Location of Cerium in Coal-Combustion Fly Ashes

Given the worldwide demand for rare earth elements (REEs) in modern electronics, all potential sources of the REEs should be investigated. Coal-combustion fly ash represents a potential source of REEs. Fly ashes, derived from the combustion of coals from Kentucky in the United States and Jungar in China, were examined by wavelength-dispersive spectrometry electron microprobe analysis of epoxy-bound polished pellets. From previous studies, it was known that the REEs did not show any enrichment relative to flue gas temperature at the point of collection or to the particle size, that is, external surface area, of the particles. Cerium, the most abundant of the REEs in these fly ashes, was used as a proxy for the entire suite of REEs. For fly ashes from both sources, Ce is disbursed throughout the glassy fly ash particles. For fly ash processing with respect to the recovery of REEs, this implies that the entire particle must be leached to maximize the element recovery.