of most of the elements within the amorphous material, together, possibly, with mobilization of some of the material (e.g. adsorbed ions) from the ashes with storage. The fly ash leachates developed very acidic pH values (between 2.5 and 2.8) under test conditions, attributed to the low-CaO content and the co-firing with fuel oil.

Research Highlights
► Petrographic, mineralogical and chemical characterization of anthracite fly ash.
► Identification of changes arising from the combustion process.
► Assessment of the potential environmental impacts caused by the fly ash disposal for many years.