CHARACTERIZATION OF MORPHOLOGY, CHEMISTRY, AND MAGNETIC SUSCEPTIBILITY OF COAL ASH AND APPLICATIONS FOR TRACKING THE TRANSPORT IN AQUATIC ENVIRONMENTS

We investigated the morphology, trace element chemistry, and magnetic susceptibility (χ) of three fly ash samples from TVA-operated coal-fired power plants that burn Appalachian Basin coal. A suite of 20 sediment samples from the Emory and Clinch Rivers impacted by the 2008 TVA Kingston spill were also studied. Plant fly ash was separated into magnetic and non-magnetic fractions. Ash morphologies in each fraction were optically point counted. We identified opaque, orange, and clear spheres, pleospheres, opaque, semi-opaque, clear amorphous, and lacey ash. Opaque spheres and orange spheres dominate the strongly-magnetic fraction. Clear spheres and amorphous clear particles dominate the non-magnetic fraction. Other morphologies were distributed in all fractions. Polished epoxy grain mounts were analyzed via scanning electron microscopy and energy dispersive x-ray spectroscopy to link major element chemistry to ash morphologies. All ash particles contain Si and Al. Fe is abundant in the magnetic fractions. Pleospheres have variable structure and composition with either an Al-Si sphere or a Fe-rich sphere encapsulating smaller spheres. Trace element chemistry was measured on bulk separates via inductively-coupled plasma mass spectrometry. The non-magnetic fraction is enriched in Pb, As, Se, Cd, Tl, Zn and Th which we interpret as residing within small clear spheres (0.3 to 9.2 µm) that dominate this fraction. The strongly-magnetic fraction is dominated by ferrospheres enriched in Fe, V, Cr, Co, Ni, U, Sb and Cu.

Riverbed samples collected 5 years after the Kingston spill show that most trace metal abundances correlate with total ash % and χ. Sb, U, and Tl were strongly correlated with χ. Cd, Pb, and Zn do not correlate with total ash % or χ, and may be sourced from elsewhere in the Clinch watershed. As and Se were weakly correlated with total ash % and χ. Samples with high As and Se, located in the Emory River near the source of the spill have a greater proportion of clear spheres compared with other riverbed samples. This study demonstrates complex linkages between trace element geochemistry, ash morphology, and χ and shows the potential to use these tracers to understand coal ash transport and reworking in aquatic environments.