Reuse of unburned carbon as filler substitutes in some rubber goods

Unburned Carbon (UC) in the Fly Ash (FA) was separated through froth flotation. The separated UC (SUC) was mainly comprised of irregularly-shaped carbon shells and rigid spheres of quartz and mullite. SUC was tested whether it could be substitutes replacing commercial carbon and clay fillers reinforcing the rubber goods of Chlorinated-Poly-Ethylene (CPE), Ethylene-Propylene-Diene-Monomer (EPDM) and tires (tread and carcass). Unfortunately successful replacement could not be achieved probably due to the insufficient contact between the rubber textures and inorganic microspheres within the carbon shells. To ensure sufficient contact with the microspheres, SUC underwent further pin milling, resulting in narrower size distribution as well as smaller size. Pin milled UC (PMSUC) could replace the carbon black and clay fillers partly. Since the residue in suspension leaving after froth flotation contained the Loss On Ignition (LOI) values much lower than 3 weight % limit, it will be used as an additive in cement and concrete industries. Not only by utilizing the residue as the additives of cement and concrete, but also by replacing the carbon black and clay fillers, all the ashes might have a chance to be reused, contributing to circular economy.