2025 AIChE Annual Meeting

Particle Size Distribution of Coal Fly Ash Using Dynamic Light Scattering for Design of Cyclone Separation System

Coal fly ash is the byproduct of pulverized coal combustion at coal power plants, collected from the flue gas with either electrostatic precipitators or baghouses. Coal fly ash, if handled or stored incorrectly, poses inhalation and groundwater toxicity risks, respectively. The U.S. has a very large supply of coal fly ash, some of which is used as a concrete ingredient. One recent direction for coal fly ash utilization is as a source of rare earth elements (REE). The extraction of REE from coal fly ash using solutions of organic acids in supercritical carbon dioxide is area of active research. Batch reactions have shown promising results in terms of REE yield and selectivity. A hurdle for scaling up to continuous operations 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 dynamic light scattering (DLS) on in order to collect data for design of a cyclone. The particle distributions from DLS on two different instruments, a Zetasizer and a Mastersizer, were compared with those estimated using scanning electron microscopy (SEM). The Zetasizer, readily available on campus, is typically used for civil engineering applications with monodispersed particles. The polydispersed sizes in the coal fly ash resulted in particle size distributions on the Zetasizer of approximately 0.1-1 μm, an order of magnitude smaller than expected from SEM images. Data from the Mastersizer, not available on campus, for these samples was in the 10-20 μm range, which was much more consistent with SEM data and previously reported particle size distributions. Considering instrument availability and reliability for these coal fly ash applications, SEM methods were selected for ongoing cyclone design work.