MICROSCOPIC AND GEOCHEMICAL ANALYSIS OF COAL ASH FROM THE DAN RIVER SPILL

On February 2, 2014, an estimated 82,000 tons of coal ash and 27 million gallons of contaminated water were released into the Dan River from a leaking holding pond at the Duke Energy Steam Station in Eden, NC.The spill site is upriver from several municipal water supplies, including Danville, South Boston, and Clarksville, VA. Because coal ash contains elevated concentrations of trace elements, there is a concern that the ash spill could adversely impact human, aquatic and environmental health.

Many of the trace elements contained in coal ash, including As, Se, Cr and V, are geochemically reactive, and can be both released and retained in river sediments. Our goal is to analyze the geochemical signatures of coal ash particles as they react with water and sediment in the river over space and time. Since the spill occurred, we have been collecting bimonthly samples of coal ash, river sediment and water at 10 locations along the Dan River.

Our first objective was to develop methods for separating ash from river sediment. Currently, we are using a combination of physical separation (sieving) and density separation (lithium metatungstate). After separation, we are applying a host of microscopic methods, including light, scanning electron and transmission electron microscopy, to evaluate the morphology and size of coal ash particles in sediment. We are also using electron dispersive spectroscopy to analyze the elemental composition of the ash.

Thus far, our results indicate that the coal ash contains a variety of particles, including cenospheres, with most sizes ranging from less than one micron to 53 microns, as well as vesicular char, silica glass, and barite. A significant amount of ash particles have notable concentrations of iron, which is important for our study since Fe minerals can adsorb trace elements. We are pursuing additional spectroscopic methods that can analyze trace elements. Ongoing work is addressing the changes in coal ash mineralogy, surface coatings, and elemental analysis with time and space in the river.