Particle Size Distribution of Coal Fly Ash Using Scanning Electron Microscopy for Design of Cyclone Separation System

Coal fly ash is the byproduct of pulverized coal being burnt in furnaces at coal power plants and collected from the flue gas with either electrostatic precipitators or baghouses. If coal fly ash is stored incorrectly, it can be toxic to the groundwater and pose inhalation risks. Currently, coal fly ash is produced in excess amounts in the United States and is mainly used as a concrete ingredient. Recent efforts have shifted towards extracting rare earth elements (REE) from coal fly ash. One potential strategy is the extraction of REE from coal fly ash using solutions of organic acids in supercritical carbon dioxide. Batch reactions have shown promising results in terms of REE yield and selectivity. A hurdle for scaling up to continuous operation is the separation of spent coal fly ash from the supercritical fluid while maintaining supercritical conditions.

In this study, the particle size distributions of two coal fly ash samples (class C and class F) were measured using scanning electron microscopy (SEM). SEM was used to compare with particle size distributions from light scattering techniques. Particle sizes for both coal fly ashes ranged from approximately 2-20 μm, with a poly-dispersed size pattern. The size distributions were similar between coal fly ash classes. The light scattering measurements had suggested much smaller particle sizes and appeared inconsistent, whereas the SEM particle sizes were within the expected range based on reported sizes from previous studies. The next step is computational fluid dynamics modeling of the cyclone.