Application of density gradient centrifugation to the concentration of unburned carbon types from fly ash

Although the increasing amount of unburned carbon in fly ash is known to impede the efficient use of ash in the cement industry, very little is known about the characteristics of the unburned carbon. Three different types of carbon particles have been identified microscopically: inertinite, isotropic coke and anisotropic coke, with little information on their relative absorption properties. This work presents one of the first attempts to isolate these three types of carbon. A preliminary enrichment, followed by density gradient centrifugation (DGC) with a high-density polytungstate media (2.85 g/cm³ max), resulted in an enrichment of inertinites from a starting concentration of 3.8% to 61%, isotropic coke from 13.4% to 55%, and anisotropic coke from 19.2% to 71%.