Role of coal ash morphology and composition in delivery and transport of trace metals in the aquatic environment.

Fly ash is predominately the inorganic byproduct of coal combustion for electrical power generation. It is composed of aluminosilicates with Fe, Mg, K, and Ca forming submicron to 100 μm spheres and amorphous particles. During combustion trace elements are incorporated into the heterogenous fine particles that can pose risks to the environment and human health. This study combines optical, rock magnetic, and geochemical analyses of fly ash originating from Appalachian coal to develop an integrated suite of environmental coal ash tracers. The non-magnetic portion of power plant fly ash has higher abundance of clear spheres and clear amorphous particles, combined with enrichment of As, B, Th, Ba, Li, Se, Cd, Pb, and Tl. The magnetic fraction is enriched in opaque and orange spheres and Cu, U, V, Mo, Cr, Ni, and Co. Plerospheres occur in either fraction. We investigated ash-bearing fluvial sediment from Emory-Clinch River system that was impacted by the instantaneous TVA spill in 2008 and Hyco Lake in North Carolina that was contaminated by chronic releases of fly ash since 1964. Five years after the TVA spill, most ash in the riverbed reflects one population with trace element concentrations proportional to percent total ash. This relationship does not hold for As and Se, volatile elements associated with the outer surface of clear spheres, which are affected by river transport. At Hyco Lake, small clear and opaque spheres correlate with trace elements released from storage ponds. The combination of trace elements, fly ash morphology and rock magnetism provides a powerful set of tools to assess the distribution of ash and potential impact on the environment. We conclude that dispersal of fly ash to the aquatic environment, especially small clear and opaque spheres, should be avoided in favor of dry landfills.

Duke Scholars

Author Avner Vengosh Earth and Climate Sciences

Author Robert Hill